# TODO

## Internal consistency

Findings from a sweep of `src/` and `include/`. These are consistency and
convention problems, not new functional defects — where one has a functional
consequence it is called out. Ordered roughly by blast radius. Items that
overlap the existing **Defects** list are cross-referenced rather than repeated.

### 1. Public naming conventions

**Items 1 through 6 are resolved in 0.5.0**, which is an ABI break and carries
the soname to `libakgl.so.0.5`. What changed, and what a consumer has to rename:

| Was | Is |
|---|---|
| `_ASSETS_H_`, `_CONTROLLER_H_`, `_DRAW_H_`, `_ERROR_H_`, `_JSON_HELPERS_H_`, `_PHYSICS_H_`, `_REGISTRY_H_`, `_RENDERER_H_`, `_TEXT_H_`, `_TILEMAP_H_`, `_UTIL_H_`, `_STRING_H_` | `_AKGL_<FILE>_H_` |
| `akgl_Actor_cmhf_*` (8 functions) | `akgl_actor_cmhf_*` |
| `akgl_game_updateFPS` | `akgl_game_update_fps` |
| `akgl_render_init2d`, `akgl_render_bind2d` | `akgl_render_2d_init`, `akgl_render_2d_bind` |
| `akgl_sprite_sheet_coords_for_frame` | `akgl_spritesheet_coords_for_frame` |
| `point`, `RectanglePoints` | `akgl_Point`, `akgl_RectanglePoints` |
| `window`, `bgm`, `game`, `gamemap`, `renderer`, `physics`, `camera` | the same, `akgl_`-prefixed |
| `_akgl_renderer`, `_akgl_physics`, `_akgl_camera`, `_akgl_gamemap` | `akgl_default_renderer`, `akgl_default_physics`, `akgl_default_camera`, `akgl_default_gamemap` |
| `HEAP_ACTOR`, `HEAP_SPRITE`, `HEAP_SPRITESHEET`, `HEAP_CHARACTER`, `HEAP_STRING` | `akgl_heap_actors`, `akgl_heap_sprites`, `akgl_heap_spritesheets`, `akgl_heap_characters`, `akgl_heap_strings` |
| `GAME_ControlMaps` | `akgl_controlmaps` |
| `AKGL_SPRITE_MAX_CHARACTER_NAME_LENGTH` | `AKGL_CHARACTER_MAX_NAME_LENGTH` |
| `AKGL_TIME_ONESEC_MS` | `AKGL_TIME_ONEMS_NS` |

`include/akgl/staticstring.h` also stopped guarding with `_STRING_H_` — a name
several libc implementations use for their own `<string.h>` — and its
`#include "string.h"` is now `#include <string.h>`.

`akgl_render_bind2d` was not on the original list. It is the same defect as
`akgl_render_init2d`, `2d` trailing where the six functions it installs carry it
in the middle, and renaming one without the other would have been worse than
renaming neither.

The renames were done by renaming each declaration and letting the compiler find
every use, rather than by pattern substitution. That distinction matters for
`renderer`, `physics` and `camera`, which are also parameter and struct-member
names: a `sed` would have rewritten `map->physics` and every
`akgl_RenderBackend *renderer` parameter, and nothing would have complained.

**Item 6 had a live bug behind the name**, now fixed. `akgl_game_state_lock`
counted its retry loop against a constant named "one second in milliseconds"
that held `1000000`, so it retried 10,000 times at 100 ms and blocked for
roughly sixteen minutes before reporting failure. The budget is now
`AKGL_GAME_STATE_LOCK_BUDGET_MS` (1000), with the cadence named separately as
`AKGL_GAME_STATE_LOCK_RETRY_MS`. `tests/game.c` carries
`test_game_state_lock_budget`, which holds the mutex from a second thread and
asserts the call gives up between half a second and five. The old code fails it
by timing the suite out; a build that gave up without waiting at all fails the
lower bound. Nothing exercised the contended path before — the existing lock
test only ever took an uncontended mutex, which never reaches the retry loop.

**Item 4 was not cosmetic, and the proof was sitting in the test suite.**
`renderer` was exported from the shared library, and `tests/character.c` defined
an `SDL_Renderer *renderer` of its own. Both had external linkage and the same
spelling, so the executable's definition preempted the library's:
`akgl_sprite_load_json` read a `SDL_Renderer *` through an
`akgl_RenderBackend *`, every texture load in that suite failed with
`Parameter 'renderer' is invalid`, and the suite still reported success — see
"Test suites that could not fail" below. It now binds a real backend with
`akgl_render_2d_bind`, the way `tests/sprite.c` and `tests/text.c` do. A
consuming game with a variable called `renderer` would have hit the same thing
with no test to notice.

### 2. Header/implementation surface drift

**Items 7, 8, 9, 11, 12, 13, 14 and 15 are resolved in 0.5.0.** Item 10 is
resolved for every pair it listed.

7. **Nineteen non-static functions were defined in `src/` but declared in no
   header.** Each is now declared or `static`:

   - `akgl_controller_handle_button_down`, `_button_up`, `_added`, `_removed`
     were defined as `gamepad_handle_*` while `controller.h` declared the
     `akgl_controller_handle_*` names it never defined. The definitions now
     carry the declared names, which closes this and **Defects → Known and
     still open item 10** in one change, and their documentation moved from the
     definitions to the header where the convention puts it. `tests/controller.c`
     no longer needs its local re-declarations.
   - `akgl_game_save_actors` and `akgl_game_load_versioncmp` are declared in
     `game.h` under a new "part of the internal API" block; `tests/game.c`
     reaches them through the header now instead of declaring them itself.
   - The four save-table iterators and `akgl_game_load_objectnamemap` are
     `static` and have dropped the prefix -- `save_actorname_iterator`,
     `load_objectnamemap` and so on. They are SDL enumeration callbacks and a
     file-local reader; nothing outside `game.c` has any business calling them.
   - `akgl_get_json_properties_number`, `_float`, `_double`,
     `akgl_tilemap_load_layer_image`, `akgl_tilemap_load_layer_object_actor` and
     `akgl_tilemap_load_physics` are declared in `tilemap.h`'s internal-API
     block, again with their documentation moved to the header. That is where
     the "does not need a renderer" work under **Remaining work** wanted them.
   - `akgl_path_relative_root` is `static path_relative_root`.
     `akgl_path_relative_from` is **deleted**; see below.

   **This is enforced now.** `scripts/check_api_surface.sh` reads the built
   library's dynamic symbol table, strips comments out of every public header,
   and fails when an exported `akgl_*` symbol is declared nowhere. It runs as
   the `api_surface` CTest test. Stripping comments is the point: four of these
   symbols were *mentioned* in `controller.h` prose, which is not the same as
   being declared there and is exactly how they went unnoticed.

8. **`akgl_game_init_screen` was declared and never defined.** The declaration
   is gone. Screen setup is `akgl_render_2d_init`.

9. **Static helpers used three naming styles.** They drop the `akgl_` prefix
   now, which is what it is for: `character_load_json_inner`,
   `character_load_json_state_int_from_strings`, `sprite_load_json_spritesheet`,
   alongside the `actor_visible`, `write_exact` and `write_name_field` that
   already did.

10. **Parameter names disagreed between declaration and definition.** All six
    pairs agree now. `akgl_character_initialize` takes `obj`,
    `akgl_character_state_sprites_iterate` takes `props`, `akgl_heap_release_character`
    takes `ptr`, `akgl_set_property` takes `value`, and the two `akgl_tilemap_draw*`
    functions take `map` -- the header called them `dest` and documented them as
    "Output destination populated by the function", which they are not.

    `akgl_get_json_with_default` was the interesting one: it took the incoming
    context as `err` and named its *own* context `e`, which is the name the
    convention reserves for an incoming one. It is `e` and `errctx` now, and
    renaming it was what surfaced that the two had been swapped rather than
    merely misspelled.

11. **Object-pool size macros were defined twice and the override hook was
    dead.** `AKGL_MAX_HEAP_ACTOR`, `_SPRITE`, `_SPRITESHEET` and `_CHARACTER` are
    defined once, in `heap.h`, inside the `#ifndef` guards that were always
    supposed to make them overridable. `actor.h`, `sprite.h` and `character.h`
    no longer define them.

    `tests/header_pool_override.c` is the regression test: it defines its own
    ceilings, includes `heap.h`, and `#error`s if the guard did not fire or if
    `AKGL_MAX_HEAP_SPRITE` stopped deriving from `AKGL_MAX_HEAP_ACTOR`. The
    assertion is the compile -- it deliberately disagrees with the built
    library's ceilings and never touches the pools, which is fine because
    overriding a ceiling means the library and everything linking it have to be
    rebuilt together anyway.


12. **Headers relied on their includers for types.** `iterator.h` used
    `uint32_t` without `<stdint.h>`; `json_helpers.h` used `json_t` without
    `<jansson.h>`; `util.h` used `SDL_FRect` and `bool` without any SDL include.
    Each compiled only because of `.c`-file include ordering.

    **Resolved, and enforced rather than merely fixed.** `AKGL_PUBLIC_HEADERS`
    in `CMakeLists.txt` is now the single list behind both `install()` and a
    generated translation unit per header -- each including exactly that header
    and nothing before it -- linked into the `headers` suite. A header that
    ships is a header that is checked.

    Writing that check found a case this item had missed: `registry.h` uses
    `SDL_PropertiesID` in eight declarations and included no SDL header at all.
    That is the argument for generating the check off the install list rather
    than hand-listing the headers somebody thought were at risk.

13. **Include spelling was split between quoted and angled forms.**
    **Resolved.** Every in-project include in a public header uses
    `#include <akgl/sibling.h>`, and `staticstring.h`'s `#include "string.h"` --
    a relative-first lookup that reached the system header by accident -- is
    `#include <string.h>`. `tests/*.c` still use `#include "testutil.h"`,
    correctly: that one is test-local rather than installed.

14. **Empty parameter lists.** **Resolved.** `akgl_game_init`,
    `akgl_game_update_fps`, `akgl_heap_init`, `akgl_heap_init_actor` and the
    eight `akgl_registry_init*` functions declare and define `(void)`. Before
    C23 `()` means "unspecified arguments" and suppresses argument checking, so
    these were the entry points a caller could pass anything to.

15. **`AKERR_NOIGNORE` was applied inconsistently at definition sites.**
    **Resolved.** It is on the declarations, where it does its work, and on no
    definition in `src/`.

### 3. Error-handling pattern

16. **`*_RETURN` macros are used inside `ATTEMPT` blocks, which skips `CLEANUP`.**
    **Fixed in 0.5.0.** Ten sites, found by scanning rather than from this list
    -- it named six and missed the four in `akgl_collide_rectangles`.

    The one that mattered was the success path of
    `akgl_get_json_tilemap_property`, which leaked two of the string pool's 256
    entries on every lookup that *found* what it was asked for. A map load does
    that several times per layer.

    Two needed more than swapping the macro. In
    `akgl_get_json_tilemap_property` a plain `break` would have fallen through
    to the "property not found" `FAIL_RETURN` after `FINISH`, reporting a miss
    for something found, so the success path sets a flag. In
    `akgl_collide_rectangles` the eight early exits were followed by
    `*collide = false;`, which would have overwritten the hit that broke out of
    the block; each corner test writes the flag itself, so that line is gone
    rather than moved.

    `akgl_controller_default` was the other behavioural one: its
    `SUCCEED_RETURN` was the last statement in the `ATTEMPT` block, so the path
    that falls out of `FINISH` reached the closing brace of a non-void function.

    **`scripts/check_error_protocol.py` keeps this closed**, as the
    `error_protocol` test. It also enforces the other rule with a silent failure
    mode -- no `return` out of a `HANDLE` block.

17. **NULL-check discipline varies by function.** **Fixed in 0.5.0.** The eight
    typed JSON accessors that validated their container and then wrote through
    `dest` unconditionally now check `key` and `dest` as the two string
    accessors always did; the null physics backend checks its actors like the
    arcade one; and `akgl_render_2d_frame_start`, `_frame_end` and `_shutdown`
    check `self`, which the first two read straight through.

    `tests/renderer.c` calls all three with `NULL`, which segfaulted before.

18. **Error-context variable naming is split between `errctx` and `e`.**
    **Fixed in 0.5.0**, in its own commit because it is a rename and nothing
    else. All 45 remaining sites are `errctx`; applying `\be\b -> errctx` to
    each removed line reproduces the added line exactly, and the counts match at
    333 either way.

    `e` keeps its meaning where the convention wants it -- an incoming context
    being inspected, as in `akgl_get_json_with_default(e, ...)`.

### 4. Types and macros

**Items 19 through 23 are resolved in 0.5.0.**

19. **`float`/`double` used raw where `types.h` defines aliases.** The four
    signatures and twelve struct fields that spelled them out now use
    `float32_t` and `float64_t` like the actor and character structs. They are
    plain typedefs, so this is a spelling change and not an ABI one.
    `float64_t`'s doc no longer says "unused so far".

20. **`AKGL_COLLIDE_RECTANGLES` had unbalanced parentheses.** Deleted. Three
    opens against two closes meant any expansion was a syntax error, it had no
    callers, and it duplicated `akgl_collide_rectangles`.

21. **Bitmask macros were unparenthesized.** All five are fully parenthesized,
    and `AKGL_BITMASK_CLEAR` no longer carries a semicolon inside its body.

    `tests/bitmasks.c` covers the composition cases, and writing them turned up
    something worth recording: the obvious test does **not** catch this. For a
    bit that is *set*, `!AKGL_BITMASK_HAS(mask, bit)` misparses to
    `!(mask & bit) == bit`, which is `0 == bit` -- false, the same answer the
    correct parse gives. It only diverges for a bit that is *not* set and whose
    value is not 1: `!(0)` is 1, and `1 == 64` is false where the answer should
    be true. The suite now uses that shape, and fails against the old macros.

22. **The state and iterator bit macros mixed forms.**
    `AKGL_ITERATOR_OP_UPDATE` is `(1 << 0)` like its 31 siblings, and every
    `1 << n` in `iterator.h` and `actor.h` is parenthesized, with the
    hand-aligned value columns preserved.

    The bit-pattern comments in `actor.h` are not wrong so much as unlabelled:
    each shows the pattern *within its own 16-bit half*, which is why bit 16
    looks like it restarts at bit 0. The section headings say so now. Rendering
    the full 32-bit value instead would push those lines past the 100-column
    fill.

    **Newly recorded, and still open:** `1 << 31` is undefined behaviour on a
    signed `int`. It is `(1 << 31)` in both tables and wants to be an unsigned
    shift, but `akgl_Actor::state` is `int32_t` and `akgl_Iterator::flags` is
    `uint32_t`, so the two tables do not want the same answer. Worth deciding
    deliberately rather than sneaking a `u` in.

23. **`akgl_Frame` was defined and never used.** Deleted.

### 5. `AKGL_ACTOR_STATE_STRING_NAMES` disagrees with `actor.h`

**All three resolved in 0.5.0.**

24. **The array bound differed between declaration and definition.** The
    header declared `[AKGL_ACTOR_MAX_STATES+1]` (33) and the definition was a
    literal `[32]`, so a consumer trusting the declared bound read past the
    object. Both are `[AKGL_ACTOR_MAX_STATES]` now, and the definition is sized
    by the macro rather than by a literal.

25. **Two entries named the wrong bit.** Indices 11 and 12 said
    `AKGL_ACTOR_STATE_UNDEFINED_11` and `_12` where `actor.h` has `MOVING_IN`
    and `MOVING_OUT`, so no character JSON could ever bind a sprite to either
    state -- the name it would have to write was not in the registry.

    `tests/registry.c` now walks the whole table: every entry non-`NULL`, every
    entry resolving to its own bit through
    `AKGL_REGISTRY_ACTOR_STATE_STRINGS`, no two entries sharing a name (a
    duplicate silently overwrites and makes one bit unreachable), and
    `MOVING_IN`/`MOVING_OUT` named explicitly so a regression reads as what it
    is.

26. **The generation comment was stale.** There is no generator, no Makefile
    and no `lib_src/`. The comment is gone and the file's own header now says it
    is maintained by hand and states the two invariants that keep breaking.

### 6. Doxygen drift

27. **Three struct doc comments in `tilemap.h` were rotated by one.** Already
    correct -- the doxygen rewrite fixed this before it was checked here.
    `akgl_TilemapObject`, `akgl_TilemapLayer` and `akgl_Tileset` each describe
    themselves.

28. **`point` documented as two-dimensional with an `x`, `y` and `z`.** Already
    correct, and the type is `akgl_Point` now.

29. **Doc comments on the definition rather than the header.** Resolved with
    item 7: the four controller handlers and the six tilemap loader helpers had
    their documentation moved to the header when they were declared there.

### 7. Formatting and hygiene

**Items 31 through 36, 38 and 41 are resolved in 0.5.0. Item 37 is not; see
below.**

31. **Leftover debug code.** The four `SDL_Log` lines in `src/controller.c`
    guarded by `event->type == 768 && event->key.which == 11 &&
    event->key.key == 13` -- decimal literals for one keyboard on one
    developer's machine, inside the per-event inner loop -- are gone.

32. **Large commented-out blocks.** The five abandoned `SDL_GetBasePath()`
    path-prefixing lines across `assets.c`, `sprite.c`, `character.c` and
    `tilemap.c` are gone. They were superseded by `akgl_path_relative`.

33. **Unused locals.** `curTime` in `akgl_game_update` and in
    `akgl_render_2d_draw_world`, `j` in `akgl_render_2d_draw_world` (shadowed
    by its own inner loop), `target` in `akgl_character_sprite_get`, both
    `result` declarations in `util.c`, and `screenwidth`/`screenheight` in
    `akgl_game_init`. `opflags` in `akgl_heap_release_character` is no longer
    unused -- it is what drives the state-sprite walk added for **Defects**
    item 21.

34. **`akgl_game_update`'s default flags OR-ed the same bit twice.** It reads
    `AKGL_ITERATOR_OP_UPDATE | AKGL_ITERATOR_OP_LAYERMASK` now. This is a
    statement of intent rather than a behaviour change, and the reason is worth
    knowing: **nothing in that loop reads either bit**. It never compares
    `actor->layer` to the layer it is sweeping, which is exactly **Performance**
    item 32 -- every actor updated sixteen times a frame -- and that is still
    open.

35. **`akgl_draw_background` was the only public function outside the error
    protocol.** It now takes an `akgl_RenderBackend *` like every other entry
    point in `draw.h`, returns an error context, checks the backend and its
    `sdl_renderer`, and restores the draw colour it found instead of leaving it
    changed.

    It was listed under **Remaining work** as needing the offscreen renderer
    harness. It does not, and never did -- what it needed was to stop reading
    the global. `tests/draw.c` covers the checkerboard pattern, the restored
    draw colour, zero and negative sizes, and a `NULL` backend.

36. **`akgl_registry_init_actor` was the only initializer that destroyed the
    registry it was replacing.** All eight go through one `registry_create()`
    helper now, so the other seven stop leaking an `SDL_PropertiesID` per call
    after the first -- which a game that resets between levels makes on every
    level.

    Fixed alongside it, because it is the same function: `akgl_registry_init()`
    never called `akgl_registry_init_properties()`, which is **Defects → Known
    and still open** item 3. `AKGL_REGISTRY_PROPERTIES` stayed 0 for any caller
    that did not also go through `akgl_game_init`, making `akgl_set_property` a
    silent no-op and `akgl_get_property` always return the caller's default --
    so `akgl_physics_init_arcade` and `akgl_render_2d_init` quietly ignored
    their configuration. `tests/registry.c` sets a property and reads it back.

37. **Redundant casts obscure the code.** **Still open -- but the precondition
    it named is now met.** Roughly 180 pointer casts across `src/`, a large
    majority no-ops, densest in `src/tilemap.c` and `src/character.c`.

    This item used to say the benefit only arrives once the build turns on the
    warnings those casts suppress, and that doing it first buys nothing but
    churn. `-Wall` is on now (see `AGENTS.md`, "Compiler warnings"), so the
    sweep can proceed as its own commit.

    **The argument turned out to be right, with evidence.** Turning `-Wall` on
    found three genuine signedness mismatches in `src/sprite.c`: `obj->width`,
    `obj->height` and `obj->speed` are `uint32_t` and were being passed straight
    to `akgl_get_json_integer_value(..., int *)`. A cast would have silenced all
    three. They are fixed by reading into an `int`, range-checking, and
    assigning -- which also turned up that `speed` is scaled by 1,000,000 into a
    32-bit field, so anything past 4294 ms overflowed rather than being held.

    When doing the sweep: remove a cast, rebuild, and read what the compiler
    says. A cast that was load-bearing will say so.

38. **`struct`-qualified parameters in two definitions.** `akgl_physics_null_move`
    and `akgl_physics_arcade_move` use the typedef like the other eight.

39. **`text.c` validated the wrong argument.** Resolved earlier, alongside the
    text measurement work.

40. **`akgl_path_relative_from` disagreed on the output parameter.** Moot: the
    function is deleted. See **Defects → Known and still open** item 4.

41. **`dst` vs `dest` for output parameters.** `akgl_string_copy` and
    `akgl_path_relative` take `dest` now, like everything else.


## Test suites that could not fail

Found while renaming the exported globals, and the reason item 4 above is filed
as a real defect rather than a style complaint. Both are fixed.

**Every suite reported success on any status whose low byte is zero.**
libakerror's default unhandled-error handler ends in `exit(errctx->status)`.
`exit` keeps only the low byte of what it is given, and libakgl's status band
starts at `AKERR_FIRST_CONSUMER_STATUS`, which is 256. `AKGL_ERR_SDL` is
therefore exactly 256, `exit(256)` is a wait status of 0, and CTest recorded a
pass. The most common failure status in a library built on SDL was the one
status that could not fail a test.

**`tests/character.c` was green while running one of its four tests.** It
aborted in `test_character_sprite_mgmt` with
`Failed loading asset .../spritesheet.png : Parameter 'renderer' is invalid` —
the symbol collision described in item 4 — and exited 0 because that status was
`AKGL_ERR_SDL`. Two independent defects had to line up, and they did, for long
enough that `TODO.md` recorded the suite as passing and wondered which change
had fixed it. Nothing had; it had stopped running.

**Fixed twice.** 0.5.0 worked around it here, with a
`TEST_TRAP_UNHANDLED_ERRORS()` in `tests/testutil.h` that installed a handler
collapsing any status a byte cannot carry onto 1. Once installed, no other suite
changed colour, so this was not masking anything beyond `character` — but it
could have been at any time, and nothing would have said so.

That entry ended "any consumer's test suites have this problem; that is worth
raising upstream", and it was. **libakerror 2.0.1 fixes it at the source**:
`akerr_exit()` owns the status-to-exit-code mapping and the default handler
calls it, so 0 exits 0, 1 through 255 exit themselves, and anything else exits
`AKERR_EXIT_STATUS_UNREPRESENTABLE` (125) rather than a low byte that is either
a lie or a claim of success. There is no wider `exit()` to reach for —
`_exit()`, `_Exit()`, `quick_exit()` and the raw `exit_group` syscall all
truncate the same way, and even `waitid()` reports the truncated value.

The workaround is gone as of 0.6.0, along with its 21 call sites. Verified by
putting the original failure back: a `FAIL_BREAK(AKGL_ERR_SDL)` in
`tests/character.c`'s `main` now exits 125 and CTest records a failure, where it
exited 0 and passed before.

## Coverage status

Generated with:

```sh
cmake -S . -B build-coverage -DAKGL_COVERAGE=ON -DCMAKE_BUILD_TYPE=Debug
cmake --build build-coverage --parallel
ctest --test-dir build-coverage --output-on-failure
```

Reports land in `build-coverage/coverage/` (`index.html`, `coverage.xml`).

**Line coverage 83.9%, function coverage 91.2%** (2433/2901 lines, 176/193
functions), up from 79.6% / 87.2% before the 0.5.0 defect work and from a
39.6% / 44.3% baseline. All 25 registered tests pass, and that count now
includes three non-C ones: `api_surface`, `error_protocol` and the generated
per-header compile checks inside `headers`.

The `character` suite deserves its own line. It was recorded here as passing;
it was not running. See "Test suites that could not fail" below.

Note the trap described in "Known and still open" item 13 while regenerating
these numbers: a coverage tree rebuilt after a source edit fails `coverage_reset`
with `GCOV returncode was 5`. `find build-coverage -name '*.gcda' -delete` clears
it.

| File | Lines | Functions |
|---|---|---|
| `src/actor.c` | 205/258 (80%) | 16/18 |
| `src/assets.c` | 0/21 (0%) | 0/1 |
| `src/audio.c` | 229/248 (92%) | 22/23 |
| `src/character.c` | 122/126 (97%) | 7/7 |
| `src/controller.c` | 314/349 (90%) | 17/17 |
| `src/draw.c` | 281/286 (98%) | 12/12 |
| `src/error.c` | 9/9 (100%) | 1/1 |
| `src/game.c` | 142/243 (58%) | 13/18 |
| `src/heap.c` | 116/116 (100%) | 12/12 |
| `src/json_helpers.c` | 123/123 (100%) | 11/11 |
| `src/physics.c` | 144/144 (100%) | 10/10 |
| `src/registry.c` | 83/111 (75%) | 12/13 |
| `src/renderer.c` | 61/83 (74%) | 8/8 |
| `src/sprite.c` | 102/110 (93%) | 5/5 |
| `src/staticstring.c` | 17/18 (94%) | 2/2 |
| `src/text.c` | 79/80 (99%) | 7/7 |
| `src/tilemap.c` | 276/444 (62%) | 13/20 |
| `src/util.c` | 128/130 (98%) | 7/7 |
| `src/version.c` | 2/2 (100%) | 1/1 |

`src/tilemap.c` moved the most, 47% to 62%, because the bounds and leak work
needed the loaders driven rather than merely called. `src/assets.c` is still the
one file with no coverage at all.

Branch coverage reads 24.7% and should not be used as a target. The akerror
control-flow macros (`ATTEMPT`/`CATCH`/`PROCESS`/`FINISH`, `FAIL_*_RETURN`)
expand into large branch trees per call site, most of them unreachable in normal
operation — `src/game.c` reports over 1700 branches across 230 lines. Track line
and function coverage; treat branch coverage as a relative signal within a file.

### Mutation testing

`scripts/mutation_test.py` was run over the three new files as a smoke check
(`--max-mutants 8` to 10 each, so these are samples rather than exhaustive
scores):

| File | Score | Surviving mutants |
|---|---|---|
| `src/draw.c` | 90% | Deleting the `FAIL_ZERO_BREAK` on `SDL_CreateTextureFromSurface` in `akgl_draw_flood_fill` |
| `src/audio.c` | 75% | Deleting `SUCCEED_RETURN` from the static `check_voice`; deleting `spec.freq` before opening a device |
| `src/text.c` | 50% | Three in `akgl_text_rendertextat`, which had no test yet, plus one `SUCCEED_RETURN` deletion |

The first pass over `src/audio.c` scored 50% and named two real gaps, both of
which are now tested: nothing asserted that an *unconfigured* voice is audible
(the whole reason the table defaults to a square wave at full level rather than
a zeroed struct), and no envelope test used a non-zero attack *and* decay
together, so the decay measuring from the wrong origin survived. `src/draw.c`
scored 70% first and named one: the circle was only checked at its four axis
points, which a mis-signed octant reflection survives, so it now checks that
every plotted pixel has a mirror in the other three quadrants.

Re-run as a smoke check after the akbasic API work, again at 10 sampled
mutants each:

| File | Score | Surviving mutants |
|---|---|---|
| `src/controller.c` | 40% | Three `SDL_Log` deletions; `keybuffer_head`'s initialiser; `count > 0` in `keybuffer_attach_text`; the `mod` a text-only entry is given |
| `src/audio.c` | 60% | The `break` on the last `switch` case; `errctx->handled` in the device callback; `ensure_voices()` in the mixer; the mixer's voice loop bound |

Only one of those was a real gap and it is now asserted: nothing checked that
a text-only ring entry reports no modifiers. Of the rest, three are equivalent
mutants rather than misses — a ring buffer whose head starts at 1 behaves
identically, `count > 0` cannot be false where it is checked, and deleting the
`break` on a `switch`'s last case changes nothing — and the mixer's `v <=`
bound reads one voice past a zeroed table, which is undefined rather than
observable. `SDL_Log` deletions are unobservable by construction.

What is left is honestly untestable from here. Deleting a `SUCCEED_RETURN`
leaves a non-void function falling off its end, which is undefined rather than
observably wrong, and the surviving SDL branches are allocation failures the
suite has no way to provoke. The three `src/text.c` survivors in
`akgl_text_rendertextat` are gone: it is tested now, against a software
renderer, and deleting any of its three backend checks fails the suite. That
was not free — the first draft of the test used a made-up `SDL_Renderer`
pointer, which SDL refuses on its own, so the deleted-check mutant survived it.
A live renderer was what made the check observable.

### Suites

Every suite is registered through the `AKGL_TEST_SUITES` list in
`CMakeLists.txt`, which drives target creation, CTest registration, the
`WORKING_DIRECTORY`/`TIMEOUT` properties, the link line, and the
`FIXTURES_REQUIRED akgl_coverage` list together. Adding `tests/<name>.c` and the
name to that list is all a new suite needs; it can no longer be accidentally
left out of the coverage fixture.

Shared assertion helpers are in `tests/testutil.h`: `TEST_ASSERT`,
`TEST_ASSERT_FEQ`, `TEST_EXPECT_STATUS`, `TEST_EXPECT_OK`, `TEST_EXPECT_ANY_ERROR`,
and `TEST_ASSERT_FLAG`. All except the last expand to a `break` on failure, so
they belong directly inside an `ATTEMPT` block, not inside a loop nested in one.

Done:

- `tests/physics.c` — both backends, the factory, and the full simulation loop
  including thrust clamping, drag, layer masking, parent/child positioning, and
  logic-interrupt handling. 100%.
- `tests/heap.c` — pool exhaustion for all five pools, refcount clamping,
  recursive child release, registry cleanup on release. 100%.
- `tests/json_helpers.c` — every typed accessor, both string accessors'
  allocate-vs-reuse paths, array bounds, and `akgl_get_json_with_default`. 100%.
- `tests/controller.c` — control map push and capacity, the default binding set,
  keyboard and gamepad dispatch including cross-device rejection, the dpad
  handlers, and device add/remove against the dummy drivers. 90%.
- `tests/game.c` — version gating, the save/load roundtrip, foreign-save
  rejection, truncated-table detection, the state lock, and FPS accounting. 54%.
- `tests/actor.c` — extended with the eight control-map handlers, automatic
  facing, movement logic, the animation frame state machine, `akgl_actor_update`,
  and character/sprite binding lookups. 80%.
- `tests/audio.c` — every waveform, the ADSR envelope stage by stage, gate
  expiry and release, the frequency sweep frame by frame, voice summing and
  clamping, the master level, and device open/shutdown under the dummy driver.
  92%.
- `tests/draw.c` — every primitive against a 64x64 software renderer with the
  pixels read back, including flood-fill containment, save/paste roundtrip, and
  that drawing restores the renderer's draw color. 95%.
- `tests/text.c` — font loading into the registry, both measurement entry points
  against a monospaced fixture font, and drawing through a bound backend over a
  software renderer, including every way the backend can be unusable. 100%.
- `tests/renderer.c` — the 2D vtable binding, frame start and end, both
  `draw_texture` paths, the refusals a bound-but-unrendered backend gives, and
  the `draw_mesh` stub. 56%; `akgl_render_init2d` and `akgl_render_2d_draw_world`
  are what is left, and both want the harness.
- `tests/headers.c` — that `akgl/controller.h` compiles as the first include in
  a translation unit. The assertion is the compile; `main()` only has to return
  zero.

## Remaining work

### Needs the offscreen renderer harness

`akgl_render_init2d` and `akgl_render_2d_draw_world` in `src/renderer.c` (33
lines), `akgl_draw_background` in `src/draw.c` (13), `src/assets.c` (21),
`akgl_actor_render`/`actor_visible` in `src/actor.c` (53), and the drawing half
of `src/tilemap.c` all need a live `renderer` global, a window, or the world
globals.

`akgl_text_rendertextat` was on this list and is not any more: `tests/text.c`
builds a software renderer and binds a backend to it with `akgl_render_bind2d`
in nine lines, which is enough for anything that only needs *a* renderer rather
than the whole world. `tests/renderer.c` and `tests/draw.c` do the same. The
harness is still wanted, but for what is left it is a convenience rather than
the blocker it was.

Build `tests/harness.c` / `tests/harness.h` with `akgl_test_init_headless()` and
`akgl_test_shutdown_headless()`: set the dummy video and audio drivers,
`SDL_Init()`, `akgl_heap_init()`, `akgl_registry_init()`, create a software
`SDL_CreateWindowAndRenderer`, and point the global `renderer` at it. Seven
existing tests hand-roll this today (`tests/sprite.c:194`, `tests/character.c:200`,
`tests/tilemap.c:421`, `tests/charviewer.c:42`, plus `tests/draw.c`,
`tests/renderer.c` and `tests/text.c`); collapse them onto the shared harness in
the same change.

Then:

- **`tests/renderer.c` extensions** — `akgl_render_init2d` populating the camera
  from the property registry, and `draw_world` layer ordering. `tests/renderer.c`
  exists and covers everything that does not need a world or the registry: the
  vtable binding, frame start/end against a NULL `sdl_renderer`, both
  `draw_texture` paths including `angle != 0` with a NULL center, and the
  `draw_mesh` stub. Note `defflags` at `src/renderer.c:113` is uninitialized
  until the `if` body runs.
- **`tests/assets.c`** — BGM loading into `AKGL_REGISTRY_MUSIC` under the dummy
  audio driver.
- **`tests/draw.c` extensions** — `akgl_draw_background` at zero, negative and
  oversized dimensions. `tests/draw.c` exists and covers every other primitive
  against a software renderer; `akgl_draw_background` is the one function in the
  file that still reads the global `renderer` rather than taking a backend.
- **`tests/tilemap.c` extensions** — `akgl_tilemap_draw`, `_draw_tileset`, and
  `akgl_tilemap_load_layer_image`.

### Does not need a renderer

- **`src/tilemap.c`** — `akgl_tilemap_scale_actor` is pure math over three
  branches (`src/tilemap.c:824-830`); `akgl_get_json_properties_number`,
  `_float`, and `_double` need only a JSON snippet; `akgl_tilemap_load_physics`
  needs a fixture with the physics property block present, absent, and
  malformed. Together roughly 100 of the 225 uncovered lines.
- **`src/game.c`** — `akgl_game_init`, `akgl_game_update`, `akgl_game_lowfps`,
  and `akgl_game_updateFPS`'s frame loop need a window; revisit after the
  harness lands.
- **`src/registry.c`** — `akgl_registry_load_properties` needs a fixture with a
  `properties` object, plus the missing-file, missing-key, and wrong-value-type
  cases. Assert the loop at `src/registry.c:148-158` does not leak the string
  heap.

## Defects

### Fixed while building the suites

Each was found by a test written to assert correct behavior.

1. **`akgl_physics_simulate` dereferenced `self` before its NULL check.**
   `src/physics.c:132` read `self->gravity_time` at declaration time, three
   lines above `FAIL_ZERO_RETURN(e, self, ...)`. A NULL backend segfaulted.
2. **`akgl_game_save` never flushed or closed its stream.** `CLEANUP` and
   `PROCESS` were transposed, which put the `fclose` inside the `PROCESS`
   switch, where it only ran if an error context existed and reported success.
   An ordinary save produced an empty file.
3. **`akgl_game_save_actors` wrote name-table terminators from a single char.**
   `aksl_fwrite((void *)&nullval, 1, AKGL_ACTOR_MAX_NAME_LENGTH, fp)` emitted
   127 bytes of adjacent stack memory into the save file and produced a sentinel
   the loader could not recognize.
4. **`akgl_game_load_objectnamemap` swallowed read failures.** `CATCH` used
   directly inside `while (1)` breaks the loop, not the function, so a truncated
   or corrupt name table loaded as a successful game.
5. **`akgl_Actor_cmhf_up_on` and `_down_on` dereferenced `basechar` unguarded**,
   unlike their left and right counterparts.
6. **`akgl_actor_logic_movement` checked `actor` twice** instead of checking
   `actor->basechar` before dereferencing it.
7. **The gamepad handlers checked `appstate` three times each**, so a NULL event
   or a missing player actor was never caught and `player->state` was
   dereferenced regardless.

### Known and still open

1. **`akgl_render_and_compare` compares a texture against itself.**
   **Fixed in 0.5.0**: the second pass draws `t2`. Both passes drew `t1`, so it
   always reported a match and every image assertion built on it -- including
   the ones in `tests/sprite.c` -- asserted nothing.

2. **`akgl_tilemap_release` double-frees tileset textures.**
   **Fixed in 0.5.0.** The layers loop tested `layers[i].texture` and destroyed
   `tilesets[i].texture`, so every tileset texture was freed twice on a single
   release and no image layer's texture was freed at all. Each pointer is
   cleared as it goes now, which also makes a second release safe rather than a
   use-after-free.

   `tests/tilemap.c` loads the fixture map, releases it three times, and
   asserts every texture pointer is `NULL`.

3. **`akgl_registry_init` never initializes the properties registry.**
   **Fixed in 0.5.0**, alongside internal-consistency item 36, which is the same
   function. `akgl_registry_init()` calls `akgl_registry_init_properties()` now,
   so `AKGL_REGISTRY_PROPERTIES` is live for callers that do not also go through
   `akgl_game_init` -- which is what made `akgl_set_property` a silent no-op and
   `akgl_get_property` always hand back the caller's default, and so what made
   `akgl_physics_init_arcade` and `akgl_render_2d_init` quietly ignore their
   configuration. `tests/registry.c` sets a property and reads it back.
4. **`akgl_path_relative_from` is a stub that leaks.** **Deleted in 0.5.0.**
   It claimed a heap string, never wrote its output, and never released it, so 256
   calls exhausted the string pool. It was declared in no header, called from
   nowhere, and duplicated what `akgl_path_relative` already does. Fixing an
   unfinished function nobody can reach is worse than deleting it; this also
   closes item 40, which was about the output-parameter shape it disagreed with
   the rest of the family on.
5. **`akgl_compare_sdl_surfaces` memcmps without checking geometry.**
   **Fixed in 0.5.0**: dimensions, pitch and pixel format are compared first,
   and any difference is a mismatch. `tests/util.c` compares a 32x32 surface
   against an 8x8 one in both directions, which used to read 4 KiB past the end
   of the smaller.

6. **`akgl_string_initialize` overflows by four bytes when `init` is NULL.**
   **Fixed in 0.5.0**: it zeroes `sizeof(obj->data)`. The four bytes it used to
   run past the end of the object landed on the *next* pool slot's `refcount`,
   which is the field the allocator reads to decide whether a slot is free --
   so the overrun could hand a live string out twice.

   `tests/staticstring.c` claims two adjacent slots, stamps a sentinel into the
   second's refcount, and initializes the first.

   Fixed alongside it, because it is the same file and the same class:
   `akgl_string_copy` accepted a `count` above `AKGL_MAX_STRING_LENGTH`, which
   read past the end of one pool slot and wrote past the end of another. The
   header documented that as behaviour. It is `AKERR_OUTOFBOUNDS` now, and a
   negative count is refused too.
7. **Savegame name lengths disagree between writer and reader.** **Fixed in
   0.5.0.** The reader names the same constant the writer does, per table --
   `AKGL_SPRITE_SHEET_MAX_FILENAME_LENGTH` for spritesheets and so on. It used
   `AKGL_ACTOR_MAX_NAME_LENGTH` for all four; the other three are 128 as well,
   so only the spritesheet table was wrong, and that was enough.

   **The failure was worse than "cannot be read back", which is what made the
   test interesting.** The tables carry no length prefix and end at a zeroed
   sentinel, so a reader stepping the wrong width does not run off anything --
   it finds a run of zeros somewhere inside an entry, stops early, and reports
   success with silently wrong maps. A test that only asserted the load
   succeeded passed against the broken reader.

   So `akgl_game_load` checks the stream is at EOF once the four tables are
   read. That is what turns a width disagreement into `AKERR_IO` instead of a
   corruption, and it is the assertion `tests/game.c` hangs on. The new
   roundtrip test registers a name in each of the four registries, with a
   full-length one in the spritesheet registry, and fails with `AKERR_IO`
   against a mismatched reader.

   That EOF check has to move when the objects themselves start being written;
   there is a comment at the site saying so.

   A first pass at this introduced four `AKGL_GAME_SAVE_*_NAME_WIDTH` aliases,
   one per table, on the reasoning that the on-disk format's widths are a
   separate concern from the object model's. They were removed. Each expanded to
   exactly one existing constant and had exactly one use per side, so they were
   indirection with no second consumer -- and the divergence they anticipated
   cannot happen quietly anyway: raising one of those lengths is an ABI change,
   which bumps the version, and `akgl_game_load` refuses a save whose
   `libversion` does not match before it reads a single table. What actually
   guards the widths is the EOF check, which works however they are spelled.

8. **Heap acquire functions are asymmetric.** `akgl_heap_next_string` increments
   `refcount`; `next_actor`, `next_sprite`, `next_spritesheet`, and
   `next_character` do not. `tests/heap.c` pins the current behavior and says so;
   decide whether to make them symmetric or document the split.
9. **`tests/util.c` defines `test_akgl_collide_point_rectangle_logic` but
   `main()` never calls it.** **Fixed in 0.5.0**; it is called, and passes.

10. **`controller.h` declares functions that do not exist.** **Fixed in 0.5.0**;
    the definitions carry the declared `akgl_controller_handle_*` names now. See
    internal-consistency item 7, and `scripts/check_api_surface.sh`, which is
    what stops this class of drift coming back.
11. **`akgl_controller_pushmap` and `akgl_controller_default` accept negative map
    ids.** **Fixed in 0.5.0**: both check the lower bound as well.
    `tests/controller.c` passes -1 and -4096 to each.

12. **A failed controller-DB fetch silently destroys the tracked fallback.**
    **Fixed in 0.5.0**, both halves.

    `mkcontrollermappings.sh` now runs under `set -euo pipefail`, fetches into a
    temporary directory, and moves the result into place only after checking
    three things: curl's exit status (with `--fail`, so an HTTP error is a
    status rather than an error page in the body), a plausible minimum mapping
    count, and that no mapping carries a quote or backslash that would break the
    C string literal it becomes. Any of those failing leaves the tracked header
    exactly as it was and exits non-zero. `AKGL_CONTROLLERDB_URL` and
    `AKGL_CONTROLLERDB_MIN_LINES` are environment-overridable, which is how the
    failure paths were exercised.

    Verified against all five: an unresolvable host, a 404, a truncated
    response, an empty-but-successful response -- the original failure exactly
    -- and a response containing a quote. Each refuses, and the header's
    checksum is unchanged after every one.

    The build no longer runs it. The `add_custom_command` declared
    `OUTPUT include/akgl/SDL_GameControllerDB.h` as a *relative* path, which
    CMake resolves against the binary directory while the script writes to the
    source directory, so the declared output never appeared, the command was
    permanently out of date, and every build re-ran it -- needing network access
    and leaving the tree dirty. It is an explicit `controllerdb` target now, and
    the header is no longer listed as a library source, which is all it was
    there for.

    The empty-initializer problem goes with it: `const char *SDL_GAMECONTROLLER_DB[] = {};`
    is a constraint violation in ISO C that compiles only as a GCC extension,
    and the minimum-count check is what guarantees at least one entry.

    Regenerating against the real upstream produced byte-identical mappings --
    2255 entries, no content change -- so the rewrite is faithful. The only diff
    is the `$(date)` stamp and the include guard, which is
    `_AKGL_SDL_GAMECONTROLLERDB_H_` now to match every other header. That change
    was made in the generator rather than by hand, and the tracked copy carries
    it so a future regeneration shows no spurious diff.

13. **A stale build tree in the source directory breaks the coverage run.**
    **Fixed in 0.5.0.** Both `gcovr` invocations take the build tree as an
    explicit positional search path and neither passes `--object-directory`.

    gcovr searches for `.gcda`/`.gcno` under its search paths, and with none
    given it searches `--root` -- the source directory, which is where
    developers keep their build trees. `--object-directory` does not narrow
    that; per gcovr's own help it only identifies "the path between gcda files
    and the directory where the compiler was originally run".

    **Verified by reproducing it.** Two instrumented trees were built inside the
    source directory with a source edit between them, so they described
    different line numbers for the same functions. The old invocation fails with
    `Got function write_exact on multiple lines: 46, 48` and exits 64; the new
    one exits 0 and the whole 25-test coverage run passes with the stale tree
    still sitting there.

    The second, smaller version of the same thing -- rebuilding a coverage tree
    after editing a test leaves `.gcda` files describing the old object layout,
    and `coverage_reset` fails with `GCOV returncode was 5` before it can delete
    them -- is unchanged. `find build-coverage -name '*.gcda' -delete` clears
    it. That one is gcov's, not gcovr's search path.

14. **22 public symbols shipped without a version or soname bump.** 42b60f7 added
    `akgl_draw_point`, `_line`, `_rect`, `_filled_rect`, `_circle`, `_flood_fill`,
    `_copy_region` and `_paste_region`; `akgl_audio_init`, `_shutdown`, `_tone`, `_stop`,
    `_waveform`, `_envelope`, `_volume`, `_voice_active` and `_mix`;
    `akgl_controller_poll_key` and `_flush_keys`; and `akgl_text_measure` and
    `_measure_wrapped`. `project(akgl VERSION 0.1.0)` and the `libakgl.so.0.1` soname were
    both left alone.

    That contradicts this repository's own stated rule, which `akbasic`'s `CLAUDE.md` quotes
    back: *"for both 0.x libraries the soname carries `MAJOR.MINOR` deliberately: 0.1 and 0.2
    are different ABIs."* Adding exported symbols under an unchanged soname has two
    consequences, and the first is the one that bites:

    - A binary compiled against the new headers links happily against a `libakgl.so.0.1`
      built from the old tree, because the soname says they are the same ABI. It fails at
      symbol resolution rather than at configure time.
    - `AKGL_VERSION_AT_LEAST(0, 1, 0)` is true for both trees, so a consumer cannot
      feature-test for the new API at all. `akbasic` pins the requirement by submodule commit
      instead, and says so in its README, which is not a thing a released library should make
      anybody do.

    Fix: bump `project()` to 0.2.0, which carries the soname to `libakgl.so.0.2` through the
    existing logic at `CMakeLists.txt:138`. `akstdlibConfigVersion.cmake`'s `SameMinorVersion`
    equivalent then refuses the mismatch at configure time as well.

    **Resolved by 1066ac7**, which did exactly that while this was being written — the two
    crossed, rather than one following the other. Kept rather than deleted because the *reason*
    is still the useful part: `akbasic` could not feature-test for the new API and had to pin
    `libakgl` by submodule commit in its README until this landed, which is the concrete cost of
    an additive release under an unchanged soname. Worth remembering the next time a handful of
    symbols looks too small to bump for.

### Found while rewriting the Doxygen comments

Each of these came out of reading an implementation against the contract its
header claimed. They are recorded inline as `@note` or `@warning` on the
function concerned, so a reader of the generated documentation finds them
without coming here first. Ordered by blast radius.

15. **`akgl_path_relative` leaks one error-context slot per call on its fallback
    path.** `src/util.c:120` returns `akgl_path_relative_root(...)` from inside
    the `HANDLE(e, ENOENT)` block. `FINISH` is what carries `RELEASE_ERROR`, so
    returning before it never gives the context back. libakerror hands these out
    of a fixed `AKERR_ARRAY_ERROR[128]`, and this is not a rare path — it is the
    *ordinary* one, taken every time an asset names a neighbour relative to its
    own file rather than to the working directory. Every tileset image, layer
    image and spritesheet in a map costs a slot, permanently. Once the array is
    exhausted every subsequent failure anywhere in the process has nowhere to
    report from.

    Fix: assign the result to a local, `break`, and return after `FINISH`; or
    hoist the fallback out of the handler entirely and let the `HANDLE` block
    only record that a retry is wanted. Touches `src/util.c:117-121` only.

16. **`akgl_sprite_load_json` does not bound the `frames` array.**
    **Fixed in 0.5.0.** The count is bounded against `AKGL_SPRITE_MAX_FRAMES`
    before anything is written, and each element is read into an `int` and
    narrowed deliberately rather than written through a `uint32_t *` cast of a
    `uint8_t *`. A frame number that does not fit a `uint8_t` is refused too,
    rather than truncated into an index that names a different tile.

    `tests/sprite.c` covers exactly the maximum (must load, and every id must
    arrive), one past it, and the wide frame number, against three new fixtures.
    Against the old code the middle case loads happily.

17. **Two more unbounded array loads in the tilemap loader.**
    **Fixed in 0.5.0**, both with the bound at the top of the loop body, the
    shape `akgl_tilemap_load_layers` in the same file already used.

    `tests/tilemap.c` covers both against generated fixtures: an object layer
    of exactly 128 (must load) and of 129, and a map with 17 tilesets. The
    object one is the reachable half -- 128 objects is not a large object layer
    and `akgl_TilemapObject` is not small.

18. **`akgl_get_json_with_default` defaults on a status the array accessors never
    raise.** **Fixed in 0.5.0**: a third `HANDLE_GROUP(e, AKERR_OUTOFBOUNDS)`,
    placed *above* the arm holding the `memcpy`, since `HANDLE_GROUP` emits no
    `break` and every arm falls into that body.

    `tests/json_helpers.c` covers it through the integer and object index
    accessors, so the fix is pinned to the status rather than to one call site.

    Worth knowing for the next test written against this function: it returns
    *the context it was given* when it does not handle the status, so
    `TEST_EXPECT_OK` -- which releases whatever the statement returns -- will
    double-release it against a `CLEANUP` block that also releases it, and a
    double-released context corrupts the failure instead of reporting it. The
    first draft of this test did exactly that and passed against the unfixed
    library. It takes the result into a local and hands ownership over
    explicitly now.

19. **The background music never loops.** `src/assets.c:20` initialises
    `bgmprops` to 0, `src/assets.c:44` sets `MIX_PROP_PLAY_LOOPS_NUMBER` on it,
    and `src/assets.c:46` plays the track with it. 0 is SDL's "no property set"
    sentinel, not a set this function owns, so the write is rejected —
    unchecked — and the play call is given no options. The music plays once and
    stops. `akgl_load_start_bgm` reports success either way.

    Fix: `SDL_CreateProperties()` into `bgmprops`, check it, and destroy it in
    `CLEANUP`. Touches `src/assets.c:20-47`.

20. **`akgl_character_sprite_add` leaks a sprite reference when a state is
    remapped.** **Fixed in 0.5.0**: it reads the existing entry first and
    releases it once the new binding is recorded, and the write is checked.

    The new reference is taken *before* the write and given back if the write
    fails, so there is no window where a sprite is bound with nothing behind it.
    Rebinding a state to the sprite already there is not treated as a
    displacement.

    `tests/character.c` binds, rebinds, and then runs 200 alternating rebinds,
    asserting the displaced sprite's count comes back each time. This is the
    half **Carried over** item 1 calls replacement; there is still no API to
    *remove* a binding without replacing it.

21. **`akgl_heap_release_character` abandons the whole state-to-sprite map.**
    `src/heap.c:150` zeroed the character without walking `state_sprites`, so
    every sprite reference the character took in `akgl_character_sprite_add` was
    lost and the `SDL_PropertiesID` holding the map was never destroyed. Loading
    and releasing characters in a loop — level to level — exhausted the sprite
    pool and leaked an SDL property set each time.

    **Fixed in 0.5.0.** At a refcount of zero it enumerates `state_sprites` with
    `akgl_character_state_sprites_iterate` and `AKGL_ITERATOR_OP_RELEASE`, then
    `SDL_DestroyProperties`, then zeroes the slot. The iterator existed for
    exactly this walk and simply was never called from here.

    The test was already written. `tests/character.c` has asserted this contract
    all along — "character did not reduce reference count of its child sprites
    when released" — and had never once run, for the two reasons under "Test
    suites that could not fail". It runs now, and it fails against the old code.

    Still open and separate: **item 20**, `akgl_character_sprite_add` leaking the
    displaced sprite when a state is *remapped*. Releasing at character teardown
    does not cover a binding replaced while the character is alive.

22. **`akgl_path_relative_root` uses `FAIL_RETURN` inside its `ATTEMPT` block.**
    **Fixed in 0.5.0** with internal-consistency item 16, which swept every
    such site. It is `FAIL_BREAK`, and `path_relative_root` is `static` now.
    `scripts/check_error_protocol.py` fails the build if one comes back.

23. **Three smaller leaks on failure paths.** **All three fixed in 0.5.0**, each
    by moving the release into a `CLEANUP` block.

    - `akgl_render_2d_init` released its two pooled strings only after both
      `aksl_atoi` calls succeeded, so a non-numeric `game.screenwidth` leaked
      two of the pool's 256 entries. `tests/renderer.c` runs 512 failing
      initializations against each of the two properties and asserts the pool is
      unchanged; against the old code the first loop claims every slot.
    - `akgl_controller_open_gamepads` freed the enumeration array only after the
      loop completed, so a gamepad that failed to open took the array with it.
      The open failure is recorded and reported after the loop, because a
      `FAIL_ZERO_BREAK` inside it would have broken the loop rather than the
      block. It also frees the array on the "no gamepads enumerated" path, which
      SDL still allocates for.
    - `akgl_text_rendertextat` destroyed the surface and texture only on the
      success path, so a failed upload leaked the surface and a failed draw
      leaked both -- once per frame on a HUD line.

24. **`akgl_get_property` reads past the end of the property value.**
    **Already fixed**, as **Defects the memory checker found** item 35 -- the
    two entries are the same defect found twice, from reading the code and from
    running valgrind. Recorded here only so the duplicate does not read as
    outstanding.

25. **`character_load_json_state_int_from_strings` checks the same argument
    twice.** **Fixed in 0.5.0**: the second guard's subject is `dest`, which is
    what it was always meant to be.

    **Not asserted, deliberately.** The function is `static` and has one call
    site, which passes `&stateval` -- so a `NULL` `dest` is unreachable from the
    public API and the guard cannot fire. Testing it would mean giving the
    function external linkage purely to reach a defensive check, which undoes
    internal-consistency item 9. The fix is a one-word correction to a guard
    that is there for the next call site, not for this one.

26. **`akgl_actor_render` computes a sprite's drawn height from its width.**
    **Fixed in 0.5.0**: `dest.h` takes `curSprite->height`. Every actor was
    drawn square, so a non-square sprite was stretched or squashed -- invisible
    in the fixtures because they are all square.

    `tests/actor.c` renders a 48x24 sprite through a backend whose
    `draw_texture` records the rectangle it is handed rather than drawing it,
    and asserts the destination is 48x24 and 96x48 at scale 2. That recording
    backend is also the first coverage `akgl_actor_render` has had at all --
    every other test in the file stubs `renderfunc` out.

### Found while closing the akbasic API gaps

27. **`akgl_text_rendertextat` refuses the empty string, and `akgl_text_measure` accepts it.**
    **Fixed in 0.5.0**: it returns success without rasterizing when
    `text[0] == '\0'`, matching the measure side.

    The check sits after the font, text and backend guards rather than before
    them, so drawing nothing still refuses the things drawing something refuses
    -- a caller does not get a different contract for an empty string.

    `tests/text.c` had the case written and deliberately unasserted, waiting for
    the two halves of the header to agree. It is a `TEST_EXPECT_OK` now, on both
    the wrapped and unwrapped paths, and against the old code it reports
    `AKERR_NULLPOINTER`.

## Performance

The first measured baseline is in `PERFORMANCE.md`, produced by `tests/perf.c`
and `tests/perf_render.c` (`ctest --test-dir build -L perf`). Both suites hold
every measurement to a budget set at roughly ten times the recorded baseline, so
an algorithmic regression fails the suite rather than being discovered by a
player. Read `PERFORMANCE.md` before arguing with anything below — every claim
here has a number behind it, and several of the things I expected to be slow are
not.

### Defects the perf suites found

Ordered by blast radius. Numbering continues the **Defects** list above.

28. **`akgl_path_relative` leaked an error context on every root-fallback
    resolution.** `src/util.c:118` took its `ENOENT` branch by `return`ing from
    inside the `HANDLE` block, which skips the `RELEASE_ERROR` that `FINISH`
    ends with. One entry of `AKERR_ARRAY_ERROR` was lost per call, and the 129th
    call hit "Unable to pull an error context from the array!" and **exited the
    process**. Every tilemap load resolves several paths this way, so a game
    that loaded fifty levels died in the loader.

    **Fixed.** The branch now records a flag and calls
    `akgl_path_relative_root` after `FINISH`. `tests/util.c` carries
    `test_akgl_path_relative_releases_contexts`, which resolves
    `AKERR_MAX_ARRAY_ERROR * 2` paths through that branch and asserts the pool
    is where it started; against the old code that test does not fail, it
    terminates the suite.

    This is the *only* `return` from inside a `HANDLE` block in `src/` — the
    other candidates use `SUCCEED_RETURN`, which releases correctly. Worth a
    grep before anyone writes a new one, and worth a line in AGENTS.md's
    error-handling protocol, which warns about `*_RETURN` inside `ATTEMPT` but
    not about returning out of `HANDLE`.

29. **`akgl_tilemap_load` leaks five pooled strings per load.** **Fixed in
    0.5.0**, in two steps, and the split changes what the number means.

    Three of the five were `akgl_get_json_tilemap_property` leaking two scratch
    strings on every *successful* property lookup, through a `SUCCEED_RETURN`
    inside its `ATTEMPT` block -- internal-consistency item 16. That took the
    measured leak from five per load to two.

    The remaining two were each a claim with no matching release:
    `akgl_tilemap_load_layers` never gave back the string it read every layer's
    `type` into, and `akgl_tilemap_load` never gave back the `dirname` its
    relative paths resolve against. Both release in `CLEANUP` now.

    `tests/tilemap.c` asserts the pool is exactly where it started after one
    load/release cycle and after 64 -- enough that a leak of one string per load
    could not finish. Finding the last two meant dumping the contents of every
    still-claimed slot after a cycle rather than reading the code again;
    `'tilelayer'` and an assets directory named themselves immediately.

    Fixed alongside, same file and same class:
    `akgl_tilemap_load_layer_objects` released its scratch string after reading
    each object's name and then kept using the slot -- and
    `akgl_get_json_string_value` reuses a non-`NULL` destination *without*
    taking another reference, so the slot was free while still live and any
    other claim could have been handed it.

    The tilemap-load benchmark in `tests/perf_render.c` no longer needs to
    reclaim the pool by hand between iterations.

30. **Two JSON accessors turn string-pool exhaustion into a segfault.**
    **Fixed in 0.5.0**: `FINISH(errctx, true)` in both, so a failed
    `akgl_heap_next_string` reaches the caller instead of being swallowed and
    then `strncpy`d through.

    `tests/json_helpers.c` claims every slot in the pool and asserts
    `AKGL_ERR_HEAP` comes back out of both accessors with the destination left
    untouched. Against the old code that test segfaults rather than failing --
    and so did the new tilemap property-lookup test, which is how this was
    confirmed rather than merely believed.

31. **`akgl_game_update` segfaults if `akgl_game_init` did not run.**
    **Fixed in 0.5.0**: `akgl_game_update_fps` installs `akgl_game_lowfps` when
    it finds the hook `NULL`.

    Worth keeping the reasoning. `game.fps` is 0 for the first second of the
    process, which is under the threshold, so the unguarded call fired on frame
    one. Only `akgl_game_init` installed the default -- and
    `include/akgl/renderer.h` documents the other path on purpose: a host that
    owns its own window calls `akgl_render_2d_bind` instead of
    `akgl_render_2d_init`. An embedder following that documentation crashed on
    its first frame, and `akbasic` is exactly that embedder.

    `tests/game.c` clears the hook and calls the function, which is precisely
    that state. `tests/perf_render.c` installed the default by hand as a
    workaround and no longer has to.

32. **`akgl_game_update` runs the actor update sweep once per tilemap layer.**
    **Fixed in 0.5.0.** The sweep is hoisted out of the layer loop -- updating
    an actor is not a per-layer operation, and `akgl_render_2d_draw_world`
    already walks the layers for the half that is.

    `AKGL_ITERATOR_OP_LAYERMASK` is honoured rather than ignored now, so a
    caller that genuinely wants one layer can ask for it and gets each of those
    actors once. It is no longer in the default flag set: every live actor once
    is the job, and restricting the sweep is the caller asking for less.

    `tests/game.c` counts calls into a stub `updatefunc` and asserts exactly one
    per live actor per frame, two over two frames, and the layer mask selecting
    only its own layer. Against the old code it reports 16.

    Counting is the assertion on purpose. The defect was invisible in the frame
    total because the tilemap blits are three orders of magnitude larger, so a
    timing test would have measured the rasterizer. The timing evidence is the
    gap between the `akgl_game_update` and `draw_world` rows of the same
    benchmark run: 92 us before, and noise in both directions after. See
    `PERFORMANCE.md`.

33. **`akgl_heap_release_character` leaks its `state_sprites` property set.**
    **Fixed in 0.5.0**; see item 21, which is the same defect. The
    character-load benchmark in `tests/perf_render.c` was written around it and
    no longer has to be.

### Targets

What a library like this *should* hit. These are not predictions of what the
current code does — several are missed today, and each says which. The frame
budget throughout is 16.67 ms (60 fps); where a target is stated per-operation
it is because that is the number that survives a change of renderer.

The one that governs the rest: **libakgl's own bookkeeping should never be the
reason a frame is late.** Everything the library decides — pool scans, registry
lookups, state-to-sprite mapping, physics, visibility, error contexts — should
fit in 5% of a frame, leaving 95% for the pixels and the game's own logic. At
64 actors and a screenful of tiles that is a ceiling of about 800 µs.

| # | Target | Today | Verdict |
|---|---|---|---|
| 1 | Library bookkeeping under 5% of a 60 fps frame at 64 actors + 1200 tiles | ~0.3% (excluding pixel work) | **met** |
| 2 | One actor's logic update under 200 ns | 68.4 ns | **met** |
| 3 | One actor's render bookkeeping, excluding the blit, under 500 ns | ~250 ns, by subtraction rather than direct measurement | **met, weakly measured** |
| 4 | Physics sweep under 25 ns per *live* actor, and proportional to live actors rather than pool size | 19 ns per live actor, but 63.9 ns for an *empty* pool | **partly** |
| 5 | Tilemap draw bookkeeping under 100 ns per tile, excluding the blit | ~25 ns | **met** |
| 6 | Pool acquire under 100 ns regardless of how full the pool is | 3.9 ns empty, 250.9 ns on the last free string slot | **missed** |
| 7 | Pool release proportional to the bytes actually used, not to the slot's capacity | 47.2 ns, a fixed 4 KiB wipe | **missed** |
| 8 | Re-drawing an unchanged line of text under 1 µs | 12.6 µs, every frame, no cache | **missed** |
| 9 | Zero texture creation or destruction per frame in steady state | one create + one destroy per line of text per frame | **missed** |
| 10 | A handled, routine condition costs no more than twice the path that succeeds | 616.5 ns vs 68.4 ns — 9x | **missed** |
| 11 | 256 actors simulated, updated and made ready to draw in under 1 ms | ~22 µs at 64 actors (5.8 µs measured logic + estimated render bookkeeping); linear, so ~90 µs extrapolated | **met, untested at that size** |
| 12 | Collision for 256 actors under 2 ms without the caller writing a broad phase | 54.1 µs for a whole physics step with collision at `-DAKGL_MAX_HEAP_ACTOR=256` | **met** |
| 13 | Level load under 100 ms for a map with 8 tilesets, 4 layers and 64 actors | 11.9 ms for a 2x2 map with one tileset | **unknown at that size** |
| 14 | Fixed per-load overhead under 1% of a level load | 11.5% — zeroing 26 MB of `akgl_Tilemap` | **missed** |
| 15 | Static footprint under 4 MB in the default configuration | 28 MB, 94% of it one tilemap | **missed** |
| 16 | No pool leaks across a load/release cycle of any asset type | tilemap is clean, asserted over 64 cycles; sprite, spritesheet and character cycles are not asserted | **met where tested** |
| 17 | Pool exhaustion reports `AKGL_ERR_HEAP` and never crashes | all five pools report it, and the two JSON accessors that used to `strncpy` through a NULL now report it too | **met** |
| 18 | Every benchmark held to 10x its recorded baseline, enforced in CI | done, `ctest -L perf` | **met** |

Targets 16 and 17 moved in 0.5.0, with **Defects** items 29 and 30. Target 16 is
qualified rather than met outright on purpose: the tilemap cycle is the one that
was leaking and the one that is now asserted, and nothing yet asserts the same
of a sprite, spritesheet or character load/release cycle. That is a gap in the
tests, not a known leak.

Notes on the ones worth arguing about:

- **6 and 7 are the same fix.** The acquire scan is 64x slower on a full string
  pool than an empty one purely because the pool is a megabyte and the scan
  touches one refcount per 4 KiB. A free-list index — one `int` per layer,
  remembering where the last free slot was — takes both to constant time without
  changing the "no `malloc`" rule at all. That is the change I would make first,
  and it is worth doing *before* anyone raises `AKGL_MAX_HEAP_*`, because the
  cost of the current design grows with the ceiling rather than with the usage.

- **8 and 9 are one cache.** A single entry keyed on (font, string, colour,
  wrap) would cover the common case — a HUD field that changes once a second —
  and a four- or eight-entry ring would cover the rest. This is the clearest
  optimisation in the library and it is maybe forty lines.

- **10 is a design target, not a speed target.** The answer is not a faster
  error context. It is that "this character has no sprite for this state" is a
  question with a boolean answer, and reporting it through `AKERR_KEY` costs
  nine times the update it replaces. `akgl_character_sprite_get` wants a
  companion that returns `NULL` without raising.

- **12 is a scope decision, not a defect.** The library deliberately does not
  own a broad phase, and at 64 actors the naive all-pairs loop is 0.7% of a
  frame — genuinely fine. At 256 it is 11%. Either the ceiling stays where it is
  and this target is dropped, or a uniform grid keyed on tile size goes in. I do
  not think a spatial index belongs here yet; I think the target belongs on
  record so that raising `AKGL_MAX_HEAP_ACTOR` is a decision made with the
  number in front of it.

- **14 and 15 are the same fix too.** `akgl_Tilemap` is 26 MB because every
  layer carries a 512x512 `int` grid and every tileset a 65,536-entry offset
  table, sized for the worst case at compile time. The pool rule does not
  require *this*: a layer could carry an index into one shared cell arena sized
  by `AKGL_TILEMAP_MAX_WIDTH * AKGL_TILEMAP_MAX_HEIGHT` once rather than
  sixteen times, and the offset table could be sized by `tilecount` rather than
  by the maximum. That is a real refactor with a real ABI break, so it belongs
  to 0.4 rather than to a patch release — but 28 MB of BSS on a handheld or an
  ESP32-class target is the difference between fitting and not.

- **13 is untested and should not stay that way.** The only map fixture in the
  tree is 2x2 with one tileset, which is why the load benchmark measures a PNG
  decode and a `memset` rather than a map. A realistic fixture — 128x128, four
  layers, several tilesets — would make target 13 measurable and would probably
  find something.

### The plan

The order below is the order the work should happen in, set by blast radius
per frame and per byte, not by how interesting the change is. Items 1 through
6 are the next changes; 7 through 9 are on record so the decision that
unblocks each is made with the numbers in front of it. The engine comparison
that informs several of these is in `PERFORMANCE.md` under **How other
engines spend the same frame**.

1. **String pool free-list index — targets 6 and 7, one change.** A next-free
   hint per pool in `src/heap.c` (the five scans are `src/heap.c:52-116`)
   takes the last-slot claim from 250.9 ns to constant time, and it lands
   before anyone raises `AKGL_MAX_HEAP_*`, because today's cost grows with the
   ceiling rather than the usage. Fold in item 8 under **Known and still
   open** — `akgl_heap_next_string` is the only acquire that takes a
   reference, and a free-list change touches every acquire anyway. Make the
   release wipe (`src/heap.c:211`) proportional to bytes used: either `memset`
   through `strnlen(data, AKGL_MAX_STRING_LENGTH) + 1` or a tracked length
   field — and the length-field option must respect the layout history in
   item 6, which put two real bugs on the bytes after `data`. Budgets to
   move: `tests/perf.c:317`, `:333`, `:347`; re-record the three rows in
   `PERFORMANCE.md` in the same commit.

2. **Text texture ring cache — targets 8 and 9, one cache.** A static
   four-to-eight entry ring in `src/text.c` keyed on (`TTF_Font *`, text
   bytes, `SDL_Color`, wraplength) — `x`/`y` stay out of the key, position
   only affects `dest`. Invalidate in `akgl_text_unloadfont`
   (`src/text.c:40-55`) and `akgl_text_unloadallfonts` (`:76-87`): a cached
   texture keyed on a closed font whose address was reused is a stale hit, so
   unload must sweep the ring. Verification is a counting test, not a
   stopwatch — target 9 is *zero* texture create/destroy per steady-state
   frame, so count them through a stub; plus a new perf row ("rendertextat,
   cached") with the raw-SDL control row the perf rules require. Budget to
   move: `tests/perf_render.c:391`.

3. **Non-raising sprite lookup — target 10, a design change.** Give
   `akgl_character_sprite_get` (`src/character.c:84-94`) the companion that
   returns `NULL` without raising, then convert the three sites that raise
   and handle `AKERR_KEY` for a routine condition: `akgl_actor_update`
   (`src/actor.c:165`, handled `:172`), `actor_visible` (`:209`, handled
   `:212-216`) and `akgl_actor_render` (`:241`, handled `:245-249`). While
   there, stop `akgl_actor_render` looking the sprite up twice on the success
   path (`:241` and again inside `actor_visible` at `:242`). Takes the
   sprite-less update from 616.5 ns toward the twice-success ceiling. Budget
   to move: `tests/perf.c:588`.

4. **Demote the hot-path log lines.** `akgl_actor_initialize` logs every
   spawn (`src/actor.c:51`) and `akgl_character_sprite_add` every binding
   (`src/character.c:80`); 20% of a spawn is formatting a line nobody reads,
   and that is with the output thrown away. Demote them (and
   `src/character.c:285`, `src/renderer.c:34`, `src/tilemap.c:660`) from
   `SDL_Log` to `SDL_LogDebug` — SDL checks priority before formatting, so
   the cost disappears at default priority and the messages survive for
   anyone who turns debug on. The spawn benchmark pair
   (`tests/perf.c:410`, `:429`) already measures exactly this gap.

5. **Fix the tileset scan, and the two bugs hiding in it.** The per-tile scan
   in `akgl_tilemap_draw` (`src/tilemap.c:756-798`) is the known
   O(tiles x tilesets) FIXME, worth 0.8% of the frame at eight tilesets — but
   it is also wrong twice. The range test uses `>=` on the upper bound
   (`firstgid + tilecount >= tilenum`, `src/tilemap.c:760-761`), so the tile
   one past the end of set A also matches set B's `firstgid`; and there is no
   `break` after a match, so a tile matching two ranges is blitted twice.
   Correct the test to `tilenum < firstgid + tilecount`, `break` on match,
   and skip `tilenum == 0` before scanning at all. Verify with a counting
   test — a stub `draw_texture` backend asserting exactly one blit per
   non-empty visible cell, same pattern as the `tests/game.c` update counter —
   because a boundary double-blit is invisible to a stopwatch and mostly
   invisible on screen. File alongside, same entry: `start_x`/`start_y` are
   never clamped to zero (`src/tilemap.c:719-728`), and the first-column
   `src.x +=` accumulates across rows (`:766`). Mutation testing is
   mandatory here; this is control flow. Do not reorganize the loader for
   this — 0.8% does not justify it.

6. **Bound the draw_world layer loop.** `akgl_render_2d_draw_world`
   (`src/renderer.c:150-167`) walks all `AKGL_TILEMAP_MAX_LAYERS` and rescans
   all 64 actor slots per layer — 1024 refcount checks a frame for a
   one-layer map. Bound the walk by `akgl_gamemap->numlayers` and build the
   per-layer actor lists in one pool pass into static index arrays.
   Invisible at 60 fps under the software renderer; measurable on a 2 ms GPU
   frame. Counting test, same as item 5.

7. **Target 12: done in 0.8.0, and the prediction held.** The structure is
   the incremental uniform grid, not the tree — cells keyed on tile size,
   static arrays, insert/remove as actors move, wired into the `collide` slot
   of `akgl_PhysicsBackend` that the simulation loop now calls. Construct
   measured that design at a 96% check reduction over brute force and rejected
   quadtrees as costlier to maintain; Phaser's rebuild-the-RTree-every-frame
   approach carries a documented ~5,000-body ceiling and is the counterexample.
   Citations stay in `PERFORMANCE.md`.

   Measured here rather than cited: **the grid beats the BSP by 2.6x on the
   same 64-proxy population** (44.3 ns against 116.1 ns per query), before
   counting that the tree rebuilds whenever a proxy moves and the grid's `move`
   is 11.9 ns when the cell rectangle has not changed. A whole physics step
   with collision is 15.4 µs at 64 actors and 54.1 µs at 256, against a 2 ms
   target. Over that 4x range the step grew 3.5x and the all-pairs control grew
   15.6x, which is the `n²` the index exists to avoid.

   **The BSP ships anyway.** A vtable with one implementation behind it has
   never been asked to be a vtable; `tests/partition.c` runs its whole contract
   against a table of both, so the seam is proven rather than asserted. It
   would earn its place in a world with wildly non-uniform object sizes or one
   larger than the grid's 128x128 cell array covers.

8. **Target 13 needs the fixture before it needs anything else.** A
   128x128, four-layer, multi-tileset JSON map fixture, so
   `akgl_tilemap_load` is measured on a map rather than on a PNG decode and a
   `memset`. Today the loader benchmark uses the 2x2 fixture while
   `perf_render` synthesizes its 128x128 map in-process
   (`tests/perf_render.c:141-175`) — the draw path is measured at realistic
   size and the load path is not. It would probably find something.

9. **Targets 14 and 15: the footprint refactor, sketched for when it is
   scheduled.** One shared cell arena sized
   `AKGL_TILEMAP_MAX_WIDTH * AKGL_TILEMAP_MAX_HEIGHT` once instead of
   per-layer, and tileset offset tables sized by `tilecount` instead of by
   `AKGL_TILEMAP_MAX_TILES_PER_IMAGE`. One correction to the record: the
   FIXME at `include/akgl/tilemap.h:113-128` worries about wasted *leading*
   entries per tileset, but `akgl_tilemap_compute_tileset_offsets`
   (`src/tilemap.c:179-231`) indexes by local id from zero — the table is
   merely oversized, not sparse. The refactor kills most of the 1.37 ms
   `memset` in `akgl_tilemap_load` (`src/tilemap.c:615`) and takes BSS from
   28 MB toward the 4 MB target. Real ABI break; belongs to a minor release,
   as the note above already says.

## Memory checking

`cmake --build build --target memcheck` runs **the suites that already exist**
under valgrind — `ctest -T memcheck` with the headless drivers forced, wrapped by
`scripts/memcheck.sh` so that a finding is an exit status rather than a line in a
log nobody reads. There are no memory-check test programs, and there should never
be any: `tests/benchutil.h` notices that it is running under valgrind and divides
every benchmark's iteration count by two thousand, which turns the perf suites
into the broadest path coverage in the tree at a cost valgrind can survive. The
whole run is about thirty seconds.

The two halves fit together on purpose. A benchmark is a program that walks one
path a hundred thousand times; a leak check wants every path walked once. Same
binaries, same registration, one flag apart.

Third-party findings are suppressed in `scripts/valgrind.supp`, and the run
forces `SDL_VIDEO_DRIVER=dummy` / `SDL_RENDER_DRIVER=software` /
`SDL_AUDIO_DRIVER=dummy` so the vendor GPU stack is never loaded — that removes
thousands of unfixable findings inside `amdgpu_dri.so` without suppressing
anything at all. Only *definite* losses and invalid accesses are counted; "still
reachable" is what SDL and FreeType keep for the process lifetime and says
nothing about this library.

### Defects the memory checker found

**All six are fixed.** They are kept here rather than deleted because the sizes
are measured and the reasoning is worth having next time somebody asks why a
loader ends in a `CLEANUP` block, or why a name field is staged through a zeroed
buffer. `cmake --build build --target memcheck` is clean, and the CI job that
runs it gates: the next one of these fails the build on the push that
introduces it.

Ordered by blast radius as they were found. Numbering continues the lists above.
Every size below is measured, not estimated.

34. **Every JSON loader leaks its parsed document.** There are four
    `json_load_file` calls in `src/` and not one `json_decref` anywhere in the
    library, so the whole parsed tree — objects, hashtables, strings — is
    abandoned on both the success and failure paths:

    | Loader | Site | Leaked per call |
    |---|---|---:|
    | `akgl_sprite_load_json` | `src/sprite.c:140` | ~1,500 bytes |
    | `akgl_character_load_json` | `src/character.c:232` | ~2,150 bytes |
    | `akgl_tilemap_load` | `src/tilemap.c:693` | ~9,000 bytes (2x2 fixture map) |
    | `akgl_registry_load_properties` | `src/registry.c:134` | not exercised by any test |

    Blast radius: every asset load, forever. The map figure is for the 2x2
    fixture; a real map's JSON is the size of its layer data, so a 128x128 map
    leaks on the order of a megabyte per load. A game that reloads a level on
    death leaks a level's worth of JSON each time, and this is the one item in
    this list that grows without bound.

    **Fixed.** `json_decref` in the `CLEANUP` block of each, on the success
    path as well as the failure one, with the handle nulled after so a second
    pass cannot double-release. `akgl_registry_load_properties` needed its loop
    moved inside the `ATTEMPT` block first: `props` is a borrowed reference into
    the document and was read after the block ended, so every exit from that
    loop leaked the document. The test is the memcheck run -- nothing in the
    public API can observe a jansson refcount, and inventing a hook to prove it
    would be testing the test.

35. **`akgl_get_property` reads up to 4 KiB past the end of the property
    value.** `src/registry.c:181` copies a fixed `AKGL_MAX_STRING_LENGTH` bytes
    out of whatever `SDL_GetStringProperty` returns, and what it returns is an
    `SDL_strdup` of the value — four bytes for `"0.0"`. Valgrind reports an
    invalid read on **every call**, twelve of them in `tests/physics.c` alone,
    because `akgl_physics_init_arcade` reads six properties and
    `akgl_render_init2d` reads two more.

    This has been in `registry.h` as a `@note` about the copy being "a fixed
    #AKGL_MAX_STRING_LENGTH bytes rather than the length" — filed as waste. It
    is not waste, it is an out-of-bounds read: today it walks into the rest of
    SDL's heap and returns garbage past the terminator, and on a value that
    lands at the end of a page it is a segfault in a getter.

    **Fixed.** The copy is bounded by the value's own length plus its
    terminator, and a value too long for an akgl_String is now refused with
    AKERR_OUTOFBOUNDS instead of silently truncated. The documented
    AKERR_NULLPOINTER for "unset with no default" is unchanged -- it is raised
    deliberately now rather than arriving from inside `aksl_memcpy`.
    `tests/registry.c` fills the destination with a sentinel, reads a
    three-byte property back, and asserts every byte past the terminator still
    holds the sentinel; that assertion fails against the old code.

36. **The savegame name tables read past the end of every registry key, and
    write what they find into the file.** `akgl_game_save_actorname_iterator`
    (`src/game.c:219`) writes `AKGL_ACTOR_MAX_NAME_LENGTH` — 128 — bytes
    starting at the key SDL handed it, and SDL allocated that key to fit the
    name. Valgrind catches it on a 40-byte allocation. The three sibling
    iterators do the same thing at `src/game.c:248`, `src/game.c:280` and
    `src/game.c:308`, with 128, 512 and 128 byte fixed widths; only the actor
    one is reached by the current tests, because the other registries are empty
    in the save roundtrip.

    Two consequences, and the second is the interesting one. The read can fault
    if the key sits at the end of a page. And whatever it reads goes into the
    save file, so a savegame contains up to 500 bytes of this process's heap per
    registered object — anything that happened to be next to the key. That is a
    file a player might send someone.

    **Fixed.** All four iterators now write through `write_name_field`, which
    stages the key into a zeroed fixed-width buffer, so the padding is
    deterministic and nothing but the name leaves the process. A
    negative-array-size typedef fails the build if any of the four widths ever
    outgrows the staging buffer. Still open and unrelated to the overread:
    **Defects -> Known and still open** item 7, the same tables disagreeing
    about their widths between writer and reader.

37. **`akgl_controller_list_keyboards` leaks the array SDL gives it.**
    `src/controller.c:188` calls `SDL_GetKeyboards`, which allocates, and never
    calls `SDL_free` on the result. Four bytes per call in the test environment
    — one keyboard id — but it is per call, and the function is shaped like
    something a game calls when a device is hotplugged.

    **Fixed.** One `SDL_free`, in a `CLEANUP` block so a failure inside the
    loop cannot take the array with it. Still worth asking the same question of
    every SDL enumeration in `src/controller.c`: `SDL_GetGamepads` has the same
    contract, and the dummy driver reports no gamepads, so no test reaches it.

38. **A font, once loaded, is never freed and cannot be.**
    `akgl_text_loadfont` (`src/text.c:20`) opens a `TTF_Font`, puts the pointer
    in `AKGL_REGISTRY_FONT`, and that is the last anyone can do about it: the
    header exposes no way to close a font, and `SDL_Quit` destroying the
    property registry drops the last reference. 10,523 bytes per font — 736 of
    them SDL_ttf's, the rest FreeType's.

    This is bounded by how many fonts a game loads, so it is not the runaway
    that item 34 is. It was a gap in the API rather than only a leak: a game
    that switches fonts between scenes, or a tool like `charviewer` that reloads
    one while the user picks a size, had no way to give the old one back.

    **Fixed**, and this one is a new public symbol rather than a repair:
    `akgl_text_unloadfont(char *name)` clears the registry entry and closes the
    font. `akgl_text_loadfont` calls it when it replaces a live name, which
    closes the second leak the header used to document as intended behaviour --
    but only after the new font has opened, so a failed reload leaves the caller
    with the font they already had. The version goes to 0.4.0 with it: an 0.3
    consumer cannot be handed this library and told it is the same ABI.

    Still open: nothing closes the registry's remaining fonts at shutdown. A
    game that exits without unloading leaks them exactly once, which valgrind
    reports against the process rather than against a loop, and which
    `akgl_game_shutdown` would be the natural home for if it existed.

39. **Vendored `deps/semver`'s own unit test leaks 188 bytes** across 16 blocks,
    from the `calloc`s in `test_strcut_first` and `test_strcut_second`
    (`deps/semver/semver_unit.c:8` and `:21`). Not libakgl's code and not
    libakgl's to fix; recorded so that nobody re-diagnoses it, and because
    `semver_unit` is registered as one of our CTest tests and so shows up in our
    memcheck run.

    **Suppressed**, which is what this list said the answer would be if it ever
    became noise, and gating the job made it noise. The two entries in
    `scripts/valgrind.supp` name the functions rather than the file, so a
    rewrite of those cases stops being suppressed and comes back as a finding.
    They are the only entries there that hide a real leak in a program this
    build runs; the alternative was a fork of a vendored dependency.

### Not defects, and why

- **`tests/util.c` fixtures were reading uninitialised stack floats.** Three
  null-pointer tests declared `SDL_FRect` and `point` fixtures without
  initializing them and then made one real call with them at the end, which is
  sixteen "conditional jump depends on uninitialised value" findings for a test
  that is not about coordinates. The fixtures are zeroed now. The library was
  never at fault; a memory checker that reports noise gets ignored, which is the
  only reason this was worth touching.
- **"Still reachable" at exit is not counted.** SDL's global state, the hint
  table, the property registry and FreeType's library instance are one per
  process and are reclaimed by `SDL_Quit` / `TTF_Quit`. Counting them would
  bury the six findings above under a hundred that mean nothing.
- **The GPU driver's findings are avoided rather than suppressed.** Running the
  suite against the real driver produces thousands of findings inside
  `amdgpu_dri.so`; running it headless produces none, and headless is what the
  suites are written for anyway.

### Found while embedding libakgl in a consumer

40. ~~**Shadowing `add_test()` unconditionally broke every embedding consumer.**~~ **Fixed in
    the same release it was introduced in**, and worth keeping because the CMake behaviour
    behind it is not obvious and will catch the next person.

    18399f2 moved the vendored-dependency block out from behind
    `if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)` — which was the point of that
    commit — and took the `add_test()`/`set_tests_properties()` override out with it. The
    override's own comment claimed "an embedding consumer's `add_test()` still reaches CTest".
    It does not, and cannot.

    **CMake chains command overrides exactly one level deep.** Overriding `add_test` makes the
    builtin available as `_add_test`; overriding it a *second* time rebinds `_add_test` to the
    *first* override and the builtin becomes unreachable to everybody, permanently — there is
    no `__add_test`. Verified directly rather than inferred from the documentation:

    ```cmake
    function(add_test) _add_test(${ARGV}) endfunction()   # _add_test  -> builtin
    function(add_test) _add_test(${ARGV}) endfunction()   # _add_test  -> the first override
    if(COMMAND __add_test) ... endif()                    # absent
    ```

    So two projects in one tree cannot both shadow it. `akbasic` shadows it first — it has to,
    for `libakerror` and `libakstdlib`, which register their tests unconditionally — and its own
    registrations then recursed until CMake stopped at "Maximum recursion depth of 1000
    exceeded". A consumer had no way to work around it: once the builtin is gone it is gone for
    that project too.

    **Fix:** the override is guarded on being top-level again, exactly as it was before 18399f2
    and exactly as `libakstdlib` guards its own. The vendored-dependency block stays
    unconditional, which is what that commit was actually for. An embedded `libakgl` leaves
    `add_test` alone and lets its consumer suppress what it does not want — machinery the
    consumer has to have anyway.

## Build notes

The vendored SDL satellite libraries are built into per-project subdirectories
that are not on the loader's default search path, and `LD_LIBRARY_PATH` is
searched ahead of RPATH — so a developer who has previously run `rebuild.sh` had
their installed `libakgl.so` shadow the one under test, and a developer who had
not saw every test abort before `main()` with "cannot open shared object file".
`CMakeLists.txt` now sets `BUILD_RPATH` on the library, the utility, and every
test target, and prepends the build tree to `LD_LIBRARY_PATH` for the CTest run.

## API gaps blocking akbasic

`akbasic` (the C port of the BASIC interpreter, `source.starfort.tech/andrew/akbasic`) is
being built to link into `libakgl` as a scripting engine for game authors.

**All ten items are resolved.** Items 1 through 4 landed first and `akbasic` has since
consumed every one of them: its `libakgl`-backed text sink, its graphics backend, its sound
backend and its input backend are written and tested, and the BASIC 7.0 graphics verbs
(`GRAPHIC`, `COLOR`, `DRAW`, `BOX`, `CIRCLE`, `PAINT`, `SCALE`, `SSHAPE`, `GSHAPE`, `LOCATE`),
the sound verbs (`SOUND`, `ENVELOPE`, `VOL`, `PLAY`, `TEMPO`) and the console input verbs
(`GET`, `GETKEY`, `SCNCLR`) all work against them.

Doing that turned up **items 5 through 9**. Four were things `akbasic` had to work around to
build at all; each workaround is commented at its site over there with the words "filed
upstream". **Those workarounds can now be deleted** — including the five `add_subdirectory`
lines for the vendored SDL projects and the hand-assigned render vtable in
`tests/akgl_backends.c`.

Building the *standalone* SDL frontend on top of all that — a real window, a real event pump
and a line editor — turned up **item 10**, and re-confirmed items 6 and 7: both workarounds
had to be written a second time, in `src/frontend_akgl.c`, because a host that owns a window is
exactly the caller they inconvenience.

These were filed here rather than worked around in `akbasic` because growing `libakgl` to serve
a consumer is the wanted outcome. Each entry says what the BASIC verb needs, what the
`akgl_*` entry point should look like, and what would cover it.

Items 7, 9 and 10 add public symbols and item 9 adds three fields to `akgl_AudioVoice`, so the
project version goes to **0.3.0** and the soname with it — an 0.2 consumer cannot be handed
this library and told it is compatible.

1. **No way to measure rendered text.** `include/akgl/text.h` exposes `akgl_text_loadfont()`
   and `akgl_text_rendertextat()`, and nothing that reports how large a string will be in a
   given font. A terminal-style text surface cannot be built on that: a cursor needs the
   advance width of one cell, and wrapping needs to know where a string crosses the right
   margin. The reference interpreter got this from SDL2_ttf's `font.SizeUTF8("A")` and derived
   its whole character grid from it.

   Wants `akerr_ErrorContext AKERR_NOIGNORE *akgl_text_measure(TTF_Font *font, char *text, int *w, int *h);`
   over `TTF_GetStringSize`, and probably a companion
   `akgl_text_measure_wrapped(font, text, wraplength, w, h)` matching the `wraplength`
   argument `akgl_text_rendertextat` already takes. Tests: a known string in a known font at a
   known size, the empty string, and a wrapped string wide enough to force two lines.

   This is the only one of the four that blocks work already designed and waiting. **`akbasic`
   cannot render any output through `libakgl` until it lands.**

   **Resolved.** `akgl_text_measure(font, text, w, h)` and
   `akgl_text_measure_wrapped(font, text, wraplength, w, h)` are in
   `include/akgl/text.h`, over `TTF_GetStringSize` and `TTF_GetStringSizeWrapped`.
   Neither needs a renderer. A negative `wraplength` is refused with
   `AKERR_OUTOFBOUNDS` rather than passed through, because SDL_ttf reads it as a
   very large unsigned width and silently stops wrapping. `tests/text.c` covers
   both against `tests/assets/akgl_test_mono.ttf`, a 10 KB monospaced ASCII
   subset added for the purpose — being monospaced, it lets the suite assert
   `width("AAAA") == 4 * width("A")` instead of hardcoding glyph metrics that
   FreeType is free to round differently. Same change fixed item 39 below:
   `akgl_text_loadfont` checked `name` twice and never checked `filepath`.

2. **No immediate-mode drawing.** `include/akgl/draw.h` declares exactly one function,
   `akgl_draw_background(int w, int h)`, and `src/draw.c` is at 0% coverage. BASIC 7.0's
   graphics verbs are all immediate-mode plotting against the current screen: `DRAW` (line and
   point), `BOX`, `CIRCLE`, `PAINT` (flood fill), `LOCATE` (set the pixel cursor), `COLOR`,
   and `SSHAPE`/`GSHAPE` (save and restore a rectangle of pixels).

   Wants an `akgl_draw_*` family taking the renderer the host already initialized --
   `akgl_draw_line`, `_rect`, `_filled_rect`, `_circle`, `_point`, `_flood_fill`,
   `_copy_region` -- in the shape of the existing `akgl_render_2d_draw_texture`. SDL3's
   `SDL_RenderLine`/`SDL_RenderRect`/`SDL_RenderFillRect` cover most of it; the circle and the
   flood fill do not exist in SDL3 and need writing. Tests belong with the offscreen renderer
   harness described under "Remaining work": render a known shape, read the target back, and
   compare against a reference surface with the existing `akgl_compare_sdl_surfaces`.

   **Resolved.** `include/akgl/draw.h` now declares `akgl_draw_point`, `_line`,
   `_rect`, `_filled_rect`, `_circle`, `_flood_fill`, `_copy_region` and
   `_paste_region`, all taking the `akgl_RenderBackend *` the host initialized,
   in the shape of `akgl_render_2d_draw_texture`. Decisions worth knowing:

   - **Color is an argument, not state.** There is no current-color global to
     get out of step with the caller's own. Each call saves and restores the
     renderer's draw color, so drawing a line does not change what the host's
     next `SDL_RenderClear` paints. `tests/draw.c` asserts that.
   - **The circle is a midpoint circle**, integer arithmetic with eight-way
     symmetry, plotted eight points per step through `SDL_RenderPoints`.
   - **The flood fill reads the target back, fills on the CPU, and blits only
     the bounding box of what changed.** It keeps a fixed
     `AKGL_DRAW_MAX_FLOOD_SPANS` (4096) stack of horizontal runs at file scope
     rather than recursing per pixel; running out reports `AKERR_OUTOFBOUNDS`
     and leaves the region partially filled, which is stated in the header. It
     is therefore not reentrant — neither is anything else that draws to a
     single `SDL_Renderer`.
   - `_copy_region` allocates when `*dest` is `NULL` and otherwise copies into
     the caller's surface, matching `akgl_get_json_string_value` and friends. A
     region that would be clipped by the target edge is refused rather than
     silently returning a smaller surface.

   `tests/draw.c` draws into a 64x64 software renderer under the dummy video
   driver and reads pixels back, so it did not need the offscreen harness. That
   harness is still wanted for `src/renderer.c`, `src/text.c` and `src/assets.c`.
   `akgl_draw_background` is untouched and still outside the error protocol
   (item 35).

3. **No audio API at all.** `SDL3_mixer` is a vendored dependency and `registry.h` declares
   `AKGL_REGISTRY_MUSIC`, but there is no `src/audio.c`, no `include/akgl/audio.h`, and no
   `akgl_*` symbol that opens a mixer, loads a chunk, or plays a note. BASIC 7.0's sound verbs
   are `SOUND` (a tone on a voice, with a duration), `PLAY` (a string of notes in a
   Commodore-specific notation), `ENVELOPE` (ADSR per voice), `FILTER`, `VOL` and `TEMPO`.

   `PLAY` and `ENVELOPE` want a synthesised voice rather than a sample, which SDL3_mixer does
   not provide directly -- the honest first step is a small tone generator feeding
   `SDL_AudioStream`, with `akgl_audio_init`, `akgl_audio_tone(voice, hz, ms)`,
   `akgl_audio_envelope(voice, a, d, s, r)` and `akgl_audio_volume(level)`. This is the largest
   of the four and the one most worth designing before writing. Tests can run under the dummy
   audio driver and assert state transitions rather than sound.

   **Resolved.** `include/akgl/audio.h` and `src/audio.c` add a three-voice tone
   generator over `SDL_AudioStream`: `akgl_audio_init`, `_shutdown`, `_tone`,
   `_stop`, `_waveform`, `_envelope`, `_volume`, `_voice_active` and `_mix`.
   It is deliberately separate from the SDL3_mixer side of the library, which
   plays audio *assets*; nothing in `audio.c` reads a file. Decisions worth
   knowing:

   - **The voice table works with no device open.** `akgl_audio_init` connects
     it to one; without that a host can still pull samples itself through
     `akgl_audio_mix`. That is not only for embedding — it is what makes the
     suite deterministic. A device pulls samples on SDL's audio thread whenever
     it likes, so a test that opened one and then asserted on voice state would
     be racing the callback. `tests/audio.c` mixes by hand and opens a device
     only in its last test.
   - **Phase is derived from the frame counter, not accumulated.** A float
     increment of `hz / 44100` is not exact, and adding it 44100 times a second
     walks a held note off pitch.
   - **A voice that was never configured is audible.** A zeroed voice has a
     sustain of 0.0, which is silence with no error to explain it, so the table
     defaults to a square wave held at full level.
   - **Three voices summing past full scale are clamped, not scaled**, so one
     voice plays at the level it was asked for rather than a third of it.
   - Everything that touches the table takes the stream lock when a device is
     open, since the callback reads it on another thread.

   Still missing for a complete BASIC sound vocabulary: `FILTER` (SDL3 has no
   filter primitive; this would need writing), `TEMPO` and the `PLAY` note-string
   parser, both of which belong in the interpreter rather than here.

4. **No non-blocking keystroke read.** `include/akgl/controller.h` is built around SDL event
   handlers the host pumps (`akgl_controller_handle_event` and friends), which suits a game
   loop and does not suit `GET` and `GETKEY` -- those ask "is there a keystroke waiting, yes or
   no" and must not require the interpreter to own the event loop. Goal 3 of `akbasic` forbids
   it owning one.

   Wants `akerr_ErrorContext AKERR_NOIGNORE *akgl_controller_poll_key(int *keycode, bool *available);`
   reading a small ring buffer that `akgl_controller_handle_event` already fills, so the host
   keeps pumping events and the interpreter drains characters at its own pace. Tests: push
   synthetic `SDL_EVENT_KEY_DOWN` events through the existing handler and drain them, plus the
   empty-buffer and overflow cases.

   **Resolved.** `akgl_controller_poll_key(int *keycode, bool *available)` and
   `akgl_controller_flush_keys(void)` are in `include/akgl/controller.h`, over a
   fixed `AKGL_CONTROLLER_KEY_BUFFER` (32) ring in `src/controller.c`.
   `akgl_controller_handle_event` records every `SDL_EVENT_KEY_DOWN` *before* it
   scans the control maps, so a key bound to an actor still reaches a polling
   caller — the scan returns as soon as a binding claims the event, and doing it
   afterwards would have lost exactly the keys a game also acts on. An empty
   buffer is success with `available` false, not an error. A full buffer drops
   the newest key rather than overwriting the oldest, matching the Commodore
   keyboard buffer and keeping what was typed first. `tests/controller.c` covers
   drain order, the release-is-not-a-keystroke case, a key shared with a control
   map, flush, both NULL arguments, and overflow plus reuse afterwards.

5. **An embedded `libakgl` demands its dependencies be installed, while vendoring them.**
   `CMakeLists.txt:17` gates the whole vendored-dependency block on
   `CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR`, so `deps/SDL`, `deps/SDL_image`,
   `deps/SDL_mixer`, `deps/SDL_ttf` and `deps/jansson` are added only when this repository is
   the top-level project. Embedded with `add_subdirectory()`, the `else()` branch at `:51`
   runs `find_package(SDL3 REQUIRED)` and friends instead, and configure fails on a machine
   that has none of them installed — with the submodules sitting right there in `deps/`,
   already checked out by the recursive clone the consumer just did.

   `akbasic` works around it by adding those five subdirectories itself, immediately before
   `add_subdirectory(deps/libakgl)`. That works only because every lookup in the `else()`
   branch is guarded with `if(NOT TARGET ...)` — which is the same escape hatch
   `akerror::akerror` and `akstdlib::akstdlib` already rely on, and it should not be the
   documented answer. **Fix:** add the vendored dependencies on both paths, still guarded by
   `if(NOT TARGET ...)` so a consumer that has already declared them wins. The suppression of
   their CTest registration should move with them.

   **Resolved.** The vendored block no longer sits behind
   `CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR`. An
   `akgl_add_vendored_dependency(<target> <dir>)` macro adds each of the seven submodules when
   nothing has already declared that target *and* the submodule is actually checked out; the
   `find_package` lookups for anything left over run afterwards, unchanged, so a checkout
   without submodules still resolves against the system. A macro rather than a function
   because `add_subdirectory()` inside a function runs in that function's variable scope.

   The CTest suppression moved with them, and is lifted again before this project registers
   its own suites, so an embedding consumer's `add_test()` still reaches CTest. Two smaller
   consequences of the move: `find_package(PkgConfig)` now runs only when something has to
   come from the system (a fully vendored build needs no pkg-config of its own, though
   `deps/SDL_mixer` asks for it separately), and the build-tree RPATH block keys on whether
   anything was vendored rather than on being the top-level project, so an embedded build's
   tests can also find the satellite libraries.

   Verified by configuring and building a scratch consumer that embeds this repository with
   `CMAKE_DISABLE_FIND_PACKAGE_SDL3`, `_SDL3_image`, `_SDL3_mixer`, `_SDL3_ttf`, `_akerror`,
   `_akstdlib` and `_jansson` all set, so any reliance on an installed copy would have failed
   the configure. It configures, builds and links. **The five `add_subdirectory` lines in
   `akbasic`'s `CMakeLists.txt` can be deleted.**

6. **`include/akgl/controller.h` does not compile on its own.** Lines 35, 36 and 41 declare
   handler function pointers taking an `akgl_Actor *`, and the header includes only
   `SDL3/SDL.h`, `akerror.h` and `types.h` — none of which declares that type. Any translation
   unit that includes `akgl/controller.h` before `akgl/actor.h` fails with *"unknown type name
   'akgl_Actor'"*. `src/controller.c` never notices because it includes `akgl/game.h` first.

   This is the house rule in `AGENTS.md` — keep headers self-contained, include what you use.
   **Fix:** `#include "actor.h"` in `controller.h`, or forward-declare
   `struct akgl_Actor` if the include order makes that circular. A one-line test that includes
   only `akgl/controller.h` would have caught it and would keep catching it.

   **Resolved.** `controller.h` includes `<akgl/actor.h>`. Not a forward declaration:
   `akgl_Actor` is a typedef of a named struct, and repeating a typedef is C11, not C99. The
   include closes no cycle — `actor.h` reaches only `types.h` and `character.h`, neither of
   which knows about the controller.

   `tests/headers.c` is the test, and it is a whole suite for one `#include` on purpose: a
   second `#include` after the first proves nothing about the second, because by then the
   first has dragged its dependencies in. Covering another header means another file shaped
   like that one. It also stopped being true that `tests/controller.c` has to include
   `akgl/actor.h` first, and the comment there saying so is gone.

7. **There is no way to attach a 2D backend to a renderer the caller already has.**
   `akgl_render_init2d()` (`src/renderer.c:17`) does two separable things: it creates a window
   and an `SDL_Renderer` from the `game.screenwidth`/`game.screenheight` properties and writes
   to the `camera` global, and it installs the six function pointers that make an
   `akgl_RenderBackend` usable. A caller who already owns an `SDL_Renderer` wants only the
   second half — and that caller is not hypothetical, it is precisely the embedding host the
   API-gap section above exists to serve, since an embedded interpreter must not create the
   window.

   Today the only options are to call `akgl_game_init()` and let libakgl own the window, or to
   assign the six pointers by hand, which is what `akbasic`'s `tests/akgl_backends.c` does.
   **Fix:** split out `akgl_render_bind2d(akgl_RenderBackend *self)` that installs the vtable
   and nothing else, and have `akgl_render_init2d()` call it after it has made its window.
   `tests/renderer.c` could then cover the vtable half without a display at all.

   **Resolved.** `akgl_render_bind2d(akgl_RenderBackend *self)` installs the six pointers and
   returns; `akgl_render_init2d()` calls it once the window and the camera exist. It
   deliberately does *not* touch `self->sdl_renderer`, which is the whole point — a host that
   already owns one keeps it, and a host that does not gets a backend whose entry points all
   report `AKERR_NULLPOINTER` instead of crashing.

   `tests/renderer.c` is new and needs no display: it covers the binding (including that the
   caller's `SDL_Renderer` survives it, and that binding a backend without one is legal),
   frame start and end and both `draw_texture` paths against a software renderer under the
   dummy video driver, the refusals a bound-but-unrendered backend gives, and the `draw_mesh`
   "not implemented" stub. `src/renderer.c` goes from 10% line coverage to 56%; what is left
   is `akgl_render_init2d` itself and `akgl_render_2d_draw_world`, both of which want the
   offscreen harness and the world globals. **`akbasic`'s hand-assigned vtable in
   `tests/akgl_backends.c` can be deleted.**

8. **`akgl_text_rendertextat()` dereferences an uninitialised backend vtable.**
   `src/text.c` calls `renderer->draw_texture(renderer, ...)` with no NULL check on either
   `renderer` or the function pointer, so a backend that has an `SDL_Renderer` but has not been
   through `akgl_render_init2d()` segfaults on the first line of text. That is exactly the
   state item 7 leaves a host in, and it is the same class of defect the draw commit at
   42b60f7 added a test for — *"a backend that exists but was never given an SDL_Renderer,
   which is the state a host is in between allocating one and initializing it; every draw
   entry point has to report it rather than dereference it."* The text path still has it.

   **Fix:** `FAIL_ZERO_RETURN` on `renderer`, on `renderer->sdl_renderer` and on
   `renderer->draw_texture`, reporting `AKGL_ERR_SDL` or `AKERR_NULLPOINTER` as the draw
   entry points do. Test alongside the existing `tests/draw.c` backend-without-a-renderer case.

   **Resolved.** All three are checked, with `AKERR_NULLPOINTER` to match the draw entry
   points, and they are checked *before* anything is rasterized rather than after: refusing
   early costs nothing and leaks nothing, where refusing after the rasterize would hit the
   leak the `@note` on this function already describes.

   `tests/text.c` grew a software renderer under the dummy video driver — bound with the new
   `akgl_render_bind2d`, which is what made this cheap — and covers all three refusals plus
   the successful draw, wrapped and unwrapped. `src/text.c` goes from 58% to **100%** line
   coverage, and the three `akgl_text_rendertextat` mutants the mutation run left surviving
   are dead. The third case is the one that matters: with a *live* `SDL_Renderer` behind a
   backend that was never bound, the old code got all the way to a NULL function pointer.
   Checking it against a made-up renderer pointer, as the first draft of the test did, is
   worth nothing — SDL refuses the bogus handle and the call fails for the wrong reason, which
   a deleted-check mutant survives.

   Found while writing that test and filed below as item 27: SDL_ttf refuses the empty string
   on both rasterizing paths, so drawing an empty line is an error while measuring one is not.

9. **`SOUND`'s frequency sweep has no `akgl_audio_*` equivalent.** BASIC 7.0's
   `SOUND voice, freq, dur, dir, min, step` ramps the pitch from `freq` toward `min` in `step`
   increments per tick, in the direction `dir` selects — a siren, a laser, the whole reason
   `SOUND` has six arguments. `akgl_audio_tone(voice, hz, ms)` holds one pitch for one
   duration, and nothing changes pitch over the life of a note.

   `akbasic` refuses those three arguments rather than faking them, and the reasoning is worth
   recording because it is what makes this a `libakgl` gap rather than an interpreter one: the
   only way to fake a sweep from the interpreter is to re-issue tones from its step loop, which
   ties audible pitch to how often the host happens to call it — a tune that changes key with
   the frame rate. It has to be advanced on the mixer's own frame counter, which is where the
   phase is already derived from and which only this library can see.

   **Fix:** `akgl_audio_sweep(int voice, float32_t from_hz, float32_t to_hz, float32_t step_hz, uint32_t ms)`,
   advanced in `akgl_audio_mix()` beside the envelope. Tests would drive `akgl_audio_mix` by
   hand and assert the frame at which the pitch has moved, exactly as `tests/audio.c` already
   does for the envelope stages.

   **Resolved.** `akgl_audio_sweep(voice, from_hz, to_hz, step_hz, ms)` is in
   `include/akgl/audio.h`, with the step taken in `akgl_audio_mix()` off the mixer's own frame
   counter. Decisions worth knowing:

   - **One step every 1/60 second** (`AKGL_AUDIO_SWEEP_TICK_HZ`), because that is the rate the
     machine this vocabulary comes from advanced its sweep at, and its tunes are written for
     it. It divides 44100 exactly, so a step boundary always lands on a whole frame — which is
     what lets the suite assert the exact frame the pitch moves on rather than a tolerance.
   - **Direction comes from the two frequencies, not from the sign of the step.** `step_hz`
     stays positive; `to_hz` below `from_hz` sweeps down. A negative step is refused rather
     than silently meaning something.
   - **It arrives and holds.** The last step is clamped to `to_hz` rather than overshooting,
     and equal frequencies are a legal held tone rather than an error, so a caller computing
     its own limits does not have to special-case them.
   - **`akgl_audio_tone` is now the same start path with a step of 0**, which is also what
     makes a voice reused for a plain tone stop sweeping. That is one function, `start_note`,
     rather than two copies of the same six assignments.
   - **A swept voice accumulates its phase** instead of deriving it from the frame counter.
     Deriving assumes a constant frequency; under a sweep it jumps the waveform at every step,
     which is an audible click. The drift the derived form exists to avoid is not something a
     note that is changing pitch anyway can be said to suffer from.

   `tests/audio.c` drives the mixer by hand: one tick's frames do not move the pitch, the next
   frame does, both directions clamp at their target, a gate shorter than the sweep cuts it off
   part way, and a plain tone on a swept voice stays put. `src/audio.c` holds at 92%.

   Still missing for a complete `SOUND`: the oscillating third direction (C128 `dir` 2), which
   is a re-issue on arrival rather than a third kind of sweep, and `FILTER`, `TEMPO` and the
   `PLAY` note-string parser as before.

10. **The keystroke ring carries a keycode and nothing else, so Shift is invisible.**
    `akgl_controller_handle_event()` (`src/controller.c:104-105`) pushes `event->key.key` into
    the ring and drops the rest of the event, and `akgl_controller_poll_key(int *keycode, bool
    *available)` hands back only that. Item 4 asked for a non-blocking keystroke read and got
    one; what it did not ask for, and what a *line editor* turns out to need, is which
    character the keystroke actually produced.

    `akbasic` has now built one — an `INPUT` and a REPL prompt drawn in the window, in
    `src/sink_akgl.c` — and the consequence is concrete: no shifted character is reachable, so
    `"`, `!`, `(`, `)`, `:` and `;` cannot be typed at all, and lower case cannot be typed
    either. A BASIC line editor that cannot type a double quote cannot enter a string literal.
    The interpreter folds letters to upper case, which is what a C128 does anyway and is the
    right resolution for letters; it is not a resolution for punctuation, and there is nothing
    the caller can do about it because the modifier state was discarded two layers down.

    Note this is not solvable by the caller polling `SDL_GetModState()` at read time: by then
    the key is long released, and the whole point of a ring is that reads are decoupled from
    events.

    **Fix:** widen the ring entry to carry the modifier state and the composed text SDL already
    computes. Either

    ```c
    typedef struct akgl_Keystroke {
        SDL_Keycode key;
        SDL_Keymod  mod;
        char        text[8];    /* UTF-8, from SDL_EVENT_TEXT_INPUT; "" for a non-printing key */
    } akgl_Keystroke;

    akerr_ErrorContext AKERR_NOIGNORE *akgl_controller_poll_keystroke(akgl_Keystroke *dest, bool *available);
    ```

    alongside the existing `akgl_controller_poll_key()`, which stays as it is so nothing
    breaks — a game asking "was the up arrow pressed" wants exactly what it already gets.
    Filling `text` means handling `SDL_EVENT_TEXT_INPUT` as well as `SDL_EVENT_KEY_DOWN`, which
    is the only correct way to get a character out of SDL anyway: it is what makes a keyboard
    layout, a compose key and a dead key work, none of which a keycode can express.

    Tests would push a shifted key-down plus its text-input event through
    `akgl_controller_handle_event()` and assert both the keycode and the composed character
    come back, mirroring what `tests/controller.c` already does for the plain ring.

    **Resolved.** `akgl_Keystroke` (keycode, `SDL_Keymod`, and eight bytes of UTF-8) and
    `akgl_controller_poll_keystroke(akgl_Keystroke *dest, bool *available)` are in
    `include/akgl/controller.h`; the ring now holds those instead of bare keycodes.
    `akgl_controller_poll_key()` is untouched from its caller's side. Decisions worth knowing:

    - **The text is attached to the press that is still waiting for it**, tracked by a flag
      rather than by "whatever entry is newest". Without the flag, a press dropped by a full
      buffer hands its text to some older key that happens to be sitting at the end of the
      ring — which is wrong in exactly the case where things are already going badly.
    - **Text with no press behind it is buffered on its own**, with a keycode of 0. An input
      method commit and a character finished by a dead key have no key press of their own, and
      a line editor wants the character regardless. `akgl_controller_poll_key()` discards those
      on the way past rather than reporting a keystroke with no key.
    - **Oversized text is cut on a code point boundary.** An IME can commit several characters
      at once and an entry holds one; truncating on a byte boundary would leave a partial UTF-8
      sequence that nothing downstream can render.
    - **SDL only sends `SDL_EVENT_TEXT_INPUT` while text input is started**, so a host that
      wants `text` populated calls `SDL_StartTextInput()` on its window. Without it `key` and
      `mod` still arrive. That is documented on the function rather than left to be discovered.

    `tests/controller.c` covers the shifted-key case end to end (the `"` that started this),
    a non-printing key composing to nothing, a text-only entry through both pollers, text that
    outlived its own press, the code-point-boundary truncation, and both NULL arguments.
    `src/controller.c` holds at 91%.

## Truncated registry keys can collide

Found while turning `-Wall` on. `akgl_actor_initialize` and
`akgl_character_initialize` document their name fields as "Truncated, not
rejected, if the source name is longer", and that is what they do -- the copy is
`aksl_strncpy` bounded to the field, so it always terminates now.

Termination was the overread half, and it is fixed. The other half is not: the
truncated name **is the registry key**. Two distinct 200-character names
truncate to the same 127-byte key, and the second `SDL_SetPointerProperty`
silently replaces the first. The objects are different; the registry cannot tell.

The same applies to `akgl_Sprite::name` (128), `akgl_SpriteSheet::name` (512)
and the tilemap's object and tileset names.

Whether that matters depends on whether long asset names are realistic, and 127
bytes is generous for a hand-written name in a JSON file. Recording it rather
than fixing it, because the fix is a contract change -- refuse an over-long name
with `AKERR_OUTOFBOUNDS` instead of truncating -- and every one of those headers
currently promises the opposite. `aksl_strncpy` already reports exactly that
status when the bytes do not fit, so the change is to stop capping `n` at
`size - 1` and let it raise.

## akgl.pc names no dependencies

`akgl.pc.in` carries `Libs: -L${libdir} -lakgl` and no `Requires:` or
`Requires.private:` line, so a consumer that finds libakgl through pkg-config is
told nothing about libakerror, libakstdlib, SDL3, SDL3_image, SDL3_mixer,
SDL3_ttf or jansson.

That has always been wrong, and libakerror 2.x makes it sharper: `akerror.h` is
part of libakgl's *public* interface -- `IGNORE` and the `FAIL_*` macros expand
in the consumer's own translation units and reference `__akerr_last_ignored`,
which is thread-local as of 2.0.0. A consumer that builds against whatever
`akerror.h` happens to be on its include path and links whatever `libakerror.so`
the loader finds can get a mismatch that pkg-config had every opportunity to
prevent and did not mention.

The fix is a `Requires:` line for the libraries whose headers libakgl's headers
include (akerror, akstdlib, SDL3) and `Requires.private:` for the rest, plus a
version floor of `akerror >= 2.0.1`. Not done here because it changes what
`pkg-config --libs akgl` emits for every existing consumer, and that wants to be
its own commit with an install-tree test behind it. The CMake path is not
affected -- `akglConfig.cmake` re-finds the targets.

## libakstdlib wrappers not yet adopted

`libakgl` links `libakstdlib` and uses ten of its wrappers. It calls the raw
libc function at a good many more sites. Adopting the four that were carrying a
real defect is done (see the 0.6.0 commit); this is what is left, and the reason
each is left.

**Adopted, for the record:** `aksl_fclose` (an unchecked close in
`akgl_game_save` lost buffered data silently), `aksl_fgetc` (`fgetc(3)` spells
EOF and a read error the same way), `aksl_snprintf` at two sites that were
truncating under a silenced `-Wformat-truncation`, and `aksl_strncpy` at the two
`src/game.c` sites the fixed-width copy sweep missed.

### The pure-arithmetic wrappers are deliberately not adopted

`memset` (38 sites), `strlen` (14), `strcmp` (9), `strncmp` (9), `memcpy` (6),
`memcmp` (2). Every one of these can only fail on a NULL argument, and at all
but a handful of those sites the argument is a stack object whose address cannot
be NULL. `aksl_memset` and `aksl_memcpy` are used twice each, which is the
inconsistency worth naming: there is no rule distinguishing those two sites from
the other 44.

Converting them costs an `errctx` check per line and buys a NULL check the
compiler already knows is redundant. Not converting them leaves the file mixing
two spellings of the same operation. **Pick one and write it down** -- the
recommendation is to convert only where the argument is a parameter or a heap
pointer, and say so in `AGENTS.md`, rather than either extreme.

### `DISABLE_GCC_WARNING_FORMAT_TRUNCATION` is now dead

`include/akgl/error.h` exports it and `RESTORE_GCC_WARNINGS`, and after the
`aksl_snprintf` conversion nothing in the tree uses either. They are public
macros, so removing them is an API change and is not done here. Both suppressed
sites turned out to be real truncations, which is the argument for deleting
rather than keeping them: the two times this library silenced that warning, the
compiler was right.

### No wrapper is used for the collections

`aksl_HashMap`, `aksl_List` and `aksl_TreeNode` exist and libakgl uses SDL
property sets for every registry instead. That is not an oversight -- the
registries hand `SDL_PropertiesID` values to callers and SDL owns the lifetime.
Recorded so nobody re-derives it.

## Arcade physics feel

Found by building `tests/physics_sim.c`, which runs the arcade backend as a game
would -- a Mario-esque jump and fall, Zelda-style top-down movement, and a
fast run reversed at speed -- and prints what the actor actually did. Three
defects it found are fixed in 0.6.0 (an unbounded first step, release handlers
zeroing the gravity accumulator, and per-axis thrust caps composing to a 141%
diagonal). These are what it found and did **not** fix.

### No terminal velocity

`akgl_physics_arcade_gravity` adds `gravity_y * dt` to `ey` every step and
nothing bounds it. `sy` caps *thrust*, deliberately -- it is the character's own
top speed, not a speed limit on the world -- so a fall accelerates without limit
for as long as it lasts. The jump simulation reaches 560 px/s in 0.7 s and would
keep going.

Drag is the mechanism that exists for this: `physics.drag.y` makes `ey`
approach `gravity_y / drag_y` instead of diverging. So the behaviour is
reachable, it just is not the default and is not documented as the way to get a
terminal velocity. Either document it that way or add an explicit
`physics.terminal_velocity`. Touches `src/physics.c` and
`include/akgl/physics.h`; no ABI change if it is a property rather than a field.

### Releasing a direction stops the actor dead

`akgl_actor_cmhf_*_off` sets `tx` (or `ty`) to zero, so a character running at
full speed stops within one frame of the key coming up -- the top-down
simulation measures 0.0 px of drift in the second after release. That is correct
for Zelda and wrong for Mario, who slides. There is no deceleration or ground
friction anywhere in the arcade backend; `ax` is the only rate, and it applies
only while a direction is held.

The shape that fits the existing model is a per-character deceleration that
decays `tx` toward zero over several frames instead of assigning zero, with the
current behaviour as the value that means "instant". That is a new
`akgl_Character` field and an ABI break, so it wants to land with other
character changes rather than alone.

### Integration is explicit Euler, so trajectories are frame-rate dependent

Velocity is applied to position using the velocity computed *this* step, and
thrust is accumulated before the cap, so the same jump traces a slightly
different arc at 30 Hz than at 144 Hz. The reversal simulation measures 0.500 s
to turn around where the closed form predicts 0.489 s -- about 2% at 60 Hz, and
it grows with the step.

`max_timestep` bounds how bad it gets (that is half of why it exists), and 2% is
not a bug a player can see. It is recorded because the fix -- a fixed-step
accumulator, integrating in whole `max_timestep` slices and carrying the
remainder -- would also remove the slow-motion trade that bounding the step
currently makes, and the two are the same piece of work.

### A large drag coefficient can invert velocity

`actor->ex -= actor->ex * self->drag_x * dt` is a first-order decay, so it only
decays for `drag * dt < 1`. Past that it overshoots zero, and past `2` it
diverges. With `dt` bounded to the default 0.05 s that needs a drag coefficient
above 20, which is not a plausible setting, so this is a sharp edge rather than
a live defect -- but nothing rejects it, and `max_timestep` is caller-settable.
`src/physics.c`, in the three drag blocks. The exact fix is
`expf(-drag * dt)` instead of `1 - drag * dt`, which is unconditionally stable.

## Carried over

1. **Make character-to-sprite state bindings release their references symmetrically.**
   `akgl_character_sprite_add()` increments the sprite refcount for every state-map
   binding, but no corresponding removal API exists. Replacing a state binding
   also leaves the previous sprite's refcount incremented. When
   `akgl_heap_release_character()` drops the character refcount to zero, it clears
   the character registry entry and zeroes the structure without enumerating
   `state_sprites`, decrementing the bound sprites, or destroying the SDL property
   map. Implement binding removal/replacement so each removed binding releases
   exactly one sprite reference. On final character release, enumerate every
   remaining binding (the existing `akgl_character_state_sprites_iterate()` release
   path may be reusable), release each reference, destroy `state_sprites`, and then
   clear the character. Add tests for removal, replacement, duplicate sprite
   bindings across multiple states, and final character release.

   **The final-release half is done in 0.5.0** — see **Defects** item 21.
   `akgl_heap_release_character` now enumerates every remaining binding, releases
   each reference, destroys `state_sprites`, and then clears the character, and
   `akgl_character_state_sprites_iterate` is covered by that path.

   **Replacement is done too**, as **Defects** item 20:
   `akgl_character_sprite_add` releases the sprite it displaces, and
   `tests/character.c` covers binding, rebinding, and 200 alternating rebinds.

   **Still open: removal.** There is no API to unbind one state without binding
   something else over it -- `akgl_character_sprite_del` -- and no test for
   duplicate sprite bindings across several states. Neither leaks anything
   today; they are a gap in the surface rather than a defect.

2. **An actor cannot be scaled per axis.** `akgl_Actor::scale` is one `float32_t` applied
   to both `dest.w` and `dest.h`, so there is no way to express "twice as wide, the same
   height". The VIC-II has had separate x- and y-expand bits since 1982 and Commodore
   BASIC 7.0's `SPRITE` verb exposes both, so a BASIC interpreter drawing through libakgl
   cannot implement its own documented verb.

   Two shapes are plausible and the choice is a design decision rather than an obvious
   fix: add `scale_x` / `scale_y` and keep `scale` as a convenience that writes both, or
   replace `scale` outright and take the ABI break while the major version is still 0.
   The second is cleaner and the soname already carries `MAJOR.MINOR`.

   Related to defect 26, and reached the same way: `akbasic`'s sprites are Commodore
   sprites, 24 wide and 21 high, and `SPRITE n,,,,1` expands one axis. It works around
   both by installing its own `renderfunc` on each actor rather than patching around the
   library.

   **Half of that workaround is no longer needed.** Defect 26 -- `akgl_actor_render`
   taking the drawn height from the sprite's width -- is fixed in 0.5.0, so a
   non-square sprite draws at its own proportions through the library's own
   `renderfunc`. This item is the half that remains: one uniform `scale`, with no way
   to expand a single axis.

## Found while writing the manual

Twenty-one chapters and two tutorial games were written against `src/` rather than
against the header comments, and the exercise turned up two distinct classes of problem.
Both are recorded here because publishing a problem you cannot fix yet is still a
contribution, and because the second class is the more dangerous one: **every item in it
was documented, in a header, incorrectly.**

The manual documents each of these where a reader would hit it, and points here.

### Defects with no prior entry

1. **`akgl_game_update` calls `simulate` through a NULL pointer.** `akgl_game_update`
   invokes `akgl_physics->simulate(akgl_physics, NULL)` with no NULL check, and
   `akgl_default_physics` is zeroed BSS — all four method pointers are NULL. A program
   that does not call `akgl_physics_init_arcade`/`_null` itself therefore **segfaults on
   its first frame**, measured as exit 139, rather than raising `AKERR_NULLPOINTER`.
   `physics.h:8-9,195` tells the reader `akgl_game_init` selects a backend from a
   `physics.engine` property, so a caller who believes the header writes exactly the
   program that crashes. This is the worst first-contact experience in the library and
   the fix is a NULL check. Closing it touches `src/game.c` only.

2. **Parent/child offset is double-counted at draw time.** `src/physics.c:192-197` writes
   a child's `x` as `parent->x + vx` — an absolute world coordinate. `src/actor.c:273-279`
   then draws it at `parent->x + obj->x`, while `actor_visible` three lines above tests
   the camera against the raw `obj->x` as absolute. Two readings of one field inside one
   function. Confirmed by measurement: with the player at (280,146) and a (-14,+10)
   offset, the guarded draw lands at (130,114) and the unguarded one at (410,260), off a
   320x240 screen; rendering both and hashing `SDL_RenderReadPixels` gives different
   images. Invisible only while the parent sits at the origin. `actor.h` documents **both**
   readings, in two places. `examples/jrpg` works around it with a `renderfunc` that nulls
   `obj->parent` for the duration of the draw.

3. **Actors and characters unregister under a different key than they register.**
   `akgl_actor_initialize` (`src/actor.c:46`) and `akgl_character_initialize`
   (`src/character.c:39`) register under the caller's untruncated `name`, while
   `akgl_heap_release_actor` (`src/heap.c:132`) and `_release_character`
   (`src/heap.c:165`) clear using the object's truncated 128-byte field. Past 127 bytes
   those are different keys, so releasing leaves a live registry entry pointing at a
   zeroed pool slot. Distinct from "Truncated registry keys can collide" above, which
   describes sprites and spritesheets, where the truncated name genuinely *is* the key.

4. **Every actor spawned from a map is invisible on frame one.**
   `akgl_actor_initialize` sets `movement_controls_face`, and the default `facefunc`
   clears every facing bit and re-sets one only from a *movement* bit. An NPC has no
   movement bit, so state 17 falls to 16, which maps to no sprite, and the actor is
   silently skipped by the draw. The same thing makes a player character vanish the
   moment they stop walking. Both tutorials clear the field on every live actor after
   loading a map; that workaround should not be necessary.

5. **`use_own_physics` is set and never read.** `akgl_tilemap_load_physics` builds a
   complete `akgl_PhysicsBackend` on the map when it declares a `physics.model` property,
   and sets `map->use_own_physics` — and nothing in the library ever consults it. A map's
   declared physics is silently ignored unless the application writes the switch itself.
   `README.md` used to show that `if`, which made a caller-side workaround read like a
   library feature.

6. **`akgl_TilemapLayer` does not record a layer's name.** `akgl_tilemap_load_layers`
   reads `id`, `opacity`, `visible`, `x`, `y` and `type` and drops the `name` Tiled
   wrote; the only `name` retained anywhere is per-object. A game therefore cannot ask
   for "the terrain layer" and must hard-code a numeric layer id, which changes whenever
   somebody reorders layers in the editor. Both tutorials hard-code one.

7. **`akgl_character_sprite_add` leaks a reference when the same sprite is re-added.**
   `ref->refcount += 1` is unconditional but the matching release is guarded by
   `displaced != ref`, so re-adding a sprite to a state it already occupies leaks a pool
   slot per call.

8. **`akgl_tilemap_compute_tileset_offsets` silently requires `spacing == 0` and
   `margin == 0`.** It adds `spacing` to the tile pitch but sets row 0's y offset to
   `spacing` rather than 0, and ignores `margin` entirely. A tileset with a gutter — which
   is most published tileset packs — renders misaligned with no diagnostic. This
   materially constrains what art the library can consume; it ruled out several otherwise
   suitable CC0 packs while sourcing the tutorial assets.

9. **`akgl_actor_render` hard-codes `SDL_FLIP_NONE`** (`src/actor.c:283`). There is no
   mirrored blit, so a side-on character needs both facings drawn in the sheet. That is
   why `docs/tutorials/assets/sidescroller/player.png` carries six frames rather than
   three, and it doubles the art cost of every such character.

10. **`akgl_Actor::layer` is unbounded but `draw_world` stops at `AKGL_TILEMAP_MAX_LAYERS`.**
    An actor assigned layer 16 or above is accepted, updated, simulated — and never drawn.

11. **`akgl_registry_load_properties` leaks one string-pool slot per failed property.**
    The per-property `CLEANUP` block is empty. The string pool is 256 slots, so a
    sufficiently malformed properties file drains it.

12. **`speedtime` is dead.** It is loaded from character JSON (`src/character.c:263`),
    written through `(int *)&obj->speedtime` on a `uint64_t` field — correct only because
    the struct was zeroed and the host is little-endian — and then read by nothing. Frame
    timing comes from `sprite->speed`.

13. **`AKGL_SPRITE_MAX_REGISTRY_SIZE` is dead.** Defined in `sprite.h`, referenced
    nowhere in `src/`, `include/`, `tests/` or `util/`.

14. **`AKGL_TILEMAP_MAX_TILES_PER_IMAGE` is checked nowhere**, and costs 512 KiB per
    tileset regardless of the image's real tile count.

15. **There is no sound-effect API.** `akgl_audio_*` is a synthesizer that reads no files;
    `akgl_load_start_bgm` is the only file-audio entry point, and its infinite-loop
    request is set on property set 0, so background music plays once. A game cannot load
    and play a sound effect through this library at all.

16. **A literal 512x512 tilemap is rejected.** Both bounds are `>=`, so the documented
    `AKGL_TILEMAP_MAX_WIDTH`/`_HEIGHT` of 512 is off by one and 512x511 is the largest
    map that loads.

17. **Unverified asset provenance.** `tests/assets/World_A1.png` and
    `util/assets/Actor1.png` carry the default filenames of RPG Maker's bundled art and
    ship with no license file, while `tests/assets/akgl_test_mono.ttf` sits beside
    `akgl_test_mono.LICENSE.txt`. RPG Maker's bundled assets are licensed to users of that
    product; redistributing them inside a C library is not something that license covers.
    The tutorial assets under `docs/tutorials/assets/` deliberately do not depend on
    either file, and `tests/docs_setups/tilemap.sh` says why it stages a different image.
    Closing this means replacing two fixtures and the maps that reference them.

18. **`util/assets/littleguy.json` does not load.** The sample data for `charviewer`, the
    one demo program the library ships, uses the pre-0.5.0 unprefixed state names
    (`ACTOR_STATE_ALIVE`) and `velocity_x`/`velocity_y` instead of `speed_x`/`speed_y`.
    The current loader accepts neither.

19. **A control map could not say "any keyboard", so binding one was a coin flip.**
    `akgl_controller_handle_event` matched `event->key.which == curmap->kbid` exactly, and
    there was no way to express "whatever keyboard the player types on". That is not a
    theoretical gap, because the id a key event *carries* is chosen by the video backend
    and does not have to be an id `SDL_GetKeyboards()` reports: on X11 without XInput2
    every key event carries `SDL_GLOBAL_KEYBOARD_ID` (0) while SDL registers the keyboard
    as `SDL_DEFAULT_KEYBOARD_ID` (1), and with XInput2 the events carry the physical slave
    device's `sourceid` while `SDL_GetKeyboards()[0]` may be the master. A game that bound
    `SDL_GetKeyboards()[0]` -- the obvious thing -- got a map that matched nothing and
    controls that silently did nothing. `examples/sidescroller` shipped exactly that.

    **Fixed**: `kbid`/`jsid` of 0 now match any device of that kind. 0 is safe to spend
    because SDL documents `which` as 0 when the source is unknown or virtual and joystick
    ids start at 1, so no real device is 0. A non-zero id still matches only that device,
    which is what keeps two local players apart. `util/charviewer.c` was already passing 0
    and depending on the old accidental behaviour, so it works under XInput2 now too.

    The reason this reached a release is worth keeping: **every test in
    `tests/controller.c` dispatched an event whose id equalled the id the map was bound
    with**, so none of them could see it, and the sidescroller's smoke test called the
    handlers directly rather than dispatching events, so it passed against a control map
    that matched nothing. Both are fixed -- `test_controller_wildcard_device_ids` asserts
    the contract, and the smoke test now drives `akgl_controller_handle_event` from a
    non-zero device id and fails if the press does not arrive.

### Header comments that describe code that has changed

Twenty-seven claims across the public headers were false when checked against `src/`.
`AGENTS.md` already warns that this file "carried eleven entries describing code that had
already changed"; this is the same failure in the headers, and Doxygen publishes it.

Nothing catches these. `WARN_IF_UNDOCUMENTED` proves a symbol *has* a comment, not that
the comment is true, and `api_surface` strips comments precisely because prose is not a
declaration. The full list is in the manual, each noted in the chapter that covers the
subsystem, but the ones that would actively mislead a caller are:

- `physics.h:8-9,195` — the `physics.engine` property and `akgl_game_init` calling the
  factory. Neither exists. See defect 1 above for what this costs.
- `README.md` (now corrected) — "ONLY supports TilED TMJ tilemaps with tileset **external**
  references". Backwards: `"source"` appears nowhere in `src/tilemap.c`, and
  `akgl_tilemap_load_tilesets_each` reads `columns`/`firstgid`/`tilecount`/`image` inline.
  Only **embedded** tilesets load.
- `renderer.h` — `frame_start`/`frame_end`/`draw_texture` "dereference `self` before it is
  checked". Each function's first statement is `FAIL_ZERO_RETURN(errctx, self, ...)`.
- `sprite.h` — `speed` is "seconds, scaled to milliseconds". It is milliseconds scaled to
  nanoseconds. Also claims `frames` is unbounded (bounded at `src/sprite.c:207`) and that
  `akgl_sprite_initialize` overreads via `memcpy` (it uses `aksl_strncpy`).
- `character.h` — `speedtime` "in seconds" (milliseconds), and `sprite_add` never releasing
  a displaced sprite (`src/character.c:60,77-79` releases it).
- `actor.h` — the `cmhf` block comment says the `_off` handlers zero acceleration, thrust,
  environmental *and* velocity. They zero only `ax`/`tx` or `ay`/`ty`; zeroing `ey` was the
  gravity-cancel defect fixed in 0.6.0, and two `@note`s still describe it.
- `json_helpers.h` — the conventions block says `dest` is not NULL-checked and that only
  `akgl_get_json_string_value` checks its key. All eleven accessors check `dest`, and all
  seven key-taking accessors check `key`.
- `assets.h:17-18` — "`akgl_game_init` (or a bare `akgl_audio_init`) has to have run
  first". `akgl_mixer` is created only in `akgl_game_init`; `akgl_audio_init` opens the
  synthesizer's stream and never touches it, so `akgl_load_start_bgm` after only that
  hands NULL to `MIX_LoadAudio`.
- `registry.h:54` — `akgl_registry_init` creating seven registries and not properties. It
  creates eight including properties; the genuinely false part is that `akgl_game_init`
  never calls it at all, calling the eight individually in a different order.
- `tilemap.h:59-60,354-357,447-450,462-468` — object and tileset counts unbounded, and
  `akgl_tilemap_release` double-freeing. All fixed; the surviving half of the last one is
  that `release` does not release the map's actors.
- `controller.h:232-234,262-263` — a negative `controlmapid` not rejected. Both call sites
  check.

### Entries in this file that are themselves stale

- **"Known and still open" item 15** — `akgl_path_relative` leaking an error-context slot
  per ENOENT call — is fixed. `src/util.c:115-129` sets a flag in the `HANDLE` block and
  calls `path_relative_root` after `FINISH`, which is exactly the fix the item proposes.
- **`TODO.md:2027`**, under "akgl.pc names no dependencies", says "`akglConfig.cmake`
  re-finds the targets". No such file is generated or installed — `install()` ships the
  library, the headers and `akgl.pc` only, so `find_package(akgl)` cannot work against an
  install tree at all. That makes the section's problem worse than it states.
- **`AGENTS.md:636`** says `sim_step()` sets `gravity_time` to `now - dt`.
  `tests/physics_sim.c` sets it to `0` and drives the step through `max_timestep`; the
  `now - dt` form was replaced because it went red under parallel `ctest`.

## tg is vendored and has no consumer

`deps/tg` is pinned at v0.7.9 and **nothing in the tree uses it**. It was
evaluated alongside `deps/libccd` for the collision work and lost, for two
reasons that are properties of the library rather than preferences:

- **It is 2D permanently.** Its own documentation says the z coordinate is
  "only carried along and serve[s] no other purpose than to be available for
  when it's desired to export to an output representation"; no predicate reads
  it. libccd is natively 3D, so the 2D case is a restriction that lifts later.
- **Its predicates return `bool`.** Resolving a collision needs a minimum
  translation vector, and `tg_geom_intersects` cannot supply one.

Secondary: every coordinate in its API is `double` against libakgl's
`float32_t`; `tg.c` is a single 16,000-line amalgamation that embeds a second
JSON parser next to the jansson already vendored; and it ships no build system,
so `akgl_add_vendored_dependency` would silently do nothing for it.

It is kept rather than dropped because there is one job it does that libccd
structurally cannot: **indexed point-in-polygon against concave polygons with
holes.** GJK and MPR are convex-only, always. A trigger volume or walkable
region authored as a concave Tiled polygon is the case, and tg answers it at
10M+ ops/sec with its own segment index.

**This entry is the deadline.** Either that consumer appears, or `deps/tg` comes
out. A vendored dependency with no caller is a question every future reader has
to answer, and 6 MB of it is cloned by every recursive checkout in CI. Closing
it means either writing the region-query API or `git rm` -- not leaving it here.

## Actor rotation, and collision under it

**No actor carries an angle.** `akgl_actor_render` hard-codes `SDL_FLIP_NONE`,
every collision shape is axis-aligned, and both example games depend on that
being true. Adding rotation is a small change in five named places and a large
change in one, and this entry exists so the large one is not a surprise.

What it touches, in the order it would have to be done:

1. **`akgl_Actor` grows an `angle`**, in radians, about z. Render consumes it:
   `SDL_RenderTextureRotated` takes an angle in *degrees* and a centre, so
   `akgl_actor_render` converts and picks a centre. The centre is a decision,
   not a detail — a sprite rotating about its frame centre and one rotating
   about its feet look nothing alike.
2. **`collision_support` rotates `dir` into local space** at the top and rotates
   the answer back. That one function is written so this is *the whole
   narrowphase change*: every arm of its switch already answers in the shape's
   own frame, and the world centre is added by `collision_ccdobj` rather than
   inside the switch. A `ccd_quat_t` on `collision_ccdobj`, one `ccdQuatRotVec`
   in and one `ccdQuatRotVec` out, and MPR and GJK both work on rotated shapes
   with nothing else touched. `collision_center` is unaffected — the centre of a
   shape rotated about its own centre is the same point.
3. **The box fast path stops being valid for a rotated pair.** `collision_box_box`
   is a closed form that assumes both boxes are axis-aligned; a rotated pair has
   to fall through to MPR. That is a branch on `(a->angle != 0 || b->angle != 0)`
   and a measurable cost — the fast path is 2-7x cheaper (`PERFORMANCE.md`,
   "Collision, measured"), so a game that rotates everything pays for it.
4. **The broad-phase bound becomes the rotated bound.** `akgl_collision_shape_bounds`
   returns the shape's own AABB; a rotated shape needs the AABB *of the rotated
   shape*, which is larger. The function grows an angle parameter, and every
   caller — `akgl_collision_settle`, the grid's `insert`/`move`, `ss_grounded` in
   the sidescroller — passes one. A broad phase that keeps returning the
   unrotated bound under-reports, which is the one failure mode the partitioner
   contract forbids.
5. **`akgl_collision_proxy_sync` copies the angle** alongside the shape and the
   position, since that is the one place the proxy's copy is refreshed.

**The z-extrusion invariant is unaffected.** Rotation is about z, so a shape's
half-extent along z does not change and `AKGL_COLLISION_DEPTH_RATIO` still makes
z overlap exceed any achievable planar penetration. See
[Chapter 15](docs/15-collision.md), "Why a 2D shape has a depth".

**What it does not touch:** the response. `akgl_actor_collide_block` works on a
normal and a velocity and does not care how the normal was found. Angular
velocity, torque and rotational response are a *different* piece of work and are
not implied by any of the above — a rotated shape that resolves linearly is a
perfectly coherent intermediate state, and it is the one a top-down shooter
actually wants.

## Swept narrowphase for fast movers

`AKGL_COLLISION_FLAG_BULLET` is defined, documented as reserved, and **does
nothing**. Sub-stepping bounds how far an actor travels between tests and it is
capped at `AKGL_COLLISION_MAX_SUBSTEPS` (8) sub-steps of at most
`AKGL_COLLISION_SUBSTEP_FRACTION` (0.5) of a cell, so the speed above which
tunnelling returns is:

```
    v_max = substeps * fraction * cellsize / max_timestep
          = 8 * 0.5 * 16 / 0.05
          = 1280 px/s        on 16-pixel tiles at the default max_timestep
```

Check your own numbers against that: a game with 8-pixel tiles halves it, and a
game that raises `physics.max_timestep` lowers it proportionally. A walking
character is nowhere near it; a projectile is a projectile.

The fix is a swept test rather than more sub-steps — sweeping the shape's AABB
over the sub-step's motion, testing that, and resolving at the time of first
contact rather than at the end position. It belongs behind the flag so it is
paid for only by the shapes that need it.

## The ccd arena is single-threaded and sized by measurement

`src/collision_arena.c` is one static arena of `AKGL_CCD_ARENA_BYTES` (64 KB)
with a bump pointer, reset at the top of every `akgl_collision_test`. Two things
follow that are true today and would not survive a change:

- **It is not thread-safe.** libakgl is single-threaded behind
  `akgl_game.statelock`, and two threads in the narrowphase at once would
  interleave allocations in the same arena. Threading libakgl means an arena per
  thread, or a lock, before anything else.
- **The size is a measurement, not a guess.** One GJK/EPA box pair measures
  7,264 bytes. Exhaustion is reported, not crashed: `ccdGJKPenetration` returns
  -2 and `akgl_collision_test` raises `AKGL_ERR_COLLISION` with the high-water
  mark in the message, so the failure names its own fix. MPR — the default on
  the frame path — allocates nothing at all, so the arena is only under pressure
  from a caller who has explicitly asked for EPA's manifold.

`akgl_ccd_arena_highwater()` is public so a game can assert its own ceiling.

## `akgl_collide_rectangles` stays; the corner helpers did not

The collision plan's last step was to **delete `akgl_rectangle_points`,
`akgl_collide_point_rectangle` and `akgl_collide_rectangles`** once the shape API
landed, on the grounds that collision now has a real narrowphase. Two of the
three went, in 0.8.0, along with `akgl_Point` and `akgl_RectanglePoints`. The
third stays, and this is the reasoning rather than an oversight.

**Why the two went.** They were the intermediate form of an implementation that
changed. `akgl_collide_rectangles` was eight corner-containment tests built on
them; it is four span comparisons now and does not go through either. Nothing
outside `tests/` called them, and a point-in-rectangle test is four comparisons a
caller can write without a struct conversion in front of it.

**Why the third stays.**

- **It has callers that are correct.** `examples/sidescroller/player.c` uses it
  twice, for coins and for hazards. Those are overlap *questions* asked from an
  `updatefunc` -- "am I touching this" -- and the right answer is a `bool`.
  Routing them through a collision shape would mean a proxy, a broad-phase insert
  and a narrowphase call to compute a normal and a depth that nothing reads.
- **It was fixed in this same series**, not left broken. It missed the cross case
  and truncated through `akgl_Point`'s `int` members; it is exact in `float32_t`
  now. Deleting it two commits after fixing it is a strange thing to do to a
  caller.
- **A game-level overlap question is not always a physics question.** A minimap
  marker, a UI hit test, "is the cursor over this". None of those wants to be
  pushed, and none of them belongs in a collision world.

One thing found while doing this and fixed rather than recorded:
`akgl_RectanglePoints`' Doxygen comment still said `akgl_collide_rectangles`
"works corner by corner rather than by comparing edge spans", which had been
false since the fix. It went with the type.
