Take libakerror 2.0.1 and drop the workaround it makes obsolete

Every libakgl test suite could report success while failing. libakerror's
default unhandled-error handler ended in exit(errctx->status), an exit
status is one byte wide, and libakgl's band starts at 256 -- so
AKGL_ERR_SDL, the most common failure a library built on SDL can have,
exited 0 and CTest recorded a pass. tests/character.c aborted at its
second of four tests on a bad renderer and was green for months.

0.5.0 worked around that here with TEST_TRAP_UNHANDLED_ERRORS() in
tests/testutil.h, and TODO.md ended the entry saying any consumer's
suites have the same problem and it was worth raising upstream. It was.
2.0.1 fixes it at the source: akerr_exit() owns the 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). The
trap and its 21 call sites are gone.

Verified by putting the original failure back rather than by reading the
release notes: a FAIL_BREAK(AKGL_ERR_SDL) in tests/character.c's main
exits 125 and CTest reports a failure. A standalone consumer raising the
same status unhandled exits 125 where it exited 0 before.

tests/actor.c installs its own handler and called exit(errctx->status)
from it, which is the same defect one layer up. It calls akerr_exit()
now.

2.0.0 also makes the error pool and the status registry thread safe,
which libakgl needs more than it knew: audio_stream_callback raises
error contexts on SDL's audio thread. With an unlocked pool that
callback and the main thread could scan AKERR_ARRAY_ERROR at the same
time and be handed the same slot. The comment there says so.

This is a hard dependency floor, not a preference. 2.0.0 moved
__akerr_last_ignored to thread-local storage and made akerr_next_error()
return a context that already holds its reference, and both expand at
libakgl's call sites -- and at a consumer's, because akerror.h is part
of libakgl's public interface. Mixing headers and libraries across that
line double-counts every reference and never returns a pool slot. The
soname moved to libakerror.so.2; include/akgl/error.h now also feature-
tests AKERR_EXIT_STATUS_UNREPRESENTABLE, which is the narrowest probe
for 2.0.1 since libakerror publishes no version macro.

0.7.0 for that reason: libakgl's own ABI is unchanged, but the one it
re-exports through its headers is not.

TODO.md records the pkg-config gap this makes sharper -- akgl.pc names
no dependencies at all, so nothing tells a pkg-config consumer which
libakerror it needs.

Clean build, 26/26 ctest, memcheck clean, warning-clean at -Wall
-Werror. libakgl.so.0.7 links libakerror.so.2.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01B8T5FAYXE8HEJqFLCYwNNc
Co-Authored-By: Andrew Kesterson <andrew@aklabs.net>

AGENTS.md

@@ -592,13 +592,17 @@ if ( defaulted != NULL ) {
 }
 ```
 
-**Every suite's `main()` must call `TEST_TRAP_UNHANDLED_ERRORS()` immediately
-after `akgl_error_init()`.** libakerror's default unhandled-error handler ends
-in `exit(errctx->status)`, `exit` keeps only the low byte, and libakgl's status
-band starts at 256 — so a suite that failed with `AKGL_ERR_SDL` exited 0 and
-CTest recorded a pass. That is not hypothetical: `tests/character.c` aborted at
-its second of four tests on a bad renderer and was green until 0.5.0. The trap
-in `tests/testutil.h` collapses any status a byte cannot carry onto 1. Add focused tests as `tests/<feature>.c`, create a matching `test_<feature>` target, and register it with `add_test`. Put reusable fixtures in `tests/assets/` and keep paths compatible with tests launched from the build tree. Coverage mode wraps the suite in a CTest fixture so counters are reset before tests and reports are generated afterward.
+**Never `exit(3)` on an akerr status — call `akerr_exit()`.** An exit status is
+one byte wide and libakgl's status band starts at 256, so `exit(AKGL_ERR_SDL)`
+is a wait status of 0 and a shell sees a clean run. Every suite in this
+directory once reported success on the most common failure a library built on
+SDL can have: `tests/character.c` aborted at its second of four tests on a bad
+renderer and was green until 0.5.0. `akerr_exit()` (libakerror 2.0.1) maps 0 to
+0, 1–255 to themselves, and anything else to
+`AKERR_EXIT_STATUS_UNREPRESENTABLE` (125). The default unhandled-error handler
+calls it, so an ordinary suite needs no trap of its own — `tests/testutil.h`
+carried one until 0.6.0 and it is gone. A suite that installs its *own* handler
+still has to call `akerr_exit()` from it; `tests/actor.c` does. Add focused tests as `tests/<feature>.c`, create a matching `test_<feature>` target, and register it with `add_test`. Put reusable fixtures in `tests/assets/` and keep paths compatible with tests launched from the build tree. Coverage mode wraps the suite in a CTest fixture so counters are reset before tests and reports are generated afterward.
 
 ### Physics simulations