Fix miscounted break-visit expectation in TODO.md 1.8

The bullet said breaking at tree[3] in pre-order should assert 4 visits.
Pre-order is 0, 1, 3, 4, 2, 5, 6, so the correct count is 3 -- which is what
tests/test_tree_iterate_break.c already asserts. The TODO was written before
that test existed and had the number wrong, not the test.

Also point the bullet at the existing pre-order test, and give the in-order
and post-order traversals with their break points so the remaining work does
not need the count re-derived.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.gitea/workflows/ci.yaml

@@ -0,0 +1,77 @@
+name: libakstdlib CI Build
+run-name: ${{ gitea.actor }} libakstdlib test
+on: [push]
+
+jobs:
+  cmake_build:
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo "Triggered by ${{ gitea.event_name }} from ${{ gitea.repository }}@${{ gitea.ref }}. Building on ${{ runner.os }}."
+      - name: Check out repository code
+        uses: actions/checkout@v4
+        with:
+          # A top-level build uses deps/libakerror via add_subdirectory, so the
+          # submodule has to be present or the configure step fails outright.
+          submodules: recursive
+      - name: dependencies
+        run: |
+          sudo apt-get update -y
+          sudo apt-get install -y cmake gcc moreutils
+          # Depends on libakerror@main
+          git clone https://source.starfort.tech/andrew/libakerror.git
+          cd libakerror
+          cmake -S . -B build
+          cmake --build build
+          cmake --install build
+      - name: build and test
+        run: |
+          cmake -S . -B build
+          cmake --build build
+          sudo cmake --install build
+          ctest --test-dir build --output-on-failure
+      - run: echo "🍏 This job's status is ${{ job.status }}."
+
+  mutation_test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out repository code
+        uses: actions/checkout@v4
+        with:
+          # The harness copies the repo and builds the copy top-level, so it
+          # needs deps/libakerror present just like the main job does.
+          submodules: recursive
+      - name: dependencies
+        run: |
+          sudo apt-get update -y
+          sudo apt-get install -y cmake gcc moreutils python3
+      # Verify the tests actually catch bugs: break the library many ways and
+      # confirm the suite fails. Gated on src/stdlib.c (fast, deterministic);
+      # run the full default target locally for the macro header as well.
+      #
+      # The threshold is a ratchet, not a quality bar. The score on the section
+      # 1.0 suite is 46.8% (81/173 killed): the list and tree functions are
+      # covered, and everything else in src/stdlib.c -- the printf family, the
+      # ato* family, realpath, the memory and stream wrappers -- has no tests
+      # yet, so its mutants survive. 40 leaves headroom for the runner while
+      # still failing on a real regression (tests deleted, or new untested code
+      # added). Raise it as TODO.md sections 1.1-1.9 land.
+      - name: mutation testing
+        run: |
+          python3 scripts/mutation_test.py \
+            --target src/stdlib.c \
+            --junit mutation-junit.xml \
+            --threshold 40
+      # Publish even when the threshold gate fails, so survivors are visible --
+      # each one is a missing test. Display-only (fail_on_failure: false); the
+      # --threshold above is the gate. annotate_only avoids the Checks API 404
+      # on Gitea (mikepenz/action-junit-report#23).
+      - name: publish mutation results
+        if: always()
+        uses: mikepenz/action-junit-report@v4
+        with:
+          report_paths: 'mutation-junit.xml'
+          annotate_only: true
+          detailed_summary: true
+          include_passed: true
+          fail_on_failure: 'false'
+      - run: echo "🍏 This job's status is ${{ job.status }}."

.githooks/pre-push

@@ -0,0 +1,100 @@
+#!/usr/bin/env bash
+#
+# pre-push: build libakstdlib and run the test harnesses before anything leaves
+# this machine.
+#
+# Install (once per clone):
+#
+#     git config core.hooksPath .githooks
+#
+# Runs by default, a few seconds all in:
+#
+#     * default build      + ctest
+#     * ASan/UBSan build   + ctest
+#
+# Opt in to the slow harness (~25 minutes -- it rebuilds and re-runs the whole
+# suite once per mutant):
+#
+#     AKSL_HOOK_MUTATION=1 git push
+#
+# Bypass everything (git's own escape hatch):
+#
+#     git push --no-verify
+#
+# Builds go under .git/aksl-prepush so the hook never disturbs whatever is in
+# your own build/ directory. Override with AKSL_HOOK_BUILD_DIR if you want them
+# somewhere else.
+
+set -u
+
+# Keep in sync with the --threshold in .gitea/workflows/ci.yaml, so a push that
+# would fail CI fails here first.
+MUTATION_THRESHOLD="${AKSL_MUTATION_THRESHOLD:-40}"
+
+ZERO_SHA=0000000000000000000000000000000000000000
+
+root=$(git rev-parse --show-toplevel) || exit 1
+cd "$root" || exit 1
+
+# git feeds us one line per ref being pushed. A push that only *deletes* refs
+# has no commits to test, so there is nothing to do. An empty stdin (nothing to
+# push) lands here too, which is equally fine to skip.
+has_updates=0
+while read -r _local_ref local_sha _remote_ref _remote_sha; do
+    if [ "$local_sha" != "$ZERO_SHA" ]; then
+        has_updates=1
+    fi
+done
+if [ "$has_updates" -eq 0 ]; then
+    exit 0
+fi
+
+if [ ! -f deps/libakerror/CMakeLists.txt ]; then
+    echo "pre-push: deps/libakerror is empty. Run:" >&2
+    echo "    git submodule update --init --recursive" >&2
+    exit 1
+fi
+
+builddir="${AKSL_HOOK_BUILD_DIR:-$(git rev-parse --git-dir)/aksl-prepush}"
+mkdir -p "$builddir" || exit 1
+logfile="$builddir/last.log"
+
+# Run a step quietly; on failure, dump what it said and abort the push.
+run() {
+    if ! "$@" > "$logfile" 2>&1; then
+        echo >&2
+        echo "pre-push: FAILED: $*" >&2
+        echo "---------------------------------------------------------------" >&2
+        cat "$logfile" >&2
+        echo "---------------------------------------------------------------" >&2
+        echo "pre-push: push aborted. Use 'git push --no-verify' to override." >&2
+        exit 1
+    fi
+}
+
+echo "pre-push: default build + ctest"
+run cmake -S . -B "$builddir/default"
+run cmake --build "$builddir/default"
+run ctest --test-dir "$builddir/default" --output-on-failure
+
+echo "pre-push: sanitizer build + ctest"
+run cmake -S . -B "$builddir/asan" -DAKSL_SANITIZE=ON
+run cmake --build "$builddir/asan"
+run ctest --test-dir "$builddir/asan" --output-on-failure
+
+if [ "${AKSL_HOOK_MUTATION:-0}" = "1" ]; then
+    echo "pre-push: mutation testing, threshold ${MUTATION_THRESHOLD}% (this takes a while)"
+    # Deliberately not wrapped in run(): this one is slow enough that you want
+    # to watch it make progress.
+    if ! python3 scripts/mutation_test.py \
+            --target src/stdlib.c \
+            --threshold "$MUTATION_THRESHOLD"; then
+        echo >&2
+        echo "pre-push: mutation score below ${MUTATION_THRESHOLD}%. Push aborted." >&2
+        echo "pre-push: use 'git push --no-verify' to override." >&2
+        exit 1
+    fi
+fi
+
+echo "pre-push: OK"
+exit 0

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "deps/libakerror"]
+	path = deps/libakerror
+	url = https://source.starfort.tech/andrew/libakerror.git

CMakeLists.txt

@@ -1,6 +1,25 @@
 cmake_minimum_required(VERSION 3.10)
 project(akstdlib LANGUAGES C)
 
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -g -ggdb -pg")
+set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -g -ggdb -pg")
+set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -g -ggdb -pg")
+
+# Sanitizer build, off by default:
+#   cmake -S . -B build-asan -DAKSL_SANITIZE=ON && ctest --test-dir build-asan
+# Set before the dependency is added so libakerror is instrumented too --
+# several of the defects in TODO.md section 2 (the uninitialised %s in
+# aksl_realpath, the unbounded vsprintf in aksl_sprintf, the missing va_end in
+# the printf family) only show up under ASan/UBSan.
+option(AKSL_SANITIZE "Build the library and its tests with ASan + UBSan" OFF)
+if(AKSL_SANITIZE)
+  set(AKSL_SANITIZE_FLAGS "-fsanitize=address,undefined -fno-omit-frame-pointer -fno-sanitize-recover=all")
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${AKSL_SANITIZE_FLAGS}")
+  set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${AKSL_SANITIZE_FLAGS}")
+  set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} ${AKSL_SANITIZE_FLAGS}")
+  message(STATUS "AKSL_SANITIZE=ON: building with ASan + UBSan")
+endif()
+
 if(TARGET akerror::akerror)
   message(STATUS "FOUND akerror::akerror")
 else()
@@ -11,9 +30,36 @@ include(CTest)
 include(GNUInstallDirs)
 include(CMakePackageConfigHelpers)
 
-if(NOT TARGET akerror::akerror)
+if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+  # libakerror registers its own CTest entries unconditionally, and because we
+  # pull it in EXCLUDE_FROM_ALL its test binaries are never built -- so every
+  # one of them used to show up in our suite as "Not Run" and fail. CMake has no
+  # way to un-register a test, and set_tests_properties cannot reach across
+  # directory scopes, so add_test() is shadowed for the duration of the
+  # add_subdirectory() call. The dependency has its own CI; this project's suite
+  # should only contain this project's tests.
+  set(AKSL_SUPPRESS_ADD_TEST TRUE)
+  function(add_test)
+    if(NOT AKSL_SUPPRESS_ADD_TEST)
+      _add_test(${ARGV})
+    endif()
+  endfunction()
+  # libakerror also marks two of those tests WILL_FAIL, which would now be
+  # setting properties on tests that no longer exist, so suppress that too.
+  function(set_tests_properties)
+    if(NOT AKSL_SUPPRESS_ADD_TEST)
+      _set_tests_properties(${ARGV})
+    endif()
+  endfunction()
+
+  add_subdirectory(deps/libakerror EXCLUDE_FROM_ALL)
+
+  set(AKSL_SUPPRESS_ADD_TEST FALSE)
+else()
+  if(NOT TARGET akerror::akerror)
     find_package(PkgConfig REQUIRED)
     find_package(akerror REQUIRED)
+  endif()
 endif()
 
 set(akstdlib_install_cmakedir "${CMAKE_INSTALL_LIBDIR}/cmake/akstdlib")
@@ -67,4 +113,79 @@ install(FILES
     DESTINATION ${akstdlib_install_cmakedir}
 )
 
+# Each test is one source file tests/test_<name>.c, built into the executable
+# test_<name> and registered as the CTest test <name>. Shared helpers live in
+# tests/aksl_capture.h.
+#
+#   AKSL_TESTS                must exit 0.
+#   AKSL_WILL_FAIL_TESTS      expected to abort by design (an unhandled error
+#                             reaching FINISH_NORETURN, a deliberate contract
+#                             violation), so a non-zero exit is a pass.
+#   AKSL_KNOWN_FAILING_TESTS  assert the *correct* behaviour of a confirmed
+#                             defect from TODO.md section 2.1. They fail until
+#                             the defect is fixed, and are marked WILL_FAIL so
+#                             the suite stays green and the gap stays visible.
+#                             When one is fixed CTest reports it as failed with
+#                             "unexpectedly passed" -- that is the cue to move
+#                             it up into AKSL_TESTS.
+set(AKSL_TESTS
+    linkedlist
+    tree
+)
+
+set(AKSL_WILL_FAIL_TESTS
+)
+
+set(AKSL_KNOWN_FAILING_TESTS
+    list_append_chain     # TODO.md 2.1.1 -- append truncates lists of 2+ nodes
+    list_iterate_head     # TODO.md 2.1.2 -- iterate starts at the midpoint
+    tree_iterate_break    # TODO.md 2.1.3 -- ITERATOR_BREAK does not stop a walk
+)
+
+foreach(_test IN LISTS AKSL_TESTS AKSL_WILL_FAIL_TESTS AKSL_KNOWN_FAILING_TESTS)
+  add_executable(test_${_test} tests/test_${_test}.c)
+  target_include_directories(test_${_test} PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/tests)
+  target_link_libraries(test_${_test} PRIVATE akstdlib)
+  add_test(NAME ${_test} COMMAND test_${_test})
+endforeach()
+
+if(AKSL_WILL_FAIL_TESTS OR AKSL_KNOWN_FAILING_TESTS)
+  set_tests_properties(
+    ${AKSL_WILL_FAIL_TESTS} ${AKSL_KNOWN_FAILING_TESTS}
+    PROPERTIES WILL_FAIL TRUE
+  )
+endif()
+
+# Cap every test. The list and tree code is full of loops whose termination
+# depends on a single condition, so a plausible bug -- or a mutant from the
+# target below -- turns a test into an infinite loop. Without this, ctest waits
+# forever; the mutation harness then kills ctest at its own timeout and the
+# spinning test binary is left orphaned, holding the pipe open and burning a
+# core. The whole suite runs in well under a second, so 30s is pure headroom.
+set_tests_properties(
+  ${AKSL_TESTS} ${AKSL_WILL_FAIL_TESTS} ${AKSL_KNOWN_FAILING_TESTS}
+  PROPERTIES TIMEOUT 30
+)
+
+# Mutation testing: break the library in small ways and confirm the test suite
+# notices. This is a meta-check on the tests themselves, and it rebuilds and
+# re-runs the whole suite once per mutant, so it is a manual target rather than
+# a CTest test:
+#   cmake --build build --target mutation
+# This target covers both src/stdlib.c and include/akstdlib.h. CI runs the
+# narrower, faster src/stdlib.c set with a --threshold gate; see
+# .gitea/workflows/ci.yaml.
+find_package(Python3 COMPONENTS Interpreter)
+if(Python3_FOUND)
+  add_custom_target(mutation
+    COMMAND ${Python3_EXECUTABLE}
+            ${CMAKE_CURRENT_SOURCE_DIR}/scripts/mutation_test.py
+            --source-root ${CMAKE_CURRENT_SOURCE_DIR}
+    WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
+    USES_TERMINAL
+    COMMENT "Running mutation tests (breaks the library, expects tests to fail)"
+  )
+endif()
+
+
 # pkgconfig

README.md

@@ -0,0 +1,132 @@
+# README
+
+![build badge](https://source.starfort.tech/andrew/libakstdlib/actions/workflows/ci.yaml/badge.svg?branch=main)
+
+`libakstdlib` wraps C standard library functions so that they report failures
+through [libakerror](https://source.starfort.tech/andrew/libakerror)'s
+`ATTEMPT { ... } HANDLE { ... }` error contexts instead of through return codes
+and `errno`. It also provides a few data structures built on the same
+convention (a doubly-linked list and a binary tree).
+
+Every entry point returns `akerr_ErrorContext *` and is marked `AKERR_NOIGNORE`.
+See `TODO.md` for the current state of the library: what is covered by tests,
+which corner cases are still open, and which libc functions are not yet wrapped.
+
+## Building
+
+```sh
+git submodule update --init --recursive   # deps/libakerror
+cmake -S . -B build
+cmake --build build
+cmake --install build
+```
+
+A top-level build compiles the vendored `deps/libakerror`. When `libakstdlib` is
+consumed as a subproject, it uses whatever `akerror::akerror` target or installed
+package the parent provides instead.
+
+## Testing
+
+There are three harnesses. The first two take seconds; the third takes about
+half an hour.
+
+### 1. The test suite
+
+```sh
+cmake -S . -B build
+cmake --build build
+ctest --test-dir build --output-on-failure
+```
+
+Tests live one per file in `tests/test_<name>.c` and share the helpers in
+`tests/aksl_capture.h` — `AKSL_CHECK()` for plain assertions (unlike `assert()`
+it survives `-DNDEBUG`), `AKSL_CHECK_STATUS(call, expected)` to run a wrapper and
+assert on the status it returns, and an `AKSL_RUN()` driver that additionally
+fails any test which leaks a slot from libakerror's error pool.
+
+To add a test, drop `tests/test_mything.c` in place and add `mything` to
+`AKSL_TESTS` in `CMakeLists.txt`.
+
+**Reading the results.** `CMakeLists.txt` splits tests into three lists, and two
+of them invert the meaning of "Passed":
+
+| List | Meaning |
+|---|---|
+| `AKSL_TESTS` | Ordinary tests. Must exit 0. |
+| `AKSL_WILL_FAIL_TESTS` | Expected to abort by design — an unhandled error reaching `FINISH_NORETURN`, or a deliberate contract violation. Marked `WILL_FAIL`, so a non-zero exit is a pass. |
+| `AKSL_KNOWN_FAILING_TESTS` | Assert the *correct* behaviour of a confirmed defect (see `TODO.md` §2.1). Also marked `WILL_FAIL`. |
+
+So `ctest` reporting all green does **not** mean the library is defect-free — it
+means the known-good tests passed and the known-bad ones are still failing in the
+documented way. When a defect is fixed, its test starts passing, CTest reports it
+as failed with *unexpectedly passed*, and that is the cue to move it from
+`AKSL_KNOWN_FAILING_TESTS` into `AKSL_TESTS`.
+
+Every test is capped with a 30-second CTest `TIMEOUT`. The list and tree code is
+full of loops whose termination hangs on a single condition, so a bug of that
+shape hangs the suite rather than failing it.
+
+### 2. Sanitizers
+
+```sh
+cmake -S . -B build-asan -DAKSL_SANITIZE=ON
+cmake --build build-asan
+ctest --test-dir build-asan --output-on-failure
+```
+
+Builds the library, the tests and the vendored libakerror with ASan + UBSan and
+`-fno-sanitize-recover=all`. Several of the open items in `TODO.md` §2 only
+misbehave under instrumentation — the uninitialised `%s` in `aksl_realpath`, the
+unbounded `vsprintf` behind `aksl_sprintf`, the missing `va_end` in the `printf`
+family — so new tests for those should be run this way.
+
+### 3. Mutation testing
+
+The suite tells you the library works. Mutation testing tells you the *suite*
+works: it breaks the library in small ways, one at a time, and checks that the
+tests notice.
+
+```sh
+cmake --build build --target mutation        # src/stdlib.c + include/akstdlib.h
+```
+
+or drive the script directly for a faster or narrower run:
+
+```sh
+scripts/mutation_test.py --target src/stdlib.c            # C source only
+scripts/mutation_test.py --target src/stdlib.c --list     # enumerate, build nothing
+scripts/mutation_test.py --target src/stdlib.c --max-mutants 20
+scripts/mutation_test.py --target src/stdlib.c --threshold 40
+```
+
+A mutant that makes the tests fail is *killed* (good); one the tests still pass
+is a *survivor*, and names a missing test. The score is `killed / total`, and the
+run prints every survivor with `file:line` and the exact edit. The harness never
+touches your working tree — it copies the repo to a scratch directory and mutates
+the copy.
+
+CI runs the `src/stdlib.c` set with `--threshold 40`. That is a regression
+ratchet rather than a quality bar: the current score is 46.8%, and the survivors
+are concentrated in the wrappers that have no tests yet. Raise the threshold as
+coverage lands.
+
+## The pre-push hook
+
+`.githooks/pre-push` runs the fast harnesses — the default build and the
+sanitizer build, each followed by `ctest` — before letting a push out. Enable it
+once per clone:
+
+```sh
+git config core.hooksPath .githooks
+```
+
+It only builds when there are commits to push (a branch deletion is a no-op), and
+it builds under `.git/aksl-prepush` so it never disturbs your own `build/`.
+
+```sh
+AKSL_HOOK_MUTATION=1 git push    # also run the mutation gate (slow)
+git push --no-verify             # skip the hook entirely
+```
+
+Other knobs: `AKSL_MUTATION_THRESHOLD` (default 40, keep it in step with
+`.gitea/workflows/ci.yaml`) and `AKSL_HOOK_BUILD_DIR`.

TODO.md

@@ -0,0 +1,553 @@
+# TODO
+
+Working notes for `libakstdlib` — the akerror-wrapped libc surface.
+
+Scope of the current library (`include/akstdlib.h`, `src/stdlib.c`): 16 libc wrappers
+(`fopen`, `fread`, `fwrite`, `fclose`, `malloc`, `free`, `memset`, `memcpy`, `printf`,
+`fprintf`, `sprintf`, `atoi`, `atol`, `atoll`, `atof`, `realpath`), one hash helper
+(`aksl_strhash_djb2`), a doubly-linked list (`append`/`pop`/`iterate`) and a binary tree
+iterator (`aksl_tree_iterate`).
+
+Items marked **[CONFIRMED]** were reproduced by building the library and running a probe
+program against it, not just read off the source.
+
+---
+
+## 1. Unit tests that should be written
+
+### 1.0 Test-harness prerequisites — **DONE** (branch `feature/test-harness`)
+
+`ctest` is green: 5/5, no *Not Run* entries. Everything in §1.1–1.9 can now be written
+against `tests/aksl_capture.h` and added to the `AKSL_TESTS` list.
+
+- [x] **The current tests cannot fail.** `tests/test_linkedlist.c` asserted nothing at all;
+      it printed node names and returned `0` unconditionally, so any of the list bugs in
+      §2.1 would pass it. Rewritten as 15 assertion-based cases covering the append, iterate
+      and pop behaviour that is correct today.
+- [x] **`tests/test_tree.c` was red.** `ctest` reported `tree (Failed)`, exit 136, because
+      `parms.steps` was never reset between the three searches, so the second assertion
+      compared an accumulated `14` against `7`. Each search now builds its own tree and
+      params. The file records that its step counts do not actually distinguish the three
+      traversal orders — real order assertions remain §1.8.
+- [x] **Adopt libakerror's test conventions.** `tests/aksl_capture.h` provides `AKSL_CHECK()`
+      (an `NDEBUG`-proof assert), `AKSL_CHECK_STATUS()`/`AKSL_CHECK_OK()` which run an
+      akerror-returning call, assert on its status and release the context,
+      `AKSL_CHECK_MSG_CONTAINS()`, a capturing `akerr_log_method`, `aksl_slots_in_use()` for
+      pool-leak checks, and an `AKSL_RUN()` driver that additionally fails any test which
+      leaks an error-pool slot.
+- [x] **One test source per behaviour, registered with CTest via a list variable.**
+      `tests/test_<name>.c` → executable `test_<name>` → CTest test `<name>`, driven by
+      `AKSL_TESTS` in `CMakeLists.txt`.
+- [x] **Add a `WILL_FAIL` category.** Two lists: `AKSL_WILL_FAIL_TESTS` for tests that abort
+      by design (empty for now) and `AKSL_KNOWN_FAILING_TESTS` for the confirmed defects in
+      §2.1 — see the note at the head of §2.1.
+- [x] **Fix the four permanently-failing submodule tests.** `deps/libakerror` is added
+      `EXCLUDE_FROM_ALL`, so akerror's `add_test` entries registered but its test binaries
+      were never built, and `ctest` reported `err_catch`, `err_cleanup`, `err_trace`,
+      `err_improper_closure` as *Not Run* → failed on every run. Neither the pinned commit
+      nor upstream `main` guards that registration, CMake has no way to un-register a test,
+      and `set_tests_properties` cannot reach across directory scopes — so `add_test` and
+      `set_tests_properties` are shadowed for the duration of the `add_subdirectory` call.
+      The dependency has its own CI; this suite now contains only this project's tests.
+- [x] **Wire in a memory-error build.** `cmake -S . -B build-asan -DAKSL_SANITIZE=ON` adds
+      `-fsanitize=address,undefined -fno-sanitize-recover=all` to the library, the tests and
+      the vendored libakerror. Currently clean, and it is the intended way to test the items
+      in §2 that only misbehave under instrumentation (uninitialised `%s` in
+      `aksl_realpath`, unbounded `vsprintf`, missing `va_end`).
+- [x] **Port `scripts/mutation_test.py` from libakerror.** Retargeted at `src/stdlib.c` and
+      `include/akstdlib.h` (178 mutants) and exposed as
+      `cmake --build build --target mutation`. CI runs the narrower `src/stdlib.c` set (173
+      mutants) as its own `mutation_test` job with `--threshold 40` and a JUnit report.
+      **Current score: 46.8%** — 81 killed, 92 survived. The survivors are concentrated
+      exactly where §1.1–1.9 have yet to be written:
+
+      | surviving mutants | function |
+      |---|---|
+      | 10 | `aksl_tree_iterate` |
+      | 6 each | `aksl_fread`, `aksl_fwrite`, `aksl_fprintf`, `aksl_sprintf` |
+      | 5 | `aksl_printf` |
+      | 4 each | `aksl_memcpy`, `aksl_realpath`, `aksl_strhash_djb2`, `aksl_list_append` |
+      | 3 each | `aksl_malloc`, `aksl_free`, `aksl_memset`, `aksl_fopen`, `aksl_fclose`, `aksl_atoi`, `aksl_atol`, `aksl_atoll`, `aksl_atof` |
+      | 1 | `aksl_list_iterate` |
+
+      The threshold is a regression ratchet, not a quality bar; raise it as sections below
+      land. Each surviving mutant is a concrete missing test — `mutation-junit.xml` lists
+      them with `file:line` and the exact edit.
+- [x] **Cap every test with a CTest `TIMEOUT`.** Found while measuring the above: a mutant
+      that deletes `fast = fast->next->next` turns `aksl_list_iterate` into an infinite
+      loop, so `ctest` waited forever, the mutation harness killed `ctest` at its own
+      120 s timeout, and the orphaned test binary kept spinning at 100% CPU while holding
+      the pipe open — the run wedged and had to be killed by hand. `TIMEOUT 30` on every
+      test makes `ctest` reap its own child, so those mutants are now killed in 30 s and
+      leave nothing behind. It also guards the real suite against the same class of bug.
+- [x] **CI could not have run any of this.** `actions/checkout@v4` was not fetching
+      submodules, so `add_subdirectory(deps/libakerror)` had nothing to descend into and the
+      configure step failed before ever reaching the tests. Added `submodules: recursive`,
+      and swapped `cmake --build build --target test` for `ctest --output-on-failure` so a
+      failure is diagnosable from the job log. The deeper problem — CI installing
+      `libakerror@main` while the build actually compiles the pinned submodule — is §2.3.
+
+### 1.1 Memory wrappers
+
+- [ ] `aksl_malloc` — happy path returns non-NULL and writes through `dst`.
+- [ ] `aksl_malloc(n, NULL)` → `AKERR_NULLPOINTER`, message content asserted.
+- [ ] `aksl_malloc(0, &p)` — pin down the contract. Today the result depends on whether the
+      platform's `malloc(0)` returns NULL; if it does, the wrapper reports `errno`, which may
+      be `0`. See §2.2.1.
+- [ ] `aksl_malloc(SIZE_MAX, &p)` → allocation failure surfaces `ENOMEM`, and `*dst` is left
+      NULL rather than garbage.
+- [ ] `aksl_free(NULL)` → `AKERR_NULLPOINTER` (assert the documented behaviour, since
+      `free(NULL)` is legal C and callers will be surprised).
+- [ ] `aksl_free` happy path, and a malloc→free round trip under ASan.
+- [ ] `aksl_memset` — happy path fills the buffer; `n == 0` is a no-op; `s == NULL` →
+      `AKERR_NULLPOINTER`.
+- [ ] `aksl_memcpy` — happy path copies; `d == NULL` and `s == NULL` each →
+      `AKERR_NULLPOINTER`; `n == 0` with valid pointers succeeds.
+- [ ] `aksl_memcpy` with overlapping regions — decide and test whether this is rejected
+      (`AKERR_VALUE`) or documented as UB like `memcpy`.
+
+### 1.2 File I/O
+
+- [ ] `aksl_fopen` happy path on a temp file; `*fp` is written.
+- [ ] `aksl_fopen("/nonexistent/path", "r", &fp)` → `ENOENT` propagated as the status, with
+      the pathname in the message.
+- [ ] `aksl_fopen` on a mode-denied path (e.g. `/proc/1/mem`, or a `chmod 000` temp file) →
+      `EACCES`.
+- [ ] `aksl_fopen(path, mode, NULL)` → `AKERR_NULLPOINTER`.
+- [ ] `aksl_fopen(NULL, "r", &fp)` and `aksl_fopen(path, NULL, &fp)` → currently unchecked,
+      see §2.2.2. Test once the guards exist.
+- [ ] `aksl_fread` full read; short read at EOF → `AKERR_EOF`; read from a write-only stream
+      → `AKERR_IO`; `fp == NULL` → `AKERR_NULLPOINTER`; `ptr == NULL` → should be
+      `AKERR_NULLPOINTER` (see §2.2.3).
+- [ ] `aksl_fread` **partial read that is neither EOF nor error** — assert whatever the fixed
+      contract is; today this silently returns success and the caller cannot tell how many
+      members were read.
+- [ ] `aksl_fwrite` happy path; write to a read-only stream → `AKERR_IO`; write to a full
+      device (`/dev/full`) → `ENOSPC`/`AKERR_IO`; `fp == NULL` → `AKERR_NULLPOINTER`.
+- [ ] `aksl_fclose` happy path; `NULL` → `AKERR_NULLPOINTER`; double-close is caught or
+      documented as UB.
+- [ ] `aksl_fclose` on a stream whose buffered flush fails (`/dev/full`) → non-zero `fclose`
+      surfaces `errno`.
+- [ ] Round-trip test: `fopen` → `fwrite` → `fclose` → `fopen` → `fread` → compare bytes.
+
+### 1.3 Formatted output
+
+- [ ] `aksl_printf` / `aksl_fprintf` / `aksl_sprintf` happy paths, asserting both the byte
+      count written through `count` and the produced text.
+- [ ] Each of the three with every pointer argument NULL in turn → `AKERR_NULLPOINTER`.
+- [ ] `aksl_fprintf` to a closed / read-only stream → error path, and confirm `*count` is not
+      left holding `-1` as if it were a valid length.
+- [ ] `aksl_sprintf` with a format that overflows the destination — currently unbounded
+      (§2.2.4). Test the `aksl_snprintf` replacement once it exists.
+- [ ] Regression test for the missing `va_end` (§2.1.4) — a test that calls each variadic
+      wrapper many times in a loop, run under valgrind/ASan.
+- [ ] Format-string/arg mismatch is caught at compile time once
+      `__attribute__((format(printf, ...)))` is added (§2.2.5) — a negative compile test.
+
+### 1.4 String → number
+
+- [ ] `aksl_atoi` / `atol` / `atoll` / `atof` happy paths, including negative values and
+      leading whitespace.
+- [ ] NULL `nptr` and NULL `dest` for each → `AKERR_NULLPOINTER`.
+- [ ] **Non-numeric input** (`"not a number"`) — **[CONFIRMED]** currently returns *success*
+      with `*dest == 0`. Test the `AKERR_VALUE` behaviour once §2.1.5 is fixed.
+- [ ] **Overflow** (`"99999999999999999999"`) — **[CONFIRMED]** currently returns success with
+      a garbage value (`-1` on this box). Test for `ERANGE`.
+- [ ] Empty string, `"  "`, `"12abc"` (trailing junk), `"0x10"`, `"inf"`/`"nan"` for `atof`.
+- [ ] `LONG_MIN`/`LONG_MAX`/`LLONG_MIN`/`LLONG_MAX` boundary strings round-trip exactly.
+
+### 1.5 `aksl_realpath`
+
+- [ ] Happy path on an existing file and on a symlink chain; result matches `realpath(3)`.
+- [ ] Non-existent path → `ENOENT`.
+- [ ] A path component that is not a directory → `ENOTDIR`.
+- [ ] Symlink loop → `ELOOP`.
+- [ ] `path == NULL` → `AKERR_NULLPOINTER`.
+- [ ] `resolved_path == NULL` — currently unchecked and leaks (§2.1.6). Test once fixed.
+- [ ] A failure case where `resolved_path` is an *uninitialised* buffer — this is the crash
+      case in §2.1.6; run it under ASan/MSan.
+
+### 1.6 `aksl_strhash_djb2`
+
+- [ ] Known-answer vectors: `djb2("")` == 5381; a handful of fixed strings with their
+      pre-computed 32-bit values.
+- [ ] `len == 0` returns 5381 regardless of `str` contents.
+- [ ] NULL `str` and NULL `hashval` → `AKERR_NULLPOINTER`.
+- [ ] **High-bit bytes** (`"\xff\xfe"`) — pins down the sign-extension bug in §2.2.6; the
+      expected value must be the `unsigned char` one.
+- [ ] Embedded NUL bytes are hashed (the function is length-driven, not NUL-driven).
+- [ ] Same input → same output across two calls (no hidden state).
+
+### 1.7 Linked list
+
+- [ ] **`aksl_list_append` builds a correct chain of N nodes** — **[CONFIRMED BROKEN]**, see
+      §2.1.1. Appending `n1..n4` to `n0` yields the chain `n0 -> n4`; `n1`, `n2`, `n3` are
+      silently dropped. This is the single most important test to add.
+- [ ] `append` sets `obj->prev` to the real tail and `obj->next` to NULL.
+- [ ] `append` onto an empty (single, zeroed) node.
+- [ ] `append` NULL list / NULL obj → `AKERR_NULLPOINTER`.
+- [ ] `append` onto a list containing a cycle → `AKERR_CIRCULAR_REFERENCE`, for a self-loop,
+      a 2-node cycle, and a cycle that does not include the head.
+- [ ] `append` a node that is already in the list (aliasing) — define and test the contract.
+- [ ] **`aksl_list_iterate` visits every node exactly once, starting at the head** —
+      **[CONFIRMED BROKEN]**, see §2.1.2: it starts iterating from the *midpoint* left behind
+      by the cycle detector, so the head is never visited. Assert both the visit count and
+      the visit order.
+- [ ] `iterate` over a single-node list visits exactly one node.
+- [ ] `iterate` NULL list / NULL iter → `AKERR_NULLPOINTER`.
+- [ ] `iterate` over a cyclic list → `AKERR_CIRCULAR_REFERENCE` (self-loop, 2-node,
+      tail-to-middle).
+- [ ] `iterate` where the callback raises `AKERR_ITERATOR_BREAK` → iteration stops at that
+      node, the wrapper returns success, and the visit count proves the early exit.
+- [ ] `iterate` where the callback raises some *other* error → that error propagates out
+      unchanged, with the callback's message intact.
+- [ ] `aksl_list_pop` on a middle node relinks `prev`/`next` correctly and clears the popped
+      node's pointers.
+- [ ] `pop` on the head node, on the tail node, and on a single-node list.
+- [ ] `pop(NULL)` → `AKERR_NULLPOINTER`.
+- [ ] `pop` then `iterate` — the list is still traversable and the popped node is gone.
+- [ ] Pool-accounting test: after a long sequence of list operations including failures,
+      `akerr_slots_in_use() == 0`.
+
+### 1.8 Tree
+
+- [ ] Visit **order** assertions, not just counts, for `DFS_PREORDER`, `DFS_INORDER` and
+      `DFS_POSTORDER` over the 7-node tree — record the visited node pointers into an array
+      and compare against the expected sequence. The current test only counts steps, which
+      cannot distinguish the three orders (all three visit 7 nodes).
+- [ ] **`AKERR_ITERATOR_BREAK` aborts the whole traversal** — **[CONFIRMED BROKEN]**, see
+      §2.1.3. The pre-order case exists as `tests/test_tree_iterate_break.c`: pre-order
+      visits 0, 1, 3, so breaking at `tree[3]` must stop the walk at **3** visits, and today
+      it runs on to all 7. Add the equivalent for in-order (3, 1, 4, 0, 5, 2, 6 → breaking at
+      `tree[4]` gives 3) and post-order (3, 4, 1, 5, 6, 2, 0 → breaking at `tree[5]` gives 4).
+- [ ] `AKSL_TREE_SEARCH_BFS` and `AKSL_TREE_SEARCH_BFS_RIGHT` → `AKERR_NOT_IMPLEMENTED`
+      today; replace with real order assertions once implemented (§3 / §2.2.9).
+- [ ] **Unknown `searchmode`** (e.g. `99`) — **[CONFIRMED]** currently returns *success*
+      having visited nothing. Should be `AKERR_VALUE`.
+- [ ] **`AKSL_TREE_SEARCH_VISIT`** (defined in the header, `5`) — **[CONFIRMED]** falls into
+      the same silent-success hole. Either implement it or reject it.
+- [ ] `root == NULL` / `iter == NULL` → `AKERR_NULLPOINTER`.
+- [ ] Single-node tree (no children) visits exactly once, in all three orders.
+- [ ] Left-only and right-only degenerate chains.
+- [ ] Callback raising a non-`ITERATOR_BREAK` error propagates out of the recursion with the
+      original status and message.
+- [ ] Custom `lalloc`/`lfree` are actually invoked — **currently they are stored and never
+      called** (§2.2.8), so this test will fail until BFS lands.
+- [ ] Deep/degenerate tree (e.g. 100k-node left chain) — documents the recursion-depth limit
+      (§2.2.7).
+- [ ] A tree containing a cycle (child pointing back at an ancestor) — currently infinite
+      recursion; test for `AKERR_CIRCULAR_REFERENCE` once guarded.
+
+### 1.9 Cross-cutting
+
+- [ ] **Error-pool accounting**: for *every* wrapper, a test that drives the failure path
+      `AKERR_MAX_ARRAY_ERROR + 10` times and asserts the pool does not leak
+      (`akerr_slots_in_use() == 0` after each handled error).
+- [ ] **Stack-trace content**: assert that the file/function/line recorded by each wrapper's
+      `FAIL` points at `src/stdlib.c` and the right function name.
+- [ ] **`AKERR_NOIGNORE` is effective**: a negative compile test where a wrapper's return is
+      discarded and `-Werror=unused-result` fires.
+- [ ] **Thread safety**: libakerror's `AKERR_ARRAY_ERROR` is a process-global array with no
+      locking. If `libakstdlib` is meant to be callable from threads, add a concurrent
+      smoke test under TSan — and if it is not, say so in the README.
+
+---
+
+## 2. Corner cases in existing functionality that should be resolved
+
+### 2.1 Confirmed defects (reproduced against the built library)
+
+The first three now have a failing test apiece, registered in `AKSL_KNOWN_FAILING_TESTS`
+and therefore marked `WILL_FAIL` so the suite stays green while the gap stays visible:
+`tests/test_list_append_chain.c`, `tests/test_list_iterate_head.c` and
+`tests/test_tree_iterate_break.c`. When one of these defects is fixed, CTest reports that
+test as failed with *unexpectedly passed* — that is the cue to move it into `AKSL_TESTS`.
+
+1. **`aksl_list_append` does not find the tail — it silently truncates the list.**
+   `src/stdlib.c:194`. The function conflates Floyd cycle detection with tail-finding:
+   `tail` is set to `slow` *before* `slow` advances, so it tracks the node *behind the
+   midpoint*, not the tail. Appending `n1`, `n2`, `n3`, `n4` to `n0` produces the chain
+   `n0 -> n4`; `n1`–`n3` are unlinked and lost. The fix is to keep the cycle check but walk
+   a separate cursor to the real tail (`while (tail->next) tail = tail->next;`), or run
+   Floyd first and then walk to the end.
+
+2. **`aksl_list_iterate` skips the first half of the list.** `src/stdlib.c:324`. After the
+   cycle-detection loop, `slow` is left at the list midpoint, and the visiting loop then
+   starts from `slow` instead of from `list`. The head node is never passed to the callback.
+   Fix: iterate from `list`, not from `slow`.
+
+3. **`AKERR_ITERATOR_BREAK` does not stop a tree traversal.** `src/stdlib.c:251`. The
+   recursive frame in which the callback raises the break handles it in its own
+   `PROCESS`/`HANDLE(e, AKERR_ITERATOR_BREAK)` block and returns *success*; the parent's
+   `PASS` therefore sees no error and continues on to the sibling subtree. Breaking at
+   `tree[3]` in pre-order still visits all 7 nodes. Fix by splitting the recursion: an
+   internal helper that propagates `AKERR_ITERATOR_BREAK` unhandled, and a public entry point
+   that swallows it exactly once at the top. `tests/test_tree.c` currently passes only
+   because the search target is the last node in all three orders.
+
+4. **`va_end` is never called.** `src/stdlib.c:96`, `:109`, `:122` each call `va_start` with
+   no matching `va_end` on any path — happy or error. This is undefined behaviour per the C
+   standard and leaks register-save state on some ABIs.
+
+5. **`aksl_atoi`/`atol`/`atoll`/`atof` cannot report a conversion failure.**
+   `src/stdlib.c:135`–`169`. `atoi("not a number")` returns success with `0`;
+   `atoi("99999999999999999999")` returns success with a wrapped value. Since the entire
+   point of this library is turning silent libc failures into error contexts, these should be
+   reimplemented over `strtol`/`strtoll`/`strtod` with `errno = 0` before the call, an
+   `endptr` check for "no digits consumed" and "trailing junk", and a range check —
+   raising `AKERR_VALUE` and `ERANGE` respectively. Keep the `atoi`-compatible names but
+   document the stricter contract, or add `aksl_strtol`-family wrappers alongside.
+
+6. **`aksl_realpath` mishandles `resolved_path`.** `src/stdlib.c:171`.
+   - `resolved_path` is never NULL-checked. `realpath(path, NULL)` is valid and mallocs a
+     buffer, but the wrapper discards `result`, so the caller gets nothing and the buffer
+     leaks.
+   - On failure the message formats `resolved_path` with `%s` while `realpath` leaves it
+     unspecified — for the normal caller who passed an uninitialised stack buffer, the error
+     path itself reads uninitialised memory and can crash.
+   - There is no way to express the buffer's size, so callers must know to supply `PATH_MAX`
+     bytes. Consider `aksl_realpath(const char *path, char *buf, size_t buflen)`, or an
+     allocating variant that returns the malloc'd pointer through an out-param.
+
+### 2.2 Latent issues and API contract gaps
+
+1. **`errno` is used as an error status where it may be stale.** `aksl_malloc` reports
+   `errno` when `malloc` returns NULL, but `malloc(0)` may legitimately return NULL without
+   setting `errno`, producing a `FAIL` with `status == 0` — an error context that every
+   `DETECT`/`CATCH` will read as *success* while still holding a pool slot. Guard every
+   `errno`-sourced status with a fallback (`errno ? errno : AKERR_IO`) and set `errno = 0`
+   before the call being wrapped.
+
+2. **`aksl_fopen` does not validate `pathname` or `mode`.** `fopen(NULL, ...)` is UB. Add
+   `AKERR_NULLPOINTER` guards.
+
+3. **`aksl_fread`/`aksl_fwrite` lose the transfer count and hide short transfers.**
+   - `ptr` is never NULL-checked in either function.
+   - Neither has an out-param for the number of members actually transferred, so a caller who
+     gets `AKERR_EOF` cannot tell how much data arrived. Add `size_t *nmemb_out`.
+   - If `nmemr != nmemb` but neither `feof` nor `ferror` is set, both functions fall through
+     to `SUCCEED_RETURN` — a short transfer reported as complete success.
+   - `aksl_fwrite`'s error message reads `"Error reading file"` (`src/stdlib.c:83`), and
+     checking `feof()` on a write path is meaningless.
+
+4. **`aksl_sprintf` wraps `vsprintf`, which is unbounded.** There is no way for a caller to
+   bound the destination. Add `aksl_snprintf`/`aksl_vsnprintf` and consider deprecating the
+   `sprintf` wrapper, or reject it outright — an "error-handling" wrapper around an
+   unbounded write is a sharp edge the library exists to remove.
+
+5. **No `format` attribute on the variadic wrappers.** Adding
+   `__attribute__((format(printf, 2, 3)))` (and the equivalents) restores the compile-time
+   format/argument checking that callers lose by going through the wrapper.
+
+6. **`aksl_strhash_djb2` sign-extends bytes ≥ 0x80.** `src/stdlib.c:181` iterates a
+   `char *`, which is signed on x86/ARM Linux, so high bytes contribute a sign-extended
+   negative value and the hash differs from the canonical djb2 — and differs across
+   platforms where `char` is unsigned. Iterate a `const unsigned char *`. Also take
+   `const char *` in the signature so callers need not cast away constness.
+
+7. **`aksl_tree_iterate` recursion is unbounded and cycle-blind.** A deep or degenerate tree
+   overflows the stack, and a child pointer that loops back to an ancestor recurses forever.
+   Add a depth limit (raising `AKERR_OUTOFBOUNDS`) and/or a visited check raising
+   `AKERR_CIRCULAR_REFERENCE`, consistent with what the list functions already do.
+
+8. **`lalloc`, `lfree` and `queue` are dead parameters.** `lalloc`/`lfree` are defaulted and
+   then never called; `queue` is entirely unused (it is the only `-Wunused-parameter` warning
+   in the file). The doc comment even tells the caller to "pass NULL here", which is a sign
+   the queue belongs in an internal helper rather than the public signature. Either
+   implement BFS so they are used, or drop them from the public API until it is.
+
+9. **Unknown `searchmode` values return success.** The `switch` in `aksl_tree_iterate` has no
+   `default:`; `searchmode == 99` and the header-defined `AKSL_TREE_SEARCH_VISIT` (5) both
+   fall straight through to `SUCCEED_RETURN` having visited nothing. Add
+   `default: FAIL_RETURN(e, AKERR_VALUE, ...)`.
+
+10. **`AKSL_TREE_SEARCH_BFS`/`BFS_RIGHT` are unimplemented** (`AKERR_NOT_IMPLEMENTED`), and
+    `AKSL_TREE_SEARCH_VISIT` is declared in the header with a documented meaning but no
+    implementation anywhere.
+
+11. **`aksl_memset`'s and `aksl_memcpy`'s inner checks are dead code.** `memset` returns `s`
+    and `memcpy` returns `d`, both unconditionally; neither can fail. The
+    `FAIL_ZERO_RETURN(e, memset(...), errno, ...)` and `(memcpy(...) == d)` checks can never
+    fire and only obscure the intent. Also, `memcpy` with overlapping ranges is UB — either
+    document that or dispatch to `memmove`.
+
+12. **`aksl_list_pop` cannot tell the caller the new head.** Popping the head leaves the
+    caller's head pointer dangling at a now-detached node. Add an out-param for the new head,
+    or a `aksl_list_pop(aksl_ListNode **head, aksl_ListNode *node)` form.
+
+13. **`aksl_free` does not clear the caller's pointer**, so double-free remains easy. Consider
+    an `aksl_freep(void **ptr)` that frees and NULLs.
+
+14. **No initialisers for the public structs.** Every caller must remember to `memset` an
+    `aksl_ListNode`/`aksl_TreeNode` to zero before use (both existing tests do). Add
+    `aksl_list_node_init`/`aksl_tree_node_init` or `AKSL_LIST_NODE_INIT` macros.
+
+15. **`aksl_TreeNode.parent` is declared but never set or read** by any library function.
+
+16. **Header hygiene**: no `extern "C" { }` guard for C++ consumers; no version macros
+    (`AKSL_VERSION_MAJOR`…); `akstdlib.h` pulls in `stdio.h`/`stdlib.h`/`string.h`/`stdint.h`
+    into every consumer's namespace.
+
+17. **Doxygen coverage is 2 functions out of 20.** A `Doxyfile` exists but only
+    `aksl_tree_iterate` and `aksl_list_iterate` have doc comments. Every public function
+    needs `@param`/`@throws`/`@return`, especially the ones whose contract deviates from libc
+    (`aksl_free(NULL)` is an error; `aksl_atoi` will become strict).
+
+### 2.3 Build, CI and repository
+
+- [ ] **`CMakeLists.txt:4-6` sets `CMAKE_CXX_FLAGS` in a C-only project**, so `-g -ggdb -pg`
+      never reach the C compiler. Use `CMAKE_C_FLAGS` — or better, drop `-pg` from the
+      default build entirely (it is what produces the stray `gmon.out` sitting untracked in
+      the repo root) and let `CMAKE_BUILD_TYPE` control debug info.
+- [ ] **No warning flags.** Add `-Wall -Wextra` (and ideally `-Werror` in CI). The only
+      current warning is the unused `queue` parameter, so the cost of turning them on is low.
+- [ ] `src/stdlib.c` triggers **"ISO C99 requires at least one argument for the `...`"** on
+      roughly 20 lines under `-Wpedantic`, because `FAIL_*` is called with a bare message and
+      no varargs. Either always pass an argument, or add a zero-arg-safe form in libakerror.
+- [ ] **The `deps/libakerror` submodule is pinned 11 commits behind `main`** (pinned at
+      `4fad0ce "Add gitea workflow"`; upstream is at `4212ff0`). The pin predates the
+      refcount-leak fix, the stack-trace buffer-overflow fix, the `AKERR_MAX_ERR_VALUE`
+      correction and the format-string fix. Bump it.
+- [ ] **CI does not build against the submodule it pins.** `.gitea/workflows/ci.yaml` clones
+      `libakerror@main` and installs it, while the build it then runs is top-level and so
+      compiles `deps/libakerror` at the pinned commit — two different libakerror versions
+      depending on where you build, and the installed one is never actually linked. Pick
+      one. (The submodule is at least *present* in CI now: §1.0 added
+      `submodules: recursive` to the checkout, without which configure failed outright.)
+- [x] **`ctest` was red** (`tree` failing plus four *Not Run* submodule tests) — fixed in
+      §1.0. The build badge in `README.md` means something again.
+- [ ] **Untracked build litter** in the repo root: `build/`, `gmon.out`,
+      `CMakeLists.txt-akstdlib`, and a dozen `*~` editor backups. Add a `.gitignore`
+      (libakerror has one; this repo does not).
+- [ ] **`README.md` is a build badge and nothing else.** It needs at minimum: what the
+      library is, the akerror wrapper contract, the list of wrapped functions, and the
+      deviations from libc semantics.
+- [ ] **Indentation is inconsistent** — `src/stdlib.c` mixes hard tabs and 4-space indents
+      within the same functions. libakerror standardised on Stroustrup style
+      (commit `e5f7616`); apply the same here, ideally with a checked-in `.clang-format`.
+
+---
+
+## 3. libc functions not yet wrapped
+
+Ordered roughly by how much a caller of this library would miss them. Each entry means "add
+an `aksl_`-prefixed wrapper that turns the documented failure modes into an
+`akerr_ErrorContext`".
+
+### 3.1 High priority — gaps in areas the library already covers
+
+**Memory (`stdlib.h`, `string.h`)**
+- [ ] `calloc`, `realloc`, `reallocarray` — `realloc`'s "returns NULL and the old pointer is
+      still valid" trap is exactly what this library should be hiding.
+- [ ] `aligned_alloc`, `posix_memalign`
+- [ ] `memmove`, `memcmp`, `memchr`
+
+**Bounded string formatting (`stdio.h`)**
+- [ ] `snprintf`, `vsnprintf` — needed to make §2.2.4 fixable.
+- [ ] `vprintf`, `vfprintf`, `vsprintf` — the `va_list` forms, so consumers can build their
+      own variadic wrappers on top.
+- [ ] `asprintf` / `vasprintf` (GNU) as an allocating alternative.
+
+**String → number (`stdlib.h`)**
+- [ ] `strtol`, `strtoll`, `strtoul`, `strtoull`, `strtod`, `strtof`, `strtold` — the correct
+      foundation for §2.1.5.
+
+**Strings (`string.h`)**
+- [ ] `strlen`, `strnlen`
+- [ ] `strcpy`, `strncpy`, `strcat`, `strncat` — with truncation reported as an error rather
+      than silently accepted, which is the whole value proposition here.
+- [ ] `strdup`, `strndup`
+- [ ] `strcmp`, `strncmp`, `strcasecmp`, `strncasecmp`, `strcoll`
+- [ ] `strchr`, `strrchr`, `strstr`, `strcasestr`, `strpbrk`, `strspn`, `strcspn`
+- [ ] `strtok_r`, `strsep`
+- [ ] `strerror_r`
+
+**Stream I/O (`stdio.h`)**
+- [ ] `fseek`, `ftell`, `rewind`, `fgetpos`, `fsetpos`, `fseeko`, `ftello`
+- [ ] `fflush`
+- [ ] `fgets`, `fputs`, `fgetc`/`getc`/`getchar`, `fputc`/`putc`/`putchar`, `ungetc`
+- [ ] `getline`, `getdelim`
+- [ ] `freopen`, `fdopen`, `fileno`
+- [ ] `setvbuf`, `setbuf`
+- [ ] `clearerr`, `feof`, `ferror` — thin, but worth exposing so callers never touch raw
+      `FILE *` internals.
+- [ ] `sscanf`, `fscanf`, `scanf` — the return-value semantics (items matched vs `EOF`) are a
+      classic silent-failure source.
+- [ ] `remove`, `rename`, `tmpfile`, `mkstemp`, `mkdtemp`
+- [ ] `perror` — or an akerror-native equivalent.
+
+### 3.2 POSIX file and process API (likely the next major surface)
+
+**`unistd.h` / `fcntl.h`**
+- [ ] `open`, `close`, `read`, `write`, `pread`, `pwrite`, `lseek`
+- [ ] `readv`, `writev`
+- [ ] `dup`, `dup2`, `pipe`, `fcntl`
+- [ ] `fsync`, `fdatasync`, `truncate`, `ftruncate`
+- [ ] `unlink`, `link`, `symlink`, `readlink`, `rmdir`, `mkdir`
+- [ ] `access`, `faccessat`, `chmod`, `fchmod`, `chown`, `fchown`, `umask`
+- [ ] `chdir`, `fchdir`, `getcwd`
+- [ ] `isatty`, `ttyname_r`
+- [ ] `sysconf`, `pathconf`
+- [ ] `sleep`, `usleep`, `nanosleep`
+
+**`sys/stat.h`**
+- [ ] `stat`, `fstat`, `lstat`, `fstatat`
+- [ ] `statvfs`, `fstatvfs`
+
+**`dirent.h`**
+- [ ] `opendir`, `fdopendir`, `readdir`, `readdir_r`, `closedir`, `rewinddir`, `scandir`
+
+**Process control**
+- [ ] `fork`, `execve` / `execvp` / `execl` family, `waitpid`, `wait`
+- [ ] `posix_spawn`
+- [ ] `system`, `popen`, `pclose`
+- [ ] `getpid`, `getppid`, `getuid`, `geteuid`, `setuid`, `setgid`
+- [ ] `atexit`, `exit`, `_exit`, `abort` — mostly to give akerror a hook on shutdown.
+- [ ] `getenv`, `setenv`, `unsetenv`, `putenv`, `clearenv`
+
+**`sys/mman.h`**
+- [ ] `mmap`, `munmap`, `mprotect`, `msync`, `madvise`
+
+### 3.3 Time
+
+- [ ] `time`, `clock_gettime`, `clock_getres`, `gettimeofday`
+- [ ] `localtime_r`, `gmtime_r`, `mktime`, `timegm`, `difftime`
+- [ ] `strftime`, `strptime`
+- [ ] `clock`, `times`
+
+### 3.4 Sorting, searching and misc `stdlib.h`
+
+- [ ] `qsort`, `qsort_r`, `bsearch` — comparator errors currently have nowhere to go; an
+      akerror-aware comparator signature would be a genuine improvement.
+- [ ] `abs`, `labs`, `llabs`, `div`, `ldiv`, `lldiv`
+- [ ] `rand`, `srand`, `random`, `srandom`, `getrandom`/`arc4random`
+
+### 3.5 Lower priority / larger projects
+
+- [ ] **Sockets**: `socket`, `bind`, `listen`, `accept`, `connect`, `send`/`sendto`/`sendmsg`,
+      `recv`/`recvfrom`/`recvmsg`, `shutdown`, `setsockopt`/`getsockopt`, `getaddrinfo`/
+      `freeaddrinfo`/`gai_strerror`, `inet_ntop`/`inet_pton`
+- [ ] **Multiplexing**: `select`, `poll`, `ppoll`, `epoll_create1`/`epoll_ctl`/`epoll_wait`
+- [ ] **Signals**: `sigaction`, `sigprocmask`, `sigemptyset`/`sigaddset`, `kill`, `raise`,
+      `signalfd`
+- [ ] **Threads**: `pthread_create`/`join`/`detach`, `pthread_mutex_*`, `pthread_cond_*`,
+      `pthread_rwlock_*`, `sem_*` — blocked on resolving the thread-safety question in §1.9
+      (libakerror's error pool is an unlocked process-global array).
+- [ ] **Dynamic loading**: `dlopen`, `dlsym`, `dlclose`, `dlerror`
+- [ ] **Locale / wide chars**: `setlocale`, `mbstowcs`, `wcstombs`, `iconv_*`
+- [ ] **Math**: the `math.h` functions that set `errno`/raise FP exceptions (`sqrt`, `log`,
+      `pow`, `acos`, …) — probably better served by a dedicated `libakmath`.
+
+### 3.6 Non-libc additions the current data structures imply
+
+Not libc wrappers, but the existing list/tree API is visibly incomplete:
+
+- [ ] List: `prepend`, `insert_after`/`insert_before`, `length`, `find`, `reverse`,
+      `concat`, `free_all`, reverse iteration, and a head/tail-tracking container type so
+      `append` is O(1) instead of O(n).
+- [ ] Tree: `insert`, `remove`, `find`, `height`, `count`, `free_all`, and the BFS traversal
+      the `lalloc`/`lfree`/`queue` parameters were designed for.
+- [ ] Hash map built on `aksl_strhash_djb2`, plus additional hashes (FNV-1a, xxHash) and a
+      NUL-terminated `aksl_strhash_djb2_str` convenience form.
+- [ ] Growable buffer / string-builder type, to make the `snprintf` and `strcat` wrappers
+      pleasant to use.

include/akstdlib.h

@@ -5,6 +5,33 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <stdint.h>
+
+typedef struct aksl_ListNode {
+    void *data;
+    struct aksl_ListNode *next;
+    struct aksl_ListNode *prev;
+} aksl_ListNode;
+
+typedef struct aksl_TreeNode {
+    struct aksl_TreeNode *parent;
+    struct aksl_TreeNode *left;
+    struct aksl_TreeNode *right;
+    void *leaf;
+} aksl_TreeNode;
+
+#define AKSL_TREE_SEARCH_BFS           0    /** Breadth-first search mode for tree nodes. Currently unsupported. */
+#define AKSL_TREE_SEARCH_BFS_RIGHT     1    /** Right-hand breadth-first search mode for tree nodes. Currentl unsupported. */
+#define AKSL_TREE_SEARCH_DFS           2    /** Alias for AKSL_TREE_SEARCH_DFS_PREORDER */
+#define AKSL_TREE_SEARCH_DFS_PREORDER  2    /** Depth first pre-order (root, left, right) search mode for tree nodes */
+#define AKSL_TREE_SEARCH_DFS_INORDER   3    /** Depth first in-order (left, root, right) search mode for tree nodes. Currently unsupported. */
+#define AKSL_TREE_SEARCH_DFS_POSTORDER 4    /** Depth first post-order (left, right, root) search mode for tree nodes. Currently unsupported. */
+#define AKSL_TREE_SEARCH_VISIT         5    /** Used when iterating through a tree structure as a control flag: don't traverse the children, just visit the node */
+
+typedef akerr_ErrorContext AKERR_NOIGNORE *(*aksl_ListNodeIterator)(aksl_ListNode *node, void *data);
+typedef akerr_ErrorContext AKERR_NOIGNORE *(*aksl_TreeNodeIterator)(aksl_TreeNode *node, void *data);
+typedef akerr_ErrorContext AKERR_NOIGNORE *(*aksl_AllocFunc)(size_t size, void **dest);
+typedef akerr_ErrorContext AKERR_NOIGNORE *(*aksl_FreeFunc)(void *ptr);
 
 akerr_ErrorContext AKERR_NOIGNORE *aksl_fopen(char *pathname, char *mode, FILE **fp);
 akerr_ErrorContext AKERR_NOIGNORE *aksl_fread(void *ptr, size_t size, size_t nmemb, FILE *stream);
@@ -16,7 +43,6 @@ akerr_ErrorContext AKERR_NOIGNORE *aksl_memset(void *s, int c, size_t n);
 akerr_ErrorContext AKERR_NOIGNORE *aksl_memcpy(void *d, void *s, size_t n);
 akerr_ErrorContext AKERR_NOIGNORE *aksl_free(void *ptr);
 
-
 akerr_ErrorContext AKERR_NOIGNORE *aksl_printf(int *count, const char *restrict format, ...);
 akerr_ErrorContext AKERR_NOIGNORE *aksl_fprintf(int *count, FILE *restrict stream, const char *restrict format, ...);
 akerr_ErrorContext AKERR_NOIGNORE *aksl_sprintf(int *count, char *restrict str, const char *restrict format, ...);
@@ -28,4 +54,14 @@ akerr_ErrorContext AKERR_NOIGNORE *aksl_atof(const char *nptr, double *dest);
 
 akerr_ErrorContext AKERR_NOIGNORE *aksl_realpath(const char *restrict path, char *restrict resolved_path);
 
+akerr_ErrorContext AKERR_NOIGNORE *aksl_strhash_djb2(char *str, size_t len, uint32_t *hashval);
+
+// Linked list functions
+akerr_ErrorContext AKERR_NOIGNORE *aksl_list_append(aksl_ListNode *list, aksl_ListNode *obj);
+akerr_ErrorContext AKERR_NOIGNORE *aksl_list_pop(aksl_ListNode *node);
+akerr_ErrorContext AKERR_NOIGNORE *aksl_list_iterate(aksl_ListNode *list, aksl_ListNodeIterator iter, void *data);
+
+// Tree functions
+akerr_ErrorContext AKERR_NOIGNORE *aksl_tree_iterate(aksl_TreeNode *root, aksl_TreeNodeIterator iter, aksl_AllocFunc lalloc, aksl_FreeFunc lfree, uint8_t searchmode, void *data, aksl_ListNode *queue);
+
 #endif

scripts/mutation_test.py

@@ -0,0 +1,436 @@
+#!/usr/bin/env python3
+"""
+Mutation testing harness for libakstdlib.
+
+Mutation testing measures how good the test suite is at catching bugs. It works
+by making many small, deliberate breakages ("mutants") to the library source --
+flipping a comparison, deleting a statement, swapping true/false -- and then
+running the whole CTest suite against each one. If the tests fail, the mutant is
+"killed" (good: the tests noticed the bug). If the tests still pass, the mutant
+"survived" (bad: a real bug of that shape would slip through unnoticed).
+
+The mutation score is killed / (killed + survived). Surviving mutants are printed
+with file:line and the exact change so they can be turned into new test cases.
+
+This harness has no third-party dependencies (Python stdlib + the project's
+normal cmake/ctest toolchain). It never mutates the real working tree: it copies
+the repo to a scratch directory and mutates there.
+
+Usage:
+    scripts/mutation_test.py [options]
+
+    --source-root DIR   repo root to copy (default: parent of this script's dir)
+    --target FILE       source file to mutate, relative to root; repeatable.
+                        Default: src/stdlib.c and include/akstdlib.h
+    --work DIR          scratch dir for the mutated copy (default: a temp dir)
+    --timeout SECONDS   per-suite ctest timeout (default: 120)
+    --threshold PCT     exit non-zero if mutation score < PCT (default: 0 = off)
+    --list              only list the mutants that would be run, then exit
+    --keep              keep the scratch working copy on exit (for debugging)
+    -j N                (reserved) currently runs sequentially
+"""
+
+import argparse
+import os
+import re
+import shutil
+import subprocess
+import sys
+import tempfile
+
+# --------------------------------------------------------------------------- #
+# Mutation operators
+#
+# Each operator yields zero or more (start, end, replacement) edits for a single
+# line of source. The driver applies exactly one edit per mutant so every mutant
+# differs from the original by one localized change.
+# --------------------------------------------------------------------------- #
+
+# Relational operator replacement: map each operator to the alternatives that
+# meaningfully change behaviour (not merely the strict negation).
+_REL = {
+    "==": ["!="],
+    "!=": ["=="],
+    "<=": ["<", "=="],
+    ">=": [">", "=="],
+    "<": ["<=", ">"],
+    ">": [">=", "<"],
+}
+# Match a relational operator that is NOT part of ->, <<, >>, =>, <=, >=, ==, !=
+# unless we intend it. We tokenize the two-char operators first, then single.
+_REL_TWO = re.compile(r"(==|!=|<=|>=)")
+_REL_ONE = re.compile(r"(?<![-<>=!+])([<>])(?![=<>])")
+
+_LOGICAL = {"&&": "||", "||": "&&"}
+_LOG_RE = re.compile(r"(&&|\|\|)")
+
+_BOOL = {"true": "false", "false": "true"}
+_BOOL_RE = re.compile(r"\b(true|false)\b")
+
+# Arithmetic / compound-assignment on whitespace-delimited operands only, to
+# avoid touching ++, --, ->, unary signs, or pointer/format punctuation.
+_ARITH_RE = re.compile(r"(?<=\s)([+\-])(?=\s)")
+_ARITH = {"+": "-", "-": "+"}
+_COMPOUND_RE = re.compile(r"(\+=|-=)")
+_COMPOUND = {"+=": "-=", "-=": "+="}
+
+# Integer literal replacement: 0 <-> 1 (word-bounded, not inside identifiers or
+# larger numbers, not a float).
+_INT_RE = re.compile(r"(?<![\w.])([01])(?![\w.])")
+_INT = {"0": "1", "1": "0"}
+
+
+def _op_edits(line):
+    """Yield (tag, start, end, replacement) for every candidate mutation."""
+    # Relational (two-char first so we don't split them with the one-char pass)
+    for m in _REL_TWO.finditer(line):
+        for alt in _REL[m.group(1)]:
+            yield ("ROR", m.start(1), m.end(1), alt)
+    for m in _REL_ONE.finditer(line):
+        for alt in _REL[m.group(1)]:
+            yield ("ROR", m.start(1), m.end(1), alt)
+    for m in _LOG_RE.finditer(line):
+        yield ("LCR", m.start(1), m.end(1), _LOGICAL[m.group(1)])
+    for m in _BOOL_RE.finditer(line):
+        yield ("BCR", m.start(1), m.end(1), _BOOL[m.group(1)])
+    for m in _COMPOUND_RE.finditer(line):
+        yield ("AOR", m.start(1), m.end(1), _COMPOUND[m.group(1)])
+    for m in _ARITH_RE.finditer(line):
+        yield ("AOR", m.start(1), m.end(1), _ARITH[m.group(1)])
+    for m in _INT_RE.finditer(line):
+        yield ("ICR", m.start(1), m.end(1), _INT[m.group(1)])
+
+
+# Statement-deletion: neutralize a whole statement. We only delete statements
+# that are safe to drop without guaranteeing a compile error, so a surviving
+# deletion is a genuine test gap rather than compiler noise.
+_STMT_DELETABLE = re.compile(
+    r"""^\s*(
+          break |
+          return\b[^;]* |
+          [A-Za-z_][-\w>().\[\]* ]*\s*=\s*[^;]* |   # assignments
+          [A-Za-z_][\w]*\s*\([^;]*\)                # bare function calls
+        )\s*;\s*(\\?)\s*$""",
+    re.VERBOSE,
+)
+
+
+# --------------------------------------------------------------------------- #
+# Deciding which lines are eligible to mutate
+# --------------------------------------------------------------------------- #
+
+# Skip preprocessor control and the block of constant/error-code #defines in the
+# template header: mutating buffer sizes or renumbering error codes produces
+# equivalent or uninteresting mutants that swamp the signal.
+_SKIP_LINE = re.compile(
+    r"""^\s*(
+          \#\s*(include|ifn?def|ifdef|if|elif|else|endif|error|pragma|undef) |
+          \#\s*define\s+AKERR_(MAX|LAST|NULLPOINTER|OUTOFBOUNDS|API|ATTRIBUTE|
+              TYPE|KEY|INDEX|FORMAT|IO|VALUE|RELATIONSHIP|EOF|CIRCULAR_REFERENCE|
+              ITERATOR_BREAK|NOT_IMPLEMENTED|BADEXC|NOIGNORE|USE_STDLIB)\b |
+          \*  | //                                   # comment bodies / line comments
+        )""",
+    re.VERBOSE,
+)
+
+
+def _is_comment_or_blank(line):
+    s = line.strip()
+    return (not s) or s.startswith("//") or s.startswith("/*") or s.startswith("*")
+
+
+def eligible(line):
+    if _is_comment_or_blank(line):
+        return False
+    if _SKIP_LINE.match(line):
+        return False
+    return True
+
+
+class Mutant:
+    __slots__ = ("path", "lineno", "op", "before", "after", "col")
+
+    def __init__(self, path, lineno, op, before, after, col):
+        self.path = path
+        self.lineno = lineno
+        self.op = op
+        self.before = before
+        self.after = after
+        self.col = col
+
+    def describe(self):
+        return (f"{self.path}:{self.lineno} [{self.op}] "
+                f"col{self.col}: {self.before.strip()}  ->  {self.after.strip()}")
+
+
+def generate_mutants(root, rel_target):
+    """Enumerate all mutants for one target file."""
+    abspath = os.path.join(root, rel_target)
+    with open(abspath, "r") as fh:
+        lines = fh.readlines()
+
+    mutants = []
+    for i, line in enumerate(lines, start=1):
+        if not eligible(line):
+            continue
+        # substitution operators
+        seen = set()
+        for tag, s, e, repl in _op_edits(line):
+            key = (s, e, repl)
+            if key in seen:
+                continue
+            seen.add(key)
+            mutated = line[:s] + repl + line[e:]
+            if mutated == line:
+                continue
+            mutants.append(Mutant(rel_target, i, tag, line, mutated, s))
+        # statement deletion
+        m = _STMT_DELETABLE.match(line)
+        if m:
+            indent = line[: len(line) - len(line.lstrip())]
+            cont = "\\" if line.rstrip().endswith("\\") else ""
+            deleted = f"{indent}/* mutant: deleted */ {cont}\n" if cont else f"{indent};\n"
+            mutants.append(Mutant(rel_target, i, "SDL", line, deleted, 0))
+    return mutants
+
+
+# --------------------------------------------------------------------------- #
+# Build / test orchestration against a scratch copy
+# --------------------------------------------------------------------------- #
+
+class Runner:
+    def __init__(self, work, timeout):
+        self.work = work
+        self.build = os.path.join(work, "build")
+        self.timeout = timeout
+
+    def _run(self, cmd, timeout=None):
+        return subprocess.run(
+            cmd, cwd=self.work, stdout=subprocess.PIPE, stderr=subprocess.STDOUT,
+            timeout=timeout,
+        )
+
+    def configure(self):
+        r = self._run(["cmake", "-S", ".", "-B", "build"], timeout=self.timeout)
+        return r.returncode == 0, r.stdout
+
+    def build_and_test(self):
+        """Return ('killed-compile' | 'killed-test' | 'killed-timeout' | 'survived')."""
+        try:
+            b = self._run(["cmake", "--build", "build"], timeout=self.timeout)
+        except subprocess.TimeoutExpired:
+            return "killed-timeout"
+        if b.returncode != 0:
+            return "killed-compile"
+        try:
+            t = subprocess.run(
+                ["ctest", "--test-dir", "build", "--output-on-failure",
+                 "--stop-on-failure"],
+                cwd=self.work, stdout=subprocess.PIPE, stderr=subprocess.STDOUT,
+                timeout=self.timeout,
+            )
+        except subprocess.TimeoutExpired:
+            return "killed-timeout"
+        return "survived" if t.returncode == 0 else "killed-test"
+
+
+def _xml_escape(s):
+    return (s.replace("&", "&amp;").replace("<", "&lt;").replace(">", "&gt;")
+            .replace('"', "&quot;"))
+
+
+def write_junit(path, records, targets):
+    """Write a JUnit XML report. One <testcase> per mutant; a surviving mutant
+    is a <failure> (test-suite gap), a killed mutant is a passing case."""
+    by_file = {t: [] for t in targets}
+    for m, result in records:
+        by_file.setdefault(m.path, []).append((m, result))
+
+    total = len(records)
+    total_fail = sum(1 for _, r in records if r == "survived")
+    out = ['<?xml version="1.0" encoding="UTF-8"?>',
+           f'<testsuites name="mutation" tests="{total}" failures="{total_fail}">']
+    for f, items in by_file.items():
+        if not items:
+            continue
+        fails = sum(1 for _, r in items if r == "survived")
+        out.append(f'  <testsuite name="mutation:{_xml_escape(f)}" '
+                   f'tests="{len(items)}" failures="{fails}">')
+        for m, result in items:
+            name = _xml_escape(m.describe())
+            cls = "mutation." + _xml_escape(m.path)
+            if result == "survived":
+                detail = _xml_escape(f"{m.before.strip()}  ->  {m.after.strip()}")
+                out.append(f'    <testcase name="{name}" classname="{cls}" time="0">')
+                out.append(f'      <failure message="survived mutant '
+                           f'({_xml_escape(m.op)} at {_xml_escape(m.path)}:'
+                           f'{m.lineno})">{detail}</failure>')
+                out.append('    </testcase>')
+            else:
+                out.append(f'    <testcase name="{name}" classname="{cls}" '
+                           f'time="0"><system-out>{_xml_escape(result)}'
+                           '</system-out></testcase>')
+        out.append('  </testsuite>')
+    out.append('</testsuites>')
+    with open(path, "w") as fh:
+        fh.write("\n".join(out) + "\n")
+
+
+def copy_tree(src, dst):
+    ignore = shutil.ignore_patterns("build", ".git", "*.o", "*.so", "*~",
+                                    "#*#", "*.iso", "*.png")
+    shutil.copytree(src, dst, ignore=ignore, symlinks=True)
+
+
+def read_lines(path):
+    with open(path) as fh:
+        return fh.readlines()
+
+
+def write_lines(path, lines):
+    with open(path, "w") as fh:
+        fh.writelines(lines)
+
+
+def main():
+    # Line-buffer stdout so progress is visible live under CI / the cmake target.
+    try:
+        sys.stdout.reconfigure(line_buffering=True)
+    except (AttributeError, ValueError):
+        pass
+    here = os.path.dirname(os.path.abspath(__file__))
+    default_root = os.path.dirname(here)
+
+    ap = argparse.ArgumentParser(description="Mutation testing for libakstdlib")
+    ap.add_argument("--source-root", default=default_root)
+    ap.add_argument("--target", action="append", default=None)
+    ap.add_argument("--work", default=None)
+    ap.add_argument("--timeout", type=int, default=120)
+    ap.add_argument("--threshold", type=float, default=0.0)
+    ap.add_argument("--junit", default=None,
+                    help="write a JUnit XML report to this path")
+    ap.add_argument("--max-mutants", type=int, default=0,
+                    help="cap the run at N evenly-sampled mutants (0 = all)")
+    ap.add_argument("--list", action="store_true")
+    ap.add_argument("--keep", action="store_true")
+    ap.add_argument("-j", type=int, default=1)
+    args = ap.parse_args()
+
+    root = os.path.abspath(args.source_root)
+    targets = args.target or ["src/stdlib.c", "include/akstdlib.h"]
+
+    # Enumerate mutants from the pristine sources.
+    all_mutants = []
+    for t in targets:
+        all_mutants.extend(generate_mutants(root, t))
+
+    print(f"Generated {len(all_mutants)} mutants across {len(targets)} file(s):")
+    for t in targets:
+        n = sum(1 for m in all_mutants if m.path == t)
+        print(f"    {t}: {n}")
+
+    # Optional even-strided sampling to bound run time (CI / smoke tests).
+    if args.max_mutants and len(all_mutants) > args.max_mutants:
+        step = len(all_mutants) / args.max_mutants
+        sampled = [all_mutants[int(i * step)] for i in range(args.max_mutants)]
+        print(f"Sampling {len(sampled)} of {len(all_mutants)} mutants "
+              f"(--max-mutants {args.max_mutants}).")
+        all_mutants = sampled
+
+    if args.list:
+        for m in all_mutants:
+            print("  " + m.describe())
+        return 0
+
+    if not all_mutants:
+        print("No mutants generated; nothing to do.")
+        return 0
+
+    # Scratch working copy.
+    work_parent = args.work or tempfile.mkdtemp(prefix="akerr_mut_")
+    work = os.path.join(work_parent, "src") if args.work else work_parent
+    if os.path.exists(work):
+        shutil.rmtree(work)
+    print(f"\nCopying sources to scratch dir: {work}")
+    copy_tree(root, work)
+
+    runner = Runner(work, args.timeout)
+
+    print("Configuring baseline ...")
+    ok, out = runner.configure()
+    if not ok:
+        sys.stderr.write(out.decode(errors="replace"))
+        sys.stderr.write("\nBaseline configure FAILED; aborting.\n")
+        return 2
+
+    print("Verifying baseline is green (no mutation) ...")
+    baseline = runner.build_and_test()
+    if baseline != "survived":
+        sys.stderr.write(f"Baseline is not green ({baseline}); aborting. "
+                         "Fix the suite before mutation testing.\n")
+        return 2
+    print("Baseline OK.\n")
+
+    # Group mutants by file so we mutate one file at a time and restore it.
+    killed = {"killed-compile": 0, "killed-test": 0, "killed-timeout": 0}
+    survivors = []
+    records = []
+    total = len(all_mutants)
+
+    # Cache pristine contents per target.
+    pristine = {t: read_lines(os.path.join(work, t)) for t in targets}
+
+    for idx, m in enumerate(all_mutants, start=1):
+        tgt_abs = os.path.join(work, m.path)
+        lines = list(pristine[m.path])
+        lines[m.lineno - 1] = m.after
+        write_lines(tgt_abs, lines)
+        try:
+            result = runner.build_and_test()
+        finally:
+            write_lines(tgt_abs, pristine[m.path])  # always restore
+
+        records.append((m, result))
+        if result == "survived":
+            survivors.append(m)
+            mark = "SURVIVED"
+        else:
+            killed[result] += 1
+            mark = result.upper()
+        print(f"[{idx}/{total}] {mark:16} {m.describe()}")
+
+    total_killed = sum(killed.values())
+    score = 100.0 * total_killed / total if total else 100.0
+
+    print("\n" + "=" * 72)
+    print("MUTATION TESTING SUMMARY")
+    print("=" * 72)
+    print(f"  total mutants   : {total}")
+    print(f"  killed (test)   : {killed['killed-test']}")
+    print(f"  killed (compile): {killed['killed-compile']}")
+    print(f"  killed (timeout): {killed['killed-timeout']}")
+    print(f"  survived        : {len(survivors)}")
+    print(f"  mutation score  : {score:.1f}%")
+    if survivors:
+        print("\nSurviving mutants (test-suite gaps -- turn these into tests):")
+        for m in survivors:
+            print("  " + m.describe())
+
+    if args.junit:
+        junit_path = os.path.abspath(args.junit)
+        write_junit(junit_path, records, targets)
+        print(f"\nJUnit report written to: {junit_path}")
+
+    if not args.keep and not args.work:
+        shutil.rmtree(work_parent, ignore_errors=True)
+    else:
+        print(f"\nScratch working copy kept at: {work}")
+
+    if args.threshold > 0 and score < args.threshold:
+        print(f"\nFAIL: mutation score {score:.1f}% < threshold {args.threshold:.1f}%")
+        return 1
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())

src/stdlib.c

@@ -4,6 +4,7 @@
 #include <errno.h>
 #include <string.h>
 #include <stdarg.h>
+#include <stdint.h>
 
 akerr_ErrorContext AKERR_NOIGNORE *aksl_malloc(size_t size, void **dst)
 {
@@ -98,6 +99,7 @@ akerr_ErrorContext AKERR_NOIGNORE *aksl_printf(int *count, const char *restrict
     PREPARE_ERROR(e);
     FAIL_ZERO_RETURN(e, count, AKERR_NULLPOINTER, "count=%p, format=%p", (void *)count, (void *)format);
     FAIL_ZERO_RETURN(e, format, AKERR_NULLPOINTER, "count=%p, format=%p", (void *)count, (void *)format);
+    va_start(args, format);    
     *count = vprintf(format, args);
     FAIL_NONZERO_RETURN(e, (*count == -1), errno, "Short write");
     SUCCEED_RETURN(e);
@@ -111,6 +113,7 @@ akerr_ErrorContext AKERR_NOIGNORE *aksl_fprintf(int *count, FILE *restrict strea
     FAIL_ZERO_RETURN(e, count, AKERR_NULLPOINTER, "count=%p, stream=%p, format=%p", (void *)count, (void *)stream, (void *)format);
     FAIL_ZERO_RETURN(e, stream, AKERR_NULLPOINTER, "count=%p, stream=%p, format=%p", (void *)count, (void *)stream, (void *)format);
     FAIL_ZERO_RETURN(e, format, AKERR_NULLPOINTER, "count=%p, stream=%p, format=%p", (void *)count, (void *)stream, (void *)format);
+    va_start(args, format);
     *count = vfprintf(stream, format, args);
     FAIL_NONZERO_RETURN(e, (*count == -1), errno, "Short write");
     SUCCEED_RETURN(e);
@@ -174,3 +177,174 @@ akerr_ErrorContext AKERR_NOIGNORE *aksl_realpath(const char *restrict path, char
     FAIL_ZERO_RETURN(e, result, errno, "path=%s, dest=%s", path, resolved_path);
     SUCCEED_RETURN(e);
 }
+
+akerr_ErrorContext AKERR_NOIGNORE *aksl_strhash_djb2(char *str, size_t len, uint32_t *hashval)
+{
+    PREPARE_ERROR(e);
+    FAIL_ZERO_RETURN(e, str, AKERR_NULLPOINTER, "str");
+    FAIL_ZERO_RETURN(e, hashval, AKERR_NULLPOINTER, "hashval");
+    uint32_t h = 5381;
+    while (len--) {
+	h = ((h << 5) + h) + *str++;
+    }
+    *hashval = h;
+    SUCCEED_RETURN(e);
+}
+
+akerr_ErrorContext AKERR_NOIGNORE *aksl_list_append(aksl_ListNode *list, aksl_ListNode *obj)
+{
+    PREPARE_ERROR(e);
+    FAIL_ZERO_RETURN(e, list, AKERR_NULLPOINTER, "list");
+    FAIL_ZERO_RETURN(e, obj, AKERR_NULLPOINTER, "obj");
+    aksl_ListNode *slow = list;
+    aksl_ListNode *fast = list;
+    aksl_ListNode *tail = list;
+    while ( fast != NULL && fast->next != NULL ) {
+	tail = slow;
+	slow = slow->next;
+	fast = fast->next->next;
+	if ( fast == slow) {
+	    FAIL_RETURN(e, AKERR_CIRCULAR_REFERENCE, "%p", list);
+	}
+    }
+    if ( fast != NULL ) {
+	tail = fast;
+    }
+    tail->next = obj;
+    obj->next = NULL;
+    obj->prev = tail;
+    SUCCEED_RETURN(e);
+}
+
+akerr_ErrorContext AKERR_NOIGNORE *aksl_list_pop(aksl_ListNode *node)
+{
+    PREPARE_ERROR(e);
+    FAIL_ZERO_RETURN(e, node, AKERR_NULLPOINTER, "node");
+    if ( node->prev != NULL ) {
+	node->prev->next = node->next;
+    }
+    if ( node->next != NULL ) {	
+	node->next->prev = node->prev;
+    }
+    node->next = NULL;
+    node->prev = NULL;
+    SUCCEED_RETURN(e);
+}
+
+/**
+ * @brief Iterates over a tree structure in breadth or depth first order, executing a callback function on each node.
+ *
+ * This function recursively calls itself to traverse a binary tree datastructure. 
+ *
+ * @param[in] root The tree structure to search
+ * @param[in] iter An aksl_TreeNodeIterator function which will be called for each node found
+ * @param[in] lalloc An aksl_AllocFunc function which will be used to allocate aksl_ListNode elements for the search, or NULL to use the default allocator (aksl_malloc)
+ * @param[in] lfree An aksl_FreeFunc function which will be used to free the elements procured with lalloc, or NULL to use the default free function (aksl_free)
+ * @param[in] searchmode One of the AKSL_TREE_SEARCH_BFS* defines
+ * @param[in] data Any user data that should be provided when the iterator is called
+ * @param[in] queue The linked list node to use as the head of the queue. The caller should pass NULL here.
+ *
+ * @throws AKERR_NULLPOINTER On null pointer inputs
+ * @return akerr_ErrorContext
+ */
+
+akerr_ErrorContext AKERR_NOIGNORE *aksl_tree_iterate(
+    aksl_TreeNode *root,
+    aksl_TreeNodeIterator iter,
+    aksl_AllocFunc lalloc,
+    aksl_FreeFunc lfree,
+    uint8_t searchmode,
+    void *data,
+    aksl_ListNode *queue)
+{
+    PREPARE_ERROR(e);
+    FAIL_ZERO_RETURN(e, root, AKERR_NULLPOINTER, "root");
+    FAIL_ZERO_RETURN(e, iter, AKERR_NULLPOINTER, "iter");
+    if ( lalloc == NULL ) {
+	lalloc = &aksl_malloc;
+    }
+    if ( lfree == NULL ) {
+	lfree = &aksl_free;
+    }
+    ATTEMPT {
+	switch ( searchmode ) {
+	case AKSL_TREE_SEARCH_DFS_PREORDER:
+	    CATCH(e, iter(root, data));
+	    if ( root->left != NULL ) {
+		PASS(e, aksl_tree_iterate(root->left, iter, lalloc, lfree, searchmode, data, NULL));
+	    }
+	    if ( root-> right != NULL ) {
+		PASS(e, aksl_tree_iterate(root->right, iter, lalloc, lfree, searchmode, data, NULL));
+	    }
+	    break;
+	case AKSL_TREE_SEARCH_DFS_POSTORDER:
+	    if ( root->left != NULL ) {
+		PASS(e, aksl_tree_iterate(root->left, iter, lalloc, lfree, searchmode, data, NULL));
+	    }
+	    if ( root-> right != NULL ) {
+		PASS(e, aksl_tree_iterate(root->right, iter, lalloc, lfree, searchmode, data, NULL));
+	    }
+	    CATCH(e, iter(root, data));
+	    break;
+	case AKSL_TREE_SEARCH_DFS_INORDER:
+	    if ( root->left != NULL ) {
+		PASS(e, aksl_tree_iterate(root->left, iter, lalloc, lfree, searchmode, data, NULL));
+	    }
+	    CATCH(e, iter(root, data));
+	    if ( root-> right != NULL ) {
+		PASS(e, aksl_tree_iterate(root->right, iter, lalloc, lfree, searchmode, data, NULL));
+	    }
+	    break;
+	case AKSL_TREE_SEARCH_BFS:
+	case AKSL_TREE_SEARCH_BFS_RIGHT:
+	    FAIL_RETURN(e, AKERR_NOT_IMPLEMENTED, "Searchmode %d", searchmode);
+	    break;
+	}
+    } CLEANUP {
+    } PROCESS(e) {
+    } HANDLE(e, AKERR_ITERATOR_BREAK) {
+	// This is not an error condition, it's just telling us to stop early
+	SUCCEED_RETURN(e);
+    } FINISH(e, true);
+    SUCCEED_RETURN(e);
+}
+
+/**
+ * @brief Iterates over a linked list and execute a callback function on each node
+ *
+ * @param[in] list The linked list to iterate
+ * @param[in] iter An aksl_ListNodeIterator function which will be called for each node found
+ * @param[in] data Any user data that should be provided when the iterator is called
+ *
+ * @throws AKERR_NULLPOINTER on null pointer inputs
+ * @throws AKERR_CIRCULAR_REFERENCE when the linked list contains a circular reference
+ * 
+ * @return akerr_ErrorContext
+ */
+akerr_ErrorContext AKERR_NOIGNORE *aksl_list_iterate(aksl_ListNode *list, aksl_ListNodeIterator iter, void *data)
+{
+    PREPARE_ERROR(e);
+    FAIL_ZERO_RETURN(e, list, AKERR_NULLPOINTER, "list");
+    FAIL_ZERO_RETURN(e, iter, AKERR_NULLPOINTER, "iter");
+    aksl_ListNode *slow = list;
+    aksl_ListNode *fast = list;
+    while ( fast != NULL && fast->next != NULL ) {
+	slow = slow->next;
+	fast = fast->next->next;
+	if ( fast == slow) {
+	    FAIL_RETURN(e, AKERR_CIRCULAR_REFERENCE, "%p", list);
+	}
+    }
+    while ( slow != NULL ) {
+	ATTEMPT {
+	    CATCH(e, iter(slow, data));
+	    slow = slow->next;
+	} CLEANUP {
+	} PROCESS(e) {
+	} HANDLE(e, AKERR_ITERATOR_BREAK) {
+	    // This is not an error condition, it's just telling us to stop early
+	    SUCCEED_RETURN(e);
+	} FINISH(e, true);
+    }
+    SUCCEED_RETURN(e);
+}

tests/aksl_capture.h

@@ -0,0 +1,216 @@
+#ifndef AKSL_TEST_CAPTURE_H
+#define AKSL_TEST_CAPTURE_H
+
+/*
+ * Shared test helpers for libakstdlib.
+ *
+ * Modelled on libakerror's tests/err_capture.h, with additions for the shape of
+ * this library: almost every akstdlib entry point returns an
+ * akerr_ErrorContext * that the caller owns and must release, so the common
+ * assertion is "this call returned status X" rather than "this call logged Y".
+ *
+ * What is here:
+ *
+ *   AKSL_CHECK()            an NDEBUG-proof assertion. Fails the test by
+ *                           returning 1 from the enclosing function (unlike
+ *                           assert(), which is compiled out in release builds
+ *                           and would silently turn a test into a no-op).
+ *   AKSL_CHECK_STATUS()     run an akerror-returning expression, assert on the
+ *                           status it came back with, and release the context
+ *                           so the error pool does not leak.
+ *   AKSL_CHECK_OK()         the status == 0 (success) case of the above.
+ *   aksl_last_status/...    the status, message and function name of the most
+ *                           recent context taken by AKSL_CHECK_STATUS.
+ *   aksl_capture_install()  swap in a capturing akerr_log_method so a test can
+ *                           assert on the *content* of stack traces and
+ *                           unhandled-error output.
+ *   aksl_slots_in_use()     how many slots are currently checked out of
+ *                           AKERR_ARRAY_ERROR, for pool-leak assertions.
+ *   AKSL_RUN()              run one test function and tally the result.
+ *
+ * Tests are written as a set of `static int test_xxx(void)` functions that
+ * return 0 on success and non-zero on failure, driven from main() by AKSL_RUN.
+ */
+
+#include <akstdlib.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <string.h>
+
+/* ---------------------------------------------------------------------- */
+/* Log capture                                                            */
+/* ---------------------------------------------------------------------- */
+
+#define AKSL_CAPTURE_BUFSZ 65536
+static char aksl_capture_buf[AKSL_CAPTURE_BUFSZ];
+static size_t aksl_capture_len = 0;
+
+static void __attribute__((unused)) aksl_capture_logger(const char *fmt, ...)
+{
+    va_list ap;
+    va_start(ap, fmt);
+    int n = vsnprintf(aksl_capture_buf + aksl_capture_len,
+		      AKSL_CAPTURE_BUFSZ - aksl_capture_len, fmt, ap);
+    va_end(ap);
+    if ( n > 0 ) {
+	aksl_capture_len += (size_t)n;
+	if ( aksl_capture_len >= AKSL_CAPTURE_BUFSZ ) {
+	    aksl_capture_len = AKSL_CAPTURE_BUFSZ - 1;
+	}
+    }
+}
+
+static void __attribute__((unused)) aksl_capture_reset(void)
+{
+    aksl_capture_len = 0;
+    aksl_capture_buf[0] = '\0';
+}
+
+/*
+ * Install the capturing logger. akerr_init() only assigns a default logger when
+ * akerr_log_method is NULL, and it is idempotent, so calling this either before
+ * or after the first PREPARE_ERROR keeps our logger in place.
+ */
+static void __attribute__((unused)) aksl_capture_install(void)
+{
+    aksl_capture_reset();
+    akerr_log_method = &aksl_capture_logger;
+}
+
+/* ---------------------------------------------------------------------- */
+/* Error pool accounting                                                  */
+/* ---------------------------------------------------------------------- */
+
+/* Count array slots currently checked out of the pool (refcount != 0). */
+static int __attribute__((unused)) aksl_slots_in_use(void)
+{
+    int n = 0;
+    for ( int i = 0; i < AKERR_MAX_ARRAY_ERROR; i++ ) {
+	if ( AKERR_ARRAY_ERROR[i].refcount != 0 ) {
+	    n++;
+	}
+    }
+    return n;
+}
+
+/* ---------------------------------------------------------------------- */
+/* Taking ownership of a returned error context                           */
+/* ---------------------------------------------------------------------- */
+
+static int aksl_last_status = 0;
+static char aksl_last_message[AKERR_MAX_ERROR_CONTEXT_STRING_LENGTH];
+/* Sized to match akerr_ErrorContext.function, which akerror declares with
+ * AKERR_MAX_ERROR_FNAME_LENGTH rather than AKERR_MAX_ERROR_FUNCTION_LENGTH. */
+static char aksl_last_function[AKERR_MAX_ERROR_FNAME_LENGTH];
+
+/*
+ * Record the status/message/function of a returned context, release it back to
+ * the pool, and hand back the status. A NULL context means success, which is
+ * status 0. Every akstdlib call in a test should go through this (or through
+ * AKSL_CHECK_STATUS, which wraps it) so that no test leaks a pool slot.
+ */
+static int __attribute__((unused)) aksl_take(akerr_ErrorContext *e)
+{
+    akerr_ErrorContext *released = NULL;
+
+    aksl_last_message[0] = '\0';
+    aksl_last_function[0] = '\0';
+    if ( e == NULL ) {
+	aksl_last_status = 0;
+	return 0;
+    }
+    aksl_last_status = e->status;
+    snprintf(aksl_last_message, sizeof(aksl_last_message), "%s", e->message);
+    snprintf(aksl_last_function, sizeof(aksl_last_function), "%s", e->function);
+    /*
+     * akerr_release_error is marked warn_unused_result, and a (void) cast does
+     * not silence that in GCC, so the result is assigned and discarded.
+     */
+    released = akerr_release_error(e);
+    (void)released;
+    return aksl_last_status;
+}
+
+/* ---------------------------------------------------------------------- */
+/* Assertions                                                             */
+/* ---------------------------------------------------------------------- */
+
+#define AKSL_CHECK(cond)					\
+    do {							\
+	if ( !(cond) ) {					\
+	    fprintf(stderr, "  CHECK FAILED: %s at %s:%d\n",	\
+		    #cond, __FILE__, __LINE__);			\
+	    return 1;						\
+	}							\
+    } while ( 0 )
+
+/*
+ * Run an akerr_ErrorContext *-returning expression and assert on its status.
+ * The context is always released, including on the failure path, so a failing
+ * assertion does not also corrupt the pool-leak checks that follow it.
+ */
+#define AKSL_CHECK_STATUS(__expr, __expected)				\
+    do {								\
+	int __st = aksl_take(__expr);					\
+	if ( __st != (__expected) ) {					\
+	    fprintf(stderr,						\
+		    "  CHECK FAILED: %s\n"				\
+		    "    got      %d (%s) \"%s\"\n"			\
+		    "    expected %d (%s)\n"				\
+		    "    at %s:%d\n",					\
+		    #__expr,						\
+		    __st, akerr_name_for_status(__st, NULL),		\
+		    aksl_last_message,					\
+		    (__expected),					\
+		    akerr_name_for_status((__expected), NULL),		\
+		    __FILE__, __LINE__);				\
+	    return 1;							\
+	}								\
+    } while ( 0 )
+
+#define AKSL_CHECK_OK(__expr) AKSL_CHECK_STATUS(__expr, 0)
+
+#define AKSL_CHECK_CONTAINS(needle)				\
+    AKSL_CHECK(strstr(aksl_capture_buf, (needle)) != NULL)
+
+#define AKSL_CHECK_NOT_CONTAINS(needle)				\
+    AKSL_CHECK(strstr(aksl_capture_buf, (needle)) == NULL)
+
+/* Assert on the message of the context most recently taken. */
+#define AKSL_CHECK_MSG_CONTAINS(needle)				\
+    AKSL_CHECK(strstr(aksl_last_message, (needle)) != NULL)
+
+/* ---------------------------------------------------------------------- */
+/* Test driver                                                            */
+/* ---------------------------------------------------------------------- */
+
+/*
+ * Run one test function, report it, and tally failures. Also asserts that the
+ * test left the error pool as it found it -- a wrapper that fails to release a
+ * context is a bug in the library, not just in the test.
+ */
+#define AKSL_RUN(__failures, __fn)					\
+    do {								\
+	int __before = aksl_slots_in_use();				\
+	int __r = __fn();						\
+	int __after = aksl_slots_in_use();				\
+	if ( __r != 0 ) {						\
+	    fprintf(stderr, "FAIL %s\n", #__fn);			\
+	    (__failures)++;						\
+	} else if ( __after != __before ) {				\
+	    fprintf(stderr,						\
+		    "FAIL %s (leaked %d error pool slot(s))\n",		\
+		    #__fn, __after - __before);				\
+	    (__failures)++;						\
+	} else {							\
+	    fprintf(stderr, "ok   %s\n", #__fn);			\
+	}								\
+    } while ( 0 )
+
+#define AKSL_REPORT(__failures)						\
+    do {								\
+	fprintf(stderr, "%s: %d failure(s)\n", __FILE__, (__failures));	\
+	return (__failures) == 0 ? 0 : 1;				\
+    } while ( 0 )
+
+#endif // AKSL_TEST_CAPTURE_H

tests/test_linkedlist.c

@@ -0,0 +1,319 @@
+/*
+ * Linked-list behaviour that the library gets right today.
+ *
+ * The two confirmed list defects (TODO.md 2.1.1 aksl_list_append truncating the
+ * chain, and 2.1.2 aksl_list_iterate skipping the head) are asserted separately
+ * in tests/test_list_append_chain.c and tests/test_list_iterate_head.c, which
+ * are registered as known-failing. Everything in this file must pass.
+ *
+ * Note that the list-shape assertions here build their lists by hand rather
+ * than with aksl_list_append: append cannot be trusted to produce a chain
+ * longer than two nodes until 2.1.1 is fixed, and using it would make these
+ * tests fail for a reason that has nothing to do with what they are checking.
+ */
+
+#include "aksl_capture.h"
+
+#define MAX_VISITS 16
+
+typedef struct VisitLog
+{
+    int count;
+    aksl_ListNode *seen[MAX_VISITS];
+    int break_at;               /* visit index to raise ITERATOR_BREAK on, or -1 */
+    int fail_at;                /* visit index to raise AKERR_VALUE on, or -1 */
+} VisitLog;
+
+static void visitlog_init(VisitLog *log)
+{
+    memset((void *)log, 0x00, sizeof(VisitLog));
+    log->break_at = -1;
+    log->fail_at = -1;
+}
+
+static akerr_ErrorContext AKERR_NOIGNORE *record_visit(aksl_ListNode *node, void *data)
+{
+    VisitLog *log = NULL;
+    int idx = 0;
+
+    PREPARE_ERROR(e);
+    FAIL_ZERO_RETURN(e, node, AKERR_NULLPOINTER, "node");
+    FAIL_ZERO_RETURN(e, data, AKERR_NULLPOINTER, "data");
+    log = (VisitLog *)data;
+    idx = log->count;
+    if ( idx < MAX_VISITS ) {
+	log->seen[idx] = node;
+    }
+    log->count += 1;
+    if ( log->fail_at == idx ) {
+	FAIL_RETURN(e, AKERR_VALUE, "iterator failed at visit %d", idx);
+    }
+    if ( log->break_at == idx ) {
+	FAIL_RETURN(e, AKERR_ITERATOR_BREAK, "stop at visit %d", idx);
+    }
+    SUCCEED_RETURN(e);
+}
+
+/* ---------------------------------------------------------------------- */
+/* aksl_list_append                                                       */
+/* ---------------------------------------------------------------------- */
+
+static int test_append_single_node(void)
+{
+    aksl_ListNode head;
+    aksl_ListNode tail;
+
+    memset((void *)&head, 0x00, sizeof(head));
+    memset((void *)&tail, 0x00, sizeof(tail));
+
+    AKSL_CHECK_OK(aksl_list_append(&head, &tail));
+    AKSL_CHECK(head.next == &tail);
+    AKSL_CHECK(head.prev == NULL);
+    AKSL_CHECK(tail.prev == &head);
+    AKSL_CHECK(tail.next == NULL);
+    return 0;
+}
+
+static int test_append_null_arguments(void)
+{
+    aksl_ListNode node;
+
+    memset((void *)&node, 0x00, sizeof(node));
+
+    AKSL_CHECK_STATUS(aksl_list_append(NULL, &node), AKERR_NULLPOINTER);
+    AKSL_CHECK_STATUS(aksl_list_append(&node, NULL), AKERR_NULLPOINTER);
+    return 0;
+}
+
+static int test_append_detects_self_cycle(void)
+{
+    aksl_ListNode head;
+    aksl_ListNode node;
+
+    memset((void *)&head, 0x00, sizeof(head));
+    memset((void *)&node, 0x00, sizeof(node));
+    head.next = &head;
+
+    AKSL_CHECK_STATUS(aksl_list_append(&head, &node), AKERR_CIRCULAR_REFERENCE);
+    return 0;
+}
+
+static int test_append_detects_two_node_cycle(void)
+{
+    aksl_ListNode a;
+    aksl_ListNode b;
+    aksl_ListNode node;
+
+    memset((void *)&a, 0x00, sizeof(a));
+    memset((void *)&b, 0x00, sizeof(b));
+    memset((void *)&node, 0x00, sizeof(node));
+    a.next = &b;
+    b.prev = &a;
+    b.next = &a;
+
+    AKSL_CHECK_STATUS(aksl_list_append(&a, &node), AKERR_CIRCULAR_REFERENCE);
+    return 0;
+}
+
+/* ---------------------------------------------------------------------- */
+/* aksl_list_iterate                                                      */
+/* ---------------------------------------------------------------------- */
+
+static int test_iterate_null_arguments(void)
+{
+    aksl_ListNode node;
+    VisitLog log;
+
+    memset((void *)&node, 0x00, sizeof(node));
+    visitlog_init(&log);
+
+    AKSL_CHECK_STATUS(aksl_list_iterate(NULL, &record_visit, &log), AKERR_NULLPOINTER);
+    AKSL_CHECK_STATUS(aksl_list_iterate(&node, NULL, &log), AKERR_NULLPOINTER);
+    AKSL_CHECK(log.count == 0);
+    return 0;
+}
+
+static int test_iterate_single_node(void)
+{
+    aksl_ListNode node;
+    VisitLog log;
+
+    memset((void *)&node, 0x00, sizeof(node));
+    visitlog_init(&log);
+
+    AKSL_CHECK_OK(aksl_list_iterate(&node, &record_visit, &log));
+    AKSL_CHECK(log.count == 1);
+    AKSL_CHECK(log.seen[0] == &node);
+    return 0;
+}
+
+static int test_iterate_detects_self_cycle(void)
+{
+    aksl_ListNode head;
+    VisitLog log;
+
+    memset((void *)&head, 0x00, sizeof(head));
+    head.next = &head;
+    visitlog_init(&log);
+
+    AKSL_CHECK_STATUS(aksl_list_iterate(&head, &record_visit, &log),
+		      AKERR_CIRCULAR_REFERENCE);
+    return 0;
+}
+
+static int test_iterate_detects_two_node_cycle(void)
+{
+    aksl_ListNode a;
+    aksl_ListNode b;
+    VisitLog log;
+
+    memset((void *)&a, 0x00, sizeof(a));
+    memset((void *)&b, 0x00, sizeof(b));
+    a.next = &b;
+    b.prev = &a;
+    b.next = &a;
+    visitlog_init(&log);
+
+    AKSL_CHECK_STATUS(aksl_list_iterate(&a, &record_visit, &log),
+		      AKERR_CIRCULAR_REFERENCE);
+    return 0;
+}
+
+/* An error other than ITERATOR_BREAK must come back out of the iteration with
+ * its status and message intact. */
+static int test_iterate_propagates_callback_error(void)
+{
+    aksl_ListNode node;
+    VisitLog log;
+
+    memset((void *)&node, 0x00, sizeof(node));
+    visitlog_init(&log);
+    log.fail_at = 0;
+
+    AKSL_CHECK_STATUS(aksl_list_iterate(&node, &record_visit, &log), AKERR_VALUE);
+    AKSL_CHECK_MSG_CONTAINS("iterator failed at visit 0");
+    AKSL_CHECK(log.count == 1);
+    return 0;
+}
+
+/* ITERATOR_BREAK is a control signal, not a failure: the caller sees success. */
+static int test_iterate_break_is_not_an_error(void)
+{
+    aksl_ListNode node;
+    VisitLog log;
+
+    memset((void *)&node, 0x00, sizeof(node));
+    visitlog_init(&log);
+    log.break_at = 0;
+
+    AKSL_CHECK_OK(aksl_list_iterate(&node, &record_visit, &log));
+    AKSL_CHECK(log.count == 1);
+    return 0;
+}
+
+/* ---------------------------------------------------------------------- */
+/* aksl_list_pop                                                          */
+/* ---------------------------------------------------------------------- */
+
+static int test_pop_middle_node(void)
+{
+    aksl_ListNode a;
+    aksl_ListNode b;
+    aksl_ListNode c;
+
+    memset((void *)&a, 0x00, sizeof(a));
+    memset((void *)&b, 0x00, sizeof(b));
+    memset((void *)&c, 0x00, sizeof(c));
+    a.next = &b;
+    b.prev = &a;
+    b.next = &c;
+    c.prev = &b;
+
+    AKSL_CHECK_OK(aksl_list_pop(&b));
+    AKSL_CHECK(a.next == &c);
+    AKSL_CHECK(c.prev == &a);
+    AKSL_CHECK(b.next == NULL);
+    AKSL_CHECK(b.prev == NULL);
+    return 0;
+}
+
+static int test_pop_head_node(void)
+{
+    aksl_ListNode a;
+    aksl_ListNode b;
+
+    memset((void *)&a, 0x00, sizeof(a));
+    memset((void *)&b, 0x00, sizeof(b));
+    a.next = &b;
+    b.prev = &a;
+
+    AKSL_CHECK_OK(aksl_list_pop(&a));
+    AKSL_CHECK(b.prev == NULL);
+    AKSL_CHECK(b.next == NULL);
+    AKSL_CHECK(a.next == NULL);
+    AKSL_CHECK(a.prev == NULL);
+    return 0;
+}
+
+static int test_pop_tail_node(void)
+{
+    aksl_ListNode a;
+    aksl_ListNode b;
+
+    memset((void *)&a, 0x00, sizeof(a));
+    memset((void *)&b, 0x00, sizeof(b));
+    a.next = &b;
+    b.prev = &a;
+
+    AKSL_CHECK_OK(aksl_list_pop(&b));
+    AKSL_CHECK(a.next == NULL);
+    AKSL_CHECK(a.prev == NULL);
+    AKSL_CHECK(b.next == NULL);
+    AKSL_CHECK(b.prev == NULL);
+    return 0;
+}
+
+static int test_pop_only_node(void)
+{
+    aksl_ListNode a;
+
+    memset((void *)&a, 0x00, sizeof(a));
+
+    AKSL_CHECK_OK(aksl_list_pop(&a));
+    AKSL_CHECK(a.next == NULL);
+    AKSL_CHECK(a.prev == NULL);
+    return 0;
+}
+
+static int test_pop_null_argument(void)
+{
+    AKSL_CHECK_STATUS(aksl_list_pop(NULL), AKERR_NULLPOINTER);
+    return 0;
+}
+
+int main(void)
+{
+    int failures = 0;
+
+    akerr_init();
+
+    AKSL_RUN(failures, test_append_single_node);
+    AKSL_RUN(failures, test_append_null_arguments);
+    AKSL_RUN(failures, test_append_detects_self_cycle);
+    AKSL_RUN(failures, test_append_detects_two_node_cycle);
+
+    AKSL_RUN(failures, test_iterate_null_arguments);
+    AKSL_RUN(failures, test_iterate_single_node);
+    AKSL_RUN(failures, test_iterate_detects_self_cycle);
+    AKSL_RUN(failures, test_iterate_detects_two_node_cycle);
+    AKSL_RUN(failures, test_iterate_propagates_callback_error);
+    AKSL_RUN(failures, test_iterate_break_is_not_an_error);
+
+    AKSL_RUN(failures, test_pop_middle_node);
+    AKSL_RUN(failures, test_pop_head_node);
+    AKSL_RUN(failures, test_pop_tail_node);
+    AKSL_RUN(failures, test_pop_only_node);
+    AKSL_RUN(failures, test_pop_null_argument);
+
+    AKSL_REPORT(failures);
+}

tests/test_list_append_chain.c

@@ -0,0 +1,59 @@
+/*
+ * KNOWN FAILING -- TODO.md section 2.1.1
+ *
+ * aksl_list_append conflates Floyd cycle detection with finding the tail: the
+ * `tail` cursor is assigned from `slow` *before* `slow` advances, so it tracks
+ * the node behind the list midpoint rather than the last node. Appending to any
+ * list of two or more nodes therefore overwrites an interior link and silently
+ * drops every node after it.
+ *
+ * Appending n1..n4 to n0 produces the chain "n0 -> n4"; this test asserts the
+ * correct "n0 -> n1 -> n2 -> n3 -> n4" and so fails until append is fixed.
+ * It is registered in AKSL_KNOWN_FAILING_TESTS, which marks it WILL_FAIL; when
+ * the fix lands, CTest will report it as unexpectedly passing, which is the
+ * signal to move it into AKSL_TESTS.
+ */
+
+#include "aksl_capture.h"
+
+#define CHAIN_LEN 5
+
+static int test_append_builds_full_chain(void)
+{
+    aksl_ListNode node[CHAIN_LEN];
+    aksl_ListNode *walk = NULL;
+    int i = 0;
+
+    memset((void *)node, 0x00, sizeof(node));
+
+    for ( i = 1; i < CHAIN_LEN; i++ ) {
+	AKSL_CHECK_OK(aksl_list_append(&node[0], &node[i]));
+    }
+
+    /* Forward links, head to tail. */
+    walk = &node[0];
+    for ( i = 0; i < CHAIN_LEN; i++ ) {
+	AKSL_CHECK(walk == &node[i]);
+	walk = walk->next;
+    }
+    AKSL_CHECK(walk == NULL);
+
+    /* Back links, tail to head. */
+    walk = &node[CHAIN_LEN - 1];
+    for ( i = CHAIN_LEN - 1; i >= 0; i-- ) {
+	AKSL_CHECK(walk == &node[i]);
+	walk = walk->prev;
+    }
+    AKSL_CHECK(walk == NULL);
+
+    return 0;
+}
+
+int main(void)
+{
+    int failures = 0;
+
+    akerr_init();
+    AKSL_RUN(failures, test_append_builds_full_chain);
+    AKSL_REPORT(failures);
+}

tests/test_list_iterate_head.c

@@ -0,0 +1,71 @@
+/*
+ * KNOWN FAILING -- TODO.md section 2.1.2
+ *
+ * aksl_list_iterate runs a Floyd cycle check that leaves `slow` sitting at the
+ * list midpoint, and then starts the visiting loop from `slow` instead of from
+ * `list`. Every node before the midpoint -- including the head -- is never
+ * passed to the callback.
+ *
+ * The list here is built by hand rather than with aksl_list_append so that this
+ * test fails only for the iterate defect, not for the separate append defect in
+ * TODO.md 2.1.1.
+ *
+ * Registered in AKSL_KNOWN_FAILING_TESTS (WILL_FAIL). When iterate is fixed,
+ * CTest reports this as unexpectedly passing -- move it into AKSL_TESTS then.
+ */
+
+#include "aksl_capture.h"
+
+#define CHAIN_LEN 3
+
+typedef struct VisitLog
+{
+    int count;
+    aksl_ListNode *seen[CHAIN_LEN];
+} VisitLog;
+
+static akerr_ErrorContext AKERR_NOIGNORE *record_visit(aksl_ListNode *node, void *data)
+{
+    VisitLog *log = NULL;
+
+    PREPARE_ERROR(e);
+    FAIL_ZERO_RETURN(e, node, AKERR_NULLPOINTER, "node");
+    FAIL_ZERO_RETURN(e, data, AKERR_NULLPOINTER, "data");
+    log = (VisitLog *)data;
+    if ( log->count < CHAIN_LEN ) {
+	log->seen[log->count] = node;
+    }
+    log->count += 1;
+    SUCCEED_RETURN(e);
+}
+
+static int test_iterate_visits_every_node_from_the_head(void)
+{
+    aksl_ListNode node[CHAIN_LEN];
+    VisitLog log;
+    int i = 0;
+
+    memset((void *)node, 0x00, sizeof(node));
+    memset((void *)&log, 0x00, sizeof(log));
+
+    for ( i = 1; i < CHAIN_LEN; i++ ) {
+	node[i - 1].next = &node[i];
+	node[i].prev = &node[i - 1];
+    }
+
+    AKSL_CHECK_OK(aksl_list_iterate(&node[0], &record_visit, &log));
+    AKSL_CHECK(log.count == CHAIN_LEN);
+    for ( i = 0; i < CHAIN_LEN; i++ ) {
+	AKSL_CHECK(log.seen[i] == &node[i]);
+    }
+    return 0;
+}
+
+int main(void)
+{
+    int failures = 0;
+
+    akerr_init();
+    AKSL_RUN(failures, test_iterate_visits_every_node_from_the_head);
+    AKSL_REPORT(failures);
+}

tests/test_tree.c

@@ -0,0 +1,113 @@
+/*
+ * Depth-first tree search.
+ *
+ * Previously this test shared one TreeSearchParams across all three searches
+ * without resetting it, so `steps` accumulated (7, then 14, then 21) and the
+ * second assertion failed -- `tree` was a red test on every run. Each search
+ * now gets its own params.
+ *
+ * Caveat worth knowing when reading the step counts below: the value is hidden
+ * in tree[6], which is the last node visited in pre-, in- and post-order alike,
+ * so "7 steps" holds for all three orders and does not actually distinguish
+ * them -- nor does it prove that AKERR_ITERATOR_BREAK stopped anything (it does
+ * not; see tests/test_tree_iterate_break.c and TODO.md 2.1.3). Visit-order
+ * assertions that tell the three traversals apart are TODO.md section 1.8.
+ */
+
+#include "aksl_capture.h"
+
+#define MAX_LEAVES     7
+#define HIDDEN_VALUE   ((void *)17336)
+
+typedef struct TreeSearchParams
+{
+    void *value;
+    int steps;
+    aksl_TreeNode *node;
+} TreeSearchParams;
+
+static akerr_ErrorContext AKERR_NOIGNORE *find_value(aksl_TreeNode *node, void *data)
+{
+    TreeSearchParams *parms = NULL;
+
+    PREPARE_ERROR(e);
+    FAIL_ZERO_RETURN(e, node, AKERR_NULLPOINTER, "node");
+    FAIL_ZERO_RETURN(e, data, AKERR_NULLPOINTER, "data");
+    parms = (TreeSearchParams *)data;
+    parms->steps += 1;
+    if ( node->leaf == parms->value ) {
+	parms->node = node;
+	FAIL_RETURN(e, AKERR_ITERATOR_BREAK, "stop");
+    }
+    SUCCEED_RETURN(e);
+}
+
+/*
+ * Build the 3-level tree used by every case here, with the search value hidden
+ * in the bottom-right leaf.
+ *
+ *       LEFT            RIGHT
+ *               TREE[0]
+ *       +--------^^---------+
+ *       |                   |
+ *    TREE[1]              TREE[2]
+ *  +---^^---+           +---^^---+
+ *  |        |           |        |
+ *TREE[3] TREE[4]     TREE[5]  TREE[6]
+ */
+static void build_tree(aksl_TreeNode *tree, TreeSearchParams *parms)
+{
+    memset((void *)tree, 0x00, sizeof(aksl_TreeNode) * MAX_LEAVES);
+    tree[0].left = &tree[1];
+    tree[0].right = &tree[2];
+    tree[1].left = &tree[3];
+    tree[1].right = &tree[4];
+    tree[2].left = &tree[5];
+    tree[2].right = &tree[6];
+    tree[6].leaf = HIDDEN_VALUE;
+
+    memset((void *)parms, 0x00, sizeof(TreeSearchParams));
+    parms->value = HIDDEN_VALUE;
+}
+
+static int search_finds_hidden_value(uint8_t searchmode)
+{
+    aksl_TreeNode tree[MAX_LEAVES];
+    TreeSearchParams parms;
+
+    build_tree(tree, &parms);
+
+    AKSL_CHECK_OK(aksl_tree_iterate(&tree[0], &find_value, NULL, NULL,
+				    searchmode, &parms, NULL));
+    AKSL_CHECK(parms.node == &tree[6]);
+    AKSL_CHECK(parms.steps == MAX_LEAVES);
+    return 0;
+}
+
+static int test_dfs_preorder(void)
+{
+    return search_finds_hidden_value(AKSL_TREE_SEARCH_DFS_PREORDER);
+}
+
+static int test_dfs_inorder(void)
+{
+    return search_finds_hidden_value(AKSL_TREE_SEARCH_DFS_INORDER);
+}
+
+static int test_dfs_postorder(void)
+{
+    return search_finds_hidden_value(AKSL_TREE_SEARCH_DFS_POSTORDER);
+}
+
+int main(void)
+{
+    int failures = 0;
+
+    akerr_init();
+
+    AKSL_RUN(failures, test_dfs_preorder);
+    AKSL_RUN(failures, test_dfs_inorder);
+    AKSL_RUN(failures, test_dfs_postorder);
+
+    AKSL_REPORT(failures);
+}

tests/test_tree_iterate_break.c

@@ -0,0 +1,89 @@
+/*
+ * KNOWN FAILING -- TODO.md section 2.1.3
+ *
+ * AKERR_ITERATOR_BREAK does not abort a tree traversal. aksl_tree_iterate
+ * recurses into itself, and the frame in which the callback raises the break
+ * handles it in its own PROCESS/HANDLE(e, AKERR_ITERATOR_BREAK) block and
+ * returns *success*. The parent frame's PASS therefore sees no error at all and
+ * carries straight on into the sibling subtree, so the traversal runs to
+ * completion.
+ *
+ * The 7-node tree below is walked pre-order (0, 1, 3, 4, 2, 5, 6) with the
+ * callback breaking on tree[3], the third node visited. A working break stops
+ * the walk at 3 visits; today the callback is invoked all 7 times.
+ *
+ * tests/test_tree.c cannot catch this: it hides its value in tree[6], which is
+ * the last node visited in all three depth-first orders, so a break that never
+ * fires is indistinguishable from one that fires on the final node.
+ *
+ * Registered in AKSL_KNOWN_FAILING_TESTS (WILL_FAIL). When the break semantics
+ * are fixed, CTest reports this as unexpectedly passing -- move it into
+ * AKSL_TESTS then.
+ */
+
+#include "aksl_capture.h"
+
+#define MAX_LEAVES 7
+
+typedef struct BreakParams
+{
+    aksl_TreeNode *stop_at;
+    int visits;
+} BreakParams;
+
+static akerr_ErrorContext AKERR_NOIGNORE *break_at_node(aksl_TreeNode *node, void *data)
+{
+    BreakParams *parms = NULL;
+
+    PREPARE_ERROR(e);
+    FAIL_ZERO_RETURN(e, node, AKERR_NULLPOINTER, "node");
+    FAIL_ZERO_RETURN(e, data, AKERR_NULLPOINTER, "data");
+    parms = (BreakParams *)data;
+    parms->visits += 1;
+    if ( node == parms->stop_at ) {
+	FAIL_RETURN(e, AKERR_ITERATOR_BREAK, "stop");
+    }
+    SUCCEED_RETURN(e);
+}
+
+static int test_break_aborts_the_whole_traversal(void)
+{
+    aksl_TreeNode tree[MAX_LEAVES];
+    BreakParams parms;
+
+    memset((void *)tree, 0x00, sizeof(tree));
+    memset((void *)&parms, 0x00, sizeof(parms));
+
+    /*
+     *               TREE[0]
+     *       +--------^^---------+
+     *       |                   |
+     *    TREE[1]              TREE[2]
+     *  +---^^---+           +---^^---+
+     *  |        |           |        |
+     *TREE[3] TREE[4]     TREE[5]  TREE[6]
+     */
+    tree[0].left = &tree[1];
+    tree[0].right = &tree[2];
+    tree[1].left = &tree[3];
+    tree[1].right = &tree[4];
+    tree[2].left = &tree[5];
+    tree[2].right = &tree[6];
+
+    parms.stop_at = &tree[3];
+
+    AKSL_CHECK_OK(aksl_tree_iterate(&tree[0], &break_at_node, NULL, NULL,
+				    AKSL_TREE_SEARCH_DFS_PREORDER, &parms, NULL));
+    /* Pre-order visits 0, 1, 3 -- the break on tree[3] must stop the walk there. */
+    AKSL_CHECK(parms.visits == 3);
+    return 0;
+}
+
+int main(void)
+{
+    int failures = 0;
+
+    akerr_init();
+    AKSL_RUN(failures, test_break_aborts_the_whole_traversal);
+    AKSL_REPORT(failures);
+}