Version at 0.2.0: complete the wishlist, document it, gate the docs

Closes what was left of TODO.md sections 1, 2 and 3, and rewrites that
file to hold outstanding items only.

The API break gets a minor bump, because pre-1.0 the soname carries
MAJOR.MINOR and 0.1 and 0.2 are therefore different ABIs. Five
signatures changed and the ato* contract with them; UPGRADING.md is new
and lists every one, with the before/after for the cases the compiler
cannot warn about.

Section 3.1 is finished: reallocarray with the multiplication checked,
aligned_alloc and posix_memalign, asprintf/vasprintf, scanf/vscanf.
Four functions on that list are deliberately absent rather than missing
-- sprintf, strtok, setbuf and perror -- and TODO.md now says which and
why, so nobody adds them thinking they were forgotten.

Section 1.9, the cross-cutting tests:

  tests/test_pool.c    drives every failure path AKERR_MAX_ARRAY_ERROR
                       + 10 times and checks the pool after each round,
                       because a wrapper that leaks a slot fails a
                       hundred calls later in unrelated code. It also
                       asserts that each error names the function and
                       file it was raised from, which is what catches a
                       FAIL that migrates into a helper during a
                       refactor: status right, message right, origin
                       quietly lying.
  tests/negative/      two sources that must FAIL to compile, built with
                       -Werror and registered WILL_FAIL. AKERR_NOIGNORE
                       and the format attributes are enforced by the
                       compiler and by nothing else; drop either and
                       every ordinary test still passes.

Thread safety is answered rather than tested: the library is not
thread-safe and cannot be made so from here, because libakerror's error
pool is an unlocked process-global array. README.md says so plainly and
TODO.md carries it as the item blocking any future pthread wrappers.

Doxygen is configured and gated. All 147 public functions have @brief,
a @param each, @throws per status and @return; EXTRACT_ALL is off and
WARN_NO_PARAMDOC on, so `cmake --build build --target docs` fails on an
undocumented entity. It ran to 0 warnings. The Doxyfile carries no
version -- cmake/RunDoxygen.cmake feeds PROJECT_NUMBER in from
project(), so that stays the one place a version is written.

CI now builds against the submodule it pins instead of also installing
libakerror@main and never linking it, adds -Werror, and gains a
sanitizer job. The pre-push hook matches, and runs the docs check too.

Coverage: 99.5% of lines (1643/1651), 100% of functions (147/147). The
eight uncovered lines are each uncovered on purpose and TODO.md says
which and why.

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

tests/test_format.c

@@ -224,6 +224,51 @@ static int test_printf_rejects_null_arguments(void)
     return 0;
 }
 
+/*
+ * The allocating form. No fixed buffer means no truncation case, which is what
+ * makes it the right answer when the length is not knowable in advance and the
+ * result is too short-lived to want a whole aksl_StrBuf.
+ */
+static int test_asprintf_allocates_to_fit(void)
+{
+    char *out = NULL;
+    int count = -1;
+    int i = 0;
+
+    AKSL_CHECK_OK(aksl_asprintf(&count, &out, "%s=%d", "key", 42));
+    AKSL_CHECK(out != NULL);
+    AKSL_CHECK(strcmp(out, "key=42") == 0);
+    AKSL_CHECK(count == 6);
+    AKSL_CHECK_OK(aksl_freep((void **)&out));
+
+    /* Far longer than any buffer a fixed-size wrapper would have used. */
+    AKSL_CHECK_OK(aksl_asprintf(&count, &out, "%01000d", 7));
+    AKSL_CHECK(count == 1000);
+    AKSL_CHECK(strlen(out) == 1000);
+    AKSL_CHECK_OK(aksl_freep((void **)&out));
+
+    /* An empty result is a valid empty string, not NULL. */
+    AKSL_CHECK_OK(aksl_asprintf(&count, &out, "%s", ""));
+    AKSL_CHECK(count == 0);
+    AKSL_CHECK(out != NULL && out[0] == '\0');
+    AKSL_CHECK_OK(aksl_freep((void **)&out));
+
+    /* Repeatedly, so a leak shows up under the sanitizer build. */
+    for ( i = 0; i < 256; i++ ) {
+	AKSL_CHECK_OK(aksl_asprintf(&count, &out, "iteration %d of %d", i, 256));
+	AKSL_CHECK((size_t)count == strlen(out));
+	AKSL_CHECK_OK(aksl_freep((void **)&out));
+    }
+
+    out = (char *)0x1;
+    AKSL_CHECK_STATUS(aksl_asprintf(NULL, &out, "x"), AKERR_NULLPOINTER);
+    AKSL_CHECK_STATUS(aksl_asprintf(&count, NULL, "x"), AKERR_NULLPOINTER);
+    AKSL_CHECK_STATUS(aksl_asprintf(&count, &out, NULL), AKERR_NULLPOINTER);
+    /* Cleared before the format is even looked at. */
+    AKSL_CHECK(out == NULL);
+    return 0;
+}
+
 /*
  * The va_list forms are what the variadic ones are built on, and TODO.md 3.1
  * wanted them exposed so consumers can write their own variadic wrappers. This
@@ -298,6 +343,7 @@ int main(void)
     AKSL_RUN(failures, test_printf_writes_to_stdout);
     AKSL_RUN(failures, test_printf_rejects_null_arguments);
 
+    AKSL_RUN(failures, test_asprintf_allocates_to_fit);
     AKSL_RUN(failures, test_va_list_forms_are_usable_from_outside);
     AKSL_RUN(failures, test_variadic_wrappers_survive_repeated_calls);