Take libakerror 2.0.1 and drop the workaround it makes obsolete

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

0.5.0 worked around that here with TEST_TRAP_UNHANDLED_ERRORS() in
tests/testutil.h, and TODO.md ended the entry saying any consumer's
suites have the same problem and it was worth raising upstream. It was.
2.0.1 fixes it at the source: akerr_exit() owns the mapping and the
default handler calls it, so 0 exits 0, 1 through 255 exit themselves,
and anything else exits AKERR_EXIT_STATUS_UNREPRESENTABLE (125). The
trap and its 21 call sites are gone.

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

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

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

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

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

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

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

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

CMakeLists.txt

@@ -2,7 +2,7 @@ cmake_minimum_required(VERSION 3.10)
 # The single source of truth for the library version. It drives the generated
 # include/akgl/version.h, the shared library's VERSION and SOVERSION, and the
 # Version field in akgl.pc. Bump it here and nowhere else.
-project(akgl VERSION 0.6.0 LANGUAGES C)
+project(akgl VERSION 0.7.0 LANGUAGES C)
 
 # Memory checking reuses the suites that already exist -- `ctest -T memcheck`
 # runs every registered test under valgrind -- rather than adding programs of its
@@ -135,8 +135,17 @@ akgl_add_vendored_dependency(SDL3_image::SDL3_image deps/SDL_image)
 akgl_add_vendored_dependency(SDL3_mixer::SDL3_mixer deps/SDL_mixer)
 akgl_add_vendored_dependency(SDL3_ttf::SDL3_ttf deps/SDL_ttf)
 
-# libakerror 1.0.0 sizes its own status-name registry; consumers no longer do.
-# libakgl claims its status codes at runtime in akgl_heap_init() instead.
+# libakerror sizes its own status-name registry; consumers no longer do. libakgl
+# claims its status codes at runtime in akgl_heap_init() instead.
+#
+# The floor is 2.0.1, and it is a hard one. 2.0.0 moved __akerr_last_ignored to
+# thread-local storage and made akerr_next_error() return a context that already
+# holds its reference -- both of which expand at *libakgl's* call sites through
+# IGNORE and the FAIL macros, and at a *consumer's* too, because akerror.h is
+# part of libakgl's public interface. A tree that mixes headers and libraries
+# across that line double-counts every reference and never returns a pool slot.
+# The soname moved to libakerror.so.2 to stop it happening by accident; the
+# #error in include/akgl/error.h catches a stale header in an install tree.
 
 set(AKGL_SUPPRESS_DEPENDENCY_TESTS FALSE)
 
@@ -165,7 +174,8 @@ endif()
 # No version here: libakerror ships no akerrorConfigVersion.cmake, so asking
 # for one makes find_package reject every install. The floor is enforced by
 # the #error in include/akgl/error.h instead, which feature-tests
-# AKERR_FIRST_CONSUMER_STATUS.
+# AKERR_FIRST_CONSUMER_STATUS and AKERR_EXIT_STATUS_UNREPRESENTABLE -- the
+# latter arriving in 2.0.1, which is the version libakgl needs.
 if(NOT TARGET akerror::akerror)
   find_package(akerror REQUIRED)
 endif()