Main-pinned cowns — a new PinnedCown subclass holds its
value as a plain PyObject * on the main interpreter, never
round-tripped through XIData. Behaviors whose request set contains
any pinned cown are routed by the scheduler to a single-consumer
main-thread queue and drained by the new pump entry point
(or implicitly by wait, which auto-pumps when pinned cowns
exist). Designed for objects that cannot survive cross-interpreter
shipping — pyglet shapes, Tk widgets, GPU contexts, open file
handles, ctypes pointers. The companion examples/boids.py
rewrite demonstrates the coarse-grained pinned-dispatch pattern:
per-cell physics stays on workers, and one @when(PinnedCown)
per frame batches the write-back into main-thread matrices.
Also in this release: quiesce, a non-tearing-down
checkpoint primitive.

New Features

• quiesce(timeout=None, *, stats=False, noticeboard=False) —
  blocks until every in-flight behavior completes, without tearing
  down workers or the noticeboard thread. Implemented via a new
  terminator_seed_inc peer of terminator_seed_dec
  (Pyrona-style seed-up / seed-down pairing) so quiescence becomes
  a checkpoint rather than a shutdown. Useful for parallel-search
  patterns that need to inspect a best-so-far cown between rounds
  and for tests that must read a worker-produced send queue
  before its producer interpreter is destroyed. The stats and
  noticeboard flags mirror wait: returns None by
  default, a per-worker stats list[dict] when stats=True,
  a noticeboard dict[str, Any] when noticeboard=True, or a
  WaitResult when both are set. Raises TimeoutError
  if quiescence is not reached within timeout. Exported from
  bocpy.__all__.
• PinnedCown(Cown[T]) — a cown whose value lives
  permanently on the main interpreter. Constructible only from the
  main interpreter (raises RuntimeError from workers);
  the value is never picklable, never reified twice, and never
  reconstructed in a worker. The capsule handle remains a
  first-class cross-interpreter shareable — workers may hold it,
  embed it in a regular Cown value graph, and place it in
  noticeboard entries, but only the main thread may acquire the
  value. See the new pinned_cowns page for the full
  contract and the coarse-grained-dispatch pattern.
• pump(deadline_ms=None, max_behaviors=None, raise_on_error=False)
  — drains the main-thread queue of behaviors whose request sets
  contain a PinnedCown. Call from your event loop's
  idle / on-tick hook (pyglet schedule_interval, Tk after,
  asyncio task, …); script-mode programs need not call it
  explicitly because wait pumps internally. Non-preemptive:
  deadline_ms gates starting the next behavior, not
  interrupting one already running. Body exceptions default to
  landing on the result cown's .exception;
  raise_on_error=True re-raises the first body exception after
  drain. Returns a new PumpResult NamedTuple
  (executed, deadline_reached, raised).
• set_pump_watchdog(warn_ms=1000, raise_ms=None, on_starve=None)
  — configure the pinned-queue starvation watchdog. Both thresholds
  gate on queue-non-empty time, not raw last-pump time, so
  programs running only unpinned work never trip them. Default is
  warn-only; users opt into fail-fast via an explicit raise_ms
  so interactive debugger sessions are not wedged by a breakpoint.
• set_wait_pump_poll(ms=50) — set the poll cadence for
  wait's auto-pump loop. Re-read every iteration so a
  concurrent call updates the active wait immediately.
• bocpy.PumpResult — three-field NamedTuple returned by
  pump. executed counts pinned behaviors whose lifecycle
  completed (including acquire-failure paths whose MCS chain still
  drained). deadline_reached is True only when the
  deadline_ms budget tripped before the queue drained.
  raised counts only body exceptions captured to a result cown
  (cleanup-path failures use PyErr_WriteUnraisable and do not
  count). Exported from bocpy.__all__.
• Coarse-grained pinned-dispatch examples/boids.py — the
  per-cell send("update") / main-thread receive("update")
  barrier is replaced by per-cell physics on workers plus one
  pinned @when per frame that captures every per-cell result
  cown together with the two main-thread PinnedCown matrices
  and performs the batched write-back. Same visual output, fully
  worker-parallel per-cell work, single main-thread touchpoint.

Public C ABI

• bocpy_main_interpid() — new static inline helper in
  <bocpy/bocpy.h> returning PyInterpreterState_GetID( PyInterpreterState_Main()) pre-typed as int_least64_t to
  match bocpy_interpid for owner-field equality checks.
  Safe to call from a worker sub-interpreter for diagnostic /
  assert use. Additive — existing consumers recompile unchanged;
  BOCPY_ABI is unchanged at 1. The
  templates/c_abi_consumer bocpy~= pin moves to
  ~=0.9 to signal the new ABI surface it was authored against.

Improvements

• @when loop-variable snapshot via default arg — the
  transpiler now accepts def b(c, i=i) as an explicit
  loop-snapshot idiom in addition to the existing implicit form
  (just reference the loop variable in the body). Trailing
  positional parameters beyond the cown count are also
  auto-captured by name (def b(c, factor) captures
  factor).
• @when alias decorators — the transpiler now recognises
  from bocpy import when as boc_when and import bocpy [as alias] followed by @bocpy.when(...) or
  @alias.when(...), provided the aliasing import is at module
  level. Previously only the bare @when form was detected.
• Behaviors.start() compiles the export module on main —
  the transpiler's rewritten module is now also instantiated as an
  in-memory types.ModuleType on the main thread (plus a
  linecache entry for traceback fidelity) so pump can
  resolve __behavior__N the same way workers do via their
  bootstrap.
• Scheduler-owned behavior pre-header — bq_node and the
  new pinned OR-fold byte moved out of the opaque
  BOCBehavior into a scheduler-owned boc_behavior_prehdr_t
  allocated immediately before each behavior (CPython
  _PyGC_Head style). boc_sched.c no longer needs any
  knowledge of BOCBehavior's internal layout; layout drift
  between the scheduler and its users is impossible by
  construction.
• terminator_wait_pumpable — new entry in
  boc_terminator.{c,h} lets the auto-pump loop wake on either
  count-zero or main-pinned-depth-becoming-non-zero, both wired
  through the existing single condition variable. Single-pumper
  enforcement on free-threaded builds (Py_GIL_DISABLED) lives
  alongside via a MAIN_PUMP_THREAD CAS that raises
  RuntimeError if a second thread tries to pump
  concurrently, cleared on every exit path including
  BaseException.

Bug Fixes

• CWE-401: inheriting INCREF leak in cown_decref_inline —
  CownCapsule_reduce packs an encoded XIData payload by
  taking an inheriting COWN_INCREF per embedded
  CownCapsule, normally balanced when the bytes are
  unpickled inside a worker. On the orphan-death path (the
  consumer side never deserialised the payload) the matching
  COWN_DECREFs never fired and every embedded cown leaked.
  cown_decref_inline now feeds the encoded bytes through
  pickle.loads and immediately drops the result, which lets
  CPython's GC fire the matching COWN_DECREFs recursively.
  Gated on the pickled flag so native XIData round-trips
  (e.g. Matrix) skip the work entirely.
• Main-pump behavior reference leak — both
  _core_main_pump_bounded and _core_main_pump_drain_all
  popped a BehaviorCapsule from MAIN_PINNED_QUEUE but
  never released the strong reference the capsule held on the
  underlying BOCBehavior. Each pinned behavior leaked
  one reference until the runtime was torn down. The pump
  helpers now BEHAVIOR_DECREF the behavior immediately after
  the worker-equivalent cleanup runs.
• MSVC <stdatomic.h> compatibility — Microsoft's
  <stdatomic.h> (used by CPython's headers on Windows) does
  not expose the unsigned atomic_uint_least64_t or
  atomic_uintptr_t forms that the pinned-pump bookkeeping
  used. MAIN_PINNED_DEPTH, MAIN_PINNED_NONEMPTY_SINCE_NS,
  LAST_PUMP_NS, WATCHDOG_WARN_MS, WATCHDOG_LAST_WARN_NS,
  WATCHDOG_ON_STARVE and MAIN_PUMP_THREAD are now
  atomic_int_least64_t / atomic_intptr_t. Depth never
  goes negative; pointer bits round-trip losslessly through the
  signed atomic boundary.
• CPython 3.10/3.11 PyErr_SetRaisedException polyfill —
  added to include/bocpy/xidata.h alongside the existing
  PyErr_GetRaisedException polyfill so the public C ABI's
  exception-stash pattern compiles on Python versions before
  3.12. BOCPY_ABI is unchanged.
• Portable boc_max_align_t — added to boc_compat.h as
  a union of the most-strictly-aligned fundamental types
  (long long, long double, void *, function pointer).
  MSVC exposes the C11 max_align_t only under /std:c11,
  which the CPython build does not pass; the
  boc_behavior_prehdr_t size assertion now uses
  alignof(boc_max_align_t) so the alignment contract holds on
  every supported toolchain.
• PEP 678 add_note 3.10 fallback — the new
  Behaviors.quiesce exception-context shim attaches a note
  describing the seed-inc / seed-dec balance on failure. CPython
  3.10 predates BaseException.add_note; the shim now
  writes to BaseException.__notes__ directly when add_note
  is missing.
• Transpiler except ... as X mis-classification —
  ExceptHandler binds X on the handler node
  itself rather than via Name `Stor...

Vector-oriented Matrix API — six new methods (vecdot,
cross, normalize, perpendicular, angle,
magnitude_squared), two new read-only properties (size,
length), and a unified in_place= keyword on every unary
method round out Matrix as a first-class vector and
batch-of-vectors type — plus an internal X-macro template refactor
of every _math.c op family that restores the compiler's
auto-vectoriser. 44 of 71 benched rows improved by ≥10%, with
representative wins of −50% to −88% on aggregates, broadcast
arithmetic, and normalize. The _math extension now ships
with -O3 (Linux/macOS) / /O2 (Windows) so end users pick
up the wins by default.

New Features

• Vector-oriented Matrix methods — six new methods designed
  for the Nx2 / 2xN / Nx3 / 3xN vector and
  batch-of-vectors shapes that show up in examples/boids.py and
  similar simulation code:

  • magnitude_squared(axis=None) — squared L2 norm without the
    sqrt step. Cheaper than magnitude() and safe for
    sub-normal thresholding.
  • vecdot(other, axis=None) — axis-aware inner product matching
    numpy.linalg.vecdot. Not equivalent to numpy.dot;
    use @ for matrix multiplication. Same-shape, row-broadcast
    (1xN vs MxN), and column-broadcast (Mx1 vs MxN)
    operands are all supported.
  • cross(other, axis=None) — 2D scalar z-component or 3D cross
    product. Five shape paths share one method: 1x2 / 2x1
    returns a float; 1x3 / 3x1 returns a same-orientation
    Matrix; Nx2 / 2xN batches collect per-vector
    scalars; Nx3 / 3xN batches return same-shape Matrix
    results. axis= disambiguates the square 2x2 / 3x3
    shapes (default per-row).
  • normalize(axis=None, in_place=False) — divide every element
    by its magnitude. Zero-magnitude rows / columns are returned as
    exact zeros (no NaN, no division by zero). axis= selects
    per-row, per-column, or total normalisation.
  • perpendicular(axis=None, in_place=False) — rotate every 2D
    vector 90° counter-clockwise: (x, y) -> (-y, x). Accepts a
    single 2D vector, an Nx2 row batch, or a 2xN column
    batch.
  • angle(axis=None) — polar angle atan2(y, x) of every 2D
    vector. Returns a float for a single 2D vector input,
    otherwise a Matrix of per-vector angles.

• Matrix.size property — total element count
  (rows * columns). Matches numpy.ndarray.size.

• Matrix.length property — Frobenius (L2) magnitude as a
  read-only @property so vector-like code reads naturally
  (direction.length, velocity.length) without the
  parentheses of a method call. Equivalent to magnitude() with
  no axis argument.

• in_place= keyword on every unary Matrix method —
  transpose, ceil, floor, round, negate,
  abs, plus the new normalize and perpendicular all
  accept in_place=True to mutate self and return it.
  Replaces the older transpose_in_place() method (see
  Breaking Changes below).

• axis= keyword on aggregate methods — sum, mean,
  min, max, magnitude, and the new magnitude_squared
  now share a tri-state axis= argument (None / 0 / 1)
  decoded through a single classifier. Negative axes (-1 /
  -2) accepted for NumPy parity.

Improvements

• Auto-vectorised _math.c op kernels — the binary,
  aggregate, unary, and two-operand-aggregate op families inside
  _math.c are now stamped from per-family descriptor tables,
  one kernel per (op, shape) combination. Each per-element body is
  literally substituted into its own monomorphic inner loop,
  restoring the precondition for GCC's / Clang's auto-vectoriser.
  Representative wins (lower is better):

  Bench row	0.7.0 (ns)	0.8.0 (ns)	Δ
  mean() shape=(1000, 100)	44179.6	9001.6	−79.6%
  mean(1) shape=(1000, 100)	51699.4	7058.5	−86.3%
  max(1) shape=(1000, 100)	97184.2	11322.7	−88.3%
  magnitude() shape=(1000, 3)	1098.2	306.8	−72.1%
  add col-bcast shape=(1000, 100)	37823.4	20172.5	−46.7%
  div same-shape shape=(1000, 100)	80134.2	45458.9	−43.3%
  normalize() shape=(1000, 3) axis=None	3644.6	1775.5	−51.3%

  Four rows in code paths untouched by the refactor regressed by
  5–15% from layout drift (_math.so .text grew +125% from
  kernel specialisation); none are on a hot path. No behavioural
  change; test_matrix.py passes unchanged.

• -O3 / /O2 on bocpy._math — the math extension now
  sets per-platform extra_compile_args in setup.py
  (-O3 -fno-plt on Linux/macOS, /O2 on Windows) so end-user
  wheels and editable installs both pick up the auto-vectoriser
  wins above. Other bocpy extensions are unaffected. The SBOM
  hash for _math.*.so will drift accordingly — see
  :doc:sbom for the auditor-facing note.

Breaking Changes

• Matrix.transpose_in_place() removed — superseded by
  Matrix.transpose(in_place=True), which returns self and
  so composes the same way every other unary method does.
  Migration is mechanical: replace m.transpose_in_place() with
  m.transpose(in_place=True).

Documentation

• New Matrix API entries in :doc:api for size, length,
  magnitude_squared, vecdot, cross, normalize,
  perpendicular, and angle, plus updated in_place=
  keyword signatures on the existing unary methods.

Tests

• 234 new test cases for the new Matrix methods and
  properties (1571 → 1805 passed). Coverage includes a stub-guard
  test that greps __init__.pyi for every new C-level name and
  in-cown coverage exercising each new method inside @when.
• Portable overflow regex + cross 2x3/3x2 contract pinning —
  the cross-product test for the doubly-valid 2x3 / 3x2
  shapes now pins the 2D-batch interpretation explicitly, locking
  the documented behaviour.

Internal

• scripts/bench_matrix.py — bench harness used to gate the
  refactor: --json append mode, --report-median per-row
  merge, 200 ms warmup, batch-size auto-tuning.
• scripts/validate_wheel.py +
  scripts/_vendored_warehouse_wheel.py — stdlib-only wheel
  RECORD validator and a vendored slice of Warehouse's wheel
  parser; used by the PR gate to catch RECORD regressions
  before PyPI does.

CI / build

• cibuildwheel v3.4.0 → v3.4.1 and clang-format-action
  pin normalised to the underlying commit SHA (Dependabot's
  preferred format). Both pins move in lock-step with the
  github-actions Dependabot group.
• idna 3.16 → 3.17 in ci/constraints-docs.txt. Five
  other Dependabot proposals (docutils 0.23, ruamel-yaml
  0.19, sphinx-tabs 3.4.7+, sphinx-toolbox 4.2, and
  standard-imghdr 3.13) require Python ≥3.11 and so cannot
  enter a universal lock that still includes Python 3.10; a
  comment above requires-python = ">=3.10" in
  pyproject.toml lists them for the post-3.10-EOL bump.
• flake8 extend-exclude for .copilot/, build/,
  sphinx/build/, and the scratch .env* venvs so the walker
  no longer trips on generated or vendored Python files.

Cown-lifecycle correctness fixes — three use-after-free paths in the
CownCapsule pickle / acquire / noticeboard machinery now hold the
inner BOCCown alive across the writer's wrapper drop — plus
supply-chain hardening: pinned and hash-verified Python dependencies,
SHA-pinned GitHub Actions, dependabot coverage, vulnerability scanning,
and PEP 770 SBOMs embedded in every wheel.

New Features

• PEP 770 SBOMs in every wheel — every wheel built by
  .github/workflows/build_wheels.yml now embeds a
  CycloneDX 1.6 <https://cyclonedx.org/specification/overview/>_
  JSON SBOM under <dist>-<version>.dist-info/sboms/bocpy.cdx.json.
  Generation runs inside cibuildwheel's repair step on every platform
  (Linux auditwheel, macOS delocate, Windows direct injection)
  via the new stdlib-only scripts/build_sbom.py. The
  inject subcommand rewrites the wheel's RECORD atomically
  (temp file + rename).
• SBOM verification in CI — the new verify_sboms job in
  build_wheels.yml re-downloads the extracted SBOM artifact and
  runs two checks: scripts/validate_sbom.py (stdlib-only
  structural validator pinning bocpy's wire format) and
  grype <https://github.com/anchore/grype>_ (third-party SBOM
  scanner) with --fail-on high. A separate sboms artifact is
  also uploaded by the merge job for downstream consumers.
• bocpy.__version__ — a runtime version attribute derived
  from importlib.metadata.version("bocpy"), with a
  PackageNotFoundError fallback. Exported from bocpy.__all__
  and documented in __init__.pyi. pyproject.toml remains the
  single source of truth for the version.
• New documentation — :doc:sbom walk-through covering the
  embedded SBOM format, extraction recipes, and verification commands.
• wait(noticeboard=True) final-state capture — :func:wait
  now accepts a noticeboard keyword that returns the final
  noticeboard contents as a plain dict at shutdown (after the
  noticeboard thread exits, before the entries are freed). Useful
  for surfacing an early-stopping result, last error, or aggregated
  counter that a behavior deposited just before the runtime
  quiesced, replacing the older send / receive handshake
  that earlier examples used. Combined with stats=True it
  returns a new :class:WaitResult NamedTuple (also exported
  from bocpy.__all__) carrying both snapshots. The
  examples/prime_factor.py example was migrated to the new
  pattern.

Bug Fixes

• Cown-in-cown use-after-free — a Cown embedded inside
  another cown's value, a message-queue payload, or a noticeboard
  snapshot was previously freed when the writer's local wrapper
  dropped, because pickle bytes carry no refcount on their own.
  CownCapsule_reduce now takes an inheriting COWN_INCREF that
  _cown_capsule_from_pointer_inheriting consumes on unpickle, so
  the inner BOCCown survives until the consumer drops its
  decoded wrapper. Affects every cross-cown reference shape — see
  the new TestCownInCown class for the full container-shape fuzz.
• Acquire-failure poisoned-state — when pickle.loads failed
  partway through cown_acquire, the cown was left in a
  half-acquired state with the encoded bytes still in place. A retry
  would re-run pickle against bytes whose embedded inherited refs
  had already been partially consumed by pickle's error path,
  risking dereferences of freed BOCCown* pointers. The cown's
  xidata is now recycled on the failure path and a guard at the
  top of cown_acquire rejects any future acquire with a
  deterministic RuntimeError; the worker recovery arm surfaces
  it on the failing behavior's result cown.
• Noticeboard hidden-cown audit — when a noticeboard value
  reached a Cown via a route the pin walker cannot see — custom
  __reduce__ / __getstate__, copyreg.dispatch_table,
  closure capture, module-level cache — the borrowing reconstructor
  produced a token whose inner BOCCown was not held alive by
  the entry's pin set, leaving the next reader to UAF after the
  writer's wrapper dropped. A per-thread borrowing context
  (BOC_NB_CTX) now audits every CownCapsule_reduce against
  the caller's pin set during the noticeboard write pickle and
  fails the whole notice_write / notice_update closed if
  any cown is unaccounted for.
• UnicodeDecodeError on non-UTF-8 Windows locales —
  Behaviors.start read worker.py with open(path), which
  picks up locale.getpreferredencoding(False). On cp1252
  (English Windows) the UTF-8 em-dashes in the worker source were
  silently mojibake-d; on cp949 (Korean Windows) the read failed
  with UnicodeDecodeError: 'cp949' codec can't decode byte 0xe2
  and bocpy could not start at all (reported in
  #14 <https://github.com/microsoft/bocpy/issues/14>_ by
  @Forthoney <https://github.com/Forthoney>_). Fixed by passing
  encoding="utf-8" explicitly in Behaviors.start, and the
  same fix was applied to every other open() site in the repo
  that reads or writes text known to contain non-ASCII bytes
  (sphinx/source/conf.py, examples/sketches.py x2,
  export_module.py).
• Silent worker-startup failures — Behaviors.start_workers
  ran interpreters.create() and interpreters.run_string()
  on the worker thread without a try/except, so a failure in either
  killed the thread without ever replying on boc_behavior. The
  parent's bounded receive() then timed out with no diagnostic.
  Both calls are now wrapped, and every failure path sends a
  formatted traceback over boc_behavior so the parent sees a
  structured error instead of a timeout.
• Silent worker bootstrap import failures — the generated
  bootstrap script that loads the user module into each worker
  sub-interpreter is now wrapped in a top-level try/except. Any
  BaseException is formatted with the user module name and sent
  over boc_behavior (falls back to sys.stderr if the
  message-queue send itself raises), then re-raised so
  run_string reports it as well. Module-import failures that
  previously surfaced only as a worker-startup timeout now arrive
  as a proper traceback.
• boc_sched_worker_pop_slow skipped popped_local — the
  slow-path pending-fallback and WSQ-dequeue branches returned
  work without bumping popped_local (the fast path always
  did), so the documented producer/consumer identity in
  :c:type:boc_sched_stats_t was violated whenever the fairness
  arm fired or a worker entered the slow path directly. Both
  branches now increment popped_local and reset the batch
  budget, matching the fast path. The header's reconciliation
  paragraph was also tightened to a "near-identity" that explicitly
  accounts for fairness-token pops (which are re-enqueued via raw
  boc_wsq_enqueue rather than boc_sched_dispatch, leaving
  consumer-side counters without a matching producer-side bump).

Supply Chain

• Hashed and pinned Python dependencies — every CI dependency is
  resolved into a ci/constraints-<extra>.txt file via
  uv pip compile --universal --generate-hashes and installed with
  pip install --require-hashes. Covers the test, linting,
  docs, and new audit extras. bocpy itself is then
  installed via pip install -e . --no-deps so an editable build
  cannot smuggle in an unpinned transitive dependency.
• Vulnerability scanning — new audit job in pr_gate.yml
  runs pip-audit --strict against every constraints file on every
  PR. pip-audit itself is pinned via ci/constraints-audit.txt
  and self-checked. A new .github/workflows/nightly_audit.yml
  re-runs the audit nightly against main.
• SHA-pinned GitHub Actions — every uses: line in
  .github/workflows/ is now pinned to a full 40-char commit SHA
  with a trailing # vX.Y.Z comment.
• Dependabot coverage — new .github/dependabot.yml covers
  three ecosystems (pip rooted at /ci, github-actions
  rooted at /, pip rooted at
  /templates/c_abi_consumer), grouped weekly per ecosystem.
• Downstream template pinned — templates/c_abi_consumer
  pins bocpy~=MAJOR.MINOR as both a build requirement and a
  runtime dependency. The finalize-pr skill bumps it in
  lock-step with the root version.
• New SUPPLY_CHAIN.md — top-level policy doc describing
  everything above with the exact regeneration commands.

Documentation

• Cown pickle-leak note — :class:Cown now documents that
  pickle.dumps on a cown produces bytes that carry one strong
  reference per embedded cown; orphan bytes (never unpickled in the
  producing process) leak one strong ref per byte string. The bocpy
  runtime never produces orphan bytes; the leak surface only
  applies to third-party code that calls pickle.dumps(cown)
  directly.
• Noticeboard cown-lifetime guarantee — :func:notice_write and
  :func:notice_update now document that values may embed
  :class:Cown references and that the noticeboard keeps each
  embedded cown alive for as long as the entry remains. The new
  paragraph in :doc:noticeboard mirrors this guarantee for
  readers.
• Noticeboard final-state capture guide — :doc:noticeboard
  gained a "Reading the Final State at Shutdown" section covering
  the wait(noticeboard=True) contract, the combined
  wait(stats=True, noticeboard=True) form returning
  :class:WaitResult, the empty-dict fallbacks for the
  never-started and never-written cases, and the recommendation
  to use snap.get(key) since :func:wait quiesces as soon as
  every behavior ...

Public C ABI for downstream extensions, enabling C-level participation
in behavior-oriented concurrency across worker sub-interpreters.

New Features

• Decorator composition with @when — decorators stacked below
  @when are now preserved on the generated behavior function and
  compose with the behavior body on the worker. Decorators placed
  above @when raise a SyntaxError at transpile time with
  actionable guidance. async def functions with @when are
  also explicitly rejected.
• Public C ABI (<bocpy/bocpy.h>) — downstream C extensions can
  now link against bocpy to register custom Python types as
  cross-interpreter shareable so :class:Cown can carry instances of
  them across worker interpreters. The header is C-only, version-gated
  via the BOCPY_ABI macro, and bumped on any incompatible change
  to bocpy.h or xidata.h. Wheels remain CPython-version-tagged
  so a runtime ABI mismatch cannot occur.
• bocpy.get_include() / bocpy.get_sources() — Python-level
  helpers that downstream setup.py files use to locate the bocpy
  headers and the small set of C sources that must be compiled into
  the consuming extension.
• templates/c_abi_consumer/ — a ready-to-copy template for
  building a C extension against the bocpy ABI, including a
  setup.py, a probe extension exercising the public surface, and
  a pytest suite (test_public_c_abi.py) that validates the ABI
  end-to-end.
• C source reorganisation — the per-subsystem translation units
  introduced in 0.5.0 have been renamed with a boc_ prefix
  (boc_compat.[ch], boc_sched.[ch], boc_tags.[ch],
  boc_terminator.[ch], boc_noticeboard.[ch], boc_cown.h)
  to give the public ABI a stable, namespaced identity. xidata.h
  has moved under include/bocpy/ alongside bocpy.h.

Documentation

• New :doc:c_abi, :doc:messaging, and :doc:noticeboard pages
  in the Sphinx site; the API reference has been expanded to cover
  the public ABI surface.

Breaking Changes

• noticeboard_version removed — the global monotonic version
  counter introduced in 0.4.0 has been removed. It exposed an
  implementation detail of the snapshot cache that did not survive
  the C ABI review and had no use case that was not better served
  by notice_sync plus an explicit noticeboard() read.

Highlights

This release delivers a Verona-RT-style work-stealing scheduler, a global noticeboard (shared key-value store), removal of the central scheduler thread in favour of direct dispatch, and a major C source refactor into per-subsystem translation units with a portable atomics layer.

New Features

• Work-stealing scheduler — the single behavior queue is replaced with a distributed scheduler. Each worker owns an MPMC behavior queue, pops locally first, and steals from peers when idle. Idle workers park on per-worker condition variables and are signalled directly by producer/victim.
• Per-worker fairness tokens — a token node advances through each worker's queue so long-running behaviors cannot monopolise dispatch slots; also drives cooperative shutdown.
• Noticeboard — a shared key-value store (up to 64 keys) readable/writable without acquiring cowns. Writes are non-blocking; reads return a cached per-behavior snapshot. Includes notice_write, notice_read, notice_update, notice_delete, notice_sync, noticeboard_version, and the REMOVED sentinel.
• Distributed scheduler — two-phase locking, request linking, and dispatch run directly on the caller's thread in C; cown release runs on the executing worker. MCS-style intrusive linked list per cown for zero-bounce handoff.
• Cown.exception property — indicates whether the held value is from an unhandled exception.
• compat.h / compat.c portability layer — uniform BOCMutex, BOCCond, boc_atomic_*_explicit, monotonic-time, and sleep primitives across MSVC, pthreads, and C11 <threads.h>.
• xidata.h cross-interpreter shim — centralised _PyXIData_* / _PyCrossInterpreterData_* version ladders for CPython 3.12–3.15 (including free-threaded builds).
• fanout_benchmark example — fan-out/fan-in benchmark exercising scheduler throughput under heavy producer load.
• Prime factor example (examples/prime_factor.py) — parallel factorisation via Pollard's rho with noticeboard-coordinated early termination.
• Benchmark harness (examples/benchmark.py) — micro-benchmarks for scheduling throughput, message-queue latency, and noticeboard contention.

Bug Fixes

• Transpiler aliased imports — visit_Import / visit_ImportFrom now track alias names (import X as Y), preventing spurious "name not found" errors and duplicate whencall injection.
• Global variable capture — @when closure capture falls back to frame.f_globals when a name is not in any local scope, fixing NameError for module-level variables.

Improvements

• In-memory transpiled-module loading — workers exec the transpiled source from a string literal instead of writing to disk, eliminating filesystem round-trips and leftover .py files.
• Nested @when capture — the transpiler recurses into nested @when-decorated functions when computing outer captures, so child behaviors can close over the outer frame.
• C extension split — _core.c reduced from ~5,000 to ~3,500 lines by extracting sched.{c,h}, noticeboard.{c,h}, terminator.{c,h}, tags.{c,h}, cown.h, compat.{c,h}, and xidata.h.
• Direct dispatch on cown release — behavior_release_all hands resolved successors directly to workers via boc_sched_dispatch, removing one queue hop per handoff.
• Cooperative worker shutdown — boc_sched_worker_request_stop_all / boc_sched_unpause_all provide a clean stop/drain protocol.
• Matrix docstrings — all Matrix C methods now carry built-in docstrings.
• Examples package relocated — moved to top-level examples/ directory (still importable as bocpy.examples).
• Filtered PyPI README — setup.py strips <!-- pypi-skip-start --> regions before publishing.
• Documentation refresh — expanded coverage of noticeboard, distributed scheduler, and new APIs.

Internal Test Modules (opt-in via BOCPY_BUILD_INTERNAL_TESTS=1)

• _internal_test_atomics — correctness tests for compat.h typed-atomics.
• _internal_test_bq — torture tests for the MPMC behavior queue.
• _internal_test_wsq — tests for work-stealing primitives (fast pop, slow pop, steal, park/unpark).

Test Suite

• test_noticeboard.py — snapshot semantics, notice_update atomicity, REMOVED, notice_sync, version monotonicity.
• test_scheduler_integration.py, test_scheduler_stats.py, test_scheduler_steal.py — end-to-end and per-primitive scheduler tests.
• test_compat_atomics.py — portable atomics smoke tests.
• test_stop_retry_composition.py — stop()/start()/wait() retry composition.
• test_scheduling_stress.py — expanded with fan-out, work-stealing, and shutdown stress scenarios.
• test_transpiler.py — AST extraction, capture rewriting, aliased imports, module export.

Full changelog: v0.3.1...v0.5.0

CownCapsule serialization support for nested cowns.

Bug Fixes

• Removed the ownership check in _cown_shared that prevented a
  CownCapsule from being serialized to XIData when it was the value
  of another Cown. The check was unnecessary — _cown_shared only
  stores a pointer and ownership is enforced at acquire time.

Improvements

• Added CownCapsule.__reduce__ with COWN_INCREF pinning so that a
  CownCapsule embedded in a container (dict, list, etc.) can survive
  the pickle round-trip used by object_to_xidata. A module-level
  reconstructor (_cown_capsule_from_pointer) inherits the pin without
  a redundant COWN_INCREF, and validates the process ID on unpickle to
  guard against cross-process misuse.

Improvements

• Added CownCapsule.disown() — abandons a cown's value without
  serializing it and resets ownership to NO_OWNER. Used during worker
  cleanup to safely discard orphan cowns before the owning interpreter
  is destroyed, preventing dangling Python object references.
• Rewrote receive to use a two-phase spin-then-park strategy for
  single-tag untimed receives. Phase 1 spins for BOC_SPIN_COUNT
  iterations; Phase 2 parks the thread on a per-queue condvar, eliminating
  busy-wait CPU burn. Timed receives and multi-tag receives use
  spin-then-backoff with exponential sleep (1 µs → 1 ms cap).
• Added platform-abstracted condvar primitives (BOCParkMutex /
  BOCParkCond) with implementations for Windows (SRWLOCK /
  CONDITION_VARIABLE), macOS (pthreads), and Linux (C11 threads).
• Each BOCQueue now carries a waiters counter, park_mutex, and
  park_cond. Producers signal parked receivers after enqueue;
  drain and set_tags broadcast to wake all parked threads.
• Replaced the fixed thrd_sleep in send with a sched_yield /
  SwitchToThread, reducing send-side latency.
• Refactored the monolithic _core_receive into receive_single_tag
  and receive_multi_tag, each with its own backoff/parking logic.
• Moved the BOC_QUEUE_DISABLED check earlier in get_queue_for_tag
  so callers skip disabled queues instead of returning NULL after
  tag resolution.
• Added Windows-compatible atomic_load_explicit /
  atomic_fetch_add_explicit / atomic_fetch_sub_explicit macros
  using InterlockedExchangeAdd64.
• Declared Py_mod_gil = Py_MOD_GIL_NOT_USED in both _core and
  _math C extensions so that importing bocpy on a free-threaded
  Python build (3.13t+) does not re-enable the GIL.
• Replaced PyDict_GetItem (borrowed reference) with
  PyDict_GetItemRef (strong reference) in BOCRecycleQueue_recycle
  on Python 3.13+, improving forward-compatibility with free-threaded
  builds.

Bug Fixes

• Fixed a deadlock when the same cown is passed multiple times to @when
  (e.g. @when(c, c)). Duplicate requests for the same cown caused the
  MCS-queue-based two-phase locking to spin-wait on itself. Requests are
  now deduplicated by target cown in Behavior.__init__, with
  compensating resolve_one calls to maintain the behavior count
  invariant.

Tests

• TestLostWakeStress: single-producer random delays, bursty producer,
  and repeated single-message wake to detect lost-wake races.
• TestMultiTagBackoff: multi-tag receive correctness — second-tag hit,
  delayed arrival, per-tag FIFO ordering, timeout, and interleaved
  producers.
• TestTimeoutAccuracy: lower-bound / upper-bound wall-clock checks and
  zero-timeout immediacy.
• Added tests for duplicate cowns in @when: same cown twice, thrice,
  non-adjacent duplicates, duplicates within a group, and mutation
  aliasing semantics.

CI

• Added a free-threaded CI job that tests against Python 3.13t and
  3.14t on Linux, with explicit assertions that the GIL remains disabled
  after import.

Full Changelog: v0.2.2...v0.3.0

Improvements

• Added an ASAN/UBSAN CI job that builds CPython 3.14.2 from source with AddressSanitizer and UndefinedBehaviorSanitizer, then runs the full test suite against instrumented builds of bocpy.
• Updated GitHub Actions to latest versions (actions/checkout@v6, actions/setup-python@v5).

Bug Fixes

• Fixed a false positive warning message for deallocation of xidata on the main
  interpreter after module shutdown.
• Changed the clear logic when recycling

Bugfix release including some minor improvements.

Improvements

• Examples are now included in the package, with script entrypoints for each.
• The drain low-level API function is now exposed at the package level
• wait() will now acquire frame-local Cown objects before shutting down the workers

Dev Tools

• Added an internal cown and behavior reference tracking utility

Bug Fixes

• Fixed a reference counting bug with cown lists
• Fixed an issue where the boids example did not run on windows due a font
  setting.