docs(release): draft 0.8.6 notes — test mop-up

Five test-only fixes close the last actionable audit findings: behavioral
drain check, exact threading-budget deposit total, sync Client decoder-
escape peer, sync Bulkhead Hypothesis suite, sync on_error BaseException
propagation tests. No production code change, no behavior change.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: lesnik512

planning/releases/0.8.6.md

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+# httpware 0.8.6 — test mop-up
+
+**Patch release. Test-only changes. No API change, no production code change, no behavior change for users.** Closes 5 audit findings — all in the test suite.
+
+## What changed
+
+- **`test_no_slot_leak_after_drain` is behavioral, not internals-peek.** The Hypothesis property test for `AsyncBulkhead` no longer asserts against `bulkhead._sem._value`; it submits `max_concurrent` fresh acquires after drain and confirms they all succeed under a tight `acquire_timeout`.
+- **`test_threading_with_shared_budget` asserts the exact deposit count.** The previous `len(budget._deposits) > 0` was a smoke check that would have passed under deque corruption with even one survivor. The new assertion locks the count to `(N_SYNC_THREADS * N_OPS_PER_THREAD) + N_ASYNC_TASKS` = 220, made deterministic by the 0.8.3 deposit-hoist.
+- **`test_optional_extras_pydantic_missing.py` covers the sync `Client` escape hatch.** The async test pinned `AsyncClient(decoder=fake)` bypassing the pydantic fail-fast; the sync `Client` had no peer. Now it does. `_FakeDecoder` hoisted to module top to keep the two tests DRY.
+- **Sync `Bulkhead` has Hypothesis property tests.** New file `tests/test_bulkhead_sync_props.py` mirrors `tests/test_bulkhead_props.py` using `threading.Thread` + `ThreadPoolExecutor` instead of `asyncio.gather`. Three properties: in-flight never exceeds cap; fail-fast rejects at capacity; no slot leak after drain.
+- **Sync `on_error` `BaseException` propagation is tested.** Two new tests in `test_middleware_sync.py` pin the invariant that the sync `on_error` decorator's `except Exception` clause does NOT catch `KeyboardInterrupt` or `SystemExit` — both must propagate through `compose`.
+
+## Audit status
+
+35 audit findings, all addressed across 0.8.1 → 0.8.6 plus the in-place doc-staleness sweep on `main`. One chunk-3 hand-review item was excluded as INVALID (the audit looked for `AsyncClient` construction tests in `tests/test_client_methods.py` — they actually live in `tests/test_client_construction.py` + `tests/test_client_lifecycle.py`).
+
+## Upgrade
+
+```bash
+uv add httpware==0.8.6
+# or
+pip install -U 'httpware==0.8.6'
+```
+
+No import changes. No API changes. Nothing observable from the consumer side.