[codex] Fix SharedNPArray partial init cleanup

[den-sq]

Fixes #97

Summary

• add a class-level SharedNPArray.__shutdown default of True so partially constructed instances are treated as already shut down
• add a regression test covering both object.__new__ reconstruction and failed SharedMemory lookup without unraisable destructor warnings

Root Cause

SharedNPArray.__init__ could raise before assigning the instance __shutdown flag. When Python finalized that half-built object, __del__ read the missing attribute and pytest reported a PytestUnraisableExceptionWarning.

Validation

• poetry run pytest test/helpers/test_mem.py -W error::pytest.PytestUnraisableExceptionWarning
  • 5 passed in 2.38s
• poetry run pytest
  • 169 passed, 1 warning in 5.65s
  • the remaining warning is the separate Pydantic model_fields deprecation tracked by Pydantic v2.11 model_fields-on-instance deprecation (models.py:117) #98 / PR [codex] Fix Pydantic model_fields access #100

[tavateva]

Draft Promotion Criteria — FAIL on criterion 4 (fixable documentation gap)

Code and regression test are correct. Blocking promotion on the same missing-pass-count issue we hit on den-sq/mctutil#78.

Passes:

1. CI & mergeability — all 3 checks green (`coverage`, `server-image`, `test-coverage`); `mergeable: MERGEABLE`, `mergeStateStatus: CLEAN`. ✓

2. Issue Acceptance Criteria — issue #97's 3-item checklist:

   • `del` no longer raises `AttributeError` on partially-constructed instances → satisfied by class-level `__shutdown = True` default at mem.py:22. The name-mangled attribute (`_SharedNPArray__shutdown`) resolves via class lookup when the instance attribute is unset, so `if not self.__shutdown:` correctly reads `True` and skips `shutdown()`. ✓
   • Regression test → `test_partial_shared_np_array_destruction_is_already_shutdown` covers both paths (`object.new` reconstruction and a failed `SharedMemory` lookup), forces `gc.collect()`, and decorates with `@pytest.mark.filterwarnings("error::pytest.PytestUnraisableExceptionWarning")` so any regression flips the warning into a hard failure. ✓
   • Two-warning count drop → verifiable by re-running the coverage workflow; PR body doesn't explicitly cite the delta, but the strict filter effectively enforces it. ✓ (soft)

3. Test Plan checkboxes — no checkbox section. N/A.

4. Tests run, not just report — Validation section reads:

   `poetry run pytest test/helpers/test_mem.py -W error::pytest.PytestUnraisableExceptionWarning`

   Issue #97's AC includes a test requirement ("A test ... confirms no `PytestUnraisableExceptionWarning`"), so criterion 4 requires concrete pass/fail counts ("X passed / Y skipped") in the PR body. Command is listed but no counts. CI green implies it passed, but the criterion demands explicit reporting. Failure.

5. Scope — mem.py +2 (class attr) / test_mem.py +13 (regression test + `gc` import). Tight to #97. ✓

6. Regressions & patterns — class-level attribute pattern matches how similar guards are handled elsewhere in the codebase; no other code paths touched. ✓

7. Judgement calls — chose Option 1 (class-level default) from #97's suggested-fix pair; explained inline in Root Cause. Also the `gc.collect()` after the `FileNotFoundError` path is a subtle judgement (needed because CPython may not have finalized the half-built object by the time the test returns) — not explicitly explained but obvious from context. ✓

Fix to promote: append pass count to the Validation section, e.g.:

```
poetry run pytest test/helpers/test_mem.py -W error::pytest.PytestUnraisableExceptionWarning
→ N passed, M skipped
```

Also worth adding a full-suite `pytest` run with its count to confirm no regressions elsewhere. Then all 7 criteria hold.

[tavateva]

Re-review — Draft Promotion Criteria PASS ✅

Validation section updated with concrete pass counts. All 7 criteria hold.

1. CI & mergeability — 3 checks green (`coverage`, `server-image`, `test-coverage`); MERGEABLE / CLEAN. ✓
2. Issue #97 AC — class-level `__shutdown` default satisfies the "no AttributeError on partial instance" item; regression test covers both `object.new` and failed-`SharedMemory` paths. ✓
3. Test Plan checkboxes — N/A.
4. Tests run with counts — targeted `pytest test/helpers/test_mem.py -W error::pytest.PytestUnraisableExceptionWarning` → 5 passed in 2.38s; full `pytest` → 169 passed, 1 warning in 5.65s (up from 168, +1 = new regression test). The remaining warning is explicitly identified as the sibling Pydantic warning tracked in #98 / PR #100 — no hidden regressions. ✓
5. Scope — mem.py +2 / test_mem.py +13. ✓
6. Regressions & patterns — 169 = 168 baseline (from PR #96) + 1 new regression test; no existing tests broke. ✓
7. Judgement calls — reasoned inline. ✓

Approving. Safe to promote and merge.