Windows support: make the test suite CI-green

[dfrostar]

Context

The cross-platform CI matrix (#185) ran the full test suite on windows-latest (Python 3.12) for the first time. Result: 509 passed, 5 failed, 134 errors. Linux (3.10–3.12) and macOS (3.12) are fully green; Windows is not. Windows was therefore dropped from the gating matrix and demoted to ⚠️ Experimental in docs/COMPATIBILITY.md, and the schema.org operatingSystem claim was narrowed to "Linux, macOS". This issue tracks getting Windows back to green so it can be re-added to the gate and the support claim restored.

Failing run

What fails on Windows

1. ChromaDB temp-dir teardown — ~134 errors (test-infra)

PermissionError: [WinError 32] The process cannot access the file because it is being used by another process deleting …/neuralmind_db/chroma.sqlite3 and …/data_level0.bin during fixture teardown. ChromaDB keeps the sqlite/HNSW file handles open; Windows refuses to delete an open file, so TemporaryDirectory cleanup blows up after the test body has run.

• Fix direction: explicitly close/del the Chroma client + collection in test teardown (and likely in GraphEmbedder/backend close()), and/or use tempfile.TemporaryDirectory(ignore_cleanup_errors=True) (Py3.10+) in the shared fixtures. Audit embedder/core/backend for a close() that releases the client.

2. Event-log rotation — 3 failures (likely product code)

tests/test_event_log.py::test_tailer_recovers_from_rotation* — PermissionError renaming events.jsonl → events.jsonl.1 while a reader holds it open. POSIX allows rename-over-open; Windows does not.

• Fix direction: in the tailer/rotation path, close the read handle before rotating (or open with share-delete semantics); make the rotation logic Windows-aware.

3. Concurrent append safety — 1 failure (likely product code)

tests/test_graph_view.py::test_recent_queries_append_is_concurrency_safe — expected 40 appends (8 threads × 5), got 37. Concurrent appends lose writes on Windows; the test asserts concurrency-safety.

• Fix direction: guard the recent-queries append with a real lock (or O_APPEND-equivalent atomic write) that holds on Windows, not just POSIX atomic-append assumptions.

4. Executable-bit test — 1 failure (test-only, easy)

tests/test_cli.py::test_cmd_init_hook_makes_executable asserts S_IXUSR. Windows has no executable bit.

• Fix direction: @unittest.skipIf(os.name == "nt", …) or skip via sys.platform.startswith("win").

Done when

• Items 1–4 fixed
• windows-latest re-added to the test matrix in .github/workflows/ci.yml and green
• docs/COMPATIBILITY.md Windows row restored to ✅ Full
• docs/index.html operatingSystem restored to include Windows

https://claude.ai/code/session_016MZU3vW4yd4SJeA293foF3