fix(memory): enforce authoritative revision integrity

[knqiufan]

Which issue or RFC does this PR close?

Closes #1297.

Rationale for this change

MemoryUnitOfWork.commit() is the final persistence trust boundary, but it previously accepted incomplete or internally inconsistent revisions. A malformed direct SPI writer could persist illegal predecessor links or body/hash mismatches, and search could then return text that authoritative entry reads rejected.

What changes are included in this PR?

• Validate the stored base and the complete base-to-revision transition inside the commit transaction.
• Require the manifest, changes, new entry versions, direct predecessors, and active projections to agree exactly.
• Recompute entry hashes and validate declared/manifest hashes, canonical searchable text, and configured embedding bindings before any write.
• Revalidate entries(), expand(), projection reads, and every FTS/vector candidate against the exact authoritative revision, manifest, entry row, and current head projection.
• Add regression coverage for nonexistent, cross-entry, cross-Memory, and skipped predecessors; missing/extra/duplicate rows; hash and projection corruption; rollback behavior; and read/search/expand agreement.

Are there any user-facing changes?

Malformed commits made through the public Memory backend SPI now fail with MemoryBackendConfigurationError instead of becoming durable state. Valid service workflows and the documented no-vector degradation remain unchanged. There are no API or persisted-format migrations.

How was this change tested?

• .venv/Scripts/prek.exe run -a
• .venv/Scripts/ty.exe check
• .venv/Scripts/python.exe -m pytest tests/builtin/artifacts/memory tests/builtin/persistence/test_memory.py tests/builtin/persistence/test_memory_integrity.py tests/e2e/test_memory_search_concurrency.py tests/e2e/test_builtin_runtime.py -q (39 passed, 5 skipped)
• Manual issue reproducer: both the fake predecessor and body/hash mismatch are rejected before persistence.
• Full Windows run: 612 passed, 14 skipped; 8 unrelated platform failures remain in pre-existing symlink/POSIX-mode, python3 command, encoding, and path-separator assertions.

AI usage statement

OpenAI Codex (GPT-5) was used to inspect the issue and codebase, implement the fix, design regression tests, and review the final change.