feat(s133): embedding spaces, operator pinning and the static floor

[HackTuah]

Slice 133: embedding spaces, operator pinning and the static floor. The slice stays in_progress until the owner's two items are done: the legal review of the static weights (D7), and the 100-label audit before the eval's scored run.

What lands

• Embedding spaces: a new memory_embeddings table keyed (memory_id, space_id), and embedding_spaces, which holds each space's 14-field manifest identified by SHA-256 over RFC 8785 JSON. On Postgres the column is an untyped vector with one partial HNSW index per space, so spaces of different widths coexist. Existing vectors migrate under a legacy space with their bytes unchanged.
• Operator pinning: one active space per store.
  • mix trinity.space.retier builds the new space beside the old and moves the pointer in one transaction.
  • mix trinity.space.drop needs --confirm and refuses the active space.
  • A row that does not fit the active space makes the store refuse rather than rank.
• Declared locality: in_process, within_boundary or external. Configuration faults refuse a :regulated boot. Runtime faults turn semantic memory off with a named reason while full-text search keeps answering.
• The static embedder: pure-Elixir WordPiece plus mean pooling, with no NIF. Its weights are a derived artifact whose digest is pinned in code; the weights are not in the tree.
• Scoring: an int8 scorer, plus a sign/Hamming prefilter measured but not yet wired in. At 10^4 x 256, prefilter p95 is 10.3 ms and exact p95 24.5 ms, under the 50 ms line, so no scoring NIF is needed.
• TRINITY_WITHOUT_ML=1 builds without nx, bumblebee and exla, and that release boots, embeds and recalls.
• The eval harness and corpus. The scored run refuses until the audit is done.

Criteria

• Proven: AC1 to AC11 and AC16. AC1 and AC4 on SQLite and Postgres, AC2 on Postgres. AC8 on the author's machine, since the weights cannot go to CI before D7.
• Measured: AC13.
• Waiting on the owner:
  • AC12's second half (the Linux bundle reporting semantic memory ON) and AC15 (the Windows bundle): both need the weights bundled, which waits on D7.
  • AC14: the label audit.

Evidence

• Author's gate: exit 0, 1017 passed (21 properties, 996 tests), 31 excluded, prod_check: PASS, coverage 80.49% against 80.31%.
• Postgres full suite: 999 passed.
• Reviewer re-run before commit:
  • the 25 changed and new test files: 92 passed, 14 excluded;
  • with the weights cache set, --only static_weights: 11 passed;
  • with the variable pointing at a missing directory: 8 failed, 3 invalid. That is the owner's rule: the tests fail, never skip;
  • mix format --check-formatted OK; mix credo --strict --all found no issues.