Close the last open items on #743 before merge:
- Conformance: document two isolation arms (cross-id for all backends;
same-id/different-namespace for supports_namespace_isolation advertisers).
- No silent drop: non-advertising backends must raise UnsupportedCapabilityError
when PalaceRef.namespace is set, rather than accept-and-ignore.
- Wire require_namespace_support() into chroma/sqlite_exact; add conformance test.
- Refresh implementation-status banner now that #1727/#1731/#1732/#1734 landed.
#757 landed mtime/inode cache invalidation and mempalace_reconnect
in mcp_server._get_client(). Both are Chroma-specific (stat of
chroma.sqlite3). They should migrate into ChromaBackend.get_collection
and ChromaBackend.close_palace during the §10 cleanup so the freshness
contract lives inside the backend, not in the caller.
Addresses the actual spec defects flagged in #743 review, ignoring
operator-UX asks that are not plugin-contract concerns.
- Goal #3: 'without data loss' → mirrors §8.2's capability-conditional
lossless-vs-reembed framing. No more overpromise.
- §1.5: `server_embedder` is no longer an implicit escape hatch from
identity/dimension rules. Such backends MUST expose an effective
identity via `effective_embedder_identity()` and are bound by the
same three-state check.
- §7.3: adds `maintenance_kinds: ClassVar[frozenset[str]]` advertisement
mechanism. `run_maintenance(kind)` must raise
UnsupportedMaintenanceKindError for unadvertised kinds. Benchmark
harness reads this set rather than guessing kind names. Reserves
`analyze`/`compact`/`reindex` as well-defined names.
- §1.2: adds `update()` as optional method with a default get+merge+
upsert implementation. §2.1: `supports_update` redefined to gate
atomic single-round-trip semantics (not mere capability), since the
default impl already supports partial updates.
Operator asks explicitly NOT adopted (diplomatic shims, not contract
defects): `.to_dict()` compat on typed results, migration progress
reporting, `BaseBackend.repair()` separate from `run_maintenance`,
per-palace capability variance, identity recording on read-only ops.
Incorporates review feedback from skuznetsov (Postgres, #665) and
dekoza (Lance, #574) on issue #737:
- §1.5: split 'accepts embeddings=' (signature compliance) from
'persists embeddings as-is' (correctness). Adds
supports_embeddings_passthrough capability; the former is universal,
the latter is required to label a migration lossless.
- §1.5: model identity check becomes a three-state machine
(known_match / known_mismatch / unknown) so legacy palaces without
recorded identity don't hard-fail on upgrade.
- §1.4: makes explicit that supports_contains_fast is the ONLY
performance floor the spec promises; without it callers MUST assume
O(n). $contains is a correctness requirement, not a performance one.
- §3.3: clarifies auto-detect is an upgrade-compat path only, never
the selection mechanism for new palaces.
- §8.2: migrate CLI refuses to run against a target lacking
supports_embeddings_passthrough unless --accept-re-embed is passed;
migration record now captures lossless status and model identities.
Copilot review flagged back-references in §1.4 and §6 that still used
the pre-skuznetsov-rename names (`$contains_fast`, `sync_capable`,
`change_feed`). Updated to the `supports_*` prefix used in the §2.1
capability table.
Formalizes the BaseCollection/BaseBackend contract introduced as a seam
in #413 into an interchangeability spec that third-party backends can
build to. Driven by six in-flight backend PRs (#574, #643, #665, #697,
#700, #381) each implementing the interface differently.
Key decisions captured: entry-point distribution, typed QueryResult/
GetResult replacing Chroma dict shape, daemon-first multi-palace model
via PalaceRef, required where-clause subset (incl. $contains),
mandatory embedder injection with model-identity validation, capability
tokens, shared pytest conformance suite, and a backend-neutral
migrate/verify CLI.
Igor Lins e Silva