fix(mcp_server): address copilot review on #1303

- Resolve the EF inside the two reopen branches that actually call
  `client.get_collection` / `client.create_collection`, so warm-cache
  reads stay zero-cost (no `MempalaceConfig()` / `_resolve_providers`
  on every tool call).
- Reuse `ChromaBackend._resolve_embedding_function()` instead of
  duplicating its try/except + log message + None-fallback.
- Reword the inline + CHANGELOG explanation to clarify that ChromaDB 1.x
  persists the EF *identity* (its `name()`) but not the *instance/
  configuration* — `mempalace.embedding` documents this and spoofs
  `name()` to `"default"` precisely so the identity check passes; the
  bug was the *provider list* (lazy ONNX selection) silently differing.

mempalace/mcp_server.py

@@ -66,7 +66,6 @@ from .backends.chroma import (  # noqa: E402
     _pin_hnsw_threads,
     hnsw_capacity_status,
 )
-from .embedding import get_embedding_function  # noqa: E402
 from .query_sanitizer import sanitize_query  # noqa: E402
 from .searcher import search_memories  # noqa: E402
 from .palace_graph import (  # noqa: E402
@@ -279,23 +278,25 @@ def _get_collection(create=False):
     global _collection_cache, _metadata_cache, _metadata_cache_time
     try:
         client = _get_client()
-        # ChromaDB 1.x does not persist the embedding function with the
-        # collection, so a reader/writer that omits ``embedding_function=``
-        # silently gets the chromadb-built-in default. On bleeding-edge
+        # ChromaDB 1.x persists the EF *identity* (its ``name()``) with the
+        # collection but not the EF *instance/configuration*. So a reader or
+        # writer that omits ``embedding_function=`` silently gets chromadb's
+        # built-in ``DefaultEmbeddingFunction`` — its ``name()`` matches the
+        # one we spoof in ``mempalace.embedding`` (both report ``"default"``,
+        # the identity check passes), but the *provider list* is chromadb's
+        # default rather than the user's resolved device. On bleeding-edge
         # interpreters (#1299: python 3.14 + chromadb 1.5.x on Apple Silicon)
-        # the default's lazy ONNX provider selection can SIGSEGV the host
-        # process on first ``col.add()``. The miner / Stop hook ingest path
-        # avoids this because it routes through ``ChromaBackend.get_collection``
-        # which resolves the EF via ``mempalace.embedding.get_embedding_function``.
-        # The MCP server bypassed that abstraction; mirror its behaviour so
-        # ``tool_diary_write`` / ``tool_add_drawer`` get the same EF as mining.
-        try:
-            ef = get_embedding_function()
-        except Exception:
-            logger.exception("Failed to build embedding function; using chromadb default")
-            ef = None
-        ef_kwargs = {"embedding_function": ef} if ef is not None else {}
+        # that default provider selection can SIGSEGV the host process on
+        # first ``col.add()``. The miner / Stop hook ingest path avoids this
+        # because it routes through ``ChromaBackend.get_collection``, which
+        # resolves the EF via ``ChromaBackend._resolve_embedding_function``;
+        # the MCP server bypassed that abstraction. Resolve the EF inside the
+        # branches that actually open a collection so warm-cache reads stay
+        # zero-cost. Reuse the backend helper so the two call sites can't
+        # drift on logging or fallback semantics.
         if create:
+            ef = ChromaBackend._resolve_embedding_function()
+            ef_kwargs = {"embedding_function": ef} if ef is not None else {}
             # hnsw:num_threads=1 disables ChromaDB's multi-threaded ParallelFor
             # HNSW insert path, which has a race in repairConnectionsForUpdate /
             # addPoint (see issues #974, #965). Set via metadata on fresh
@@ -325,6 +326,8 @@ def _get_collection(create=False):
             _metadata_cache = None
             _metadata_cache_time = 0
         elif _collection_cache is None:
+            ef = ChromaBackend._resolve_embedding_function()
+            ef_kwargs = {"embedding_function": ef} if ef is not None else {}
             raw = client.get_collection(_config.collection_name, **ef_kwargs)
             _pin_hnsw_threads(raw)
             _collection_cache = ChromaCollection(raw)