feat(ccip): matcher reads the incremental prototype store (#1317, m138 step 4)

match_image now sources character references from character_prototype via a
per-character in-process cache (_load_prototypes) that reloads ONLY the
characters whose ccip_prototype_state.updated_at advanced — no request-path
rebuild, so the per-accept ~4s stall is gone once the store is populated. Cold
start (store empty pre-first-refresh) falls back to the legacy on-the-fly
reference build, so character suggestions work immediately post-deploy and the
background refresh populates the store within ~15 min. Match math + grounding
are unchanged; existing tests exercise the legacy fallback, and a new test
covers matching from the populated prototype store.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

backend/app/services/ml/ccip.py

@@ -16,7 +16,14 @@ the hands-on eval. numpy is imported lazily (API worker has it via pgvector).
 from sqlalchemy import func, select
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from ...models import ImageRegion, MLSettings, Tag, TagKind
+from ...models import (
+    CcipPrototypeState,
+    CharacterPrototype,
+    ImageRegion,
+    MLSettings,
+    Tag,
+    TagKind,
+)
 from ...models.tag import image_tag
 
 # Cosine-similarity floor to call a figure the same character. The live setting
@@ -148,6 +155,60 @@ async def _tag_names(session: AsyncSession, tag_ids: list[int]) -> dict[int, str
     )
 
 
+# Per-character normalized prototype matrices, cached per process and refreshed
+# INCREMENTALLY: only characters whose ccip_prototype_state.updated_at advanced
+# are reloaded. This replaces the request-path rebuild of the ENTIRE reference
+# blob (the ~4s stall, #1317) — the prototypes are precomputed off the request
+# path by services.ml.character_prototypes (a beat + after each retrain).
+_PROTO_CACHE: dict = {"mats": {}, "ver": {}}
+
+
+async def _load_prototypes(session: AsyncSession) -> dict:
+    """{tag_id: (P, D) L2-normalized prototype matrix} from character_prototype,
+    served from the in-process cache and reloading ONLY the characters whose
+    updated_at changed. Empty dict when the store isn't populated yet (cold start
+    → match_image falls back to the legacy on-the-fly reference build)."""
+    import numpy as np
+
+    versions = dict(
+        (
+            await session.execute(
+                select(CcipPrototypeState.tag_id, CcipPrototypeState.updated_at)
+            )
+        ).all()
+    )
+    mats = _PROTO_CACHE["mats"]
+    ver = _PROTO_CACHE["ver"]
+    # Forget characters that no longer have prototypes.
+    for tag_id in [t for t in mats if t not in versions]:
+        mats.pop(tag_id, None)
+        ver.pop(tag_id, None)
+    # Reload only the characters whose prototypes changed since we cached them.
+    stale = [t for t, u in versions.items() if ver.get(t) != u]
+    if stale:
+        rows = (
+            await session.execute(
+                select(
+                    CharacterPrototype.tag_id, CharacterPrototype.ccip_embedding
+                ).where(CharacterPrototype.tag_id.in_(stale))
+            )
+        ).all()
+        by_tag: dict[int, list] = {}
+        for tag_id, vec in rows:
+            by_tag.setdefault(tag_id, []).append(
+                np.asarray(vec, dtype=np.float32)
+            )
+        for tag_id in stale:
+            vecs = by_tag.get(tag_id)
+            if vecs:
+                mats[tag_id] = _l2norm(np.vstack(vecs), np)
+                ver[tag_id] = versions[tag_id]
+            else:
+                mats.pop(tag_id, None)
+                ver.pop(tag_id, None)
+    return mats
+
+
 async def match_image(
     session: AsyncSession, image_id: int, threshold: float | None = None
 ) -> list[dict]:
@@ -178,7 +239,13 @@ async def match_image(
     ).all()
     if not fig_rows:
         return []
-    refs = await character_references(session)
+    # Prefer the precomputed prototype store (fast, incremental). On a cold start
+    # (store not yet populated post-deploy) fall back to the legacy on-the-fly
+    # reference build so character suggestions work immediately — the background
+    # refresh populates the store within ~15 min, after which this path is used
+    # and the per-accept ~4s rebuild is gone (#1317).
+    protos = await _load_prototypes(session)
+    refs = protos if protos else await character_references(session)
     if not refs:
         return []
     applied = set(
@@ -202,7 +269,11 @@ async def match_image(
     for tag_id, vecs in refs.items():
         if tag_id in applied:
             continue
-        R = _l2norm(np.vstack([np.asarray(v, dtype=np.float32) for v in vecs]), np)
+        # Prototype matrices are already L2-normalized; legacy refs are raw
+        # vector lists that still need stacking + normalizing.
+        R = vecs if protos else _l2norm(
+            np.vstack([np.asarray(v, dtype=np.float32) for v in vecs]), np
+        )
         sims = Q @ R.T                       # (n_query_figures, n_references)
         per_figure = sims.max(axis=1)        # best reference cosine per figure
         best_figure = int(per_figure.argmax())