feat(clients): LRU mesh cache for Open3DModel recipes (etag-validated)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/presa_mano/clients/open3dmodel_cache.py

@@ -0,0 +1,45 @@
+"""In-memory LRU cache of parsed STL meshes, keyed by recipe_id + etag."""
+from __future__ import annotations
+
+from collections import OrderedDict
+from dataclasses import dataclass
+
+import numpy as np
+
+from ..perception.stl_sampler import parse_stl_bytes
+from .open3dmodel import Open3DModelClient
+
+
+@dataclass(frozen=True)
+class RecipeMesh:
+    vertices: np.ndarray   # (M, 3) float64, mm in model frame
+    triangles: np.ndarray  # (T, 3) int32
+    etag: str
+
+
+class RecipeMeshCache:
+    """LRU keyed by recipe_id. On hit, validates the etag against the client
+    and re-fetches if it changed. Singleton-friendly: thread-safe with a
+    simple lock is NOT implemented (presa-mano is single-process; if
+    concurrency becomes a need, wrap the OrderedDict ops in a lock)."""
+
+    def __init__(self, client: Open3DModelClient, capacity: int = 8):
+        self._client = client
+        self._capacity = max(1, int(capacity))
+        self._store: OrderedDict[str, RecipeMesh] = OrderedDict()
+
+    def get(self, recipe_id: str, client: Open3DModelClient | None = None
+            ) -> RecipeMesh:
+        c = client or self._client
+        body, etag = c.get_stl_bytes(recipe_id)
+        cached = self._store.get(recipe_id)
+        if cached is not None and cached.etag == etag:
+            self._store.move_to_end(recipe_id)
+            return cached
+        verts, tris = parse_stl_bytes(body)
+        mesh = RecipeMesh(vertices=verts, triangles=tris, etag=etag)
+        self._store[recipe_id] = mesh
+        self._store.move_to_end(recipe_id)
+        while len(self._store) > self._capacity:
+            self._store.popitem(last=False)
+        return mesh