fix(R7/R9): overlap-density ranking + project trust-preservation

R7: ranking scorer now uses overlap-density (overlap_count /
memory_token_count) as primary key instead of raw overlap count.
A 5-token memory with 3 overlapping tokens (density 0.6) now beats
a 40-token overview memory with 3 overlapping tokens (density 0.075)
at the same absolute count. Secondary: absolute overlap. Tertiary:
confidence. Targeting p06-firmware-interface harness fixture.

R9: when the LLM extractor returns a project that differs from the
interaction's known project, it now checks the project registry.
If the model's project is a registered canonical ID, trust it. If
not (hallucinated name), fall back to the interaction's project.
Uses load_project_registry() for the check. The host-side script
mirrors this via an API call to GET /projects at startup.

Two new tests: test_parser_keeps_registered_model_project and
test_parser_rejects_hallucinated_project.

Test count: 280 -> 281.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/atocore/memory/service.py

@@ -446,20 +446,27 @@ def _rank_memories_for_query(
 ) -> list["Memory"]:
     """Rerank a memory list by lexical overlap with a pre-tokenized query.
 
-    Ordering key: (overlap_count DESC, confidence DESC). When a query
-    shares no tokens with a memory, overlap is zero and confidence
-    acts as the sole tiebreaker — which matches the pre-query
-    behaviour and keeps no-query calls stable.
+    Primary key: overlap_density (overlap_count / memory_token_count),
+    which rewards short focused memories that match the query precisely
+    over long overview memories that incidentally share a few tokens.
+    Secondary: absolute overlap count. Tertiary: confidence.
+
+    R7 fix: previously overlap_count alone was the primary key, so a
+    40-token overview memory with 3 overlapping tokens tied a 5-token
+    memory with 3 overlapping tokens, and the overview won on
+    confidence. Now the short memory's density (0.6) beats the
+    overview's density (0.075).
     """
     from atocore.memory.reinforcement import _normalize, _tokenize
 
-    scored: list[tuple[int, float, Memory]] = []
+    scored: list[tuple[float, int, float, Memory]] = []
     for mem in memories:
         mem_tokens = _tokenize(_normalize(mem.content))
         overlap = len(mem_tokens & query_tokens) if mem_tokens else 0
-        scored.append((overlap, mem.confidence, mem))
-    scored.sort(key=lambda t: (t[0], t[1]), reverse=True)
-    return [mem for _, _, mem in scored]
+        density = overlap / len(mem_tokens) if mem_tokens else 0.0
+        scored.append((density, overlap, mem.confidence, mem))
+    scored.sort(key=lambda t: (t[0], t[1], t[2]), reverse=True)
+    return [mem for _, _, _, mem in scored]
 
 
 def _row_to_memory(row) -> Memory: