Require a token for writes and quarantine what nobody vouches for

Sixteen mutating routes now refuse a caller who cannot present the token the
server started with; queries stay open, because a question is not a write. The
environment variable is ELY_EYE_AUTH_TOKEN, following the repo's env_prefix
convention — the shorter name I reached for first returned 403 where the smoke
expected 401, and the server printed the reason.

Words from a stranger are quarantined on the way in: an HTTP upload is
third_party by definition, and a sentence carrying an instruction-shaped phrase
is quarantined whoever wrote it. A quarantined atom stays findable and stays out
of the compiled context until a second, live, unquarantined source agrees with
its rarest words. Corroboration is computed at read time because it is a
property of the corpus now, not of the moment a memory was written; it is
term-level, and the docstring says so.

forget now erases the source row and the compiled contexts beside the atoms, so
a forgotten memory leaves nothing that can still speak. The semantic cache key
carries a store revision, which fixes a real staleness: a context compiled
before new evidence arrived kept its old quarantine decision forever.

bench.audit --product still pointed at evals.py, which the p1-6 split moved into
backend/src/ely_eye/proofs/. It failed fast, but the anti-self-justification
rule had quietly stopped auditing the product; it now walks the package, and a
test pins that the package exists and holds no re-roll.

Gates: pytest 306 passed; ruff clean; mypy cold cache 24 errors in 9 files, the
recorded baseline, net zero; pyright 0 errors on the 23 backend files and the 2
bench files; go build/vet/test and gofmt clean; npm run build 221.39 kB with
eslint exit 0; bench/filesize_check clean; bench.audit --product clean over 31
harness files; scripts/mcp_write_smoke.sh PASS with the gate live across two
servers and the MCP child.

backend/src/ely_eye/cache_fabric.py

@@ -17,8 +17,9 @@ class CacheFabric:
         self.settings = settings or get_settings()
         self.db = database or Database(self.settings)
 
-    def semantic_key(self, question: str, profile: str) -> str:
-        return hashlib.sha256(f"compiler-v2\n{profile}\n{question}".encode()).hexdigest()
+    def semantic_key(self, question: str, profile: str, store_revision: int) -> str:
+        """A compiled context is only true for the corpus it was compiled from, so the corpus is part of its name."""
+        return hashlib.sha256(f"compiler-v2\n{profile}\n{store_revision}\n{question}".encode()).hexdigest()
 
     def record_hit(self, layer: str, cache_key: str, bytes_estimate: int = 0, metadata: dict[str, Any] | None = None) -> None:
         self.db.log_cache_event(layer, cache_key, "hit", bytes_estimate, metadata)
@@ -43,6 +44,16 @@ class CacheFabric:
         except (OSError, json.JSONDecodeError) as error:
             raise ValueError(f"{path}: the semantic cache entry is unreadable ({error})") from error
 
+    def drop_semantic_cache(self) -> int:
+        """Delete every compiled context: each one may quote a memory that no longer exists."""
+        directory = self.settings.cache_dir / "semantic"
+        if not directory.exists():
+            return 0
+        entries = list(directory.glob("*.json"))
+        for path in entries:
+            path.unlink()
+        return len(entries)
+
     def statuses(self) -> list[CacheLayerStatus]:
         rows = self.db.cache_layer_rows()
         statuses: list[CacheLayerStatus] = []