fix: include DB artifact cache in invalidateAllCaches (#793)

Cherry-picked from #797 — adds clearArtifacts() to gsd-db.ts and wires
it into invalidateAllCaches() so the DB artifact table is cleared
alongside state/path/parse caches.

Co-Authored-By: 0xLeathery (PR #797)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/resources/extensions/gsd/cache.ts

@@ -12,16 +12,18 @@
 import { invalidateStateCache } from './state.js';
 import { clearPathCache } from './paths.js';
 import { clearParseCache } from './files.js';
+import { clearArtifacts } from './gsd-db.js';
 
 /**
  * Invalidate all GSD runtime caches in one call.
  *
  * Call this after file writes, milestone transitions, merge reconciliation,
  * or any operation that changes .gsd/ contents on disk. Forgetting to clear
- * any single cache causes stale reads (see #431).
+ * any single cache causes stale reads (see #431, #793).
  */
 export function invalidateAllCaches(): void {
   invalidateStateCache();
   clearPathCache();
   clearParseCache();
+  clearArtifacts();
 }

src/resources/extensions/gsd/gsd-db.ts

@@ -790,6 +790,21 @@ export function upsertRequirement(r: Requirement): void {
 /**
  * Insert or replace an artifact. Uses the `path` PK for idempotency.
  */
+/**
+ * Delete all rows from the artifacts table.
+ * The artifacts table is a read cache — clearing it forces the next
+ * deriveState() to fall through to disk reads (native Rust batch parse).
+ * Safe to call when no database is open (no-op).
+ */
+export function clearArtifacts(): void {
+  if (!currentDb) return;
+  try {
+    currentDb.exec('DELETE FROM artifacts');
+  } catch {
+    // Clearing a cache should never be fatal
+  }
+}
+
 export function insertArtifact(a: {
   path: string;
   artifact_type: string;