diff --git a/kb/diagram/assets/archcenter-refs-index.json b/kb/diagram/assets/archcenter-refs-index.json
index 3ec89f1..364e4f6 100644
--- a/kb/diagram/assets/archcenter-refs-index.json
+++ b/kb/diagram/assets/archcenter-refs-index.json
@@ -1,5 +1,5 @@
 {
-  "cache_dir_mtime": 1777161774.8360987,
+  "cache_dir_mtime": 1777171058.9167857,
   "entries": {
     "active-data-guard-far-sync-dba-oracle": {
       "drawio": "kb/diagram/assets/archcenter-refs/active-data-guard-far-sync-dba-oracle/active-data-guard-far-sync-dba.drawio",
diff --git a/tools/archcenter_description_fetcher.py b/tools/archcenter_description_fetcher.py
index cd96a0c..7f1f02c 100644
--- a/tools/archcenter_description_fetcher.py
+++ b/tools/archcenter_description_fetcher.py
@@ -169,6 +169,16 @@ def main() -> None:
         print(f"  {s:25s}  {n}", file=sys.stderr)
     print(f"\nReport: {args.report.relative_to(PROJECT_ROOT)}", file=sys.stderr)
 
+    # Bump CACHE_DIR mtime so archcenter_pattern_lookup invalidates its
+    # persisted JSON index — POSIX doesn't propagate child-file changes
+    # (e.g. new _description.md inside an existing slug) to the parent
+    # dir's mtime, so we touch it explicitly.
+    if counts.get("fetched"):
+        try:
+            CACHE_DIR.touch(exist_ok=True)
+        except OSError:
+            pass
+
 
 if __name__ == "__main__":
     main()
diff --git a/tools/archcenter_pattern_lookup.py b/tools/archcenter_pattern_lookup.py
index 1289b98..04bae0f 100644
--- a/tools/archcenter_pattern_lookup.py
+++ b/tools/archcenter_pattern_lookup.py
@@ -402,7 +402,15 @@ def main() -> None:
                         "before scoring (opt-in; requires "
                         "ANTHROPIC_API_KEY). Useful for natural-language "
                         "queries the synonym table doesn't cover.")
+    parser.add_argument("--rebuild-index", action="store_true",
+                        help="Force-rebuild the cached archcenter-refs "
+                        "index (kb/diagram/assets/archcenter-refs-index.json). "
+                        "Use after a manual KB edit if mtime didn't bump.")
     args = parser.parse_args()
+    if args.rebuild_index and CACHE_INDEX_FILE.exists():
+        CACHE_INDEX_FILE.unlink()
+        print(f"[lookup] removed stale index at {CACHE_INDEX_FILE.relative_to(PROJECT_ROOT)}",
+              file=sys.stderr)
 
     queries: list[str] = list(args.queries)
     if args.query:
diff --git a/tools/archcenter_zip_downloader.py b/tools/archcenter_zip_downloader.py
index 9915ce1..29caa32 100644
--- a/tools/archcenter_zip_downloader.py
+++ b/tools/archcenter_zip_downloader.py
@@ -211,6 +211,16 @@ def main() -> None:
         print(f"  {status:30s}  {n}", file=sys.stderr)
     print(f"\nReport: {args.report.relative_to(PROJECT_ROOT)}", file=sys.stderr)
 
+    # Bump cache-dir mtime so the pattern-lookup index invalidates.
+    # New downloads create new subdirs (POSIX bumps the parent mtime),
+    # but re-downloads or unzip-overwrites of existing slugs do not —
+    # so we touch explicitly.
+    if any(counts.get(k) for k in ("downloaded", "zip_error", "no_drawio_after_extract")):
+        try:
+            args.cache_dir.touch(exist_ok=True)
+        except OSError:
+            pass
+
 
 if __name__ == "__main__":
     main()