feat(node): share the (path,size,mtime)->hash index cache across every group

An operator routinely shares the same physical folder into more than one
group (a music library, a Séries drive) — IndexCache used to be opened
once per group (data_dir/{group_id}/index_cache.db), so the second group
to reference an already-fully-hashed multi-terabyte folder paid the same
full content read the first one did. IndexCache itself carried no
group_id in its schema; only daemon.py's wiring did. Now one instance,
opened once at startup (data_dir/index_cache.db), shared by every group's
DirectoryIndexer.

Confirmed against a real deployment (2026-08-25/26): a group sharing an
already-indexed folder with an existing group indexes it instantly, with
zero rehashing.

Also fixes a related cross-group correctness gap found during this work:
media_cache.db (thumbnails, TMDB/MusicBrainz metadata — already node-wide,
untouched by this change) was pruned for a file the moment it left *one*
group's index, even if another group's index still held the same content
hash — forcing a redundant re-fetch/re-probe/re-thumbnail for a group that
never actually lost anything. Prune now runs only once no group's index
references the file_id any more.

Adds a node admin UI action ("Maintenance" card, prune-index-cache) to
drop cache rows that no longer belong to any group's roots — skips
anything under a root that is merely temporarily unavailable (indexer.py's
"a root that goes away freezes, never empties" rule extends to this
cache too, or a reconnected drive would pay a full rehash for no reason).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013XSohfUQQiaE77qyFLgSv3

1 files changed, 57 insertions, 2 deletions

diff --git a/packages/meshbay-node/src/meshbay_node/ui/app.py b/packages/meshbay-node/src/meshbay_node/ui/app.py
index 18764e8..3dc320b 100644
--- a/packages/meshbay-node/src/meshbay_node/ui/app.py
+++ b/packages/meshbay-node/src/meshbay_node/ui/app.py
@@ -169,6 +169,14 @@ def create_ui_app(state: dict) -> FastAPI:
     async def api_denylist_clear(subject: str = ""):
         return await _op(lambda: ops.clear_denylist(state, subject=subject))
 
+    @app.get("/api/index-cache")
+    async def api_index_cache_stats():
+        return await _op(lambda: ops.index_cache_stats(state))
+
+    @app.post("/api/index-cache/prune")
+    async def api_index_cache_prune():
+        return await _op(lambda: ops.prune_index_cache(state))
+
     @app.get("/api/groups/{group_id}/files")
     async def api_group_files(group_id: str):
         groups_ctx = state.get("groups_ctx", {})
@@ -458,7 +466,9 @@ def create_ui_app(state: dict) -> FastAPI:
                 "members": await roster.list_members(),
                 "invites": await roster.list_invites(),
             }
-        return _render_page(state, roster_view)
+        index_cache = state.get("index_cache")
+        cache_count = await index_cache.count() if index_cache else None
+        return _render_page(state, roster_view, cache_count)
 
     @app.get("/audit", response_class=HTMLResponse)
     async def audit_page():
@@ -540,7 +550,8 @@ def _render_roster(roster_view: dict | None) -> str:
     </p>"""
 
 
-def _render_page(state: dict, roster_view: dict | None = None) -> str:
+def _render_page(state: dict, roster_view: dict | None = None,
+                 index_cache_count: int | None = None) -> str:
     token_js = json.dumps(state.get("ui_token", ""))
     status = state.get("status", "starting")
     indexes = state.get("indexes", {})
@@ -723,6 +734,26 @@ def _render_page(state: dict, roster_view: dict | None = None) -> str:
     <p><b>Node ID:</b> <code>{state.get("endpoint_hint") or "—"}</code></p>
   </div>
 
+  <h2>Maintenance</h2>
+  <div class="card">
+    <p><b>Index cache:</b> <span id="cacheCount">{
+      index_cache_count if index_cache_count is not None else "—"
+    }</span> path(s) remembered (size/mtime → hash, shared by every group)</p>
+    <p class="muted">Removes rows whose path no longer belongs to any group's
+       root, or whose file is genuinely gone from a root that is currently
+       reachable. Never touches a root that is temporarily unavailable
+       (unplugged drive) — that one still needs its full cache back the
+       moment it returns.</p>
+    <div style="margin:10px 0">
+      <button onclick="pruneIndexCache()" id="prune-cache-btn"
+        style="padding:8px 16px;background:#3b82f6;color:#fff;border:none;
+        border-radius:6px;cursor:pointer;font-size:0.85em">
+        Prune stale entries
+      </button>
+      <span id="prune-cache-status" class="muted" style="margin-left:8px"></span>
+    </div>
+  </div>
+
   <h2>Link Node to Hub Account</h2>
   <div class="card">
     <p>To connect to your group from a browser, link this node to your hub account.
@@ -774,6 +805,30 @@ async function initGEK(groupId) {{
     if (btn) btn.disabled = false;
   }}
 }}
+async function pruneIndexCache() {{
+  const btn = document.getElementById('prune-cache-btn');
+  const status = document.getElementById('prune-cache-status');
+  if (btn) btn.disabled = true;
+  if (status) {{ status.textContent = 'Pruning...'; status.style.color = ''; }}
+  try {{
+    const resp = await fetch('/api/index-cache/prune?t=' + TOKEN, {{ method: 'POST' }});
+    const data = await resp.json();
+    if (resp.ok) {{
+      if (status) status.textContent = 'Removed ' + data.removed + ', kept ' + data.kept;
+      if (status) status.style.color = '#22c55e';
+      const count = document.getElementById('cacheCount');
+      if (count) count.textContent = data.kept;
+    }} else {{
+      if (status) status.textContent = data.error || 'Failed';
+      if (status) status.style.color = '#ef4444';
+    }}
+  }} catch (e) {{
+    if (status) status.textContent = 'Error: ' + e.message;
+    if (status) status.style.color = '#ef4444';
+  }} finally {{
+    if (btn) btn.disabled = false;
+  }}
+}}
 setTimeout(()=>location.reload(), 10000);
 </script>
 </body>