- DELETE /api/admin/users/{handle}/activities — deletes all activities/*.json, wipes _merged/ and

index.json, then triggers a rebuild. Admin-only.
  - /admin/ page — lists all users, each with a "Delete activities" button. Clicking asks for
  confirmation in a <dialog> before firing the request. Button shows "Deleted (N)" or an error inline.
  - "Admin" nav link — appears in the top-right for admins only, hidden for everyone else.

bincio/serve/server.py

@@ -437,6 +437,37 @@ async def admin_jobs(bincio_session: Optional[str] = Cookie(default=None)) -> JS
     return JSONResponse(jobs)
 
 
+@app.delete("/api/admin/users/{handle}/activities")
+async def admin_delete_activities(
+    handle: str,
+    bincio_session: Optional[str] = Cookie(default=None),
+) -> JSONResponse:
+    """Delete all activity JSON files for a user and wipe the merged cache."""
+    _require_admin(bincio_session)
+    user_dir = _get_data_dir() / handle
+    if not user_dir.is_dir():
+        raise HTTPException(404, f"No data directory for user '{handle}'")
+
+    deleted = 0
+    activities_dir = user_dir / "activities"
+    if activities_dir.is_dir():
+        for f in activities_dir.glob("*.json"):
+            f.unlink()
+            deleted += 1
+
+    # Wipe merged cache and top-level index so they don't show stale data
+    import shutil
+    merged_dir = user_dir / "_merged"
+    if merged_dir.exists():
+        shutil.rmtree(merged_dir)
+    index_file = user_dir / "index.json"
+    if index_file.exists():
+        index_file.unlink()
+
+    _trigger_rebuild(handle)
+    return JSONResponse({"ok": True, "deleted": deleted})
+
+
 # ── Write API (ported from bincio edit, auth-gated) ───────────────────────────
 
 def _user_data_dir(handle: str) -> Path: