feat: cross-process cache invalidation via signal file for reuse_port multi-process

ahserver/hotreload.py

@@ -7,9 +7,15 @@ Watches file mtimes and triggers reload of cached resources:
 - Jinja2 template cache (auto_reload already handles this)
 
 Module caches (rbac/pricing/uapi/llmage) can be cleared via:
-- HTTP endpoint: GET /__hot_reload__
+- HTTP endpoint: GET /__hot_reload__ (triggers all workers via signal file)
 - Automatic when config.json changes
 
+Cross-process cache invalidation (reuse_port multi-process):
+- GET /__hot_reload__ writes to /tmp/.sage_cache_invalidate signal file
+- All workers detect signal file mtime change within their check interval
+- Each worker independently clears its own caches
+- No cross-process IPC or Redis needed
+
 Multi-process safe: each process independently checks mtimes via stat(),
 no cross-process coordination needed. When a file changes on disk,
 all processes detect it on their next check cycle.
@@ -64,6 +70,9 @@ class FileWatcher:
         return changed
 
 
+SIGNAL_FILE = '/tmp/.sage_cache_invalidate'
+
+
 class HotReloader:
     """Hot-reload cached resources when source files change.
     
@@ -78,6 +87,11 @@ class HotReloader:
         self._i18n_paths = i18n_paths or []
         self._last_check = 0
         self._interval = 2  # seconds between checks
+        # Record current signal file mtime to avoid false trigger on startup
+        try:
+            self._last_signal_mtime = os.path.getmtime(SIGNAL_FILE)
+        except OSError:
+            self._last_signal_mtime = 0
 
     def set_interval(self, interval):
         self._interval = interval
@@ -89,11 +103,22 @@ class HotReloader:
         self._last_check = now
         return True
 
+    def _check_signal_file(self):
+        """Check if cache invalidation signal file was updated."""
+        try:
+            mtime = os.path.getmtime(SIGNAL_FILE)
+            if mtime > self._last_signal_mtime:
+                self._last_signal_mtime = mtime
+                return True
+        except OSError:
+            pass
+        return False
+
     def check_and_reload(self):
         """Check for file changes and reload if needed.
         
         Returns:
-            dict with keys 'config', 'i18n' indicating what was reloaded
+            dict with keys 'config', 'i18n', 'signal' indicating what was reloaded
         """
         if not self._should_check():
             return {}
@@ -113,6 +138,11 @@ class HotReloader:
                 self._reload_i18n()
                 reloaded['i18n'] = True
 
+        # Check signal file (cross-process cache invalidation)
+        if self._check_signal_file():
+            invalidate_all_caches()
+            reloaded['signal'] = True
+
         return reloaded
 
     def _reload_config(self):
@@ -233,16 +263,25 @@ def invalidate_all_caches():
 async def hot_reload_handler(request):
     """HTTP endpoint handler for GET /__hot_reload__.
     
-    Manually triggers cache invalidation. Useful for development
-    when database changes aren't detected automatically.
+    Triggers cache invalidation across all workers via signal file.
+    Each worker detects the signal file change within its check interval
+    and clears its own caches.
     
-    Returns JSON with list of cleared caches.
+    Returns JSON with confirmation that signal was sent.
     """
     from aiohttp import web
+    
+    # Write signal file - all workers will detect this
+    with open(SIGNAL_FILE, 'w') as f:
+        f.write(str(time.time()))
+    
+    # Also clear current worker's cache immediately
     cleared = invalidate_all_caches()
+    
     return web.json_response({
         'status': 'ok',
         'cleared': cleared,
+        'message': 'Signal sent to all workers',
         'timestamp': time.time()
     })