fix(trinity-core): return 404 for stale sessions after restart

When mcp-server restarts, activeSessions is cleared but Claude.ai may
still hold the old session ID. Previously this fell to a generic 400 error.
Now returns 404 with clear re-initialize message so clients know to
create a fresh session.

Chronicler #89

services/trinity-core/index.js

@@ -233,6 +233,14 @@ app.all('/mcp', auth, async (req, res) => {
       };
       const mcpServer = createMcpServer();
       await mcpServer.connect(transport);
+    } else if (sessionId && !activeSessions.has(sessionId)) {
+      // Stale session (e.g. after service restart) — tell client to re-initialize
+      log(`StreamableHTTP stale session ${sessionId} — returning 404`);
+      return res.status(404).json({
+        jsonrpc: '2.0',
+        error: { code: -32001, message: 'Session not found. Please re-initialize.' },
+        id: null
+      });
     } else if (!sessionId && req.method === 'GET') {
       // Legacy SSE client connecting via GET /mcp
       return legacySSE(req, res);