Multiple initialize calls per conversation breaks Mcp-Session-Id linking #458
Description
Summary
initialize is being called multiple times within a single conversation, resulting in multiple Mcp-Session-Id values. My server relies on Mcp-Session-Id to link requests together (per the spec), and this was working ~3 days ago — but something changed and now it's broken.
What I'm seeing
sequenceDiagram
participant Host as Host (Claude Desktop)
participant Server as MCP Server
Note over Host,Server: Before conversation starts
Host->>Server: POST initialize
Server-->>Host: Mcp-Session-Id: aaa-111
Host->>Server: POST resources/read<br/>Mcp-Session-Id: aaa-111
Server-->>Host: HTML (app UI)
Host->>Server: POST tools/call (discover_run)<br/>Mcp-Session-Id: aaa-111
Server-->>Host: { runId: null } (no run yet, expected)
Note over Host,Server: User types prompt...
Note over Host,Server: Second initialize — unexpected!
Host->>Server: POST initialize
Server-->>Host: Mcp-Session-Id: bbb-222
Host->>Server: POST tools/call (run_web_automation)<br/>Mcp-Session-Id: bbb-222
Note over Server: Stores run under bbb-222 ✅
Host->>Server: POST tools/call (discover_run)<br/>Mcp-Session-Id: aaa-111
Note over Server: Looks up aaa-111 → null ❌<br/>(run is under bbb-222)
My server stores a session→run mapping on run_web_automation, then the MCP App iframe calls discover_run to find that run. Because discover_run still uses the first session (aaa-111) but the run was stored under the second session (bbb-222), the lookup fails and the app can't show live status/screenshots.
What I'd expect
One initialize per conversation → one Mcp-Session-Id shared across model and app tool calls.
Happy to share server logs and more details if helpful.
Environment
- Host: Claude Desktop (latest)
- MCP Protocol Version: 2025-11-25
- Server: Custom Next.js MCP server (Streamable HTTP)
- MCP Apps SDK:
@modelcontextprotocol/ext-apps