MCP client 收到 -32600 Unknown session id 后不自动 reinitialize，重试仍原样重发旧 session id（Streamable HTTP，server 重启后）

What version of Kimi Code is running?

0.30.0（0.29.x 同现）

Which open platform/subscription were you using?

Kimi Code（managed:kimi-code，OAuth 登录）

Which model were you using?

kimi-code/k3-256k

What platform is your computer?

Microsoft Windows NT 10.0.26200.0 x64

What issue are you seeing?

Streamable HTTP 的 MCP server 重启后，server 端 session 失效，对后续每个请求返回 -32600 Unknown session id（错误文案即协议原文 "client should reinitialize"）。kimi-code client 不发起新的 initialize 握手，而是把同一个已失效的 session id 原样重发——实测连续 6 个请求（JSON-RPC id 72–77，跨度约 21 分钟）全部携带同一失效 session id，无一自愈。此后所有 MCP 调用持续失败，直到用户手动 /mcp 重连。

0.29.0 changelog 的 "Reconnect a dropped MCP server connection automatically when one of its tools is called, and retry the call once" 只覆盖传输层掉线；本 case 中 TCP/HTTP 层始终正常——server 返回了结构化的 JSON-RPC 错误响应，是应用层 session 失效，不在现有重连逻辑的触发条件内。

session wire 日志原始帧（已裁剪无关字段并脱敏；session id 为 server 端已失效的随机 hex）：

{"jsonrpc": "2.0", "id": 72, "error": {"code": -32600, "message": "Unknown session id '0fbc7f3f46a19394ee69ba83d4a726ab' for 'tools/call'; client should reinitialize"}}
{"jsonrpc": "2.0", "id": 73, "error": {"code": -32600, "message": "Unknown session id '0fbc7f3f46a19394ee69ba83d4a726ab' for 'tools/call'; client should reinitialize"}}
{"jsonrpc": "2.0", "id": 74, "error": {"code": -32600, "message": "Unknown session id '0fbc7f3f46a19394ee69ba83d4a726ab' for 'tools/call'; client should reinitialize"}}
{"jsonrpc": "2.0", "id": 75, "error": {"code": -32600, "message": "Unknown session id '0fbc7f3f46a19394ee69ba83d4a726ab' for 'tools/call'; client should reinitialize"}}
{"jsonrpc": "2.0", "id": 76, "error": {"code": -32600, "message": "Unknown session id '0fbc7f3f46a19394ee69ba83d4a726ab' for 'tools/call'; client should reinitialize"}}
{"jsonrpc": "2.0", "id": 77, "error": {"code": -32600, "message": "Unknown session id '0fbc7f3f46a19394ee69ba83d4a726ab' for 'tools/call'; client should reinitialize"}}

对应本地时间戳（epoch ms）：1785336079817 → 1785337347072，跨度约 21 分钟。client 侧工具报错原文：

Tool "mcp__unreal-mcp__call_tool" failed: Streamable HTTP error: Error POSTing to endpoint: {
        "jsonrpc": "2.0",
        "id": 72,
        "error":
        {
                "code": -32600,
                "message": "Unknown session id '0fbc7f3f46a19394ee69ba83d4a726ab' for 'tools/call'; client should reinitialize"
        }
}

What steps can reproduce the bug?

1. mcp.json 配置一个 HTTP（Streamable HTTP）MCP server（本例：Unreal Engine 5.8 编辑器内置的 Epic MCP server，http://127.0.0.1:8001/mcp；任何会随进程重启而清空 session 的 Streamable HTTP server 均应可复现）。
2. 正常调用若干工具——此时 client 持有 server 下发的 session id。
3. 重启 server 进程（server 端 session 全部失效）。
4. 再调用任意工具 → 必现 -32600，且重试不重新 initialize。

session id：da55c814-2250-4791-9e77-ffcefa3b8942（事发会话；context usage 当时未记录）。

What is the expected behavior?

client 识别 -32600 Unknown session id（或server 端明确表示 session 失效的 JSON-RPC 错误）为 session 失效信号 → 自动重发 initialize 握手获取新 session id → 重放原调用一次。至少应把「需要 /mcp 手动重连」作为显式错误提示透出，而不是静默重发同一旧 id。

Additional information

• 影响：无人值守自动化（定时心跳 + MCP 工具调用的 agent loop）在 server 重启后永久卡死且无法自愈，必须人工介入。MCP server 长驻进程重启是常态事件（编辑器重启、崩溃恢复、版本升级），该缺口使 HTTP 传输的 MCP 集成无法用于无人值守场景。
• Related：#2109 — stdio 侧同类重连缺口（server 进程意外死亡后不自动重连、调用挂起至 toolTimeoutMs）；两条一起修可补齐完整的 MCP 重连矩阵（stdio 进程死亡 / HTTP session 失效）。#1942 — Streamable HTTP 启动超时（同传输、不同问题）。

Start with the mcp.json Streamable HTTP configuration and reproduce the failure against a restarted server at /mcp, then trace the MCP client's request and retry path. Done means recognizing the -32600 unknown-session response, reinitializing to obtain a new session id, and retrying the original call once; if that is unsupported, expose an explicit reconnect error instead of resending the stale id.