`--resume` silently drops local stdio and local-HTTP MCP servers; only external HTTPS survives

Summary

When resuming a Claude Code session with claude --resume '<session-name>', MCP servers defined in project-scoped .mcp.json that use stdio or local-HTTP transports are dropped — they don't appear in /mcp at all (not "disconnected" — UNKNOWN to Claude Code). Only external HTTPS MCP servers survive the resume. A fresh (non-resumed) session re-registers everything correctly.

Environment

• Claude Code version: 2.1.113 (Claude Code)
• Platform: macOS 26.4.1
• Shell: zsh

Reproduction

1. Create a .mcp.json with mixed server types (e.g., one HTTP external, two stdio local, one HTTP local).
2. Start Claude Code with your normal flags (e.g., claude ...), named via -n '<name>'.
3. Exit the session (/exit) and resume: claude --resume '<name>' ....
4. Run /mcp. Observe that only the external HTTPS server is listed.
5. Start a fresh (non-resumed) session with the same flags. Observe all servers listed correctly.

Expected behavior

All MCP servers declared in .mcp.json should be re-registered on --resume, identical to a fresh session.

Actual behavior

Only external HTTPS servers re-register. Stdio and local-HTTP MCP servers are silently missing from /mcp (not shown as disconnected — simply absent, as if they were never declared).

Verified today that the .mcp.json is syntactically valid (parses with both python -m json.tool and jq), all keys are structurally correct, and a fresh (non-resumed) session loads every server. Only the --resume path drops local servers. Reproduced multiple times.

Example .mcp.json (minimal, redacted)

{
  "mcpServers": {
    "external-http": {
      "type": "http",
      "url": "https://api.example.com/mcp/",
      "headers": {
        "Authorization": "Bearer <REDACTED>"
      }
    },
    "local-stdio-uvx": {
      "type": "stdio",
      "command": "uvx",
      "args": ["some-mcp-package"],
      "env": {
        "SERVICE_URL": "http://192.168.1.7:8080",
        "SERVICE_TOKEN": "<REDACTED>"
      }
    },
    "local-stdio-bun": {
      "command": "bun",
      "args": ["run", "/path/to/mcp-bridge.ts"]
    },
    "local-http": {
      "type": "http",
      "url": "http://127.0.0.1:8790/mcp",
      "headers": { "X-Custom-Header": "session-name" }
    }
  }
}

After --resume, /mcp shows only external-http. The three local entries (local-stdio-uvx, local-stdio-bun, local-http) are missing from the dialog entirely.

Possibly related (not duplicates)

• #33758 — --chrome flag ignored on resume. Similar symptom class (resume doesn't re-spawn local MCP), but scoped to the --chrome CLI flag rather than .mcp.json project-scoped servers.
• #48260 — MCP connection cache race condition on resume causing "Already connected to a transport" crash. Different failure mode (crash vs. silent drop).

Workaround

Start a fresh session (not --resume). This reconnects everything but loses conversation context.

Impact

Users who rely on --resume to preserve long-running conversation context lose their MCP tool surface silently after a resume. Debugging required comparing the /mcp list against .mcp.json line-by-line and confirming the JSON was valid. There is no log line, warning, or error that indicates the servers were dropped — they just aren't there.