Bug: MCP stdio client doesn't propagate parent env to server subprocess #18

New issue

Closed

opened 2026-04-08 21:12:52 +00:00 by claude-code · 0 comments

claude-code commented

2026-04-08 21:12:52 +00:00

Collaborator

Discovered during M2.3 smoke test.

cli/main.py spawns the web researcher MCP server via StdioServerParameters. By default the mcp SDK does not pass the parent process's environment to the child, so env vars like MARCHWARDEN_MODEL set on the CLI process were silently lost.

Workaround already shipped on chore/smoke-test-1: pass env=os.environ.copy() to StdioServerParameters. This unblocks the smoke test but should be reviewed — copying the full env may be too broad. A future fix could whitelist MARCHWARDEN_* plus any keys the server actually reads.

Discovered during M2.3 smoke test. `cli/main.py` spawns the web researcher MCP server via `StdioServerParameters`. By default the `mcp` SDK does not pass the parent process's environment to the child, so env vars like `MARCHWARDEN_MODEL` set on the CLI process were silently lost. **Workaround already shipped on `chore/smoke-test-1`:** pass `env=os.environ.copy()` to `StdioServerParameters`. This unblocks the smoke test but should be reviewed — copying the full env may be too broad. A future fix could whitelist `MARCHWARDEN_*` plus any keys the server actually reads.