Deep Agents Code now expands `${VAR}` and `${VAR:-default}` references
in `.mcp.json` server commands, arguments, environment values, URLs, and
headers.
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Users who share `.mcp.json` files currently have to hard-code
machine-specific paths and credentials outside remote headers. This
makes otherwise portable MCP configuration fail for stdio servers and
remote URLs.
This resolves `${VAR}` and `${VAR:-default}` in `command`, `args`,
`env`, `url`, and `headers` when each server activates. Missing or
malformed references report the exact config field and disable only the
affected server. OAuth login follows the same behavior.
Expansion remains behind the existing project MCP trust checks, so
unapproved project configuration cannot read environment values or
initiate connections.
Mason Daugherty