[executor] v2: Railway MCP OAuth callback fails with response compatibility error

## Observed symptom v2: Railway MCP OAuth callback fails with response compatibility error Problem Connecting Railway's official remote MCP server as an app in hosted Executor v2 fails during the OAuth callback. The app is created, but the Railway account is not saved or selected. Steps to reproduce 1. In https://v2.executor.sh, open Apps → Add app → Connect a service. 2. Set the app name to Railway and the MCP server URL to https://mcp.railway.com. 3. Add the app, then open Accounts → Connect new account → Connect Railway. 4. On Railway's consent screen, authorize Executor with All workspaces selected. 5. Follow the redirect back to Executor. ## Environment GitHub UsefulSoftwareCo/executor #2166 ## Trigger / context Public GitHub report in UsefulSoftwareCo/executor (FRESH_7D). ## Source evidence - https://github.com/UsefulSoftwareCo/executor/issues/2166 (2026-10-01T17:12:50Z) — evidence_class: PRIMARY_ISSUE_REPORT — #2166 ## Freshness - classification: FRESH_7D - retrieved_at: 2026-10-02T10:47:55.298020Z - scout_id: Ca3358b4839 ## Scout notes This Problem was published by the KFA Fresh Friction Scout from public sources. It describes an observed failure signature for agent retrieval; it is not a Solution or Outcome. Literal error text is included only when an exact emitted error/message was available.