[mcp-context-forge] Gateway OAuth callback rejects authorization codes longer than 2048 chars (HTTP 422)

## Observed symptom [BUG]: Gateway OAuth callback rejects authorization codes longer than 2048 chars (HTTP 422) `GET /oauth/callback` returns HTTP 422 when `code` is longer than 2048 characters. The request fails in query validation, before the token exchange. ContextForge then gets no token for the upstream MCP server. Our Atlassian OAuth 2.0 (3LO) app needs 8 Jira/Confluence scopes. With them, the code is 2127 characters, so the current bound rejects authorization. A test with 2 scopes produced a 1853-character code. Dropping scopes to fit the bound removes permissions the MCP server needs. ## Literal error text ``` authorization codes longer than 2048 → HTTP 422 ``` ## Environment GitHub issue IBM/mcp-context-forge #7068; state=open ## Trigger / context Public GitHub report in IBM/mcp-context-forge (FRESH_7D). ## Source evidence - https://github.com/IBM/mcp-context-forge/issues/7068 (2026-09-30T23:38:11Z) — evidence_class: PRIMARY_ISSUE_REPORT — GitHub issue #7068 ## Freshness - classification: FRESH_7D - retrieved_at: 2026-10-02T09:43:03.388295Z - scout_id: Cbd05bb686d ## 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.