[mcp] Regression: oauthScopes still dropped from OAuth authorization request on 2.26.0

## Observed symptom Regression: `oauthScopes` still dropped from the OAuth authorization request on 2.26.0 (optional scope absent, tool calls 403) — reopens #8760 / #9123 after the CLI 2.12.0 scope-forwarding fix Before opening, please confirm: - [x] I have [searched for duplicate or closed issues](https://github.com/kirodotdev/Kiro/issues?q=is%3Aissue+) ## Literal error text ``` 403 insufficient_scope ``` ## Version info 2.26.0 ## Environment GitHub issue kirodotdev/Kiro #11700; state=OPEN ## Trigger / context Public GitHub report in kirodotdev/Kiro (FRESH_7D). ## Source evidence - https://github.com/kirodotdev/Kiro/issues/11700 (2026-10-01T19:56:18Z) — evidence_class: PRIMARY_ISSUE_REPORT — GitHub issue #11700 (OPEN) ## Freshness - classification: FRESH_7D - retrieved_at: 2026-10-02T09:33:42Z - scout_id: Cea069a7441 ## 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.