Stabilize Smoke Goose startup: correct model-proxy auth selection and gate MCP extension init on gateway readiness

[Copilot]

Smoke Goose was failing after engine startup due to two independent runtime faults: invalid credentials being sent to the model proxy (401/404 depending on endpoint) and deterministic MCP extension boot failures from early connection attempts to the local gateway.

• What changed

  • Model-proxy credential routing
    • Tightened Goose auth wiring so OpenAI-shaped credentials are selected for the model proxy path, preventing GitHub PAT/installation token leakage into proxy auth headers.
    • Normalized proxy endpoint handling to avoid fallback to mismatched proxy ports that surfaced as 404 Resource not found.
  • MCP gateway startup sequencing
    • Added readiness gating between gateway startup and Goose extension registration.
    • Extension initialization for safeoutputs and github now waits for /mcp/* availability instead of racing startup and failing with connection-refused.
  • Failure-mode hardening
    • Improved startup-path error handling for auth and gateway bootstrap so transient sequencing issues do not permanently poison engine initialization.

• Illustrative snippet

// Pseudocode of the startup sequencing change
gateway.Start(ctx)
if err := gateway.WaitReady(ctx, mcpEndpoints); err != nil {
    return fmt.Errorf("mcp gateway not ready: %w", err)
}

modelKey := resolveModelProxyKey(cfg) // prefers OpenAI-shaped key for proxy path
gooseClient := newGooseClient(proxyURL, modelKey)

initExtension("safeoutputs")
initExtension("github")

• Fixes [deep-report] Smoke Goose: model-proxy auth failing (401/404) + MCP gateway unreachable — new failure mode #50589

[github-actions]

PR Triage: #50660

Category: bug | Risk: medium | Priority Score: 60/100 (impact 30, urgency 15, quality 15)
Recommended action: defer
Body/diff not populated in API response at triage time — recommend manual re-check before action.

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