fix(mcp): retry AgentGateway route reconciliation

[sriaradhyula]

Description

Saved MCP servers are registered with AgentGateway asynchronously. A tool test can run before the new Gateway route is installed and receive a transient HTTP 404 even though the server was saved successfully.

Retry MCP initialization only when an AgentGateway-managed endpoint returns 404, using bounded backoff. Other HTTP failures, including authorization and upstream errors, continue to fail immediately.

This is the upstream-compatible product fix adapted from cisco-eti/ai-platform-engineering-mirror#473. Fork-specific live regression infrastructure is intentionally excluded.

Type of Change

• Bugfix
• New Feature
• Breaking Change
• Refactor
• Documentation
• Other (please describe)

Pre-release Helm Charts (Optional)

No chart changes.

Checklist

• I have read the contributing guidelines
• Existing issues have been referenced (where applicable)
• I have verified this change is not present in other open pull requests
• Functionality is documented in code
• All code style checks pass
• New code contribution is covered by automated tests
• All new and existing relevant tests pass

Validation

• npm test -- --runInBand src/app/api/mcp-servers/test-tool/__tests__/route.test.ts (5/5)
• npx tsc --noEmit
• npm run lint
• npm run build
• git diff --check