Add bounded agent-step recovery retries

[viniciusdebruin]

Summary

• add a bounded outer recovery retry for transient agent-step failures
• cover network errors, idle timeouts, rate limits, and server 5xx responses
• preserve the same run/history while emitting recovery metadata and a recovery message
• skip retries for aborts, authentication failures, and client 4xx errors

Validation

• 156 focused runtime tests passing
• typecheck reaches unrelated pre-existing missing researcher imports in read-docs-tool.test.ts and web-search-tool.test.ts