Retry stale serverless upstreams

[techulus-agent]

Summary

• evict stale serverless upstreams and retry safe requests once after fresh resolution
• limit retries to bodyless GET/HEAD requests and exclude protocol upgrades
• avoid retrying or evicting healthy cache when the client cancels
• bound retry resolution to prevent waiting for the full wake timeout

Validation

• go test ./... from agent/
• go test ./internal/serverless -count=10
• Smart review: approved