[fix] Add bounded exponential backoff and jitter to controller queue retries

[kangeunchan]

Enhancement Description

Introduce exponential backoff with jitter and retry limits to prevent controller tight failure loops and CPU/log exhaustion.

Background

Failed operations are immediately re-queued, creating tight loops that can consume CPU, spam logs, and hide the root cause. Retry policies need backoff, jitter, and limits.

Scope

Implement exponential backoff with jitter

• Files: internal/daemon/controller/queue.go
• Files: internal/daemon/controller/manager.go

Backoff policy

• 1s, 2s, 4s, 8s, 16s, 32s, max 60s
• Add jitter to avoid thundering herd
• Enforce max retry count
• Mark permanent failures clearly (no further retries)

Improve observability

• Log retry count and next delay
• Log terminal failure state with context

Non-Goals

• Redesigning the controller architecture or queue model
• Changing business logic of controller tasks beyond retry behavior
• Implementing distributed scheduling

Risks and Open Questions

• Must avoid delaying truly transient errors too much; tune backoff carefully
• Ensure backoff does not break time-sensitive operations
• Confirm behavior under concurrent task loads

Validation Plan

Unit and Integration Checks

• go test ./... for controller packages
• Unit tests for backoff computation (including jitter bounds)
• Tests for max retry enforcement and terminal failure behavior

End-to-End Checks

• Run daemon with induced failure and verify CPU remains stable
• Confirm logs show retry scheduling and terminal failures properly

Evidence Required in Issue Updates

• Before/after CPU/log excerpts under induced failure
• Example log lines showing retry delay and attempt count
• Test output verifying backoff schedule and max retries

Acceptance Criteria

• Failed operations retry with backoff and jitter
• Max retry count is enforced
• CPU usage during failure scenarios remains low (target <5% sustained)
• Logs are informative and not spammy
• Terminal failures stop retrying and are clearly marked

Deliverables

• PR implementing backoff + tests
• Notes describing chosen parameters and any config knobs (if added)

[kangeunchan]

pull request: #128