Vibe Coding Background Agent

Vibe Coding Background Agent

You build AI-powered background agents that observe developer workflow and proactively offer help without breaking flow state. You know the architectural stack: file watchers → event triage → action execution → permission gates → suggestion UX. The north star: the best background agent is one you forget is there until it saves you 10 minutes.

DECISION POINTS

Event Triage Matrix

IF event.type === 'file:saved' AND event.ext === '.ts'
  → run-typecheck (immediate, silent)
  
IF event.type === 'file:saved' AND isTestFile(event.path)
  → run-related-tests (immediate, silent)
  
IF event.type === 'build:error' AND confidence > 0.8
  → suggest-fix (immediate, requires-approval)
  
IF event.type === 'build:error' AND confidence <= 0.8
  → queue-for-batch-analysis (background, silent)
  
IF event.type === 'git:branch-switch'
  → cancel-all-running + prefetch-context (immediate, silent)
  
IF event.type === 'deps:changed' AND has-lockfile
  → generate-types + security-scan (background, notify)

Permission Decision Tree

Action has side effects?
├─ NO → silent execution
│   └─ Examples: run-tests, typecheck, fetch-docs, lint-check
└─ YES → Check determinism
    ├─ Deterministic & reversible → notify-after
    │   └─ Examples: auto-format, generate-types
    └─ Non-deterministic OR irreversible → requires-approval
        └─ Examples: suggest-fix, auto-commit, npm-publish

Cost vs Confidence Matrix

                    CONFIDENCE
           Low (<0.6)        High (>0.8)
Cost  Low  | queue-batch   | execute-immediate  |
      High | require-human | execute-with-notify |

Suggestion Timing

IF keystroke-rate > 60/min → queue-suggestions
IF idle-time > 5s AND queue-length > 0 → flush-queue
IF context-switch (file-open, branch-switch) → immediate-delivery
IF flow-state (typing-streak > 2min) → defer-non-critical

FAILURE MODES

Race Condition Cascade

• Symptoms: Multiple actions running on same file, conflicting outputs, test flake
• Detection Rule: If 2+ actions with same dedupeKey within 1s, you've hit this
• Fix: Implement proper debouncing with awaitWriteFinish: {stabilityThreshold: 200}

Permission Creep

• Symptoms: Agent asking approval for everything OR doing dangerous things silently
• Detection Rule: If approval-rate > 40% OR any git/deploy commands in silent-list, you've hit this
• Fix: Review permission policy, move destructive actions to blocked-list

LLM Cost Explosion

• Symptoms: Monthly bill > $100, agent slower than human, constant API rate limits
• Detection Rule: If LLM-calls-per-hour > 50 OR cost-per-session > $2, you've hit this
• Fix: Add deterministic rules for 80% of events, hard budget caps with kill-switch

UI Notification Spam

• Symptoms: Developer ignoring all suggestions, dismissal rate > 80%, complaints about interruptions
• Detection Rule: If visible-notifications > 3 OR dismissal-rate > 70%, you've hit this
• Fix: Reduce to 1 visible notification, batch related items, respect flow-state

Stale Context Poisoning

• Symptoms: Suggestions for old file versions, fixes that don't apply, outdated test failures
• Detection Rule: If suggestion-age > 5min OR file-modified after suggestion-created, you've hit this
• Fix: TTL all suggestions (5min max), invalidate on file-change events

WORKED EXAMPLES

Example 1: Type Generation Pipeline

Scenario: Developer saves schema.prisma file with new User model

Event Flow:

1. File watcher detects prisma extension → deterministic rule match
2. Action: generate-types (background, notify-after permission)
3. Execute: npx prisma generate with 30s timeout
4. Success → show toast: "Types generated for User model"
5. Background: queue run-typecheck to validate generated types
6. If typecheck fails → promote to approval-required suggestion with diff

Novice Miss: Would run full test suite, not just type generation Expert Catch: Chains related actions (generate → validate) with proper permission escalation

Example 2: Test Failure Auto-Triage

Scenario: Developer saves auth.ts, 3 tests fail in auth.test.ts

Decision Process:

1. Event: file:saved + test:failed within 2s window
2. Confidence analysis:
   • Test failures contain line numbers from saved file → confidence = 0.9
   • Error messages mention recently changed function → confidence = 0.95
3. High confidence → immediate notification tier
4. Show persistent toast: "3 auth tests failed - likely caused by recent changes"
5. Include 1-click action: "Show diff + suggested fixes"

Trade-offs Navigated:

• Could run auto-fix (faster) vs suggest-fix (safer) → chose safer due to test failures
• Could show all 3 failures vs batched summary → chose batched to avoid noise
• Could interrupt immediately vs wait for pause → waited 5s for natural pause

Example 3: Background Context Prefetch

Scenario: Developer switches to feature/payments branch

Agent Response:

1. Git hook fires: post-checkout event
2. Cancel all running actions (old context invalid)
3. Background tasks (silent execution):
   • Fetch README and recent commits for branch context
   • Index new/changed files for semantic search
   • Pre-warm relevant documentation (Stripe API docs based on import analysis)
4. Status bar update: "Context ready for payments feature"
5. If indexing finds potential issues (missing env vars) → queue for next pause

Context Switch Intelligence:

• Read-only checkout (git log, file browsing) → minimal activity
• Checkout + immediate editing → full context preparation
• Branch age > 7 days → extra security/dependency scanning

QUALITY GATES

• Debouncing configured: File watcher uses awaitWriteFinish with 200ms stability threshold
• Exclusions in place: node_modules, .git, dist, build directories excluded from watching
• Permission model explicit: Every action categorized as silent/notify/approval/blocked
• LLM budget enforced: Hard cap at 50 calls/hour with visible spend tracking
• Suggestion TTL active: All suggestions expire after 5 minutes or file modification
• Flow state detection: Agent queues notifications during active typing (>60 keystrokes/min)
• Related-only execution: Tests run only for files that import/are imported by changed file
• Graceful cancellation: Branch switch or manual cancel kills all background processes
• Max 3 visible: Notification UI limits to 3 concurrent items to prevent banner blindness
• Engagement tracking: Agent logs acceptance/dismissal rates for automatic tuning

NOT-FOR BOUNDARIES

This skill is NOT for:

• Chat-based AI where user explicitly asks questions → use prompt-engineer instead
• System daemon deployment with launchd/systemd → use daemon-development instead
• Real-time collaborative editing sessions → use cooperative-vibe-coding instead
• Job queue infrastructure like BullMQ or Celery → use background-job-orchestrator instead
• Long-running batch processing (>10 min) → use workflow-orchestration instead
• Security-critical operations requiring audit trails → use secure-automation instead

Delegate to other skills when:

• Agent needs to persist state across machine restarts → use daemon-development
• Multiple agents need coordination and conflict resolution → use multi-agent-coordination
• Background work involves human approval workflows → use human-in-loop-automation
• Performance monitoring and alerting required → use observability-implementation