test: add unit tests for hook/emit.go — event emission and rotation

[jpleva91]

Problem

internal/hook/emit.go has zero test coverage. emitEvent() writes governance events to a JSONL file and RotateEvents() rotates the file for ingestion by Sentinel. If these break, telemetry goes dark.

Acceptance Criteria

• Test emitEvent() appends valid JSON line to <workspace>/.chitin/events.jsonl
• Test emitEvent() creates the .chitin directory if missing
• Test emitEvent() is a no-op when CHITIN_WORKSPACE is empty
• Test detectAgent() returns correct agent name for CHITIN_AGENT, CLAUDE_HOOK_EVENT_NAME, COPILOT_HOOK_EVENT, and unknown
• Test truncate() truncates strings longer than max and passes through shorter strings
• Test RotateEvents() renames events.jsonl to a timestamped filename
• Test RotateEvents() returns empty string when no events file exists
• Test RotateEvents() returns empty string when CHITIN_WORKSPACE is empty
• All tests use t.TempDir() and t.Setenv()
• All tests pass with go test ./internal/hook/...

Hints

• File: internal/hook/emit.go
• Functions: emitEvent(), detectAgent(), truncate(), RotateEvents()
• emitEvent() is unexported — test via package-level test file in hook package
• Events file: <CHITIN_WORKSPACE>/.chitin/events.jsonl
• Create test file: internal/hook/emit_test.go

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[jpleva91]

🧠 Triage complete

Tier B — Needs Planning. Issue requires scoping and decomposition before implementation.

Reason: triage error (defaulting to safe): API returned 404: {"type":"error","error":{"type":"not_found_error","message":"model: claude-3-haiku-20241022"},"request_id":"req_011CZrvGMWN5MNquK5Yavxp4"}
Confidence: 0.00

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[jpleva91]

@claude Please implement this issue. Read the acceptance criteria carefully, check the source files mentioned in Hints, and create the test file. Run go test to verify all tests pass before finishing.

[jpleva91]

Test coverage for hook/emit.go event emission; low complexity, safe to automate.

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