Fix Copilot CLI shutdown metric segmentation

[zhangzqs]

Summary

• apply Copilot CLI shutdown modelMetrics to each completed segment in a single events.jsonl instead of overwriting the whole file with the last shutdown snapshot
• keep a segment open when session.shutdown has no modelMetrics, so later valid shutdown totals still account for earlier turns
• add regression tests for multi-shutdown session files and empty-shutdown boundaries

Test Plan

• cargo fmt --all --quiet
• cargo build --quiet
• cargo test --quiet
• cargo clippy --quiet -- -D warnings
• cargo doc --quiet

Summary by CodeRabbit

Release Notes

• Bug Fixes

  • Enhanced usage metrics attribution across multiple session shutdown events in Copilot CLI analyzer, improving per-turn accounting accuracy.

• Tests

  • Added test coverage for multiple shutdown event handling and empty metadata edge cases.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: a9a34967-9836-49ef-839e-4d631ed5485b

📥 Commits

Reviewing files that changed from the base of the PR and between eb7ef03 and 768c2bc.

📒 Files selected for processing (2)

• src/analyzers/copilot_cli.rs
• src/analyzers/tests/copilot_cli.rs

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📝 Walkthrough

Walkthrough

The Copilot CLI parser now tracks message indices across multiple session.shutdown events using a cursor variable rather than a single stored metrics option, enabling correct attribution of shutdown metrics to their corresponding segments throughout a session file.

Changes

Multi-Shutdown Segment Tracking

Layer / File(s)	Summary
State Tracking src/analyzers/copilot_cli.rs (line 688–692)	Introduces shutdown_segment_start: usize cursor to mark the beginning of entries after the most recent shutdown event.
Shutdown Event Handler src/analyzers/copilot_cli.rs (line 998–1005)	When session.shutdown includes non-empty modelMetrics, applies metric fill and token distribution only to entries[shutdown_segment_start..], then advances the cursor to entries.len().
Finalization Logic src/analyzers/copilot_cli.rs (line 1065–1068)	Applies apply_copilot_cli_live_prompt_overhead only to the tail segment entries[shutdown_segment_start..], eliminating the prior conditional branch that selected between stored metrics or overhead-only paths.
Test Coverage src/analyzers/tests/copilot_cli.rs (line 213–352)	Adds two tests: one validating per-turn token accounting across two shutdown events in a single session, and another verifying correct segment handling when early shutdown metadata is empty.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• Piebald-AI/splitrail#141: Directly modifies the same parse_copilot_cli_session_file function and shutdown-metrics handling in the Copilot CLI analyzer.

Suggested reviewers

• mike1858

Poem

🐰 A cursor hops through shutdowns bright,
Each segment tracked with pure delight,
No more one metrics lost in time,
Multiple shutdowns tracked in rhyme! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Fix Copilot CLI shutdown metric segmentation' clearly and specifically describes the main change: fixing how shutdown metrics are segmented across multiple shutdown events in the Copilot CLI analyzer.
Docstring Coverage	✅ Passed	Docstring coverage is 80.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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