perf(parser): single-pass resume detection in _first_pass (#955)

[microsasa]

Summary

Fold _detect_resume() into _first_pass() so event processing is single-pass. Rolling post-shutdown accumulators reset on each session.shutdown; after the loop they hold the post-last-shutdown values.

Closes #955

Changes

src/copilot_usage/parser.py

• Add 5 post-shutdown fields to _FirstPassResult (rolling accumulators)
• Add SESSION_RESUME to _FIRST_PASS_EVENT_TYPES
• Track post-shutdown state in _first_pass loop with if _shutdowns: guards
• Remove _detect_resume() and _DETECT_RESUME_EVENT_TYPES entirely
• Build _ResumeInfo from _FirstPassResult in _build_session_summary_with_meta

tests/copilot_usage/test_parser.py

• Convert TestDetectResumeDirect → TestResumeDetectionDirect (tests via _first_pass)
• Convert TestDetectResumeNonIndicatorEvents → TestNonIndicatorEventsNoResume
• Add 3 new edge-case tests: assistant message without tokens, pre-shutdown resume ignored, stale resume time cleared across shutdowns
• Remove 4 implementation-detail test classes (slice alloc, index access, elif chain, frozenset constant)
• Update _FIRST_PASS_EVENT_TYPES assertion to include SESSION_RESUME

Docs: architecture.md, implementation.md, changelog.md, test_docs.py updated

Verification

• All checks pass (ruff, pyright, bandit, 99% coverage, 86 e2e)
• Triple adversarial review (Opus 4.6, Sonnet 4.6, Codex) — 0 bugs, 2 test gaps found and covered
• Self-review caught and fixed a data-loss bug (assistant message without tokens not setting resumed)

[Copilot]

Pull request overview

This PR improves copilot_usage session summarization performance by folding resume detection into _first_pass(), eliminating an extra scan of events for sessions that contain shutdowns.

Changes:

• Extend _FirstPassResult with rolling post-shutdown accumulators and track them during _first_pass() (single-pass resume detection).
• Remove _detect_resume() and its event-type prefilter; construct _ResumeInfo directly from _FirstPassResult in _build_session_summary_with_meta.
• Update/reshape unit tests and documentation to reflect the new single-pass behavior and edge cases.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/copilot_usage/parser.py	Implements single-pass post-shutdown resume detection and removes _detect_resume().
tests/copilot_usage/test_parser.py	Updates direct resume-detection tests to validate _first_pass()-tracked post-shutdown fields; removes tests tied to the deleted helper.
tests/test_docs.py	Updates docs assertions to look for resume detection described under _first_pass() rather than _detect_resume().
src/copilot_usage/docs/implementation.md	Updates implementation narrative to describe rolling post-shutdown tracking inside _first_pass().
src/copilot_usage/docs/architecture.md	Updates architecture overview/pipeline to reflect single-pass resume detection in _first_pass().
src/copilot_usage/docs/changelog.md	Removes _detect_resume() from the historical helper list in the refactor entry.