fix: replace datetime truthiness checks with explicit is None guards (#862)

[microsasa]

Closes #862

Summary

Four locations across report.py and render_detail.py checked datetime | None fields using Python truthiness (if x / if not x) instead of explicit is None / is not None guards. This PR replaces them for consistency, better pyright type narrowing, and latent correctness safety.

Changes

File	Line	Before	After
report.py	158	if not session.start_time:	if session.start_time is None:
render_detail.py	184	… if summary.start_time else "—"	… if summary.start_time is not None else "—"
render_detail.py	384	if summary.start_time	if summary.start_time is not None
render_detail.py	387	if events and events[0].timestamp	if events and events[0].timestamp is not None

Verification

• All 1239 unit tests pass (the single test_wheel_excludes_docs failure is pre-existing and unrelated — uv not in PATH).
• pyright --strict passes with 0 errors.
• ruff lint and format pass cleanly.

Generated by Issue Implementer · ● 2.8M · ◷

[Copilot]

Pull request overview

This PR improves type-safety and consistency by replacing truthiness checks on datetime | None fields with explicit is None / is not None guards in the reporting/rendering layer, aligning better with strict Pyright narrowing.

Changes:

• Update _format_session_running_time() to use session.start_time is None instead of if not session.start_time.
• Update header rendering to use summary.start_time is not None in the formatted start-time expression.
• Update session detail session_start selection logic to use explicit is not None checks for summary.start_time and events[0].timestamp.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/copilot_usage/report.py	Uses an explicit None guard for SessionSummary.start_time to improve correctness and type narrowing.
src/copilot_usage/render_detail.py	Replaces datetime truthiness checks with is not None in header rendering and session start-time derivation.

[github-actions]

Quality Gate: APPROVED ✅

Low-impact correctness fix — replaces 4 Python truthiness checks (if x / if not x) with explicit is None / is not None guards on datetime | None fields in report.py and render_detail.py.

Evaluation:

• Code quality: Good. Changes are minimal, consistent with coding guidelines (strict typing), and improve pyright type narrowing.
• Tests: All 1239 unit tests pass; CI green across all 8 checks (lint, typecheck, CodeQL, etc.).
• Impact: LOW — no behavioral change (datetime objects are always truthy), no API/model/logic modifications.

Auto-approving for merge.