Clarify Inspector usage snapshot freshness

Traceability

• Spec ID: inspector-usage-snapshot-freshness
• Status: Implemented

Intent

Prevent reviewers from reading a self-contained Inspector report as a live usage feed. The Session outline and detailed Usage report must describe the latest retained context as an observed snapshot and state when that snapshot was current.

Acceptance Scenarios

• AC-1: Standalone Inspector and Harness Studio label context occupancy as the latest observed context rather than the current live context, and identify the surface as a static snapshot.
• AC-2: Snapshot freshness prefers the timestamp of the latest retained Usage progression point. When that timestamp is unavailable, the report-level generatedAt timestamp is used and labelled as generation time. When neither timestamp is valid, freshness remains explicitly unavailable.
• AC-3: The compact Session outline and detailed Usage report expose the same snapshot semantics in English and Simplified Chinese without changing token, cache-reuse, context-progression, compaction, or provider accounting values.
• AC-4: The changed Studio and standalone Usage surfaces remain keyboard reachable, avoid document and outline overflow at wide, compact, and narrow layouts, and produce no browser console or page errors.

Non-goals

• Auto-refreshing an open Inspector report or mutating native Session state.
• Changing provider adapters, usage arithmetic, context-window inference, or compaction detection.
• Collapsing edited, retried, or zero-response user Turns.

Plan and Tasks

1. Derive one bounded optional Session usageSnapshot in the report model: latest retained Usage timestamp, then report generation time, then unavailable. Older reports retain the same renderer-side fallback.
2. Pass report generation time into Studio Session Detail and render the same bounded freshness note in the outline and detailed Usage report.
3. Rename context labels and add English and Simplified Chinese copy without changing provider accounting or context evidence fields.
4. Add focused behavior assertions and run Inspector, Studio, and visual validation before review.

Test and Review Evidence

• AC-1/AC-2: npx vitest run test/reporting/harness-inspector.test.mjs passed 39 tests; the deterministic demo tests also passed 2 tests.
• Full repository regression: npm test passed 1,598 tests with 2 skipped.
• AC-1/AC-2/AC-3: npm run harness-studio:test passed 512 tests; npx playwright test test/browser/artifact-host.spec.mjs passed all 27 browser tests, including the Inspector Session and Usage flow.