Make Session Viewer easier to scan

Traceability

• Spec ID: inspector-session-view-density
• Status: Implemented

Intent

Opening a session currently spends most of a laptop-height viewport on the title, mode controls, and full normalized-activity chart before the dialogue trace begins. Reviewers should be able to keep the activity overview in sight while scanning multiple turns without losing the existing evidence details.

Use the supplied dense trace-view reference for layout rhythm only. Preserve Better Harness terminology, evidence semantics, privacy boundaries, controls, and visual tokens.

Acceptance Scenarios

• AC-1: At a 1280 by 720 desktop viewport, opening Trace keeps the session identity, mode tabs, and normalized activity overview inside the top half of the viewport, so the first Turn's prompt is readable without scrolling. A Turn longer than the remaining viewport still scrolls; the criterion bounds the pre-dialogue chrome, not the Turn body.
• AC-2: Session View uses a compact activity projection with at most four visible action lanes while retaining the full call total, the compressed long-idle axis, zoom, commit markers, and keyboard-selectable evidence. The compact projection drops the chart legend, so the numeric longest-idle span and the untimed-call notice stay in the Workbench chart only.
• AC-3: Per-turn tool-call groups start collapsed in every session. Reviewers can still expand one group, expand all groups, reveal grouped overflow, and select an individual call.
• AC-4: Turns read as dense row groups instead of separated floating cards; prompts, intermediate responses, tool groups, responses, and commits remain visibly distinct and keep their native focus and selection behavior.
• AC-5: Jump, filters, source, Trace/Replay, Continuation packet, and the Evidence Drawer remain available. At narrow widths the sidebar continues to stack without horizontal page overflow.

Non-goals

• Copying DeepSeek branding, navigation, chat composer, or model controls.
• Adding raw system prompts, tool payloads/results, schemas, or new evidence.
• Replacing the existing Evidence Drawer with a second detail system.
• Changing report data, correlation, replay semantics, or privacy projection.

Plan and Tasks

• Add an explicit compact rendering mode for the Session View activity chart; keep the Workbench chart unchanged.
• Tighten the title, tabs, timeline panel, turn groups, event rows, tool rows, and sidebar using the existing Inspector token family.
• Default per-turn tool disclosures closed while preserving all reveal and selection paths.
• Compare before/after screenshots at the same 1280 by 720 viewport and verify Trace, zoom, call expansion/selection, filters, Replay, and responsive reflow.

Test and Review Evidence

• AC-1: measured element bounds on a real rendered report — session title 58–84px, activity panel 169–349px, first Turn starting at 359px, so the pre-dialogue chrome stays inside the top half of a 720px viewport.
• AC-2/AC-3/AC-5: browser interaction checks on a real report — four lane labels with the remainder aggregated as Other activity, Reset zoom present, legend computed as display:none, zero tool groups open on load, one group expanding to its rows, expand-all and collapse-all, the Prompts filter hiding and restoring prompt events, Trace/Replay switching, and no horizontal page overflow at a narrow width.
• AC-4: focus and selection applied to a Turn's prompt button, with the focus outline and the selection ring both rendering inside the Turn card.
• Regression: full npm test at 1317 passing; the two failures were load-induced 120s timeouts in unrelated CLI suites (test/plugins/host-support.test.mjs, test/reporting/report-source-review.test.mjs) that pass when run alone. git diff --check clean. No console or page errors in the rendered report.

Risks

• Density can become illegible; keep primary dialogue text at 11px and preserve focus outlines rather than shrinking every surface uniformly.
• Fewer chart lanes can hide categories; aggregate the remainder as Other activity with a descriptive accessible title instead of dropping calls.
• Sticky regions can compete for height; keep one page scroller and verify the timeline does not cover turn content.