Read a session as a trace in the Inspector

Traceability

• Spec ID: inspector-trace-view
• Status: Implemented
• Supersedes the presentation slice of inspector-evidence-selection; its selection model, evidence vocabulary, and Compare boundary still hold.

Intent

The Inspector explained relationships but could not be read as a trace. A reviewer could not see when a session did its work, could not see individual calls at real volumes, and could not click one without making the surrounding trace unreadable. This slice keeps the Delivery Tree, Date view, three-lane workbench, and Session View, and makes the activity legible at the scale local evidence actually reaches.

Baseline measured on a real local report (20 sessions, 1 654 normalized calls, one session of 757 calls across 55 turns):

• the swimlane X axis was call ordinal, so a 3.9 h session showed no waiting;
• 577 of 757 bubbles (76 %) were drawn inside another bubble's radius at 1.89 px per call, and only 29 % of the chart was on screen at once;
• selecting a Tool Call inside Session View rendered the Drawer beneath the z-index:20 overlay and dimmed 1 034 elements to opacity:.25;
• one session reported four different turn totals (8 / 25 / 55 / 118);
• three commits predating the session were laid out inside Turn 1;
• 426 of 757 rows (56 %) were byte-identical to another row.

Acceptance Scenarios

• AC-1: When the host observed call timing, the activity chart plots calls on a wall-clock axis and marks windows with no observed call as idle. When it did not, the chart states that it fell back to call order rather than implying a time it never observed.
• AC-2: No call is hidden underneath another. Above one call per bin a lane renders counted bars; drilling in by click or drag reaches individual marks, and the view reports how many calls are in view out of the total.
• AC-3: Selecting an object never de-emphasises unrelated objects. The selected and related objects gain emphasis, and the Evidence Drawer is readable above Session View in both the side and bottom-sheet layouts.
• AC-4: Every surface quotes one turn vocabulary from a single projection, and a retained prompt links to the Turn it actually came from rather than to its position in a capped, de-duplicated array.
• AC-5: A commit joins a Turn only when its timestamp falls inside that Turn's observed window. Every other in-scope commit is held in a labelled outside-the-window track that states no Turn is claimed to have produced it.
• AC-6: Identical consecutive tool rows collapse into an expandable run, and every row carries its observed start clock so rows stay distinguishable when redaction removes the command.
• AC-7: A long session stays navigable: Jump to tracks the reader's position, calls expand and collapse in bulk, overflow rows reveal in place instead of inside a nested scroll box, and related objects are grouped and capped per type so Turns and Tool Calls are never buried by commits.
• AC-8: Session View is a navigable state. Opening it pushes history, Back and Close agree, and a view=session deep link restores the same surface.
• AC-9: Expanding the activity chart does not collapse the delivery lane, and below three-lane width the lanes stack instead of forcing the page to scroll sideways.

Non-goals

• Accepting, rejecting, or editing candidate mappings.
• Writing Feature Tree, Git, checkpoint, or native-session state.
• Inferring a start time, a duration, or an idle window the host did not observe.
• Reconstructing tool input that privacy filtering removed.
• A node-link graph canvas, compare view, search, or row virtualization.

Design Decisions

Wall-clock axis. buildToolCallTrace now retains startedAt. A merged lifecycle is canonically the result event, so lifecycleDurationObservation exports the paired request stamp and the trace prefers it; reading the merged event's own timestamp would have reported every paired call as starting when it finished. activityTimeline reports basis: "observed-time" only when at least two distinct stamps define a span, and "call-sequence" otherwise.

Density over marks. The chart is rendered in the browser from the report projection rather than baked into per-session <template> elements. That is what makes zoom possible, and it removed the duplicated SVG that inflated the report from 1.7 MB to 2.9 MB. A lane bins to ~5 px and shows counted bars; when every bin holds one call it switches to individual marks whose width is the observed latency.

Additive emphasis. De-emphasis is gone. Selection adds a ring and tint to the selected object and a rule to related ones, which keeps the trace readable and removes a full-document filter repaint across ~10 000 nodes.

Commit placement. Turn membership requires containment in the Turn's observed window. The previous default bucket sent every commit older than the first Turn into Turn 1, which is exactly the temporal-proximity-as-authorship claim the evidence vocabulary forbids.

Test and Review Evidence

• AC-1/AC-2: activity projection carries a wall-clock timeline and falls back to call order asserts both bases, the span, and that an untimed projection omits startedAt rather than defaulting it.
• AC-4: one turn vocabulary is projected and retained prompts resolve to their real Turn binds a single retained prompt to Turn 2 and freezes turnCoverage.
• AC-1/AC-3/AC-5..AC-9: Inspector explains a trace on a time axis without occluding or dimming it asserts the axis copy, idle shading, the absence of selection-unrelated and filter:saturate, Drawer layers above Session View in both layouts, the outside-the-window commit track, run collapsing, the removal of the session-call-list scroll box, scroll-spy, bulk expand, view=session plus popstate, grouped related objects, and that expanding activity no longer collapses delivery.
• Regression: npm test 1364/1364, npm run pack:verify 502 npm / 524 runtime entries.
• Browser review on a real local report: drill-down from 757 calls to 36 individual marks in two clicks; clicking a Tool Call inside Session View dimmed 0 elements against a previous 1 034 and left the Drawer on top; Session View reported 0 nested scroll boxes and 0 commits in Turn 1 against a previous 3, with 5 commits in the outside-the-window track; Back closed the view and restored the workbench URL; no page or console errors.

Risks

• Privacy: startedAt is a wall-clock stamp of the same granularity already exposed on Turns and Commits; no new input text or path is retained.
• Correlation: idle shading describes windows with no observed call, not user inactivity, and the outside-the-window commit track states its own limit.
• Scale: binning is bounded by plot width, not by call count, and the removal of per-session SVG templates reduced report size at the same evidence coverage.

Amendment (2026-08-13): the timeline is inside Session View and linked

The first slice kept the wall-clock activity chart in the workbench lane and left Session View as a vertical Turn list. In use that split the one time-axis visualization from the one place calls can be read line by line: they never shared a screen, so a reviewer could not go from a busy stretch on the chart to the calls under it, and a session whose calls carried no dialogue Turn showed "0 tool calls" on every Turn while its whole trace sat in a page-tail bucket.

This amendment moves the same chart (activityChartMarkup, re-rendered by renderActivityChart through the existing [data-activity-chart] wiring, so it shares the per-session zoom state and needs no second model) into a sticky, collapsible strip at the top of Session View, and links it to the list. No new data is projected; it reuses startedAt and Turn startMs/endMs already present.

• AC-10: Session View opens with the wall-clock strip visible above the list. A session with no dialogue Turn still renders the strip from observed call times, and its untied calls are held in one bucket ordered by observed time rather than as an unordered pile.
• AC-11: The strip is a minimap. Clicking a bar scrolls the list to the calls under it (expanding whatever disclosure hides them); a multi-call bar also zooms. Zooming in the strip and in the workbench chart share one state.
• AC-12: A short session opens every Turn's tool calls; a long session (> 12 Turns) stays collapsed and is navigated from the strip. Identical consecutive rows stay collapsed as a run so the default view is concise, not a wall of duplicates. Row virtualization and a node-link canvas remain non-goals.
• AC-13: Filtering a tool type hides both its rows and the run bands that stand in for it, and the sidebar tool total recomputes to the count that survives the current filters (a run counted once per grouped call), independent of which disclosures are open.
• AC-14: The idle legend states the shading is a window with no observed call, not a user wait; a session with no observed timing keeps the sequence-axis label rather than implying a time.
• AC-15: Above the action lanes the chart carries a ribbon that fills the whole domain: observed calls are painted over a continuous band, so the time not spent inside a tool is a visible share of the trace rather than blank canvas. The bare band is labelled unattributed — model work or waiting — and never as a model turn. The ribbon is omitted on the call-order fallback, where spacing would be an artefact of ordinal position rather than elapsed time.

Why the ribbon. The lanes plot the instant a call ran, so a reader saw only the moments a tool was executing. Measured on a real local report, 1 178 gaps between consecutive calls had a median of 6.6 s and a p90 of 29.7 s, while the idle threshold that produced any shading was 45 s: 1 113 of those gaps (94.5 %) had no visual representation at all. On one 2.2 h session the observed tool time totals 14 m — the chart was drawing 21 % of the trace and leaving 79 % blank. The ribbon makes that residue a first-class part of the picture without claiming to know what happened inside it: projectDialogue keeps note text but no note timestamp, so the host observed when tools ran, not when the model worked.

Verified on a real local report: on a dialogue-less 235-call session the strip renders on open and clicking a bar zooms to ~18 calls in view and scrolls the list to the matching rows (timestamps ascending); toggling the Bash tool moves the sidebar total 235 → 150 → 235 while its run bands hide and restore; a 10-Turn session opens all five tool blocks by default; no console errors.