ADR 0184: Dock the context usage inspector in the composer toolbar

• Status: Accepted (amended by D355 / ADR 0193)
• Date: 2026-09-08
• Deciders: PI-Desktop renderer and UX maintainers
• Amends: D103, D184, D244, ADR 0047, ADR 0103
• Related: D347, D355, E2E-060d, US-UI-61

Context

The compact context inspector (ADR 0047, ADR 0103) hung under the newest assistant turn. After the transcript scrolled, a routine remaining-capacity check required hunting for that row. Collaborators agreed to move the single entry next to the model picker instead of keeping two copies of the same numbers.

Decision

1. Render one context inspector in the composer right toolbar, immediately left of the combined model × reasoning chip. Hide it until the active session has usage.
2. Keep the data contract, as amended by D355: remaining capacity, used/window counts, turn total, and exact provider input/output/cache/reasoning/hit-rate describe the newest usage-bearing assistant message (the last model request). Completed-turn speed and the aggregate tool summary still describe that visual turn. A later streaming turn without totals does not steal that turn's tools or throughput. Delegate rows' usage does not drive the ring. Compaction marks still split overflow-retry turns so the inspector does not sum the failed attempt with the retry.
3. Keep the click/keyboard trigger, remaining-capacity ring, viewport-aware body portal, outside-click dismissal, and Escape behavior. The trigger shows the ring and percentage only; the redundant Context label is omitted because the accessible name already states remaining capacity.
4. Keep the compact summary contents. The heading is remaining tokens plus percentage. Rows below use one muted-label / tabular-value rhythm, separated by spacing. The popover keeps its floating-layer edge and does not draw inner section rules (D297).
5. Assistant meta under a completed turn keeps the optional model badge and the usage-less throughput fallback. It no longer hosts the inspector.
6. Renderer only: no protocol, storage, runtime accounting, or model metadata changes.

Consequences

• Remaining capacity stays reachable while composing, even after the transcript has scrolled.
• Historical turns no longer expose a per-row inspector; the composer chip is the single authority for the latest usage snapshot.
• The panel still opens above the dock when space allows, because placement already prefers the side with room and clamps to the viewport.

Rejected alternatives

• Keep the message-row inspector and add a second composer entry: two surfaces would show the same numbers and leave users unsure which is authoritative.
• Inner hairlines between popover sections: rejected by D297; floating layers keep an outer edge, not internal rules. The doubled heading rule is fixed by dropping the extra heading caption, not by adding borders.