Story-2283: the CCB chassis (B5a, EPIC-2270)

The section surface is live (app#568) and the backend now assembles a document_selection ContextBundle profile (functions#650). This ticket builds the vehicle that carries counsel's ask to an agent with that context attached.

The idea in one line

The CCB is a vehicle, not a toolbar. The chassis is constant — the same bar, in the same place, with the same two affordances (Command and Talk, D29) — and everything between them changes with what counsel is looking at. The verbs are cargo; the bar is the truck.

Where the pieces live

1. The chassis is constant, so it lives in the shell

The bar is mounted by document-permalink-shell.tsx — the shared chrome above Original, Insights and the machine copy. That is what makes "constant" structural rather than merely visual: there is no per-view copy of the bar to drift.

But what counsel is pointing at is known one level down, inside whichever view is mounted. So the shell provides a focus context and the view publishes into it — the section selected in the outline, the span dragged on the page, or a gutter mark clicked. A view that has no notion of focus publishes nothing, and the bar honestly falls back to "Whole document": with nothing selected, the document is the scope.

2. The verbs are data, not an if-chain

resolveCcbVerbs(focus) reads three axes and returns at most three verbs (D20's hard ceiling). The chassis maps over the result and dispatches by lane — it contains no knowledge of any individual verb, so adding one is a registry entry, never an edit to the bar.

3. The ask: gate first, then agent

The order is the whole point.

1. The context gate. The focus goes to the document_selection profile. A privileged document is REFUSED and a strategy document EXCLUDED — typed 403s decided at the query layer before a single section is read. We ask for the context before we ask the agent, so a refusal is something counsel is TOLD, not something they infer from a thin answer. A refusal stops the pipeline: no agent turn is fired.
2. The ask. Cleared by the gate, the prompt goes down Mira's EXISTING converse rail — the same module-scoped connection the Agent Dock is subscribed to.

That second choice is what buys D29's handoff continuity for free: the ask and its answer are already turns on the panel's thread, so Talk / Continue in the panel opens a conversation that CONTINUES this moment instead of restarting it. No new runtime, no broker change, no second socket.

4. Summary-as-first-frame (SS-11, ux-guidelines §19)

The instant counsel asks, the answer card paints the focused section's stored summary (D15) — already in hand from the section layer, so it costs nothing and arrives before the model has produced a token. It is labelled as what it is ("Stored read"), never passed off as the answer, and the shared AgentWorkingLine keeps the wait alive beneath it (motion + ticking seconds + phase). The live stream then replaces it.

An empty box that waits three seconds teaches counsel the surface is slow; a true sentence teaches them it is working. Where there is no stored summary (an unsegmented document), the card goes straight to the wait rather than filling the gap with a guess.

5. The refusal is said out loud

A privileged or strategy-excluded context renders the typed refusal, never a silent empty state. "We would not assemble this" and "we could not assemble this" are different sentences, and counsel is owed the right one — so a 403 with a known code renders as a refusal, and anything else renders as an error with a retry.

Reuse (nothing here was rebuilt)

• AgentWorkingLine — extracted from the Agent Chat Panel's ThinkingView so the CCB waits exactly the way the panel does. One §19 waiting state, not two that drift.
• CcbVerbChip — the shared verb chip; the floating selection bar (DocumentCounselBar, Story-2168) was migrated onto it, so there is one CCB with two presentations rather than two bars.
• useMiraConversationRail / useAgentDockStore — the existing ACP rail and dock state. Talk opens the ACP; it was not rebuilt.
• Button / PrimaryButton, Input, Popover, MICRO_TRANSITION, useTickingSeconds, the Story-2281 section layer.

Live evidence (staging backend)

POST /api/internal/matters/13/context/bundles/document-selection → 200
request:  {"budget":"M","focus":{"document_id":"be39d48c-…","schema_version":"document_focus.v1","section_ids":[]}}
response: {"schema_version":"context_bundle.v1","profile":"document_selection",
           "focus_axis":{…echoed…},"engine_state":"live","token_estimate":68,
           "version_hash":"5f30c943c72f5858…","sections":[{"kind":"doc_identity",…},
           {"kind":"section_summaries","items":[]}]}