feat(web): add the Agents panel (4/5)

[shivamhwp]

Fourth of five stacked PRs replacing #4551. Stacked on #4662 — review that first.

Surfaces the subagent data the previous PRs record. A new right-panel tab lists every subagent on the thread with its role, model, status, token usage, recent activity, and the runs it has been activated for. Read-only — it renders what the projection already contains.

Grouping lives in client-runtime rather than the component so it stays testable: workflow coordinators own their phases, phase status derives from its members, and members orphaned by a missing coordinator fall back to the flat list rather than disappearing.

Coordinators are agents too

A workflow coordinator has its own model, usage and activations, and before its members are spawned it is the only row on the thread. So it renders as a card rather than a bare heading, and it is counted in the tallies — but only while it has no members, since afterwards they represent the same work and counting both double-reports it.

Without that, a thread running a workflow showed 0 active · 0 waiting · 0 settled with nothing listed, and unexplained tokens in the header.

Token accounting

Same rule: the total keeps whatever the members did not account for. Dropping the coordinator outright erased the entire workflow whenever a provider reported workflow usage while omitting per-agent tokens — the header then read "Usage unavailable" for a workflow that had spent thousands. Both fields are populated independently in the Claude adapter, so this is reachable, not theoretical.

Testing

Typecheck and lint clean. Web 1,500 passing, client-runtime 486 passing.

Verified in a browser against a real Codex subagent run: the tab renders the agent with its role and model badges, idle status, a real token count and run count, and an expandable "Activity and runs" section.

Reviewed by an independent agent pass; the token-collapse bug and the missing coordinator card both came out of it and are fixed here.

Note

The workflow path itself (phases, coordinators) is Claude-only — no other adapter emits kind: "workflow" — so that branch has unit coverage but has not been exercised against a live provider.

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