[AlexanderZ-Band]

Why

A room can show what an agent is doing (reasoning, a tool by name, waiting on a person, memory), but older platforms and boolean-only callers must keep working. The earlier version kept detail in a per-room reporter slot, which needed ownership guards that proved unreachable or wrong, and it learned platform support from GET /api/version, which serves HTML on prod.

What

• Each turn keeps its own detail (TurnScope.activity, in the new leaf band.runtime.activity). The room shows the live owner's detail and none while an aborted owner unwinds; reporting a change never starts reporting, takes ownership, or waits on the network.
• A visible change wakes the reporter's keep-alive, the only sender of working: true, so changes made while a report is in flight coalesce to the latest. Stop and the duration cap are unchanged.
• Detail is attached once an activity response's X-API-Version advertises 1.25.0 or later. A detail-bearing 422 resends once without detail within the same deadline and disables detail for the process.
• Names only: a tool shows its name, never arguments.

Scope

First feature layer of INT-1744. ReportFn(bool) and enable_working_state (still the only switch) are unchanged. The unused _on_activity_clear seam is replaced by per-turn detail rather than filled. band-client-rest 0.0.46 already ships AgentActivityDetail, so there is no bump. A tool shorter than one report round trip may never appear, which INT-1741 accepts. The producer helpers have no callers yet; Band tools and adapters report through them in the PRs stacked above.

🤖 Generated with Claude Code

https://claude.ai/code/session_01DFmR3J53UqbsYDMmTUd3Rb

[linear-code]

INT-1744

[AlexanderZ-Band]

Cycle 1: no verified findings in the independently reviewed compatible detail-delivery delta. Combined producer-triggered findings are recorded on the producer PR.

[bandzalkin]

Scope

Approval is limited to #840's reviewed delta at 06d8124481475460782840b8854285cf7c0a2d92 against #839 at a397d8cb905d5316a87f62da23c8c5af1895e78e, as requested. This supersedes the earlier stack-level hold only for this individual PR's code review.

Constraints

Preserve boolean reporting, names-only detail, the shared request deadline, and the explicit process-wide compatibility policy.

Decisions

Platform-owned negotiation and one serialized reporter fit the existing boundaries. No parallel reporting owner or transport is needed.

Findings and proof

No new findings. Head/base and all review discussions were rechecked and are unchanged since the detailed review. The completed combined-tip verification was 1,466 passed / 69 skipped in the core contract suites and 1,372 passed / 10 skipped in coding-adapter, ACP and turn-admission suites. No additional tests were rerun for this unchanged-head approval; live platform/model acceptance and the full repository gate were not run.

Architectural / review verdict

APPROVED for the reviewed #840 delta. This does not approve #841 or clear the stack's five outstanding findings. Re-review material changes introduced by rebasing or resolving the root PR's merge conflict.

[AlexanderZ-Band]

Blocking — would be REQUEST_CHANGES on a PR by someone else.

Cycle 2: two test issues (the flow tests don't prove a change is reported immediately, and a transient-turn observation is masked by the owner's wait), eight nits. Both issues sit in code no fix touched. The aborted-previous-owner branch in _start_activity (from #839) was examined: it isn't reachable with an aborted owner and this PR doesn't rely on it, so it is out of scope.

[AlexanderZ-Band]

Cycle 3: converged, no issues. The flow mapping found no new hypothesis, and the producer move changed no behaviour. Five test nits, fixed in this round.