fleet_spawn cannot start a collaborative session — the conductor can only make single workers

[saucam]

Gap recorded in conductor-design.md §5.1 (landed in #275).

The gap

fleet_spawn creates one disposable worker. It already takes provider + model, so the conductor can deliberately put a task on Opus, Fable, or Codex — that part works.

What it cannot do is start a collaboration: a goal with role→backend bindings, a shared blackboard, and panels (collaboration.ts, shipped through #271–#274). That is the natural target when the conductor decides a task should be fanned out rather than handed to a single worker, and there is no verb for it.

Today the owner has to create a collaborative session by hand, which breaks the premise that the conductor is the front door to getting work done.

Scope

• A fleet_collaborate (name bikesheddable) verb: goal, role→backend bindings, workdir
• Send-class by definition — it must be in FLEET_SEND_TOOL_NAMES so isFleetSendTool hard-gates it, and deliberately kept OUT of allowedTools. R3 is an invariant, not a mode default
• The approval prompt carries the goal's cost roll-up, the way fleet_panel already does — a collaboration is the most expensive thing the conductor can start, so the owner should see the projected spend before approving
• Delegated identity for each role's child, same chain as fleet_spawn; a collaboration child is still a leaf unless explicitly promoted to orchestrator
• Completion returns a digest, never the collaboration's artifacts — the never-OOC guarantee applies here more than anywhere, since a collaboration produces N children's output
• fleet_list / fleet_tasks should surface a conductor-started collaboration as one unit, not N unrelated sessions

Note on the orchestrator backend

A conductor-started collaboration puts an orchestrator role on some backend. Under #245's v1 the orchestrator is pinned to claude because the fleet surface is an in-process Claude-SDK object. So either this lands after #245, or it lands with the orchestrator pinned and the pin removed by #245.

Related

• Support non-Claude orchestrators for collaborative sessions (mountable fleet MCP) #245 non-Claude orchestrators (mountable fleet MCP)
• feat: Mission system — long-running autonomous work with ZeroID mission_id, budgets, and milestones #52 mission system — a conductor-started collaboration is arguably a mission