feat(ai-autopilot): add @gemstack/ai-autopilot — Supervisor orchestration

[suleimansh]

Implements #9 — the third (and most speculative) package of the GemStack AI family. The orchestration layer: runs many agent runs under a control policy, above ai-sdk's single-agent loop.

Per the issue, this ships the smallest useful first slice rather than a broad speculative API: the supervisor/worker topology.

Seed slice: Supervisor (plan → dispatch → synthesize)

1. Plan — a planner decomposes the task into subtasks.
2. Dispatch — each subtask runs on a worker agent, with bounded concurrency, an optional token budget, and per-subtask error isolation.
3. Synthesize — a synthesizer combines the results into the final answer.

const supervisor = new Supervisor({
  plan: agentPlanner(plannerAgent),
  workers: { research: researchAgent, write: writerAgent },
  synthesize: agentSynthesizer(editorAgent),
  concurrency: 3,
  budget: { maxTotalTokens: 200_000 },
})
const { text, results, usage, stoppedEarly } = await supervisor.run('Draft a launch brief')

Surface

• Supervisor — the orchestrator. Pluggable stages: plan (a Planner), workers (a single Agent / a Record<string, Agent> routed by subtask.worker / a WorkerRouter), synthesize (a Synthesizer).
• agentPlanner(agent) — LLM decomposition via ai-sdk's Output.array (JSON subtasks).
• agentSynthesizer(agent) / defaultSynthesize — LLM synthesis, or deterministic concatenation (no LLM call).
• Guardrails: concurrency, maxSubtasks (trims + flags stoppedEarly), budget.maxTotalTokens (halts dispatch). Progress onEvent.

Answering the issue's open questions

1. Smallest useful first slice? The Supervisor (plan → dispatch → synthesize) — exactly the candidate the issue named.
2. What does it add over handoff/asTool? Those are primitives (transfer control / expose one agent as a tool). The Supervisor is a code-orchestrated topology over many runs: concurrency, budget, error isolation, result aggregation. The scope rule is enforced — if a feature just calls a primitive, it stays in ai-sdk.
3. Durable execution? In-process first, no new peer dep. A worker that pauses (client-tool / approval) is reported as a failed subtask; durable pause/resume on ai-sdk's SubAgentRunStore + resume primitives is a deferred optional adapter, along with more topologies (pipelines, debate) and queue-backed runners.

Verification

• pnpm build + pnpm typecheck — all packages ✓
• 18 tests across pool (concurrency/short-circuit), supervisor (routing, error isolation, maxSubtasks trim, budget halt, paused-worker, events), planner + synthesizer (real ai-sdk prompt + Output parsing via AiFake).
• One-directional confirmed: ai-sdk references ai-autopilot nowhere.

Changeset: @gemstack/ai-autopilot minor → 0.1.0. With this, the family's four packages (ai-sdk, ai-mcp, ai-skills, ai-autopilot) all exist.