[feat] Intent-before-action protocol: objection window logic

[NoobyGains]

Context

docs/protocols.md sec 1 ("Intent-before-action"): an agent publishes a Plan, then must wait an objection window (default 15s, configurable per Plan) before acting. Other agents may file a Disagreement during the window, which pauses the Plan until resolved. This is the protocol that turns parallel agents from a race into a coordination.

Desired behavior

A @quorum/protocol-intent module exposing:

• openObjectionWindow(planId, windowMs): Promise<"clear" | "objected">.
• Status transitions on the Plan artifact: draft -> proposed -> (clear|objected) -> approved|withdrawn.
• On Disagreement filed against the Plan within the window: emit a PlanObjected event, freeze status, surface to author via [feat] MCP stdio server stub responding to ping #9.
• On window expiry with no Disagreement: transition to approved and emit PlanCleared.
• Idempotent on replay (timer state derived from proposedAt, not in-memory).

Acceptance criteria

• Window timer survives process restart (re-derived from artifact timestamps).
• Concurrent objections handled deterministically (first-write-wins via chore(ci)(deps): Bump actions/checkout from 4 to 6 #2 CAS).
• Default window 15s, per-Plan override honored.
• Unit tests pass.
• Integration test against real git repo (no mocks) — reproduce docs/protocols.md t+12s -> t+31s sequence end to end.

Implementation notes

• No setTimeout in long-lived state; recompute deadline on every tick from artifact proposedAt.
• Depends on chore(ci)(deps): Bump actions/setup-node from 4 to 6 #1, chore(ci)(deps): Bump actions/checkout from 4 to 6 #2, [infra] Set up CI matrix (Windows, macOS, Linux × Node 20/22) #4, [feat] MCP stdio server stub responding to ping #9. Exercised by [feat] Git-refs artifact store (read/write under refs/coord/*) #14.

[NoobyGains]

Closed by 8ef2d75