Adds the consumer half of the Script Coordination timing RFC (PR 2 of 2, stacked on #27149): readiness-interval derivation from the unit event log, a history section in coder exp sync status, and a new coder exp sync timeline command.

Summary

• agent/unit: new DeriveIntervals pure function that replays the event log and returns per-unit lifecycle intervals (blocked | ready | running | done). Readiness is derived, not stored: the fold mirrors recalculateReadinessUnsafe and handles the late dependency_added edge case where a ready unit flips back to blocked with no status change.
• coder exp sync status: table output gains a "History" section (time, elapsed, event) after the dependencies table. JSON output is unchanged from feat: record and expose timestamped unit events over the agent socket #27149.
• coder exp sync timeline (new): renders the full cross-unit event log as a git-log-style ASCII graph. Each unit gets a lane; every event prints a * row with an elapsed-time label; dependency-satisfaction points draw an inter-lane connector plus a derived "ready" row; lanes disappear when a unit completes. --output json emits the raw event list. Older agents without the SyncTimeline RPC get a clear "agent does not support timeline" error.

Example graph output:

*  [+0.0s]  test-unit  registered (pending)
*  [+0.0s]  test-unit  depends on dep-unit (completed)
| *  [+0.1s]  dep-unit  registered (pending)
| *  [+0.1s]  dep-unit  pending → started
| *  [+2.3s]  dep-unit  started → completed
| /
*  [+2.3s]  test-unit  ready (dependency satisfied)
*  [+2.4s]  test-unit  pending → started
*  [+8.0s]  test-unit  started → completed

Test-support change: agentsocket.NewServer gains a WithUnitManager option so CLI tests inject a mock-clock unit manager, keeping history timestamps in table goldens deterministic.

Testing

• agent/unit: DeriveIntervals covered for single-unit lifecycle, blocked-until-satisfied, the late-edge ready-to-blocked flip, multiple dependencies, status-specific requirements, and unregistered dependencies.
• cli: renderer unit tests with varied timestamps (lanes, connectors, no-false-ready), plus golden tests for sync timeline (empty, graph, JSON) and the updated sync status goldens. Reviewers should read the goldens; they are the primary review artifact for the rendering changes.

Generated by Coder Agents on behalf of @SasSwart.