feat(kap-server): move compacting from session.state to agent.state turn

[sailist]

Related Issue

Follow-up to #3532 (flat entity message protocol). Internal protocol adjustment, no linked issue.

Problem

The v3 protocol carried a compacting value on session.state.status that the projection never produced (session state is derived purely from busy → idle | running). Meanwhile, full compaction is an agent-level activity that happens inside a running turn, and subscribers had no way to observe it in real time — compaction.started / compaction.completed bus events existed but were not surfaced on any state entity.

What changed

• session.state.status narrowed to 'idle' | 'running': the never-produced 'compacting' value is removed from the schema. No runtime behavior change — the projection only ever emitted the two remaining values, so this is backward compatible for consumers.
• agent.state.turn.status gains 'compacting' (now 'thinking' | 'retrying' | 'acting' | 'aborting' | 'compacting'), an additive enum extension per the open-union evolution rule.
• The projection now produces it: AgentStateTracker holds a compacting flag driven by the per-agent compaction.started / compaction.completed / compaction.cancelled bus events (observable, already in the projection event union). While compacting, the flag takes precedence over the activity-snapshot phase mapping; when compaction ends the turn status recomputes back to the real phase. compaction.blocked never enters the compacting state. Compaction outside an active turn is not represented (the turn field only exists while running).
• agent-core-v2 is untouched: the signal is computed entirely at the kap-server projection layer from existing bus events.
• Tests: the main SessionProjection lifecycle case now drives a blocked → started → completed sequence and asserts compacting is emitted exactly once and the turn returns to acting afterwards (test count unchanged).

Checklist

• I have read the CONTRIBUTING document.
• I have linked a related issue (external PRs: the issue must have a maintainer's /approve).
• I have added tests that prove my feature works.
• Ran gen-changesets skill, or this PR needs no changeset.
• Ran gen-docs skill, or this PR needs no doc update.

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve compaction state across turn boundaries

When background auto-compaction outlives the turn that started it—a supported scenario in fullCompaction.test.ts—this reset discards the active compaction before any compaction.completed or compaction.cancelled event. If another turn begins while that task is still running, recompute() consequently reports thinking or acting instead of compacting; clear only the turn display here and retain the lifecycle flag until its matching end event.

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[chatgpt-codex-connector]

Seed compacting when attaching to a live agent

ProjectionService.forSessionLive() creates projections lazily, so the first v3 subscriber can attach after compaction.started has already fired. Because this tracker always initializes the flag to false and only subsequent bus events update it, recovery and live state never expose compacting for that in-flight operation; the eventual completion merely recomputes an ordinary phase. Seed the flag, along with the current turn snapshot, from the live agent services when tracking an existing agent.

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