refactor(coding-agent): publish session action protocol

[snimu]

Summary

Fourth PR of the session-action stack: the deliberate wire break. Queue state and session activity become separate, explicitly named projections on the daemon protocol; the executing-command queue display bug is fixed; headless completion waits for scheduler work; the restart manifest is versioned; and all transitional compatibility projections from #2/#3 are deleted. Daemon protocol 6 -> 7, schema 7 -> 8, envelope minimum raised to 7.

Stack: #572 contracts <- #573 kernel <- #574 admission <- #575 protocol (this) <- #576 cleanup

Motivation

pendingMessageCount served incompatible questions - queued future work, scheduler activity, UI rows, restart contents, busy status - and its consumers each picked their own interpretation. That ambiguity produced the "Steering /compact" display for a command that was already executing, headless modes that could exit while a command was still running, and the cross-cutting compensation attempts seen in earlier fix attempts (#565). Everything is team-internal, so rather than dual-writing old semantics, this PR makes one clean break: old clients are rejected before state exchange.

Code changes

• New SessionActionSnapshot on the wire: literal queuedCount + steering/followUps previews (queued actions only), plus optional active { kind, phase, label }. queue_update replaced by session_action_update.
• pendingMessageCount removed everywhere; every consumer audited and routed to the semantically correct projection (queuedActionCount, unfinishedActionCount, isSessionActive): cron, agent-observe/agent-message discovery and capacity limits, daemon summaries, RPC, Agents View, supervisor sync, shutdown, and update paths.
• Display fix: an executing /compact renders as activity, never as a queued row.
• Headless completion (waitForHeadlessCompletion) and extension waitForIdle bindings now use session-level idle (scheduler + lower agent), with wakeups on pause release, queue clear, and dispose (no microtask livelock, no stranded waiters).
• Protocol gate: DAEMON_PROTOCOL_VERSION 7, DAEMON_SCHEMA_REVISION 8, envelope minimum 7; compatibility maps updated; both direction tests are real socket-level tests (new-client/old-daemon rejects before writing; old-client/new-daemon receives parse rejection from a real supervisor before any state exchange).
• Recovery: versioned SessionActionRecoverySnapshot (formatVersion, structural validation, explicit unknown-version rejection on restore; stale/unreadable manifests treated as "nothing restorable" at probe sites and cleared); daemon restore_actions command; per-policy FIFO + correlation preserved on restore.
• Deleted: legacyPendingProjection, the old-manifest recovery adapter, the legacy attachment fallback to incompatible daemons, and the dead requestLegacy/useLegacyProtocol update-restart plumbing.

LOC: +524/-567 production (net -43), +1075/-667 tests, changelog entry (includes review-fix commits: projection guards, recovery validation, test-fixture migrations).

Note

Publish session action protocol replacing legacy queue API in daemon and session

• Replaces the queue_update event and pendingMessageCount/pendingMessageCount fields across the daemon, RPC, interactive, and agents-view layers with a structured session_action_update event carrying a SessionActionSnapshot (queuedCount, steering, followUps, active phase).
• Adds AgentSession.restoreSessionActions() to rehydrate session queues from a versioned SessionActionRecoverySnapshot, replacing the former piecemeal steering/follow-up/accepted-prompt restore paths.
• Bumps DAEMON_PROTOCOL_VERSION to 7 and schema revision to 8; adds a restore_actions daemon command; enforces command envelopes and rejects unenveloped commands.
• Removes legacy protocol fallbacks in daemon launch, heartbeat catalog, and update-restart flows; stale daemons now always throw instead of falling back.
• Risk: breaking protocol change — clients speaking protocol ≤6 will be rejected outright by the supervisor and daemon launcher.

Changes since #575 opened

• Modified test case 'rejects coordinator spawn errors without terminating the updater' in the update restart coordinator test suite to add explicit cleanup and verification steps [761439f]
• Added waitForProcessExit async utility function for awaiting process termination in tests [761439f]

^{Macroscope summarized ea5e528.}

---

Note

High Risk
Breaking daemon protocol and session wire shape; stale clients and daemons are rejected, and update-restart recovery depends on the new manifest format.

Overview
Breaking wire change (daemon protocol 6→7, schema 8): queue state is no longer folded into pendingMessageCount or queue_update. Clients get session_action_update with a SessionActionSnapshot: literal queued steering/follow-up previews (queuedCount) plus optional active work (kind, phase, label). Session summaries expose sessionActions, isSessionActive, and unfinishedActionCount so UI, cron, agent messaging, and busy detection use the right projection instead of one ambiguous counter.

Session core: AgentSession adds getSessionActionSnapshot, restoreSessionActions, and a versioned SessionActionRecoverySnapshot for update-restart; legacy recovery adapters and steering/follow-up snapshot APIs are removed. waitForIdle now waits on scheduler + agent work (used by headless completion and extension bindings).

Daemon / CLI: New restore_actions command; update-restart manifests store queue.actions (not per-queue message lists / accepted prompt). requestLegacy, compatible stale-daemon fallback, and legacy owned-worker frontend routing are deleted; unenveloped commands and pre-v7 daemons are rejected.

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