feat(daemon): launch ladders → step() O8 observations (coupling-core B1)

[proboscis]

What

Phase B1 of the coupling-core roadmap: the four launch ladders (W2 handleStartRun, W3 processStartRunCore, W4 processContinueRunCore, W5 handleContinueRun) and the failure arm (W7 failOpenCodeRunBootstrap) no longer write run status events. All 37 ladder append sites are replaced by O8 launch observations decided in the pure transition core.

ladder (imperative bootstrap, unchanged control flow)
  │  reportLaunchProgress(st, run, launchSignal)      ← launch-plane executor
  ▼
stepLaunchProgress (pure policy, step.go)
  stageRunCreated → queued      stageLaunchReady → booting
  stageWorkspaceOnly/stageAgentStarted → running
  failure → [error artifact, failed(reason=launch_<step>), log]
  │  effectSetStatus
  ▼
commitRunStatus (status_commit.go) ← THE single status-event constructor
  ▲
  └─ Daemon.updateStatus (monitor plane: +publish +auto-resolve +listeners)

Key decisions (run-state-machine.md §7 D-B1)

• commitRunStatus extraction: updateStatus's guard/append core is now a process-neutral function, so the worker plane (which runs SocketServer without a Daemon) commits through identical guards. Status events are constructed in exactly one place.
• Stage vocabulary in the observation, statuses in the policy — the ladders report facts; the mapping is stepLaunchProgress's.
• Terminal absorption == old store-guard behavior: launch appends on terminal runs were already silently rejected (daemon source); now the no-write is a policy decision (L4), not a discarded error.
• Launch failures carry launch_<step> reasons (new law L9), rendered by orch ps as failed(launch_session) etc.
• The implicit initial queued (fold default) is no longer materialized as a redundant event.
• Listener scope unchanged: launch transitions stay listener-invisible (widening I8 is a separate decision).

Whitelist meter

nosemgrep: run-status-write-surface: 47 → 10 (socket.go 40 → 3). Every survivor has a §6 disposition: W6/W8 (integrate v2), W9 ×4 / W10 (quarantined law boundaries), appendRunResolvedByUser (B3 verb), plus the sanctioned constructor itself.

Tests

• O8 added to the law-sweep observation set → L4 terminality, determinism, L1a idempotent convergence, and stream fixed-point laws now cover launch observations automatically.
• New: TestStepLaunchProgressStageMapping (stage→status + re-affirmation silence), TestStepLaunchFailureCarriesReason (artifact order, launch_<step>, launch_bootstrap fallback).
• go build ./..., go test ./internal/daemon (19.4s ok), make lint (all semgrep fixtures pass, 0 findings), full go test ./... — only the two pre-existing tmux-environment integration failures (TestAgentClaudeCreatesMultiplexerSession, TestAgentStatePersistence), reproduced identically on main @ f39a19b.

Docs in the same change set

run-state-machine.md §1 (writer table + single-constructor note), §2 (O8), §3 (O8 matrix rows), §5 (L9 + launch_<step> reason family), §6 (W2–W5/W7 → integrated), §7 (D-B1); AGENTS.md status-write-surface; roadmap B1 + watchlist rows 1/6.

Per the routing rule this is a core change: frontier + human review — please review before merging.

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