dashboard apply: serve argv carries --release-revision, and observed tmux absence is absence

[gunbai-bot]

Two fixes split out of the srv1 lab integration branch (#11396), which is lab-only and must not merge; review 66509 on that PR asked for exactly this split.

What

• gunbc.roadmap.roadmap_dashboard_instance dashboard_instance_serve_argv takes the release revision and emits --release-revision, which serve has required since Phase A: bind release identity to the serve process, compare it at readiness #7909. roadmap_dashboard_instance_apply dashboard_ensure_service reads it from git rev-parse HEAD in the instance's repo root before starting the service, and refuses (typed, dashboard_exec_refused) when that read fails or is empty rather than launching a serve that will refuse later.
• extdeps.tmux tmux_has_session_stderr_is_absent: tmux has-session exits 1 both for can't find session: <name> (cmd-find.c) and for no-server (the client.c spellings already modeled). Both are observed absence. dashboard_instance_observe no longer reports an absent service session as an unobservable one; every other nonzero exit still refuses.

Test plan

• roadmap_dashboard_instance_apply_witness_test dashboard_service_is_named_and_scoped_off_production updated to assert the --release-revision argv. These commits ran on the srv1 lab branch (they are what got the lab dashboard serving); no local interpreter in this session, so CI is the executing evidence here.

🤖 Generated with Claude Code

[gunbai-bot]

review 66635: the empty CommitSha sentinel is gone. dashboard_apply_plan now takes CommitSha?. Apply-after-preflight passes Present with the admitted source revision; bootstrap and ensure-roots pass none because those plans cannot contain DashboardEnsureService. dashboard_ensure_service itself takes a required CommitSha and no longer string-compares emptiness. If ensure-service ever reached a fold that did not admit a revision, that arm refuses before launch.

— sent from quick-lynx-569