[teamleaderleo]

What was wrong

#28480 (main) and #28484 (feat-cmux-next) added the dead-label rule (simple_pool_picker.blacksmith_dead(): nothing running on a label and no job started on it in the hour before the snapshot; a truncated snapshot proves nothing) to the DEV daily picker and nightly_sign_runner.py. The cmux-next macOS cascade (next_macos_cascade.py) still judged Blacksmith labels by the oldest-wait stall rule alone. So once blacksmith-12vcpu-macos-26's queue was cleared, its five slots read as free, and the cascade sent jobs, overflow and the bot's retry_runner to a label that had started nothing for about a day (2026-10-30).

What changed

One wrapper, simple_pool_picker.dead_macos_26(), built on #28484's blacksmith_dead(), is now read by every picker on this branch. When every label shows dead it returns nothing, because with no label showing life the snapshot gives nothing to choose between. Pickers changed:

• next_macos_cascade.py: Seen.dead carries the dead labels from the fresh snapshot, from a stale reservation reading, or from a snapshot only old enough to show dead labels (stale_seen(), up to the six-hour evidence window). A dead label:

  • is stalled whatever its queue says, so it gets no slot and is not the retry_runner;
  • counts as full for a feed's compile (fresh_stalled);
  • is a dead 6 vCPU, which takes no overflow even when the owned route is a dead end, since dead_end() no longer waives it.

  With no fresh counts, a feed's compile no longer takes a 6 vCPU label that the older snapshot shows dead.

• nightly_sign_runner.pick(): with no fresh snapshot it skipped nothing. It now skips a dead variable label. dev_landing_place.py's overflow (OVERFLOW_LABEL, 12 vCPU) and nightly_build_runner.py use this pick. dead() now delegates to the cascade instead of keeping its own copy.

• nightly_build_runner.blacksmith_route(): a label a stale snapshot shows dead is no alternative to the excluded one.

• simple_pool_picker.state_from() (ci.yml's picker on this branch): a dead macOS 26 label has no free slot.

Nothing changes when there is no start evidence: no label_started map (an older janitor), a truncated listing, a snapshot older than six hours, or every label dead.

The main side (ci.yml's simple_pool_picker.state_from() there) is #28516.

Tests

New regression tests, each run against the old scripts first. All 12 fail there (6 failures and 6 errors) and pass here:

• tests/test_ci_next_macos_cascade.py DeadLabel (5)
• tests/test_nightly_sign_runner.py test_an_unverified_pick_skips_a_dead_variable_label
• tests/test_nightly_build_runner.py DeadLabel
• tests/test_dev_landing_place.py test_the_overflow_skips_a_dead_label_a_stale_snapshot_shows
• tests/test_ci_simple_pool_picker.py test_a_dead_macos_26_label_with_its_queue_cleared_has_no_free_slot

Every suite that imports these pickers passes locally (19 files, including test_cmux_next_checks_workflow.py, test_ci_side_lane_placement.py, test_ci_pr_runner_pool.py and test_ci_runs_on_fallback.py).

Risk: placement only. It acts only on positive start evidence from a complete, recent snapshot, and the worst wrong call keeps a job on the label that last showed life.

Overlap: #28249 and #28391 (open, same owner lane family) add a separate label_full_or_dead adapter fed by bs_health and gates. This PR does not touch that adapter. The two compose: each only adds labels to stall.

🤖 Generated with Claude Code
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[github-actions]

cmux status _{(one comment, edited in place; each line is updated by the job that owns it)}

Review 03c8b08: HQ feed card · gallery before/after runs · checks

App of this head (app.zip, kept 1 day)

gh workflow run reload-build.yml -R manaflow-ai/cmux --ref feat-cmux-next -f tag=pr28515 -f ref=dep-fleet/cascade-dead-label -f platform=macos -f backend_mode=local

[teamleaderleo]

Owned by an agent session · session

[github-actions]

Shipped in:

• cmux NEXT nightly 1.0.0-nightly.4112547320201 (3e65269f80)
• cmux NEXT nightly 1.0.0-nightly.4112891057101 (ac6b39be7f)
• cmux NEXT nightly 1.0.0-nightly.4112983685701 (81085d9646)
• cmux NEXT nightly 1.0.0-nightly.4113159963901 (9408230f7a)