[teamleaderleo]

The Mac queue was full. At 12:43Z glaeda-gui-std had 11/11 busy and 57 queued, glaeda-side-std had 44 queued, blacksmith-6vcpu-macos-26 was at its cap with 47 queued (oldest 120 min), and blacksmith-12vcpu-macos-26 had started nothing in 15 h. Every Mac job a PR doesn't need makes that wait longer for the PRs that do.

The rule (Leo, 2026-10-27): "skip compiles that add no signal before adding machines ... a PR that changes no Swift does not Mac-compile".

Why #28326 still got both Mac jobs

At 5d76d56, #28326 changes only plans/cmux-next/sidebar-owner.md, yet run 41055761832 queued cmux-next fast tier and cmux-next swift test. The cause is in ci-target-graph.py. It records a test target's reads as the repository paths its string literals name, and it cuts an interpolated literal at its first \(. ActionSurfaceParityTests.planURL and LinkExportTests.planURL build "plans/cmux-next/\(name)". So the graph lists all of plans/cmux-next/ as a read of CmuxNextActionsTests and CmuxNextAppTests. Every design note there (411 files) then routed to swift test and the generated tier.

Those helpers only ever open action-surfaces.json, actions.md and links.json, and all three are generated outputs.

What changes

1. Docs under a directory read. A doc (.md, .html or image) under a directory read counts as read only when one of these holds:

   • a string literal in the reading target's Swift sources (comment lines excluded) names it;
   • a literal names the directory itself, as a test that lists the directory would;
   • a generator writes it (scripts/cmux-next/generated_outputs.py).

   Otherwise it is a doc no test reads, and on its own it runs no Mac tier, as any other doc already does. Non-doc files there (JSON, text) keep the directory read, because a computed name may open them. A doc that no directory read covers, or one under Packages/, routes exactly as before.

2. The Mac fast tier follows its own inputs. It builds only the CmuxNext package and runs a few of its suites (fast-tier.json's swift entries). So a new route output, fast_tier, is true only for these changes:

   • a package target or a local package it uses;
   • a file a test reads;
   • a generated input;
   • an input of every tier;
   • the Release-compile inputs;
   • the tier's own registry and runner.

   A cmux-tui-only or app-host-only PR keeps its daemon and scheme tiers but no longer starts the Mac fast tier. fast-tier-cargo still runs on Linux. The fast-tier job's if: and the placement's CASCADE_RUNS both read the new output. A failed route (no output) and a feat-cmux-next push run the fast tier as before. A skipped job reports as skipped, as the Mac fast tier already does on a web-only PR.

3. The routing replay compares fast_tier too. A base router without the output ran the fast tier with any Mac tier. A dropped fast tier is explained only by its own reason. A narrowed Swift target set is explained only by the doc reason. A widened set is never explained.

Measured on the queue

From the 12:43Z fleet dashboard, 111 cmux-next Mac jobs were queued on 71 PR branches. I routed each PR's current files through the base router and through this one:

	jobs	PRs
queued cmux-next Mac jobs on PRs	111 (54 swift test, 53 fast tier, 3 Release compile, 1 daemon)	71
that this route skips	18 (15 fast tier, 3 swift test)	16
their summed queue time	554 min (oldest 101 min)

#28326 now routes to no Mac tier at all. The other 15 PRs are cmux-tui Rust, optchat or nightly-script changes that still run their daemon and scheme tiers. Caveat: some of those runs were at an older head than the PR's current files.

Replay of the last 60 merged feat-cmux-next PRs, base router against this one: none unexplained, 24 the same. The other 36 change as follows:

• 33 drop only the Mac fast tier, because they are cmux-tui-, optchat- or script-only.
• carry of #26682: fix(setup): report actionable harness authentication checks #28187 drops generated and swift test, because its only Mac input was plans/cmux-next/setup-DESIGN.md.
• sidebar: a hover control stays lit while its menu is open, and lights alone #27912 and cmux NEXT: one machine link state for the sidebar and the agent pane; a down machine reconnects on use #26786 narrow their Swift targets: CmuxNextActionsTests goes, because only a plans doc reached it.

A doc that no directory read covers, or one under Packages/ (it may be a bundled resource), routes as before.

Tests (red on the base router, green here)

• tests/test_cmux_next_route.py gains two classes.
  • UnreadDocs: plans: log three sidebar commits that reached the base without a Sidebar-Look trailer (base red) #28326's file alone runs no Mac tier, and beside Swift it routes like the Swift alone. actions.md (a generated export the tests name) keeps its tiers, and non-doc files keep the directory read. Literal fixtures check four cases: a comment mention, a name passed to a helper, a listed directory and an explicit path. Unreadable sources keep the read.
  • FastTierRoute: package, schema, registry and toolchain inputs run the fast tier; cmux-tui, optchat and App/ changes don't; push, full-ci and vendored pins run it.
• tests/test_cmux_next_checks_workflow.py (MacFastTierFollowsTheRoute) evaluates the job if: with the route's outputs. A daemon-only PR starts no Mac fast tier but still runs fast-tier-cargo, and the placement cascade list reads fast_tier.
• tests/test_cmux_next_route_replay.py (FastTierAndDocs) covers the replay changes above.
• Also green on the lane: test_cmux_next_checks_workflow (165), test_ci_next_macos_cascade, test_ci_side_lane_placement, test_ci_runs_on_fallback, test_car_guards, test_ci_compile_test_plan, test_ci_cmux_next_compile_status, test_job_input_fingerprint, test_settings_stamp_not_committed, test_cmux_next_generated_fold and test_cmux_next_tip_swift_suite.

Risk: low. This is routing only, with no permission, secret or runner change. The worst case is a doc that a test opens through a computed name missing its swift test on a PR. The tip Swift suite and the base push still cover it.

Agent session: agent session

🤖 Generated with Claude Code

[github-actions]

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

The feat-cmux-next push run https://github.com/manaflow-ai/cmux/actions/runs/41070142155 at 99e8529 failed: cmux-next generated files (shared build).
Those jobs last passed at 483fbe3. This pull request is one of 4 merged since: #27828, #28258, #28334, #28088.
If the failure is in your change, fix forward on feat-cmux-next. Pull requests run only the tiers their paths reach (docs/ci/cmux-next-tiers.md); label a batch PR full-ci to run them all before merging.

[github-actions]

Shipped in:

• cmux NEXT nightly 1.0.0-nightly.4107172498601 (6ce1bb31ea)
• cmux NEXT nightly 1.0.0-nightly.4107277115701 (57fa372ffc)
• cmux NEXT nightly 1.0.0-nightly.4107322527101 (f287294861)
• cmux NEXT nightly 1.0.0-nightly.4107504903001 (3c643f9b99)
• cmux NEXT nightly 1.0.0-nightly.4107718419001 (6b9c028ef3)