Second calibration pass after the cli-runner reliability whale fix
(#109772) and the stripe-wall correction (#109899): the compact group
hints drifted below loaded-fleet reality, so FFD packed the heaviest
groups into ~300s bins (checks-node-compact-large-2 at 242-314s shard
wall, up to 389s job wall) while tail bins idled.
Method: parsed [shard:*] begin/end timestamps from all 147 compact job
logs across seven green CI runs whose head SHAs carry the whale-fix
hints (runs 29605136624, 29605203485, 29605983019, 29606701461,
29611308972, 29611457693, 29611500865; 7 samples per group). Each hint
is the per-group mean after dropping cache-warm/contention outliers
outside [median/1.5, median*1.5].
Packing cap: with honest loaded walls a 220s cap no longer fits either
pool (adds one job to each); 235s keeps the same job count (6 large +
15 small + dist) and flattens the ceiling. Median job setup overhead
measured 60s (p90 87s), so a 235s bin stays near the 5-minute PR
budget.
Predicted bin shard walls (sum of measured group means):
before: large 220/301/200/219/257/112, small heavies 251/235/218/217/215, max 301
after: large 235/232/229/228/228/156, small heavies 236/234/234/234/233, max 236
large-pool max/mean 1.38 -> 1.08
Biggest hint deltas (old -> new): startup-core 98->156, core-tooling-4
71->125, core-unit-fast-isolated 50->90, core-tooling-3 82->108,
runtime-server 14->29, storage-state 55->70, media-ui 113->124,
tui-pty 103->116, runner-cli-1 18->8, unit-src-security 108->95.
Exclusive bins keep their 150s cap and 5-bin count: tui-pty (116) no
longer shares a bin with tooling-isolated (166s combined measured);
FFD now pairs tooling-2 with tooling-isolated at 144s.
STRIPE_FILE_SECONDS_HINTS left unchanged: measured stripe walls sit in
exclusive bins far below the packing ceiling (tooling stripes
94-125s), and refitting per-file hints would reshuffle stripe
membership and invalidate the measured group means above.
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