Timeline panel: a 59.9 s turn prints 60 s, and the formatter has no carry like formatMs #1783

Implementation: FlyBot (ours) — PR follows within 24h. Do not pick up without a pickup-ok comment on this issue.

Written-by: FlyBot Lead
Claimed-by: FlyBot Lead
Claim-Id: 0747d895cd8d451dacc582837536c59c
Branch: dev/4-panel-duration-carry
Base: 92a4cf2
At: 2026-10-30T05:09:57Z

Implementation: FlyBot (ours) — PR follows within 24h. Do not pick up without a pickup-ok comment.

Written-by: FlyBot Lead

What a person sees

In the Timeline panel a turn's duration under a minute is printed as 60 s for 59.9 s — a value one second short of a minute, labelled with a unit that cannot hold it. Just below it the panel prints 9.9 s; at 10 s it prints 10 s, so 10.0 s and 10 s also both appear for the same tenth.

Where

plugins/timeline/client.js:163

if (ms < 10_000) return `${(ms / 1000).toFixed(1)} s`
if (ms < 60_000) return `${Math.round(ms / 1000)} s`
if (ms < 3_600_000) return `${Math.floor(ms / 60_000)}m ${pad(Math.floor((ms % 60_000) / 1000))}s`

59_999 → Math.round(59.999) = 60 → 60 s; the m branch only starts at 60,000 ms, so the one value that should read 1m 00s reads 60 s.

Reproduction (live main 92a4cf262cb8f2469f800f12e5cfe006abb4d538)

fmtDur is module-local to the client panel; the panel's duration column is its only reader. Testable through the panel's render (the existing plugins/timeline/test/panel.test.js drives it) or by exposing the function to the test:

fmtDur(59_999) // '60 s'   ← should be '1m 00s'
fmtDur(9_999)  // '10.0 s' ← should not print a tenth it rounds away
fmtDur(60_000) // '1m 00s'

Expected

A duration never prints a number its unit cannot hold: carry into the next unit after rounding, exactly as #761 fixed plugins/timeline/src/digest.js's formatMs (60s, 60m, 1h60m) — the panel's own copy of the formatter was never fixed.

Scope

fmtDur (~5 lines) plus two boundary cases (59_999 and 9_999) in plugins/timeline/test/panel.test.js and a changelog.d/ fragment. plugins/ is outside the patch chain: no patches/, no generate.

Dedupe (searched 2026-10-30, open + closed)

• fmtDur → only formatMs carries past its unit: 60s, 60m, 1h60m in the run report #761, closed. formatMs carries past its unit: 60s, 60m, 1h60m in the run report #761 and Carry a duration into the next unit instead of printing 60s, 60m and 1h60m #763 fixed formatMs in plugins/timeline/src/digest.js; neither touched plugins/timeline/client.js, so the panel still has the old shape.
• "60 s" → 52 hits, none about this formatter.
  No duplicate.