timeline: a Bot busy across the whole window reads as a turn-less Bot #2543

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: c4482314c115496882c58bd83dfd98e4
Branch: dev/3-timeline-busy-window
Base: d400edb
At: 2026-11-05T14:27:50Z

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

Written-by: FlyBot Lead

What happens

A Bot that is busy across the whole window is reported as idle. plugins/timeline/src/digest.js:87 only raises the busy flag when turns > 0:

if (turns > 0 && busyShare >= BUSY_MIN) flags.push(`busy ${percent(busyShare)} of the window`)

and :140-143 prints either - busy N% of the window or - no turns in the window off the same condition. But turns counts only the turns that began inside the window (:78 says so in the comment), while busyShare is busyMs / windowMs. So a Bot whose turn opened before the window started and ran through it has turns === 0 and busyShare === 1, and the team run report prints - no turns in the window with no busy marker — the exact case docs/subsystems/timeline.md invariant 5 covers, and the opposite of what timeline/health answers for the same window.

Reproduction

Clean base d400edb74798b71e233eccd46f221eaef782ff5d, only the new case added to plugins/timeline/test/digest.test.js:

not ok 18 - a Bot busy the whole window reads as busy, not as a turn-less Bot
  + actual   []
  - expected [ 'busy 100% of the window' ]
# tests 18 / # pass 17 / # fail 1   (exit 1)

Run: cd plugins/timeline && TZ=UTC node --import ./test/resolve.mjs --test test/digest.test.js.

Expected

A Bot whose busy share clears the threshold reads as busy whether or not a turn began inside the window: the flag and the line both come from busyShare, not from turns. A Bot that was genuinely idle still reads - no turns in the window, and timeline/health and the digest agree on the same window (the threshold constant stays where it is).

Scope

• plugins/timeline/src/digest.js — decide busy from the busy share alone (≈+8/−1), keep the counted === 0 wording for genuinely idle Bots.
• plugins/timeline/test/digest.test.js — one case with two controls: health already calls the same window busy, and a truly idle Bot still reads - no turns in the window (≈+22/−0).
• docs/subsystems/timeline.md — one sentence aligning the invariant with the reading (≈+1/−1).
• changelog.d/<this issue>-timeline-busy-window.fixed.md.
• Generated once: none of core/client.js / patches/ds-bot/0008* / mirrors are touched by this change.

Tier: T2 (plugins/**).

Duplicate check

Searched before filing: "no turns in the window" → 0 hits; timeline busy in:title → 0; digest in:title → 22, the oldest pair #582/#583 are the feature itself (closed), none of the rest is about the busy/turns disagreement. Open PRs at filing time touching plugins/timeline/**: #2540 (src/otel.js + its test) only — no overlap with digest.js.

Done when

The new case is red on the base and green with the fix, plugins/timeline is 142/142, timeline/health and the digest agree on the same window in the new test, and TZ=UTC ARCH_DOCS_BASE=d400edb7 npm run verify is exit 0.