[Birfy]

Fixes #275

Risk tier: T1 (controller label risk:T1). Not merged yet: it shares generated files (core/client.js, patches/ds-bot/0003, 0008) and docs/subsystems/core-client.md with #434, which is awaiting approval. It merges after #434 lands, rebased if needed.

The NEW divider no longer stays in a chat for the whole visit. Once you have seen it and the chat moves on, it goes, the same as when you leave the chat and come back. This covers the case in the issue (a friend's typed line in my own Bot's chat, divider stuck while A stayed in the chat and B's next four lines came in), and it works the same way in every chat.

Cause. The divider is not specific to friend lines. It compares turn times with the visit's seen (when the chat was last left) and entered (when this visit opened), and both stayed fixed until the chat was left. So a divider that was right when you opened the chat stayed there however long you stayed, even after new turns came in below it. A friend's line in the Bot's own chat is a normal visible turn (not an exchange turn), so it went through the same path. On the reload in the self-test, the line only showed up after the reload (#420), so a divider at that moment was correct. The bug was that it never went away afterwards.

What changes (client only)

• cells.js: movedOnSince(visit, turns, hiddenTurns) is true when a turn the chat shows began after the visit opened, such as a friend's next line or my own message. Hidden exchange turns do not count. settledVisit(visit) moves seen up to entered, so no turn falls inside the "new" window any more.
• header.js NewMessagePills: it already tracks whether the divider has been on screen (view.divider === 'in-view'). Once it has, and the chat has moved on, it calls actions.settleVisit(sessionId), and the trailing divider, the reply divider and the unread opening all go. A divider that is still scrolled out of view (the ↑ pill points at it), or a chat where nothing new happened, keeps it until the visit ends, as before.
• index.js: new action settleVisit(id). The saved per-Bot "last left" clock (seenAt) and the unread dots (Friend's line on the sharing home: lands unmarked in the Bot's own chat with no unread badge, first line needs a reload; social/overview lists no per-Bot friendships #420) are unchanged.
• There is no timer, so nothing is marked seen just because time passed and nothing flickers. The divider only goes at the moment a new turn shows up at the bottom.
• Docs: docs/subsystems/core-client.md. Changelog fragment changelog.d/275-new-divider-settles.fixed.md. Regenerated core/client.js and patches/ds-bot/*.

Tests: core/test/turn-tail.test.js #275: the divider over a line that came while away is gone once the visit settles (trailing and reply dividers). movedOnSince covers only earlier turns, a turn with no start drawn yet, the next line, a hidden exchange turn and no visit. settledVisit leaves a visit with nothing unread or no record as it is. It also checks the pills → settleVisit wiring.

Docs-not-needed: user docs. Behavior is described in core-client.md and the changelog.

Ran: ARCH_DOCS_BASE=origin/main TZ=UTC npm run verify on the tip (on main 934cec9): passes (lint, arch-docs OK, bundle check, patches check, core 994 / social 269 / tree 56 / timeline 80 / scripts 88 / interop 37 / live-e2e 16, 0 failures).
Not run: two-home live run against Bot Social in a real browser (divider on screen, then the friend's next line), smoke bench, Desktop app.

[Birfy]

Self-review (Birfy, owner's Bot)

I read the full diff at the tip.

• Scope: client only. cells.js gets the two pure helpers movedOnSince and settledVisit next to unseenSince. header.js NewMessagePills gets one effect, index.js gets the settleVisit action, plus tests, docs, the changelog fragment and the regenerated bundle/patches. Nothing in host, authz, social plugin, or Add Test connection to Bot settings → Model #434's bot-settings.js / models.js / authz.js / channel.js. It also stays clear of Friend's Bot chat on the receiving home: 'Tool removed' line, turns/steps/tok/s footer, composer placeholder flips to coding copy #419's ContextCell / status-line code.
• Correctness: after settledVisit, seen === entered, so every divider condition is false: TurnTailCell (start in (seen, entered]), TurnProcessCell (end in (seen, entered]), unseenSince for the unread opening, and the ↑ pill count. The opening separator returns to the column label (--bt-first-sep), as for a read chat. A visit with seen null (no record) or already caught up is returned as is, so the state does not churn.
• When it clears: only when above.seen is true (the divider was in view, the same signal the ↑ pill uses) and a shown turn has first > entered. Hidden exchange turns (roster.exchangeTurns) do not count. There is no timer and nothing on mount (a turn that is already there cannot start after entered). A divider scrolled out of view stays. Clocks: the same server-turn-time vs browser Date.now() comparison the existing divider logic already makes.
• Persistence: seenAt (last-left clock) is still written only on leave / pagehide, and the Friend's line on the sharing home: lands unmarked in the Bot's own chat with no unread badge, first line needs a reload; social/overview lists no per-Bot friendships #420 unread dots are untouched. Leaving after a settle stores Date.now() as before.
• Consistency: the same rule in every chat, which matches the issue's "as in other chats". The decision is recorded on Received friend's typed line: the NEW divider stays after the message was read (header and People with access name fixed in #292) #275.
• Tests: 5 new Received friend's typed line: the NEW divider stays after the message was read (header and People with access name fixed in #292) #275 cases in core/test/turn-tail.test.js: divider present then gone for the trailing and reply dividers, the movedOnSince edges, settledVisit no-ops, and the wiring.
• Nit, not blocking: the wiring test is a source-text match (like looks.test.js), because NewMessagePills needs the DOM. A live browser check is listed under Not run.

Verdict: PASS
Tip SHA: fef653d
Ran: ARCH_DOCS_BASE=origin/main TZ=UTC npm run verify on the tip (passes, 0 failures); CI green on the tip.
Not run: two-home live run in a real browser (divider on screen, then the friend's next line), smoke bench, Desktop app.

[Birfy]

Verdict: PASS

Tip SHA: b1ab6e4

Ran:

• Merged origin/main (2b22965, includes #434) into fix/275 as a merge commit; regenerated generated files per AGENTS.md conflict recipe (git checkout origin/main -- patches/ds-bot, node core/scripts/build-client.mjs, node scripts/ds-bot-patches.mjs generate + check) → pass
• ARCH_DOCS_BASE=origin/main TZ=UTC npm run verify (Node 24) → pass (lint + arch-docs OK, plugin lint, bundle check, patches check, core 1002 / social 269 / tree 56 / timeline 80 / scripts 88 / interop 37 / live-e2e 16, 0 failures)

Not run:

• Two-home live run against Bot Social in a real browser (divider on screen, then friend's next line)
• Smoke bench
• Desktop app

No actionable findings at this tip. Merge of main resolved the shared generated-file conflict with #434 by rebuild, not hand-merge. Controller label remains risk:T1.