Busy ack rewrites {d}/{t} typed in the user's own message #1634

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: 1bab102216224d0f902e6261bda01285
Branch: dev/1634-busy-ack-rewrites-d-t-typed-in-the-user
Base: 331dd62
At: 2026-10-29T04:37:30Z

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

Written-by: FlyBot Lead

What happens

The busy ack (#1584, landed in #1630) quotes the human's message back inside 「…」 / "…". If that message itself contains the letters {d} or {t}, the quoted part is rewritten: {d} becomes the running tool's description and {t} gets dropped (empty when there is no tool words), so the ack no longer echoes what the person wrote.

Reproduced through the real host path (install(), live={"s1":{turn:{},tool:"bash"}}, chatOwners containing s1, uiLanguage zh-CN):

• message 把 echo ${d} 改成 echo ${t} → ack Saw "把 echo $running a command 改成 echo ${t}" — I’m running a command right now, back on it in a moment.
• message python 的 f"{d}" 也要改 with tool edit → ack 「python 的 f"改文件"…」收到，手上在改文件，这步完了就来。

The second one is the worst shape: {d} silently becomes 「改文件」 inside the user's own code, so the ack attributes words to the person that they never wrote.

Why

core/src/host/busy-ack.js:117:

const fill = index => pool[index % pool.length].replaceAll('{t}', topic).replaceAll('{d}', doing ?? '')

Two passes over the same string. The first pass inserts topic, which is text taken from the user's message (topicOf(), :27-49); the second pass then scans the freshly inserted user text as if it were template markup. Any {d} / {t} the person typed is therefore treated as a placeholder.

Repro (unit level, no host needed)

composeBusyAck({ message: '改 ${d} 这行', tool: 'bash', uiLanguage: 'zh-CN' })

Current output contains 「改 $跑命令 这行」 instead of 「改 ${d} 这行」. Keep the message short on purpose: topicOf() clips the topic at TOPIC_MAX.zh = 16 chars, so a long sentence hides the effect behind the ellipsis.

Expected

Text quoted from the message is echoed verbatim: {d} and {t} typed by the person stay {d} and {t} in the ack. Only the template's own placeholders are substituted.

Scope

S, one line plus tests:

• busy-ack.js:117 — substitute in a single pass so inserted text is never rescanned, e.g. replace(/\{(t|d)\}/g, (_, key) => key === 't' ? topic : (doing ?? '')). Keep the previous-avoidance loop and everything else as it is.
• Tests in core/test/busy-ack.test.js (and the client mirror if it renders the same text): a message containing {d} and one containing {t}, with and without a running tool — the ack quotes them unchanged; plus the existing 10 green cases untouched.

Not this issue (observed, out of scope)

• ackLanguage() (:17-25) decides zh when cjk * 2 >= latin, so a Chinese sentence carrying many Latin characters (a code snippet, a path) is answered in English: 把 echo ${d} 改成 echo ${t} → 4 CJK vs ~10 Latin → en. That is a judgement call about density, not a correctness bug; tracked separately if it is worth changing.
• The ack only fires in a Bot's own chat, never in rooms (shouldNoteBusyAck() needs ownChat). That is the gap fix(chat): busy / background send stays silent — need a short spoken acknowledgment #1584 left on the room side; separate work.