[[NO_REPLY]] marker leaks into Slack replies

[sentry-junior]

When a terminal assistant message mixes normal prose with [[NO_REPLY]], Junior posts the full text to Slack, including the reserved marker.

Observed in production: a task turn that intended silence ended with prose plus a trailing [[NO_REPLY]], and Slack received that combined message. Session: https://junior-prod.sentry.dev/conversations/slack%3AC0BSRCZ1F9T%3A1788188446.835629

Verified behavior

• Prompt/task contract: intentional silence requires the final message to be exactly [[NO_REPLY]].
• isNoReplyMarker() only matches whole-message equality (packages/junior/src/chat/no-reply.ts).
• After #1714, decideReply() suppresses only exact marker-only text and delivers any mixed marker+prose unchanged (packages/junior/src/chat/services/assistant-reply.ts).
• buildTurnResult() logs ai.no_reply_marker.mixed_text for mixed cases but still returns deliverable text that retains the marker (packages/junior/src/chat/services/turn-result.ts).
• no-reply.ts comments that containsNoReplyMarker exists to detect leaks "before publication strips or rejects them," but delivery does not strip.
• PR fix(chat): deliver answers that mention [[NO_REPLY]] #1714 description said mixed text would strip the marker and post the rest; current code and tests deliver the marker inline.

Evidence

• Thread example above (assistant reply ended with visible [[NO_REPLY]]).
• Repeated production warnings: ai.no_reply_marker.mixed_text on project sentry/junior (for example around 2026-08-31T15:03Z–15:08Z, including traces such as ff5484791527491f82bba63e031e6c83).

Related

• #1714 changed mixed mentions from silence to delivery.
• #1030 is a different no-reply terminalization bug (timeout resume).

Reported by Matt Quinn.

Requested by Matt Quinn.

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