Pass instructions to /compact so the summary can drop what the next task does not need

[KelvinChung2000]

Problem or use case

When a thread moves on to a new task, the new task needs some of the existing context but not all of it. For example, the interface decisions from the finished task stay relevant, while its debug output and dead ends do not. A plain /compact cannot be told which is which, so the summary keeps a generic mix of both.

Claude Code's /compact takes optional instructions for the summary (/compact <optional custom summarization instructions>, the argument hint T3 already receives per #14789). T3 does not pass them on. On main (98bc998):

• apps/server/src/orchestration-v2/RunExecutionService.ts:1441 routes a message to compactThread only when its whole text is /compact.
• apps/server/src/orchestration-v2/Adapters/ClaudeAdapterV2.ts:9326 replaces the message text with "/compact" inside compactThread.

So /compact drop the X debugging, keep the Y interface decisions never takes the compaction path and is sent as an ordinary turn. I have not checked what Claude Code then does with it, or how T3 renders the result.

Proposed solution

• Route /compact <text> to compactThread by matching the command rather than the whole message.
• Pass the text through to Claude Code as /compact <text>.
• A provider whose compaction takes no instructions rejects the argument with an error instead of compacting without it.

Smallest useful scope

Claude only. /compact <text> typed in the composer reaches Claude Code with its text and shows as a compaction in the timeline.

Alternatives considered

• Start a new thread with a hand-written summary. This loses the thread's lineage and takes manual work.
• Send the instructions as a normal message first, then /compact. The instructions become part of the history being summarised, and the summariser is not bound to follow them.

Related

#14789 (argument hint for /compact), #15106 (agent-initiated compaction; one comment asks to pin the task statement through compaction), #17170 (compact-before-send).