fix(web): sending to an idle Claude thread no longer auto-compacts first

[jayleaton]

Opening a Claude thread that had been idle for about an hour showed the "Resume with less context" banner. If you then sent a message without dismissing the banner, the web client first dispatched a hidden /compact turn and queued your message behind it. So the thread started compacting before your message ran. Upstream reverted that behavior in pingdotgg#15771 (2188bdd8b5), but this fork had not picked up the revert. This PR cherry-picks it.

Summary

  onSend:
-   compactBeforeSend = resumeCompactionBannerItem !== null && !compactDisabled && ...
-   if (compactBeforeSend) startThreadTurn({ text: "/compact" })   // extra turn, message queued behind it
-   startThreadTurn({ ...message, dispatchMode: compactBeforeSend ? "queue" : dispatchMode })
+   startThreadTurn({ ...message, dispatchMode })

The banner stays. Its Compact button still compacts on request, and Keep full history still dismisses it. Sending a message no longer compacts implicitly.

Evidence

• Before (live data, read-only snapshot): six /compact user messages today on Claude threads, each creationSource: web / inputIntent: turn_start. Each came after 73–1,215 min idle and was followed 6–58 s later by the owner's real message. Example: thread mcp:82e15b2e…, idle 81 min, /compact at 12:22:49.534Z started run 35, and the owner's message started run 36 at 12:22:49.738Z. None of these messages were typed by the owner.
• After: the send path no longer contains the /compact dispatch (diff above). apps/web tsc --noEmit passes. vp test run apps/web/src/components/chat/ContextWindowMeter.logic.test.ts passes (21/21). Not checked in a real client yet.
• Not covered by this PR: Codex compaction after idle (for example the Captain thread at 11:41Z). That one is native Codex auto-compaction: the previous turn ended at 90.3% of the context window, and Codex compacts at the start of the next turn. It is provider behavior, not app-triggered.

Merge Danger

Door: two-way. Straight upstream revert. It can be re-reverted.

Blast Radius: web/desktop composer. Only affects sending while the Claude resume banner is visible. Mobile never had this path.