[BUG] Remote control: background subagent work is invisible (no history, silent kill on session limit, stale View DIFF/PR chips)

Environment

• Claude Code version: 2.1.198
• Platform: win32 (Windows 11 Pro), VS Code extension entrypoint + mobile app remote control

Description

Three compounding problems make remote-control runs that delegate to a background Agent subagent effectively unauditable from the user's perspective:

1. Subagent work is invisible in session history. The user asked (from the phone) to run a long pipeline "in a new session"; the assistant spawned a background Agent subagent. The main session then contains only ~3 short messages ("I'll spawn it" / "Launched"). The subagent's full transcript (~200 entries, 30+ file edits) exists only on disk under projects/<project>/<session>/subagents/agent-*.jsonl — it is not shown in the mobile app, the session list, or included when the session is teleported. To the user the session "shows nothing" while their working tree has extensive changes.

1. Session limit kills the subagent silently mid-task. When the account session limit hit, the background agent was terminated mid-edit (partially staged changes, no report, no completion message). No notification reached the mobile app — the last thing visible there was the earlier "Launched, I'll report back" acknowledgment. Result: a half-finished uncommitted change set with no visible trail of what was done.

1. Stale "View DIFF" / "View PR" chips on mobile. Immediately after the reply, the mobile app showed View DIFF / View PR actions that linked to an old, already-merged piece of work. The run in question created no commit and no PR, so the chips could not refer to it. Misleading, made the user think the wrong work had been done.

Expected

• Subagent activity (or at least a summary/progress) should be surfaced in the parent session history and survive teleport.
• A session-limit kill of a running background agent should append a visible "agent terminated mid-task" message and notify connected remote clients.
• DIFF/PR chips should only appear when the current run actually produced a diff/PR.