Plan mode needs a discuss/debate state that doesn't wipe the plan view

Summary

While in plan mode (after EnterPlanMode, with a plan file already drafted), I tried to just discuss the plan in plain text with the user — no tool calls, no edits — before deciding whether to proceed. Two problems:

1. Sending a plain conversational turn while still flagged as "in plan mode" caused the harness to re-trigger a "returning to plan mode" event on the next turn, which appears to clear/wipe the user's view of the plan content from their screen.
2. The only sanctioned ways to end a turn while in plan mode are AskUserQuestion (structured clarification) or ExitPlanMode (request approval to execute). There's no third option for "let's just talk about this plan in freeform prose for a while before deciding anything" — every path back to normal conversation is framed as either a structured question or an approval request, and ExitPlanMode itself carries the connotation of "approve and go" even when the user's intent is just to keep debating.

Impact

The user explicitly asked to discuss/debate a plan conversationally multiple times. Each attempt either wiped their view of the plan or funneled back toward an approval prompt they hadn't asked for, causing visible frustration.

Requested improvement

Plan mode's turn-ending options should include an explicit "just discussing, not deciding yet" state — freeform back-and-forth about the plan's content, without wiping the plan display and without implying an approval decision is imminent. Something like a lightweight "stay in plan mode, keep talking" affordance distinct from both AskUserQuestion and ExitPlanMode.

Workaround used

Pasted the plan content as plain chat text (outside the plan-file UI) so it wouldn't disappear, and avoided further EnterPlanMode/ExitPlanMode calls for the rest of the session per the user's request.