[Feature Request] ExitPlanMode lacks defer/abandon option, trapping users in plan mode

Bug Description
Plan mode UX gap: no way to defer/abandon a plan.

ExitPlanMode only means "approve this plan for execution." If a user wants to park a plan and do something else (edit other files, stash context to project docs), they're locked in — plan mode restricts all file edits to the plan file only. The only escape is /compact, which resets mode state as a side effect, not a designed flow.

Three ExitPlanMode rejections happened in sequence because the tool rejection message field was the only way to communicate intent ("stash the plan and execution context locally"), but ExitPlanMode has no parameter to express "defer" or "abandon" — only "approve."

Note: The tool rejection messages the user typed were clear intent signals that the system could have interpreted as "exit plan mode without approval." The user wrote "Stash the plan and execution context locally referring the session to continue in as I need to pursue this later" — this unambiguously means "I don't want to execute now, let me out." But ExitPlanMode treats all rejections identically: stay in plan mode. The agent has no tool to break out on the user's behalf.

Suggestion: Add a defer/abandon option to ExitPlanMode (e.g., action: "defer" | "approve" | "abandon") so users can exit plan mode without implying approval. Alternatively, interpret rejection messages containing intent keywords like "stash", "later", "defer", "park" as a signal to exit plan mode gracefully.

Environment Info

• Platform: win32
• Terminal: windows-terminal
• Version: 2.1.44
• Feedback ID: 20852c01-1181-4639-b71e-5088ab9336ba