Plan mode can pass the plan straight to ExitPlanMode in sessions without a plan file

What

Plan mode is where Claude plans its work for your approval before changing anything. Normally the plan is written to a file. In sessions that have no plan file:

• Claude is told to call ExitPlanMode, the plan-approval tool, with the whole plan in Markdown as its plan argument, and not to write it to a file: "This session has no plan file, so do not write the plan to a file."
• You see the plan on an approval card. Approving ends plan mode; declining keeps plan mode so Claude revises the plan.
• In the 'sparse' version of the instructions, Claude is told never to ask about plan approval in text.
• The plan-mode reminder for these sessions gains a variant (planGoesToExitTool) with a "Phase 5: Call ..." step. Before, it said "Give your plan to the user as text in your reply".
• ExitPlanMode requires the plan argument there and refuses subagents (helper copies of Claude), empty plans and plans over a size limit: "Pass the whole plan as non-empty text in the plan argument, and pass no other argument. This session has no plan file to read it from."
• The approval result includes "Your plan has been saved to" only when a plan file exists.
• Whether a plan can return to auto mode is now decided by canPlanReturnToAutoMode instead of isAutoModeGateEnabled.

The stock ExitPlanMode description captured under this release is 1,849 characters and unchanged from the previous release.

Why

Plan mode works in sessions that have nowhere to save a plan file, and you still approve or decline the plan through the same card.