Plan mode gains a no-plan-file variant, a stricter write check and a bypass notice

What

Plan mode is the permission mode where Claude works out a plan before changing anything. Several parts of it changed.

• Plan mode now has a variant with no plan file. Claude is told: "This session has no plan file. Give your plan to the user as text in your reply, and do not write it to a file." Only the user can leave plan mode, by changing the permission mode.
• When that variant applies, Claude gets a ready-made full or shorter reminder with no plan file path. The full reminder is sent again whenever a plan file appears or disappears, and the notice for leaving plan mode leaves the path out. Before, the reminder was always built from the plan file path. The plan mode reminder now also carries planFilePath.
• With planModeWriteFloor set, a tool call that is not read-only and would otherwise go through now asks with "Cannot call X while in plan mode." Bypass modes and plugin tool.check verdicts can no longer override this. A plugin verdict that is held back is reported under the name planModeWriteFloor. Before, only a plain plan-mode permission ask existed. A related gate, tengu_auto_mode_tool_check_verdict_held, has not been read.
• If a session was started with bypass permissions, then after 800ms in plan mode a notice is added: "Session was started with bypass permissions, so plan mode won't ask before most edits or commands."
• Separately, a new reason label reads "after an earlier read of the attached claude.ai Project failed".

Why

In practice, plan mode works in sessions that have no plan file, write tools are harder to slip past it, and you are told when plan mode will not stop most edits because bypass permissions were on from the start.