Web plan-mode feature with two lifecycle-coupled halves. The node entry mounts @deepseek-ai/dsh-plan-mode with the Web product's active and default mode policies; the browser entry contributes a session-scoped selector to conversation.composer.controls.

The selector distinguishes unavailable capability (planMode === null), committed mode (active), and the target queued for the next model-request boundary (pending, including pending: false). Selecting a mode never cancels a running turn. It remains available while generation is running, disables only during its own RPC, and displays the host-confirmed pending target until a logged plan/mode event commits it. The transparent native select mirrors keyboard focus onto the visible chip and carries a dynamic accessible description of the committed and pending modes.

The model exits plan mode through the stable exit_plan_mode tool. Its plan review uses the composed Web question channel: approval schedules default mode for the next step, while rejection or custom feedback keeps plan mode active and returns the feedback to the model.

Model Experience

Indirectly, through complementary Web system-prompt sections: active mode supplies the planning policy, while default mode explicitly states that the session is not planning, permits normal implementation work, and tells the model not to call the still-registered exit_plan_mode tool; @deepseek-ai/dsh-plan-mode continues to own the exit-tool schema and rendering, logged state, and request-boundary transitions.

KV Cache effect

Entering or leaving plan mode swaps the active Web mode section and therefore changes the request prefix. The stable exit-tool registration avoids an additional tool-catalog shape change across the same transition.

Known Limitations and Deferred Work

Plan mode is guidance, not an execution sandbox — deployments that require enforced read-only planning must compose the independent sandbox and approval policies.
The control belongs to the default composer — a pending whole-composer interaction such as plan review temporarily replaces the InputBar and its mode control.
An idle pending target is process-local until the next boundary — a process exit before another prompt loses that uncommitted intent; the committed mode remains durable in the session log.