Plan mode invoked mid-session skips execution approval gate

[ASneakyToast]

Describe the bug

When plan-mode is invoked during an existing session (rather than at session start), the approval gate ("Execute the plan? yes/no") is never shown. The agent writes the plan file and immediately begins executing it without waiting for user confirmation.

Steps to reproduce

1. Start a normal (non-plan-mode) session
2. Mid-session, explicitly invoke plan mode (e.g. via slash command or prompt)
3. Agent writes the plan document
4. Agent immediately proceeds to execute — no approval prompt appears

Expected behavior

After writing the plan, execution should be gated behind user approval regardless of whether plan mode was active from session start or invoked mid-session.

Actual behavior

The agent self-authorizes execution. The questionnaire tool (or equivalent gate) is never called. The transition from plan → execute is skipped entirely.

Root cause hypothesis

The approval gate appears to be wired only at session initialization. A mid-session mode switch doesn't re-arm it, so the model has no instruction to stop and wait.

Environment

• prime-agent version: 0.7.1
• Model: claude-sonnet-4-6

[BILLKISHORE]

The root-cause hypothesis here does not match what is on main, and the real answer is probably more useful.

There is no plan mode in packages/coding-agent/src. Grepping for planMode, plan_mode or PlanMode across the source returns nothing. Plan mode exists only as an example extension at examples/extensions/plan-mode/, which a user has to install; it is not loaded by default.

In that extension the gate is not wired to session start. It runs on every agent_end:

pi.on("agent_end", async (event, ctx) => {
    if (executionMode && todoItems.length > 0) { /* ... */ return; }
    if (!planModeEnabled || !ctx.hasUI) return;
    // extract todos, then ctx.ui.select("Plan mode - what next?", [...])
});

planModeEnabled flips only through the extension's own togglePlanMode (index.ts:76). So the gate fires whenever plan mode is on, no matter when it was switched on, which is the opposite of the hypothesis.

That points at what most likely happened in your repro. Step 2 is "explicitly invoke plan mode via slash command or prompt". If it was invoked by prompt, nothing structural changed: planModeEnabled stays false, the extension never sees a mode switch, and the model simply narrates a plan and continues. There is no gate to skip because no gate was ever armed. The same is true if the extension is not installed at all, which is the default.

Worth knowing: #305 ("add plan mode: a no-edit toggle enforced inside the kernel") is open and adds this as a real feature rather than an example. A prompt-invoked plan mode that actually gates execution is what that PR would provide.

One genuine gap in the extension either way: !ctx.hasUI skips the gate entirely, so under -p or any headless run plan mode moves to execution with no approval and no signal that it did. Refusing to auto-execute headlessly seems better than silently proceeding, but that is a call for whoever owns #305.