fix(coding-agent): set executionMode: sequential on question example tool

The question extension tool blocks on ctx.ui.custom() but omitted
executionMode, so multiple question calls in one assistant turn ran
under the default parallel mode and raced on the editor slot. Only the
last question rendered; earlier calls hung pending forever.

Set executionMode: "sequential" so the agent loop serializes the
batch. Wrappers already propagate the field to the core.

closes #6189

packages/coding-agent/CHANGELOG.md

@@ -9,6 +9,7 @@
 
 ### Fixed
 
+- Fixed the question extension example to run question tool calls sequentially so multiple questions in one assistant turn remain answerable ([#6189](https://github.com/earendil-works/pi/issues/6189)).
 - Fixed `/login` to report auth storage persistence failures instead of claiming credentials were saved when `auth.json` is locked ([#6223](https://github.com/earendil-works/pi/issues/6223)).
 - Fixed split-turn compaction to serialize summary requests so single-concurrency local providers do not fail with 429 errors ([#5536](https://github.com/earendil-works/pi/issues/5536)).
 - Fixed custom session entries appended during assistant streaming to render before the live assistant message, matching persisted session order.

packages/coding-agent/examples/extensions/question.ts

@@ -47,6 +47,7 @@ export default function question(pi: ExtensionAPI) {
 		label: "Question",
 		description: "Ask the user a question and let them pick from options. Use when you need user input to proceed.",
 		parameters: QuestionParams,
+		executionMode: "sequential",
 
 		async execute(_toolCallId, params, _signal, _onUpdate, ctx) {
 			if (ctx.mode !== "tui") {