fix(coding-agent): defaulted approval slider to default tier

- Previously the slider started at the current cycle index, so execution would inherit whichever model drove planning.
- Now finds the `default` role in the cycle and anchors the slider there, falling back to `currentIndex` if no default exists.
- Explicit `executionModel` is set whenever the chosen tier differs from the restored cycle position, covering the case where the slider stays on `default` but planning ran on another model.

packages/coding-agent/src/modes/interactive-mode.ts

@@ -2040,16 +2040,20 @@ export class InteractiveMode implements InteractiveModeContext {
 				: "Approve and keep context";
 
 		// Model-tier slider: let the operator pick which configured role model
-		// (smol/default/slow/…) executes the approved plan. Left/right move it from
-		// any list position. Hidden when fewer than two role models resolve — a lone
-		// tier is no choice. `selectedTierIndex` tracks the live slider position.
+		// (smol/default/slow/…) executes the approved plan. The slider always starts
+		// on the `default` tier so execution defaults to the default model no matter
+		// which model drove the planning conversation. Left/right move it from there;
+		// hidden when fewer than two role models resolve — a lone tier is no choice.
+		// `selectedTierIndex` tracks the live slider position.
 		const cycle = this.session.getRoleModelCycle(this.session.settings.get("cycleOrder"));
-		let selectedTierIndex = cycle?.currentIndex ?? 0;
+		const defaultTierIndex = cycle ? cycle.models.findIndex(entry => entry.role === "default") : -1;
+		const startTierIndex = defaultTierIndex >= 0 ? defaultTierIndex : (cycle?.currentIndex ?? 0);
+		let selectedTierIndex = startTierIndex;
 		const slider: HookSelectorSlider | undefined =
 			cycle && cycle.models.length > 1
 				? {
 						caption: "continue with",
-						index: cycle.currentIndex,
+						index: startTierIndex,
 						segments: cycle.models.map(entry => ({
 							label: entry.role,
 							color: MODEL_ROLES[entry.role as ModelRole]?.color,
@@ -2086,6 +2090,9 @@ export class InteractiveMode implements InteractiveModeContext {
 				// applying the slider choice any earlier would be silently reverted —
 				// the bug that made "continue with slow" keep executing on the default
 				// model. Deferred application also survives newSession()/compaction.
+				// `cycle.currentIndex` is exactly that restored model, so any chosen tier
+				// differing from it needs an explicit executionModel — this also covers
+				// leaving the slider on its `default` anchor while planning ran elsewhere.
 				const executionModel =
 					cycle && selectedTierIndex !== cycle.currentIndex ? cycle.models[selectedTierIndex] : undefined;
 				await this.#approvePlan(latestPlanContent, {