test: hardened new spinner and title-latch suites against full-suite pollution

- Exported stopSharedSpinnerTicker() and wired it into InteractiveMode.stop(): a live block missed by per-component stopAnimation kept the shared 80ms interval alive as a lingering event-loop handle; the spinner suite uses it to observe a freshly armed ticker instead of one leaked by earlier files
- Title-disposal tests now save/clear/restore PI_NO_TITLE (main() in ACP/RPC mode sets it process-wide), matching the prewarm and orphan-submit precedent

packages/coding-agent/src/modes/components/tool-execution.ts

@@ -317,6 +317,19 @@ function unregisterSpinnerBlock(block: ToolExecutionComponent): void {
 	}
 }
 
+/** Stop the shared spinner ticker and drop every registered live block.
+ *  Called on interactive-mode teardown so a stray live block cannot keep the
+ *  process-wide 80ms interval alive past shutdown (lingering event-loop
+ *  handles pin the process; cf. `postmortem.quit`). Test files that assert on
+ *  ticker arming also use this to start from a clean slate. */
+export function stopSharedSpinnerTicker(): void {
+	liveSpinnerBlocks.clear();
+	if (sharedSpinnerTimer) {
+		clearInterval(sharedSpinnerTimer);
+		sharedSpinnerTimer = undefined;
+	}
+}
+
 // Stable per-instance counter so each tool execution's inline images get a
 // graphics id that survives child re-creation (the image budget keys off it).
 let toolExecutionInstanceSeq = 0;

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

@@ -166,7 +166,7 @@ import type { HookInputComponent } from "./components/hook-input";
 import type { HookSelectorComponent, HookSelectorSlider } from "./components/hook-selector";
 import { type PlanReviewAnnotationState, PlanReviewOverlay } from "./components/plan-review-overlay";
 import { StatusLineComponent } from "./components/status-line";
-import type { ToolExecutionHandle } from "./components/tool-execution";
+import { stopSharedSpinnerTicker, type ToolExecutionHandle } from "./components/tool-execution";
 import { TranscriptContainer } from "./components/transcript-container";
 import { WelcomeComponent, type LspServerInfo as WelcomeLspServerInfo } from "./components/welcome";
 import { BtwController } from "./controllers/btw-controller";
@@ -4160,6 +4160,9 @@ export class InteractiveMode implements InteractiveModeContext {
 			this.#stopLoadingAnimation(false);
 		}
 		this.#cleanupMicAnimation();
+		// Stop the shared tool-spinner ticker: a live block missed by per-component
+		// stopAnimation would otherwise keep an 80ms interval pinning the process.
+		stopSharedSpinnerTicker();
 		this.#liveCommandController.dispose();
 		this.#cancelTodoAutoClearTimer();
 		this.#cancelObserverUiSyncTimer();