Fix markdown transient cache invalidation

packages/tui/src/components/markdown.ts

@@ -295,10 +295,7 @@ export class Markdown implements Component {
 	#cachedText?: string;
 	#cachedWidth?: number;
 	#cachedLines?: readonly string[];
-	/** When true, skip the module-level LRU (lookup and insert) for this instance's
-	 *  renders. Set for in-flight streaming partials whose text changes every frame —
-	 *  caching those churns the LRU with near-duplicate full-message snapshots. */
-	transientRenderCache = false;
+	#transientRenderCache = false;
 
 	constructor(
 		text: string,
@@ -326,6 +323,16 @@ export class Markdown implements Component {
 		this.#cachedWidth = undefined;
 		this.#cachedLines = undefined;
 	}
+	get transientRenderCache(): boolean {
+		return this.#transientRenderCache;
+	}
+
+	set transientRenderCache(value: boolean) {
+		const next = value === true;
+		if (this.#transientRenderCache === next) return;
+		this.#transientRenderCache = next;
+		this.invalidate();
+	}
 
 	render(width: number): readonly string[] {
 		// L1: per-instance cache — fastest path for repeated renders of the same

packages/tui/test/markdown.test.ts

@@ -1279,6 +1279,29 @@ describe("Module-level LRU render cache", () => {
 		expect(plain).not.toContain("HIGHLIGHTED");
 	});
 
+	it("re-renders code-block highlighting when a transient instance becomes stable", () => {
+		clearRenderCache();
+		let highlightCallCount = 0;
+		const themeWithSpy = {
+			...defaultMarkdownTheme,
+			highlightCode: (_code: string, _lang?: string): string[] => {
+				highlightCallCount++;
+				return ["HIGHLIGHTED"];
+			},
+		};
+
+		const markdown = new Markdown("```ts\nconst streamed = true;\n```", 0, 0, themeWithSpy);
+		markdown.transientRenderCache = true;
+		const plain = stripVTControlCharacters(markdown.render(80).join("\n"));
+		expect(highlightCallCount).toBe(0);
+		expect(plain).toContain("const streamed = true;");
+
+		markdown.transientRenderCache = false;
+		const highlighted = stripVTControlCharacters(markdown.render(80).join("\n"));
+		expect(highlightCallCount).toBe(1);
+		expect(highlighted).toContain("HIGHLIGHTED");
+	});
+
 	it("skips nested list code-block highlighting for transient streaming renders", () => {
 		clearRenderCache();
 		let highlightCallCount = 0;