fix(tui): treated WSL scrollback replay as unsafe

packages/tui/src/tui.ts

@@ -167,6 +167,15 @@ function isMultiplexerSession(): boolean {
 	return Boolean(Bun.env.TMUX || Bun.env.STY || Bun.env.ZELLIJ);
 }
 
+function requiresNativeViewportProofForReplay(): boolean {
+	return (
+		process.platform === "win32" ||
+		(process.platform === "linux" &&
+			Boolean(Bun.env.WT_SESSION) &&
+			Boolean(Bun.env.WSL_DISTRO_NAME || Bun.env.WSL_INTEROP))
+	);
+}
+
 /**
  * Options for overlay positioning and sizing.
  * Values can be absolute numbers or percentage strings (e.g., "50%").
@@ -1429,7 +1438,10 @@ export class TUI extends Container {
 	}
 
 	#nativeViewportIsScrolled(nativeViewportAtBottom: boolean | undefined): boolean {
-		return nativeViewportAtBottom === false || (nativeViewportAtBottom === undefined && process.platform === "win32");
+		return (
+			nativeViewportAtBottom === false ||
+			(nativeViewportAtBottom === undefined && requiresNativeViewportProofForReplay())
+		);
 	}
 
 	#nativeViewportIsAtBottom(nativeViewportAtBottom: boolean | undefined): boolean {
@@ -1437,7 +1449,10 @@ export class TUI extends Container {
 	}
 
 	#canReplayNativeScrollbackAtCheckpoint(nativeViewportAtBottom: boolean | undefined): boolean {
-		return nativeViewportAtBottom === true || (nativeViewportAtBottom === undefined && process.platform !== "win32");
+		return (
+			nativeViewportAtBottom === true ||
+			(nativeViewportAtBottom === undefined && !requiresNativeViewportProofForReplay())
+		);
 	}
 
 	#padDeferredShrinkLines(lines: string[], paddedLength: number): string[] {

packages/tui/test/render-regressions.test.ts

@@ -995,6 +995,49 @@ describe("TUI terminal-state regressions", () => {
 				tui.stop();
 			}
 		});
+
+		it("treats unknown WSL Windows Terminal viewport state as scrolled", async () => {
+			const originalPlatform = process.platform;
+			const originalWtSession = Bun.env.WT_SESSION;
+			const originalWslDistroName = Bun.env.WSL_DISTRO_NAME;
+			const originalWslInterop = Bun.env.WSL_INTEROP;
+			Object.defineProperty(process, "platform", { configurable: true, value: "linux" });
+			Bun.env.WT_SESSION = "wt-test";
+			Bun.env.WSL_DISTRO_NAME = "Ubuntu";
+			delete Bun.env.WSL_INTEROP;
+
+			const term = new UnknownViewportTerminal(32, 5);
+			const tui = new TUI(term);
+			const component = new MutableLinesComponent(rows("line-", 12));
+			tui.addChild(component);
+
+			try {
+				tui.start();
+				await settle(term);
+				term.scrollLines(-2);
+				const before = term.getBufferPosition();
+				expect(before.viewportY).toBeGreaterThan(0);
+
+				component.setLines(rows("line-", 8));
+				tui.requestRender();
+				await settle(term);
+
+				const after = term.getBufferPosition();
+				expect(after.viewportY).toBe(before.viewportY);
+				expect(visible(term).map(line => line.trim())).toEqual(["line-5", "line-6", "line-7", "", ""]);
+				expect(tui.refreshNativeScrollbackIfDirty()).toBe(false);
+				expect(term.getBufferPosition().viewportY).toBe(before.viewportY);
+			} finally {
+				Object.defineProperty(process, "platform", { configurable: true, value: originalPlatform });
+				if (originalWtSession === undefined) delete Bun.env.WT_SESSION;
+				else Bun.env.WT_SESSION = originalWtSession;
+				if (originalWslDistroName === undefined) delete Bun.env.WSL_DISTRO_NAME;
+				else Bun.env.WSL_DISTRO_NAME = originalWslDistroName;
+				if (originalWslInterop === undefined) delete Bun.env.WSL_INTEROP;
+				else Bun.env.WSL_INTEROP = originalWslInterop;
+				tui.stop();
+			}
+		});
 		it("refreshes deferred native scrollback when the native viewport reaches bottom", async () => {
 			const term = new VirtualTerminal(32, 5);
 			const tui = new TUI(term);