fix(tui): guard nullish args in truncateToWidth wrapper

renderContentPreview crashed on the Windows prebuilt with "Failed to
convert napi value Null into rust type `u8`" (and the related `bool`
variant) because the wrapper forwarded `null` to napi-rs 3's
`Option<Ellipsis>` / `Option<bool>` parameters; the Windows binding
rejects null where Linux/macOS tolerates it. `maxWidth` was also passed
through unchecked, so a stray null/undefined upstream blew up the
required `u32` everywhere. Pass concrete defaults that mirror the Rust
`unwrap_or`s and clamp `maxWidth` to a sane non-negative integer.

Fixes #848

packages/tui/src/utils.ts

@@ -1,9 +1,11 @@
-import type { Ellipsis, ExtractSegmentsResult, SliceResult } from "@oh-my-pi/pi-natives";
 import {
+	Ellipsis,
+	type ExtractSegmentsResult,
 	extractSegments as nativeExtractSegments,
 	sliceWithWidth as nativeSliceWithWidth,
 	truncateToWidth as nativeTruncateToWidth,
 	wrapTextWithAnsi as nativeWrapTextWithAnsi,
+	type SliceResult,
 } from "@oh-my-pi/pi-natives";
 import { getDefaultTabWidth, getIndentation } from "@oh-my-pi/pi-utils";
 
@@ -21,7 +23,12 @@ export function truncateToWidth(
 	ellipsisKind?: Ellipsis | null,
 	pad?: boolean | null,
 ): string {
-	return nativeTruncateToWidth(text, maxWidth, ellipsisKind ?? null, pad ?? null, getDefaultTabWidth());
+	// Guard nullish napi inputs: napi-rs 3 on the Windows prebuilt rejects
+	// `null` for `Option<u8>` (Ellipsis) / `Option<bool>` (pad) (issue #848),
+	// and `maxWidth` is a required `u32` that throws on `null`/`undefined`
+	// everywhere. Pass concrete defaults that mirror the Rust `unwrap_or`s.
+	const safeWidth = Number.isFinite(maxWidth) ? Math.max(0, Math.trunc(maxWidth)) : 0;
+	return nativeTruncateToWidth(text, safeWidth, ellipsisKind ?? Ellipsis.Unicode, pad ?? false, getDefaultTabWidth());
 }
 
 export function wrapTextWithAnsi(text: string, width: number): string[] {

packages/tui/test/issue-848-repro.test.ts

@@ -0,0 +1,47 @@
+import { describe, expect, it } from "bun:test";
+import { Ellipsis, truncateToWidth } from "../src/utils";
+
+// Regression test for https://github.com/can1357/oh-my-pi/issues/848
+//
+// On Windows, rendering a saved write tool record crashed with:
+//   Error: Failed to convert napi value Null into rust type `u8`
+//       at truncateToWidth (unknown)
+//       at renderContentPreview (...)
+// and the related variant "Failed to convert napi value into rust type `bool`"
+// at the same call site.
+//
+// Root cause: the `truncateToWidth` JS wrapper coerced optional ellipsis/pad
+// arguments to literal `null` (`?? null`) before forwarding to the napi
+// binding. napi-rs 3 accepts that on Linux/macOS but rejects it on the
+// Windows prebuilt: the null hits the underlying `u8` (Ellipsis enum) /
+// `bool` (pad) conversions instead of the `Option<T>` short-circuit. The
+// wrapper must pass concrete defaults (matching the Rust `unwrap_or`s) so it
+// never depends on the platform's null-handling for `Option<T>`. Likewise,
+// `maxWidth` must not silently forward `null`/`undefined` into the required
+// `u32` parameter — the wrapper must clamp it to a sane non-negative integer.
+describe("issue #848: truncateToWidth wrapper rejects nullish napi inputs", () => {
+	it("returns a string when ellipsisKind / pad are null", () => {
+		const result = truncateToWidth("hello world", 80, null, null);
+		expect(typeof result).toBe("string");
+		expect(result).toBe("hello world");
+	});
+
+	it("returns a string when ellipsisKind / pad are undefined", () => {
+		const result = truncateToWidth("hello world", 80, undefined, undefined);
+		expect(typeof result).toBe("string");
+		expect(result).toBe("hello world");
+	});
+
+	it("does not throw a napi conversion error when maxWidth is null", () => {
+		// Matches the resumed-render code path on Windows where a width derived
+		// from terminal state can briefly be null/undefined. The wrapper must
+		// degrade to an empty truncation rather than blowing up the renderer.
+		const result = truncateToWidth("hello world", null as unknown as number, Ellipsis.Omit, null);
+		expect(typeof result).toBe("string");
+	});
+
+	it("does not throw a napi conversion error when maxWidth is undefined", () => {
+		const result = truncateToWidth("hello world", undefined as unknown as number, Ellipsis.Omit, null);
+		expect(typeof result).toBe("string");
+	});
+});