fix(tui,coding-agent): survive lone surrogates in table cells and terminate the WebP EXIF scan

packages/coding-agent/.changes/webp-exif-scan-termination.md

@@ -0,0 +1 @@
+- The WebP EXIF chunk scan reads chunk sizes as unsigned, so a crafted or corrupt image can no longer hang the process in an infinite scan loop.

packages/coding-agent/src/utils/exif-orientation.ts

@@ -14,7 +14,7 @@ function readOrientationFromTiff(bytes: Uint8Array, tiffStart: number): number {
 	};
 
 	const read32 = (pos: number): number => {
-		if (le) return bytes[pos] | (bytes[pos + 1] << 8) | (bytes[pos + 2] << 16) | (bytes[pos + 3] << 24);
+		if (le) return (bytes[pos] | (bytes[pos + 1] << 8) | (bytes[pos + 2] << 16) | (bytes[pos + 3] << 24)) >>> 0;
 		return ((bytes[pos] << 24) | (bytes[pos + 1] << 16) | (bytes[pos + 2] << 8) | bytes[pos + 3]) >>> 0;
 	};
 
@@ -66,8 +66,9 @@ function findWebpTiffOffset(bytes: Uint8Array): number {
 	let offset = 12;
 	while (offset + 8 <= bytes.length) {
 		const chunkId = String.fromCharCode(bytes[offset], bytes[offset + 1], bytes[offset + 2], bytes[offset + 3]);
+		// Unsigned: a high-bit chunk size read as negative would walk the scan backward forever.
 		const chunkSize =
-			bytes[offset + 4] | (bytes[offset + 5] << 8) | (bytes[offset + 6] << 16) | (bytes[offset + 7] << 24);
+			(bytes[offset + 4] | (bytes[offset + 5] << 8) | (bytes[offset + 6] << 16) | (bytes[offset + 7] << 24)) >>> 0;
 		const dataStart = offset + 8;
 
 		if (chunkId === "EXIF") {

packages/coding-agent/test/exif-orientation.test.ts

@@ -0,0 +1,18 @@
+import { describe, expect, it } from "vitest";
+import { applyExifOrientation } from "../src/utils/exif-orientation.js";
+import type { PhotonImageType } from "../src/utils/photon.js";
+
+type Photon = typeof import("@silvia-odwyer/photon-node");
+
+describe("exif orientation", () => {
+	it("terminates the WebP chunk scan when a chunk size has the high bit set", () => {
+		const bytes = new Uint8Array(20);
+		bytes.set([0x52, 0x49, 0x46, 0x46], 0); // RIFF
+		bytes.set([0x57, 0x45, 0x42, 0x50], 8); // WEBP
+		bytes.set([0x4a, 0x55, 0x4e, 0x4b], 12); // JUNK
+		bytes.set([0xf8, 0xff, 0xff, 0xff], 16); // chunk size 0xFFFFFFF8: read signed (-8), the scan re-visits this chunk forever
+		// Orientation resolves to 1, so neither photon nor the image is ever touched.
+		const image = {} as PhotonImageType;
+		expect(applyExifOrientation({} as Photon, image, bytes)).toBe(image);
+	});
+});

packages/tui/.changes/selection-marker-lone-surrogates.md

@@ -0,0 +1 @@
+- Table cell selection markers no longer crash the renderer when cell content contains a lone UTF-16 surrogate; the surrogate is replaced before encoding.

packages/tui/src/selection-metadata.ts

@@ -35,7 +35,9 @@ interface TableBounds {
 }
 
 function cellMarker(kind: CellMarker["kind"], row: number, column: number, segment: number, content?: string): string {
-	const encodedContent = content === undefined ? "" : `:${encodeURIComponent(content)}`;
+	// Lone surrogates would throw in encodeURIComponent; toWellFormed exists on Node>=20, lib is ES2022.
+	const wellFormed = content as undefined | (string & { toWellFormed(): string });
+	const encodedContent = wellFormed === undefined ? "" : `:${encodeURIComponent(wellFormed.toWellFormed())}`;
 	return `${TABLE_MARKER_PREFIX}${kind}:${row}:${column}:${segment}${encodedContent}\x07`;
 }
 

packages/tui/test/selection-metadata.test.ts

@@ -0,0 +1,17 @@
+import assert from "node:assert";
+import { describe, it } from "node:test";
+import {
+	extractTableCellSelectionRegions,
+	markTableCell,
+	markTableEnd,
+	markTableStart,
+} from "../src/selection-metadata.js";
+
+describe("selection metadata", () => {
+	it("marks cells containing lone surrogates without throwing", () => {
+		// The lone surrogate is replaced with U+FFFD, not crashed on.
+		const line = markTableEnd(markTableStart("") + markTableCell("cell text", 0, 0, 0, "broken \uD800 surrogate"));
+		const { regions } = extractTableCellSelectionRegions([line], () => ({}));
+		assert.equal(regions[0]?.content, "broken \uFFFD surrogate");
+	});
+});