diff --git a/src/agent/claude-code/binary.ts b/src/agent/claude-code/binary.ts
new file mode 100644
index 0000000..44becc3
--- /dev/null
+++ b/src/agent/claude-code/binary.ts
@@ -0,0 +1,61 @@
+import * as fs from "node:fs";
+import * as os from "node:os";
+import * as path from "node:path";
+
+type BinaryLookup = {
+	env: Record<string, string | undefined>;
+	platform: NodeJS.Platform;
+	homeDir: string;
+	isExecutable: (path: string) => boolean;
+};
+
+type SearchSpec = {
+	paths: path.PlatformPath;
+	names: string[];
+	knownDirs: string[];
+};
+
+function getWindowsSearchSpec(env: BinaryLookup["env"], homeDir: string): SearchSpec {
+	const paths = path.win32;
+	const appData = env.APPDATA ?? paths.join(homeDir, "AppData", "Roaming");
+	return {
+		paths,
+		names: ["claude.cmd", "claude.exe"],
+		knownDirs: [paths.join(homeDir, ".local", "bin"), paths.join(homeDir, ".claude", "local"), env.npm_config_prefix ?? paths.join(appData, "npm")],
+	};
+}
+
+function getPosixSearchSpec(env: BinaryLookup["env"], homeDir: string): SearchSpec {
+	const paths = path.posix;
+	const npmBin = env.npm_config_prefix ? paths.join(env.npm_config_prefix, "bin") : paths.join(homeDir, ".npm-global", "bin");
+	return {
+		paths,
+		names: ["claude"],
+		knownDirs: [paths.join(homeDir, ".local", "bin"), paths.join(homeDir, ".claude", "local"), npmBin, "/opt/homebrew/bin", "/usr/local/bin"],
+	};
+}
+
+export function resolveClaudeBinary({ env, platform, homeDir, isExecutable }: BinaryLookup): string | null {
+	const { paths, names, knownDirs } = platform === "win32" ? getWindowsSearchSpec(env, homeDir) : getPosixSearchSpec(env, homeDir);
+	const pathDirs = (env.PATH ?? "").split(paths.delimiter).filter(Boolean);
+	for (const dir of [...pathDirs, ...knownDirs]) {
+		for (const name of names) {
+			const candidate = paths.join(dir, name);
+			if (isExecutable(candidate)) return candidate;
+		}
+	}
+	return null;
+}
+
+function isExecutableFile(filePath: string): boolean {
+	try {
+		fs.accessSync(filePath, fs.constants.X_OK);
+		return fs.statSync(filePath).isFile();
+	} catch {
+		return false;
+	}
+}
+
+export function getClaudeBinary(): string | null {
+	return resolveClaudeBinary({ env: process.env, platform: process.platform, homeDir: os.homedir(), isExecutable: isExecutableFile });
+}
diff --git a/tests/claude-code-binary.test.ts b/tests/claude-code-binary.test.ts
new file mode 100644
index 0000000..05adf28
--- /dev/null
+++ b/tests/claude-code-binary.test.ts
@@ -0,0 +1,54 @@
+/**
+ * Claude Code binary lookup (src/agent/claude-code/binary.ts).
+ *
+ * The packaged desktop app often starts with a minimal PATH, so lookup falls
+ * back to the standard install locations. A fake isExecutable set stands in
+ * for the filesystem.
+ */
+import assert from "node:assert/strict";
+import test from "node:test";
+
+import { resolveClaudeBinary } from "../src/agent/claude-code/binary.ts";
+
+const HOME = "/home/u";
+
+function resolveWith(executables: string[], env: Record<string, string> = {}, platform: NodeJS.Platform = "linux", homeDir = HOME) {
+	const found = new Set(executables);
+	return resolveClaudeBinary({ env, platform, homeDir, isExecutable: (p) => found.has(p) });
+}
+
+test("prefers PATH hit", () => {
+	const binary = resolveWith(["/usr/bin/claude", `${HOME}/.local/bin/claude`], { PATH: "/opt/x:/usr/bin" });
+	assert.equal(binary, "/usr/bin/claude");
+});
+
+test("falls back to ~/.local/bin when PATH misses", () => {
+	const binary = resolveWith([`${HOME}/.local/bin/claude`, "/usr/local/bin/claude"], { PATH: "/usr/bin" });
+	assert.equal(binary, `${HOME}/.local/bin/claude`);
+});
+
+test("checks ~/.claude/local, npm global bin, /opt/homebrew/bin, /usr/local/bin in that order", () => {
+	const all = [`${HOME}/.claude/local/claude`, `${HOME}/.npm-global/bin/claude`, "/opt/homebrew/bin/claude", "/usr/local/bin/claude"];
+	for (let i = 0; i < all.length; i++) {
+		assert.equal(resolveWith(all.slice(i), { PATH: "" }), all[i]);
+	}
+});
+
+test("npm global bin follows npm_config_prefix when set", () => {
+	const binary = resolveWith(["/opt/npm/bin/claude", `${HOME}/.npm-global/bin/claude`], { npm_config_prefix: "/opt/npm" });
+	assert.equal(binary, "/opt/npm/bin/claude");
+});
+
+test("windows looks for claude.cmd and claude.exe", () => {
+	const winHome = "C:\\Users\\u";
+	const env = { PATH: "C:\\tools;C:\\bin", APPDATA: `${winHome}\\AppData\\Roaming` };
+	assert.equal(resolveWith(["C:\\bin\\claude.cmd"], env, "win32", winHome), "C:\\bin\\claude.cmd");
+	assert.equal(resolveWith(["C:\\bin\\claude.exe"], env, "win32", winHome), "C:\\bin\\claude.exe");
+	assert.equal(resolveWith([`${winHome}\\.local\\bin\\claude.exe`], env, "win32", winHome), `${winHome}\\.local\\bin\\claude.exe`);
+	assert.equal(resolveWith([`${winHome}\\AppData\\Roaming\\npm\\claude.cmd`], env, "win32", winHome), `${winHome}\\AppData\\Roaming\\npm\\claude.cmd`);
+	assert.equal(resolveWith(["C:\\bin\\claude"], env, "win32", winHome), null);
+});
+
+test("returns null when every location misses", () => {
+	assert.equal(resolveWith([], { PATH: "/usr/bin:/bin" }), null);
+});