fix: auto re-exec command after CLI auto-update (fixes #780) (#830)

When a CLI auto-update triggers mid-command (e.g. `spawn claude sprite`),
the updated binary now automatically re-runs with the original arguments
instead of asking the user to manually re-run. Sets SPAWN_NO_UPDATE_CHECK=1
on re-exec to prevent infinite update loops. Falls back to the old "run
again" message when no arguments were provided (bare `spawn`).

Agent: ux-engineer

Co-authored-by: A <6723574+louisgv@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cli/src/__tests__/update-check.test.ts

@@ -197,5 +197,120 @@ describe("update-check", () => {
 
       fetchSpy.mockRestore();
     });
+
+    it("should re-exec with original args after successful update", async () => {
+      const originalArgv = process.argv;
+      process.argv = ["/usr/bin/bun", "/usr/local/bin/spawn", "claude", "sprite"];
+
+      const mockFetch = mock(() =>
+        Promise.resolve({
+          ok: true,
+          json: () => Promise.resolve({ version: "0.3.0" }),
+        } as Response)
+      );
+      const fetchSpy = spyOn(global, "fetch").mockImplementation(mockFetch);
+
+      const { executor } = await import("../update-check.js");
+      const calls: string[] = [];
+      const execSyncSpy = spyOn(executor, "execSync").mockImplementation((cmd: string) => {
+        calls.push(cmd);
+      });
+
+      const { checkForUpdates } = await import("../update-check.js");
+      await checkForUpdates();
+
+      // First call: install script, second call: re-exec with original args
+      expect(calls.length).toBe(2);
+      expect(calls[0]).toContain("install.sh");
+      expect(calls[1]).toContain("spawn");
+      expect(calls[1]).toContain("claude");
+      expect(calls[1]).toContain("sprite");
+
+      // Should show rerunning message
+      const output = consoleErrorSpy.mock.calls.map((call) => call[0]).join("\n");
+      expect(output).toContain("Rerunning");
+
+      // Should set SPAWN_NO_UPDATE_CHECK=1 to prevent infinite loop
+      expect(execSyncSpy.mock.calls[1][1]).toHaveProperty("env");
+      expect(execSyncSpy.mock.calls[1][1].env.SPAWN_NO_UPDATE_CHECK).toBe("1");
+
+      expect(processExitSpy).toHaveBeenCalledWith(0);
+
+      fetchSpy.mockRestore();
+      execSyncSpy.mockRestore();
+      process.argv = originalArgv;
+    });
+
+    it("should forward exit code when re-exec fails", async () => {
+      const originalArgv = process.argv;
+      process.argv = ["/usr/bin/bun", "/usr/local/bin/spawn", "claude", "sprite"];
+
+      const mockFetch = mock(() =>
+        Promise.resolve({
+          ok: true,
+          json: () => Promise.resolve({ version: "0.3.0" }),
+        } as Response)
+      );
+      const fetchSpy = spyOn(global, "fetch").mockImplementation(mockFetch);
+
+      const { executor } = await import("../update-check.js");
+      let callCount = 0;
+      const execSyncSpy = spyOn(executor, "execSync").mockImplementation(() => {
+        callCount++;
+        if (callCount === 2) {
+          // Re-exec fails with exit code 1
+          const err = new Error("Command failed") as Error & { status: number };
+          err.status = 42;
+          throw err;
+        }
+      });
+
+      const { checkForUpdates } = await import("../update-check.js");
+      await checkForUpdates();
+
+      // Should forward the exit code from the re-exec
+      expect(processExitSpy).toHaveBeenCalledWith(42);
+
+      fetchSpy.mockRestore();
+      execSyncSpy.mockRestore();
+      process.argv = originalArgv;
+    });
+
+    it("should not re-exec when run without arguments (bare spawn)", async () => {
+      const originalArgv = process.argv;
+      process.argv = ["/usr/bin/bun", "/usr/local/bin/spawn"];
+
+      const mockFetch = mock(() =>
+        Promise.resolve({
+          ok: true,
+          json: () => Promise.resolve({ version: "0.3.0" }),
+        } as Response)
+      );
+      const fetchSpy = spyOn(global, "fetch").mockImplementation(mockFetch);
+
+      const { executor } = await import("../update-check.js");
+      const calls: string[] = [];
+      const execSyncSpy = spyOn(executor, "execSync").mockImplementation((cmd: string) => {
+        calls.push(cmd);
+      });
+
+      const { checkForUpdates } = await import("../update-check.js");
+      await checkForUpdates();
+
+      // Only one call: the install script (no re-exec)
+      expect(calls.length).toBe(1);
+      expect(calls[0]).toContain("install.sh");
+
+      // Should show "Run your spawn command again" instead
+      const output = consoleErrorSpy.mock.calls.map((call) => call[0]).join("\n");
+      expect(output).toContain("Run your spawn command again");
+      expect(output).not.toContain("Rerunning");
+
+      expect(processExitSpy).toHaveBeenCalledWith(0);
+
+      fetchSpy.mockRestore();
+      execSyncSpy.mockRestore();
+      process.argv = originalArgv;
+    });
   });
 });

cli/src/update-check.ts

@@ -85,11 +85,34 @@ function performAutoUpdate(latestVersion: string): void {
 
     console.error();
     console.error(pc.green(pc.bold(`${CHECK_MARK} Updated successfully!`)));
-    console.error(pc.dim("  Run your spawn command again to use the new version."));
-    console.error();
 
-    // Exit cleanly after update
-    process.exit(0);
+    // Re-exec the updated binary with the same arguments
+    const args = process.argv.slice(2);
+    if (args.length > 0) {
+      const binPath = process.argv[1] || "spawn";
+      const quotedBin = `'${binPath.replace(/'/g, "'\\''")}'`;
+      const quotedArgs = args.map((a) => `'${a.replace(/'/g, "'\\''")}'`).join(" ");
+      console.error(pc.dim(`  Rerunning: spawn ${args.join(" ")}`));
+      console.error();
+      try {
+        executor.execSync(`${quotedBin} ${quotedArgs}`, {
+          stdio: "inherit",
+          shell: "/bin/bash",
+          env: { ...process.env, SPAWN_NO_UPDATE_CHECK: "1" },
+        });
+        process.exit(0);
+      } catch (reexecErr) {
+        // Forward the exit code from the re-executed command
+        const code = reexecErr && typeof reexecErr === "object" && "status" in reexecErr
+          ? (reexecErr as { status: number }).status
+          : 1;
+        process.exit(code);
+      }
+    } else {
+      console.error(pc.dim("  Run your spawn command again to use the new version."));
+      console.error();
+      process.exit(0);
+    }
   } catch (err) {
     console.error();
     console.error(pc.red(pc.bold(`${CROSS_MARK} Auto-update failed`)));