diff --git a/CLAUDE.md b/CLAUDE.md
index 8e4f477..15f49ae 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -93,6 +93,12 @@ Commands use `withErrorHandling()` HOF which:
 - **Window Requirement**: Perspective viewing requires an OmniFocus window to be open
 - **Permissions**: First run requires granting Automation permissions in System Settings
 - **ESM Modules**: Uses ES modules (type: "module" in package.json), all imports need .js extensions
+- **Never call `process.exit()`**: It terminates the process before async stdout pipe writes drain, truncating piped output at ~512 bytes (issue #20). Set `process.exitCode` instead and let the event loop finish naturally.
+
+## Testing Notes
+
+- `bun run test` uses vitest; CI runs `bun test` (bun's native runner). They have different semantics — verify both locally before pushing.
+- Bun's native test runner snapshots any `process.exitCode` mutation during a test and uses it as the suite's exit code, even when reverted. Tests that need to assert exit behavior must run the code in a child process.
 
 ## Date Handling
 
diff --git a/src/cli.ts b/src/cli.ts
index ebd2ba0..5f624a1 100644
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -35,5 +35,7 @@ program.addCommand(createFolderCommand());
 program.addCommand(createMcpCommand());
 
 program.parseAsync().catch(() => {
-  process.exit(1);
+  // Set exitCode instead of calling process.exit() so any queued stdout
+  // writes finish before the process terminates. See errors.ts for details.
+  process.exitCode = 1;
 });
diff --git a/src/lib/__tests__/errors.test.ts b/src/lib/__tests__/errors.test.ts
new file mode 100644
index 0000000..df4a49f
--- /dev/null
+++ b/src/lib/__tests__/errors.test.ts
@@ -0,0 +1,126 @@
+import { describe, it, expect, beforeAll } from 'vitest';
+import { execFile } from 'child_process';
+import { promisify } from 'util';
+import { mkdtemp, writeFile, rm } from 'fs/promises';
+import { tmpdir } from 'os';
+import { join } from 'path';
+
+/**
+ * These tests run handleError in a child process. The function deliberately
+ * sets process.exitCode = 1 to fix issue #20 (stdout truncation when piped),
+ * so we can't call it inside the test runner — bun's native test runner
+ * treats any process.exitCode mutation as a suite failure, even when reverted.
+ *
+ * Spawning a child process also gives us a faithful end-to-end test: we can
+ * pipe the child's stdout and confirm that the JSON error body arrives
+ * intact (not truncated) and that the exit code is correctly propagated.
+ */
+
+const execFileAsync = promisify(execFile);
+
+interface HandleErrorResult {
+  stdout: string;
+  exitCode: number | null;
+}
+
+async function runHandleError(
+  scenario: 'omnifocus_cli_error' | 'error_not_found' | 'error_multiple' | 'error_plain' | 'non_error'
+): Promise<HandleErrorResult> {
+  const tmp = await mkdtemp(join(tmpdir(), 'of-errors-test-'));
+  const script = join(tmp, 'run.mjs');
+  try {
+    await writeFile(
+      script,
+      `
+import { handleError, OmniFocusCliError } from '${join(process.cwd(), 'src/lib/errors.ts')}';
+
+let error;
+switch (${JSON.stringify(scenario)}) {
+  case 'omnifocus_cli_error':
+    error = new OmniFocusCliError('bad request', 400);
+    break;
+  case 'error_not_found':
+    error = new Error('Task not found');
+    break;
+  case 'error_multiple':
+    error = new Error('Multiple matches for "foo"');
+    break;
+  case 'error_plain':
+    error = new Error('boom');
+    break;
+  case 'non_error':
+    error = 'something weird';
+    break;
+}
+
+handleError(error);
+// Intentionally do NOT call process.exit(). The whole point of handleError
+// is that it sets exitCode and lets the loop drain. If anything is broken
+// the test will hang or truncate.
+`,
+      'utf8'
+    );
+
+    try {
+      const { stdout } = await execFileAsync('bun', [script], { encoding: 'utf8' });
+      return { stdout, exitCode: 0 };
+    } catch (err) {
+      const e = err as { stdout?: string; code?: number | null };
+      return { stdout: e.stdout ?? '', exitCode: typeof e.code === 'number' ? e.code : null };
+    }
+  } finally {
+    await rm(tmp, { recursive: true, force: true });
+  }
+}
+
+describe('handleError', () => {
+  beforeAll(() => {
+    // Sanity check the helper compiles cleanly; nothing else needed.
+  });
+
+  it('exits with code 1 instead of calling process.exit', async () => {
+    const { exitCode } = await runHandleError('error_plain');
+    expect(exitCode).toBe(1);
+  });
+
+  it('writes a complete JSON error body when piped (no truncation)', async () => {
+    const { stdout } = await runHandleError('error_plain');
+    // The full JSON must parse — proves stdout drained before exit.
+    const parsed = JSON.parse(stdout);
+    expect(parsed).toEqual({
+      error: { name: 'omnifocus_error', detail: 'boom', statusCode: 500 },
+    });
+  });
+
+  it('serializes OmniFocusCliError with its statusCode', async () => {
+    const { stdout } = await runHandleError('omnifocus_cli_error');
+    expect(JSON.parse(stdout)).toEqual({
+      error: { name: 'cli_error', detail: 'bad request', statusCode: 400 },
+    });
+  });
+
+  it('maps "not found" errors to 404', async () => {
+    const { stdout } = await runHandleError('error_not_found');
+    expect(JSON.parse(stdout)).toEqual({
+      error: { name: 'omnifocus_error', detail: 'Task not found', statusCode: 404 },
+    });
+  });
+
+  it('maps "Multiple" errors to 400', async () => {
+    const { stdout } = await runHandleError('error_multiple');
+    expect(JSON.parse(stdout)).toEqual({
+      error: {
+        name: 'omnifocus_error',
+        detail: 'Multiple matches for "foo"',
+        statusCode: 400,
+      },
+    });
+  });
+
+  it('falls back to unknown_error for non-Error values', async () => {
+    const { stdout } = await runHandleError('non_error');
+    expect(JSON.parse(stdout)).toEqual({
+      error: { name: 'unknown_error', detail: 'An unknown error occurred', statusCode: 500 },
+    });
+  });
+});
diff --git a/src/lib/errors.ts b/src/lib/errors.ts
index eb5c099..3c52a91 100644
--- a/src/lib/errors.ts
+++ b/src/lib/errors.ts
@@ -10,7 +10,7 @@ export class OmniFocusCliError extends Error {
   }
 }
 
-export function handleError(error: unknown): never {
+export function handleError(error: unknown): void {
   let name = 'unknown_error';
   let detail = 'An unknown error occurred';
   let statusCode = 500;
@@ -31,5 +31,9 @@ export function handleError(error: unknown): never {
   }
 
   outputJson({ error: { name, detail, statusCode } });
-  process.exit(1);
+  // Set exitCode instead of calling process.exit() to let the stdout pipe
+  // buffer drain before the process terminates. Calling process.exit()
+  // truncates piped output at ~512 bytes on macOS because pipe writes are
+  // asynchronous. See https://nodejs.org/api/process.html#processexitcode
+  process.exitCode = 1;
 }