diff --git a/src/renderer/components/terminal/EmbeddedTerminal.test.tsx b/src/renderer/components/terminal/EmbeddedTerminal.test.tsx
new file mode 100644
index 00000000..3abebcd7
--- /dev/null
+++ b/src/renderer/components/terminal/EmbeddedTerminal.test.tsx
@@ -0,0 +1,172 @@
+import React, { act } from 'react';
+import { createRoot } from 'react-dom/client';
+
+import { api } from '@renderer/api';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+
+import { EmbeddedTerminal } from './EmbeddedTerminal';
+
+vi.mock('@renderer/api', () => ({
+  api: {
+    openExternal: vi.fn(),
+    terminal: {
+      spawn: vi.fn(),
+      write: vi.fn(),
+      resize: vi.fn(),
+      kill: vi.fn(),
+      onData: vi.fn(),
+      onExit: vi.fn(),
+    },
+  },
+}));
+
+vi.mock('@xterm/xterm', () => ({
+  Terminal: vi.fn().mockImplementation(() => ({
+    cols: 80,
+    rows: 24,
+    loadAddon: vi.fn(),
+    open: vi.fn(),
+    attachCustomKeyEventHandler: vi.fn(),
+    onData: vi.fn(() => ({ dispose: vi.fn() })),
+    getSelection: vi.fn(() => ''),
+    write: vi.fn(),
+    dispose: vi.fn(),
+  })),
+}));
+
+vi.mock('@xterm/addon-fit', () => ({
+  FitAddon: vi.fn().mockImplementation(() => ({
+    fit: vi.fn(),
+  })),
+}));
+
+vi.mock('@xterm/addon-web-links', () => ({
+  WebLinksAddon: vi.fn().mockImplementation(() => ({})),
+}));
+
+let frameCallbacks: Map<number, FrameRequestCallback>;
+let nextFrameId: number;
+
+function flushFrames(): void {
+  const callbacks = Array.from(frameCallbacks.values());
+  frameCallbacks.clear();
+  callbacks.forEach((callback) => callback(performance.now()));
+}
+
+async function flushReact(): Promise<void> {
+  await Promise.resolve();
+  await Promise.resolve();
+}
+
+describe('EmbeddedTerminal', () => {
+  beforeEach(() => {
+    vi.stubGlobal('IS_REACT_ACT_ENVIRONMENT', true);
+
+    frameCallbacks = new Map();
+    nextFrameId = 1;
+    vi.stubGlobal(
+      'requestAnimationFrame',
+      vi.fn((callback: FrameRequestCallback) => {
+        const id = nextFrameId;
+        nextFrameId += 1;
+        frameCallbacks.set(id, callback);
+        return id;
+      })
+    );
+    vi.stubGlobal(
+      'cancelAnimationFrame',
+      vi.fn((id: number) => {
+        frameCallbacks.delete(id);
+      })
+    );
+    vi.stubGlobal(
+      'ResizeObserver',
+      vi.fn().mockImplementation(() => ({
+        observe: vi.fn(),
+        disconnect: vi.fn(),
+      }))
+    );
+
+    vi.mocked(api.terminal.spawn).mockResolvedValue('pty-1');
+    vi.mocked(api.terminal.onData).mockReturnValue(() => undefined);
+    vi.mocked(api.terminal.onExit).mockReturnValue(() => undefined);
+  });
+
+  afterEach(() => {
+    document.body.innerHTML = '';
+    vi.clearAllMocks();
+    vi.unstubAllGlobals();
+  });
+
+  it('does not spawn twice during React StrictMode effect replay', async () => {
+    const host = document.createElement('div');
+    document.body.appendChild(host);
+    const root = createRoot(host);
+
+    await act(async () => {
+      root.render(
+        <React.StrictMode>
+          <EmbeddedTerminal command="/bin/runtime" args={['auth', 'login']} />
+        </React.StrictMode>
+      );
+      await flushReact();
+    });
+
+    expect(api.terminal.spawn).not.toHaveBeenCalled();
+
+    await act(async () => {
+      flushFrames();
+      await flushReact();
+    });
+
+    expect(api.terminal.spawn).toHaveBeenCalledTimes(1);
+    expect(api.terminal.spawn).toHaveBeenCalledWith(
+      expect.objectContaining({
+        command: '/bin/runtime',
+        args: ['auth', 'login'],
+      })
+    );
+
+    await act(async () => {
+      root.unmount();
+      await flushReact();
+    });
+  });
+
+  it('kills a PTY that resolves after the terminal unmounts', async () => {
+    let resolveSpawn: (id: string) => void = () => {};
+    vi.mocked(api.terminal.spawn).mockReturnValue(
+      new Promise<string>((resolve) => {
+        resolveSpawn = resolve;
+      })
+    );
+
+    const host = document.createElement('div');
+    document.body.appendChild(host);
+    const root = createRoot(host);
+
+    await act(async () => {
+      root.render(<EmbeddedTerminal command="/bin/runtime" args={['auth', 'login']} />);
+      await flushReact();
+    });
+
+    await act(async () => {
+      flushFrames();
+      await flushReact();
+    });
+
+    expect(api.terminal.spawn).toHaveBeenCalledTimes(1);
+
+    await act(async () => {
+      root.unmount();
+      await flushReact();
+    });
+
+    await act(async () => {
+      resolveSpawn('late-pty');
+      await flushReact();
+    });
+
+    expect(api.terminal.kill).toHaveBeenCalledWith('late-pty');
+  });
+});
diff --git a/src/renderer/components/terminal/EmbeddedTerminal.tsx b/src/renderer/components/terminal/EmbeddedTerminal.tsx
index 78acc77d..3e39c938 100644
--- a/src/renderer/components/terminal/EmbeddedTerminal.tsx
+++ b/src/renderer/components/terminal/EmbeddedTerminal.tsx
@@ -64,8 +64,43 @@ export const EmbeddedTerminal = ({
 
     term.open(container);
 
-    // Fit after opening so dimensions are correct
-    const rafId = requestAnimationFrame(() => fitAddon.fit());
+    const spawnTerminal = (): void => {
+      if (disposed) return;
+
+      const spawnOptions: PtySpawnOptions = {
+        ...(command ? { command } : {}),
+        ...(args ? { args } : {}),
+        ...(cwd ? { cwd } : {}),
+        ...(env ? { env } : {}),
+        cols: term.cols,
+        rows: term.rows,
+      };
+
+      api.terminal
+        .spawn(spawnOptions)
+        .then((id) => {
+          if (disposed) {
+            api.terminal.kill(id);
+            return;
+          }
+          ptyId = id;
+          // Send actual terminal size after spawn (fitAddon.fit() may have changed cols/rows).
+          api.terminal.resize(id, term.cols, term.rows);
+        })
+        .catch((err: unknown) => {
+          if (disposed) return;
+          term.write(
+            `\r\n\x1b[31mFailed to start terminal: ${err instanceof Error ? err.message : String(err)}\x1b[0m\r\n`
+          );
+        });
+    };
+
+    // Defer spawning until after the first frame. React StrictMode replays effects
+    // in development; canceling this RAF prevents duplicate one-shot commands.
+    const rafId = requestAnimationFrame(() => {
+      fitAddon.fit();
+      spawnTerminal();
+    });
 
     // Ctrl+C with selection → copy to clipboard (instead of sending SIGINT)
     term.attachCustomKeyEventHandler((event) => {
@@ -97,32 +132,6 @@ export const EmbeddedTerminal = ({
       }
     });
 
-    // Spawn PTY
-    const spawnOptions: PtySpawnOptions = {
-      ...(command ? { command } : {}),
-      ...(args ? { args } : {}),
-      ...(cwd ? { cwd } : {}),
-      ...(env ? { env } : {}),
-      cols: term.cols,
-      rows: term.rows,
-    };
-
-    api.terminal
-      .spawn(spawnOptions)
-      .then((id) => {
-        if (disposed) return;
-        ptyId = id;
-        // Send actual terminal size after spawn (fitAddon.fit() may have
-        // changed cols/rows via RAF after spawnOptions was constructed)
-        api.terminal.resize(id, term.cols, term.rows);
-      })
-      .catch((err: unknown) => {
-        if (disposed) return;
-        term.write(
-          `\r\n\x1b[31mFailed to start terminal: ${err instanceof Error ? err.message : String(err)}\x1b[0m\r\n`
-        );
-      });
-
     // ResizeObserver → fitAddon.fit() → pty.resize()
     const observer = new ResizeObserver(() => {
       fitAddon.fit();