diff --git a/lib/provider-detection.js b/lib/provider-detection.js
index 6952649..6557386 100644
--- a/lib/provider-detection.js
+++ b/lib/provider-detection.js
@@ -7,8 +7,9 @@ function commandExists(command) {
   if (command.includes(path.sep)) {
     return fs.existsSync(command);
   }
+  const probe = process.platform === 'win32' ? `where ${command}` : `command -v ${command}`;
   try {
-    execSync(`command -v ${command}`, { stdio: 'pipe' });
+    execSync(probe, { stdio: 'pipe' });
     return true;
   } catch {
     return false;
@@ -20,9 +21,11 @@ function getCommandPath(command) {
   if (command.includes(path.sep)) {
     return fs.existsSync(command) ? command : null;
   }
+  const probe = process.platform === 'win32' ? `where ${command}` : `command -v ${command}`;
   try {
-    const output = execSync(`command -v ${command}`, { encoding: 'utf8', stdio: 'pipe' });
-    return output.trim() || null;
+    const output = execSync(probe, { encoding: 'utf8', stdio: 'pipe' });
+    // `where` can return multiple matches (one per line); take the first.
+    return output.split(/\r?\n/)[0].trim() || null;
   } catch {
     return null;
   }
diff --git a/tests/provider-detection.test.js b/tests/provider-detection.test.js
new file mode 100644
index 0000000..396468d
--- /dev/null
+++ b/tests/provider-detection.test.js
@@ -0,0 +1,86 @@
+/**
+ * Tests for provider-detection cross-platform CLI lookup.
+ *
+ * Regression: on Windows the lookup used the POSIX builtin `command -v`,
+ * which does not exist under cmd.exe, so every provider was reported as
+ * "not found". The lookup must use `where` on win32 and `command -v` elsewhere.
+ */
+const { expect } = require('chai');
+const sinon = require('sinon');
+const childProcess = require('child_process');
+
+function withPlatform(value, fn) {
+  const original = Object.getOwnPropertyDescriptor(process, 'platform');
+  Object.defineProperty(process, 'platform', { value, configurable: true });
+  try {
+    fn();
+  } finally {
+    Object.defineProperty(process, 'platform', original);
+  }
+}
+
+describe('provider-detection', () => {
+  let execSyncStub;
+  let detection;
+
+  beforeEach(() => {
+    // Stub before requiring the module so its destructured reference is the stub.
+    execSyncStub = sinon.stub(childProcess, 'execSync');
+    delete require.cache[require.resolve('../lib/provider-detection.js')];
+    detection = require('../lib/provider-detection.js');
+  });
+
+  afterEach(() => {
+    sinon.restore();
+    delete require.cache[require.resolve('../lib/provider-detection.js')];
+  });
+
+  describe('commandExists', () => {
+    it('returns false for empty command without probing', () => {
+      expect(detection.commandExists('')).to.equal(false);
+      expect(execSyncStub.called).to.equal(false);
+    });
+
+    it('uses `where` on win32', () => {
+      execSyncStub.returns('C:\\bin\\claude.exe');
+      withPlatform('win32', () => {
+        expect(detection.commandExists('claude')).to.equal(true);
+      });
+      expect(execSyncStub.firstCall.args[0]).to.equal('where claude');
+    });
+
+    it('uses `command -v` on non-win32', () => {
+      execSyncStub.returns('/usr/bin/claude');
+      withPlatform('linux', () => {
+        expect(detection.commandExists('claude')).to.equal(true);
+      });
+      expect(execSyncStub.firstCall.args[0]).to.equal('command -v claude');
+    });
+
+    it('returns false when the probe throws (command missing)', () => {
+      execSyncStub.throws(new Error('not found'));
+      withPlatform('win32', () => {
+        expect(detection.commandExists('nope')).to.equal(false);
+      });
+    });
+  });
+
+  describe('getCommandPath', () => {
+    it('returns the first match line on win32 (`where` may return many)', () => {
+      execSyncStub.returns('C:\\a\\claude.exe\r\nC:\\b\\claude.cmd\r\n');
+      let result;
+      withPlatform('win32', () => {
+        result = detection.getCommandPath('claude');
+      });
+      expect(result).to.equal('C:\\a\\claude.exe');
+      expect(execSyncStub.firstCall.args[0]).to.equal('where claude');
+    });
+
+    it('returns null when the probe throws', () => {
+      execSyncStub.throws(new Error('not found'));
+      withPlatform('linux', () => {
+        expect(detection.getCommandPath('nope')).to.equal(null);
+      });
+    });
+  });
+});