fix(install): delay PATH cleanup until after verified install

Do not remove pipx or other strix copies before checksum and
provenance succeed, so a failed verify cannot leave the user
with no working binary (#1267).

scripts/install.sh

@@ -105,6 +105,9 @@ print_message() {
     echo -e "${color}${message}${NC}"
 }
 
+# Remove other copies of strix from PATH (pipx, leftover binaries) only after
+# a verified install has been written to INSTALL_DIR. Calling this earlier
+# would leave the user with no working Strix if checksum/provenance then fail.
 check_existing_installation() {
     local found_paths=()
     while IFS= read -r -d '' path; do
@@ -257,8 +260,6 @@ verify_provenance() {
 }
 
 check_version() {
-    check_existing_installation
-
     if [[ -x "$INSTALL_DIR/strix" ]]; then
         installed_version=$("$INSTALL_DIR/strix" --version 2>/dev/null | awk '{print $2}' || echo "")
         if [[ "$installed_version" == "$specific_version" ]]; then
@@ -332,6 +333,7 @@ download_and_install() {
     cleanup_install_temps
 
     echo -e "${GREEN}✓ Strix installed to $INSTALL_DIR${NC}"
+    check_existing_installation
 }
 
 check_docker() {

tests/test_install_script.py

@@ -235,6 +235,40 @@ def test_installer_rejects_unsupported_architecture(tmp_path: Path) -> None:
     assert not (home_path / ".strix").exists()
 
 
+def test_installer_leaves_external_strix_on_checksum_failure(tmp_path: Path) -> None:
+    repository_root = Path(__file__).resolve().parents[1]
+    archive_path = _create_release_archive(tmp_path)
+    mock_bin = _create_mock_commands(tmp_path, machine="aarch64")
+    environment, home_path, _curl_log_path = _create_installer_environment(
+        tmp_path,
+        archive_path,
+        mock_bin,
+    )
+    environment["STRIX_TEST_BAD_CHECKSUM"] = "1"
+
+    other_bin = tmp_path / "other-bin"
+    other_bin.mkdir()
+    external = other_bin / "strix"
+    _write_executable(external, "#!/bin/sh\nprintf 'strix 1.0.0\\n'\n")
+    environment["PATH"] = f"{other_bin}:{environment['PATH']}"
+    before = external.read_bytes()
+
+    result = _run_installer(repository_root, environment)
+
+    assert result.returncode != 0
+    assert "Checksum mismatch" in result.stdout
+    assert external.exists()
+    assert external.read_bytes() == before
+    assert not (home_path / ".strix/bin/strix").exists()
+    installed_result = subprocess.run(  # noqa: S603
+        [str(external), "--version"],
+        capture_output=True,
+        text=True,
+        check=True,
+    )
+    assert installed_result.stdout.strip() == "strix 1.0.0"
+
+
 def test_installer_leaves_existing_install_on_checksum_failure(tmp_path: Path) -> None:
     repository_root = Path(__file__).resolve().parents[1]
     archive_path = _create_release_archive(tmp_path)