Add handling of errors during VS Code extension installation

Ref. eng/recordflux/RecordFlux!1490

rflx/cli.py

@@ -683,7 +683,10 @@ def install(args: argparse.Namespace) -> None:
 
     elif args.ide is IDE.VSCODE:
         with importlib_resources.as_file(vscode_extension()) as extension:
-            subprocess.run(["code", "--install-extension", extension, "--force"], check=False)
+            try:
+                subprocess.run(["code", "--install-extension", extension, "--force"], check=True)
+            except (FileNotFoundError, subprocess.CalledProcessError) as e:
+                fail(f"installation of VS Code extension failed: {e}", Subsystem.CLI)
 
     else:
         assert_never(args.ide)  # pragma: no cover

tests/unit/cli_test.py

@@ -662,6 +662,18 @@ def test_install_vscode_extension(monkeypatch: pytest.MonkeyPatch, tmp_path: Pat
 
     assert run_called == [["code", "--install-extension", vscode_extension, "--force"]]
 
+    def run_mock(cmd: object, check: object) -> subprocess.CompletedProcess[object]:  # noqa: ARG001
+        raise FileNotFoundError("file not found")
+
+    monkeypatch.setattr(subprocess, "run", run_mock)
+
+    assert (
+        str(
+            cli.main(["rflx", "install", "vscode"]),
+        )
+        == "cli: error: installation of VS Code extension failed: file not found"
+    )
+
 
 def test_install_invalid() -> None:
     args = ["rflx", "install", "invalid"]