diff --git a/hermes_cli/main.py b/hermes_cli/main.py
index 57dbaaf7c2dd8..df9c9255b254f 100644
--- a/hermes_cli/main.py
+++ b/hermes_cli/main.py
@@ -7834,7 +7834,8 @@ def _update_via_zip(args):
     # may point to a Python without FTS5.  Rebuild it so the new managed
     # uv provides a fresh interpreter with FTS5 guaranteed.
     if fresh_bootstrap and uv_bin:
-        rebuild_venv(uv_bin, PROJECT_ROOT / "venv")
+        if not rebuild_venv(uv_bin, PROJECT_ROOT / "venv"):
+            raise RuntimeError("venv rebuild failed; aborting update before dependency install")
 
     pip_cmd = [sys.executable, "-m", "pip"]
     if not uv_bin:
@@ -10036,7 +10037,8 @@ def _cmd_update_impl(args, gateway_mode: bool):
         # may point to a Python without FTS5.  Rebuild it so the new managed
         # uv provides a fresh interpreter with FTS5 guaranteed.
         if fresh_bootstrap and uv_bin:
-            rebuild_venv(uv_bin, PROJECT_ROOT / "venv")
+            if not rebuild_venv(uv_bin, PROJECT_ROOT / "venv"):
+                raise RuntimeError("venv rebuild failed; aborting update before dependency install")
 
         pip_cmd = [sys.executable, "-m", "pip"]
         if not uv_bin:
diff --git a/hermes_cli/managed_uv.py b/hermes_cli/managed_uv.py
index b38893f713f94..3ff91e894546b 100644
--- a/hermes_cli/managed_uv.py
+++ b/hermes_cli/managed_uv.py
@@ -111,13 +111,17 @@ def rebuild_venv(uv_bin: str, venv_dir: Path, python_version: str = "3.11") -> b
         shutil.rmtree(venv_dir, ignore_errors=True)
 
     result = subprocess.run(
-        [uv_bin, "venv", str(venv_dir), "--python", python_version],
+        [uv_bin, "venv", str(venv_dir), "--python", python_version, "--clear"],
         capture_output=True,
         text=True,
         check=False,
     )
     if result.returncode == 0:
         venv_python = venv_dir / ("Scripts" if platform.system() == "Windows" else "bin") / "python"
+        if not venv_python.exists():
+            logger.warning("venv rebuild reported success but %s is missing", venv_python)
+            print(f"  ✗ venv rebuild failed: Python interpreter missing at {venv_python}")
+            return False
         py_ver = subprocess.run(
             [str(venv_python), "--version"],
             capture_output=True,
diff --git a/tests/hermes_cli/test_managed_uv.py b/tests/hermes_cli/test_managed_uv.py
index 89f3d8badaec4..59d060175f6f7 100644
--- a/tests/hermes_cli/test_managed_uv.py
+++ b/tests/hermes_cli/test_managed_uv.py
@@ -114,8 +114,10 @@ def test_removes_old_venv_and_creates_new(self, tmp_path):
         (venv_dir / "old_file").write_text("stale")
 
         uv_bin = str(tmp_path / "bin" / "uv")
+        commands = []
 
         def fake_run(cmd, **kwargs):
+            commands.append(cmd)
             m = MagicMock(returncode=0)
             if cmd[1] == "venv":
                 # Simulate uv creating the venv dir
@@ -133,6 +135,19 @@ def fake_run(cmd, **kwargs):
             result = rebuild_venv(uv_bin, venv_dir)
             assert result is True
             mock_rmtree.assert_called_once_with(venv_dir, ignore_errors=True)
+            assert commands[0] == [uv_bin, "venv", str(venv_dir), "--python", "3.11", "--clear"]
+
+    def test_rebuild_success_without_python_returns_false(self, tmp_path):
+        venv_dir = tmp_path / "venv"
+        uv_bin = str(tmp_path / "bin" / "uv")
+
+        with patch("hermes_cli.managed_uv.subprocess.run") as mock_run, \
+             patch("hermes_cli.managed_uv.shutil.rmtree"):
+            mock_run.return_value = MagicMock(returncode=0, stdout="")
+            from hermes_cli.managed_uv import rebuild_venv
+            result = rebuild_venv(uv_bin, venv_dir)
+            assert result is False
+            assert mock_run.call_count == 1
 
     def test_rebuild_failure_returns_false(self, tmp_path):
         venv_dir = tmp_path / "venv"
diff --git a/tests/hermes_cli/test_update_autostash.py b/tests/hermes_cli/test_update_autostash.py
index 5a255a05211f6..b9a9c7e554210 100644
--- a/tests/hermes_cli/test_update_autostash.py
+++ b/tests/hermes_cli/test_update_autostash.py
@@ -423,6 +423,37 @@ def fake_run(cmd, **kwargs):
     assert ".[all]" in install_cmds[0]
 
 
+def test_cmd_update_aborts_when_fresh_managed_uv_rebuild_fails(monkeypatch, tmp_path):
+    """A failed fresh managed-uv venv rebuild must not continue into pip install."""
+    _setup_update_mocks(monkeypatch, tmp_path)
+    monkeypatch.setattr("shutil.which", lambda name: "/usr/bin/uv" if name == "uv" else None)
+    monkeypatch.setattr(hermes_main, "_is_termux_env", lambda env=None: False)
+
+    recorded = []
+
+    def fake_run(cmd, **kwargs):
+        recorded.append(cmd)
+        if cmd == ["git", "fetch", "origin"]:
+            return SimpleNamespace(stdout="", stderr="", returncode=0)
+        if cmd == ["git", "rev-parse", "--abbrev-ref", "HEAD"]:
+            return SimpleNamespace(stdout="main\n", stderr="", returncode=0)
+        if cmd == ["git", "rev-list", "HEAD..origin/main", "--count"]:
+            return SimpleNamespace(stdout="1\n", stderr="", returncode=0)
+        if cmd == ["git", "pull", "--ff-only", "origin", "main"]:
+            return SimpleNamespace(stdout="Updating\n", stderr="", returncode=0)
+        return SimpleNamespace(returncode=0, stdout="", stderr="")
+
+    monkeypatch.setattr(hermes_main.subprocess, "run", fake_run)
+
+    with patch("hermes_cli.managed_uv.ensure_uv", return_value=("/usr/bin/uv", True)), \
+         patch("hermes_cli.managed_uv.rebuild_venv", return_value=False), \
+         pytest.raises(RuntimeError, match="venv rebuild failed"):
+        hermes_main.cmd_update(SimpleNamespace())
+
+    install_cmds = [c for c in recorded if "pip" in c and "install" in c]
+    assert install_cmds == []
+
+
 def test_install_with_optional_fallback_honors_custom_group(monkeypatch):
     """Termux update path should target .[termux-all] when requested."""
     calls = []