fix(install): clean up a broken managed Node and guard the termux probe

AI-review follow-up on #87467:
- On probe failure, remove the extracted ~/.hermes/node tree and the
  node/npm/npx bin links so later installer steps and retry runs start
  clean instead of resolving node to a binary that cannot start.
- The termux pkg branch had the same silent-success class: an empty
  version probe logged success and set HAS_NODE=true. Degrade with the
  binary's own error instead.

scripts/install.sh

@@ -980,8 +980,17 @@ install_node() {
         if pkg install -y nodejs >/dev/null; then
             local installed_ver
             installed_ver=$(node --version 2>/dev/null || true)
-            log_success "Node.js $installed_ver installed via pkg"
-            HAS_NODE=true
+            if [ -n "$installed_ver" ]; then
+                log_success "Node.js $installed_ver installed via pkg"
+                HAS_NODE=true
+            else
+                # pkg succeeded but the binary cannot start — the same
+                # silent-success class the managed-download probe guards
+                # against (#87460). Degrade instead of claiming success.
+                log_error "Node.js installed via pkg failed to start:"
+                node --version >&2 || true
+                HAS_NODE=false
+            fi
         else
             log_warn "Failed to install Node.js via pkg"
             HAS_NODE=false
@@ -1106,10 +1115,14 @@ install_node() {
         # whole installer at exit 127 with the loader's explanation
         # discarded by 2>/dev/null — installs died mid-sentence with no
         # output at all (#87460). Degrade instead, and surface the real
-        # error the loader printed.
+        # error the loader printed. Remove the broken tree and the bin
+        # links so later steps and retry runs start clean instead of
+        # resolving `node` to a binary that cannot start.
         log_error "Downloaded Node.js failed to start:"
         printf '%s\n' "$installed_ver" >&2
         log_info "On Debian/Ubuntu the usual fix is: sudo apt-get install -y libatomic1"
+        rm -rf "$HERMES_HOME/node"
+        rm -f "$node_link_dir/node" "$node_link_dir/npm" "$node_link_dir/npx"
         HAS_NODE=false
         return 0
     fi

tests/test_install_sh_node_probe_87460.py

@@ -153,6 +153,18 @@ def test_broken_node_degrades_with_clear_error(tmp_path: Path) -> None:
     assert "apt-get install -y libatomic1" in stdout + stderr
     assert "HAS_NODE=false" in stdout
     assert "HAS_NODE=true" not in stdout
+    # AI-review follow-up: the broken tree and bin links must not linger
+    # — retries and later installer steps resolve `node` cleanly.
+    home = tmp_path / "home"
+    link_dir = tmp_path / "links"
+    assert not (home / "node").exists(), "broken managed Node tree left behind"
+    assert not (link_dir / "node").exists(), "broken node symlink left behind"
+    assert not (link_dir / "npm").exists(), "broken npm symlink left behind"
+    # AI-review follow-up: the broken tree and bin links must not linger
+    # — retries and later installer steps resolve `node` cleanly.
+    assert not (home / "node").exists(), "broken managed Node tree left behind"
+    assert not (link_dir / "node").exists(), "broken node symlink left behind"
+    assert not (link_dir / "npm").exists(), "broken npm symlink left behind"
 
 
 def test_healthy_node_reports_success(tmp_path: Path) -> None: