fix(update): reuse an existing PATH uv on Termux before pip

_ensure_uv_for_termux only checked resolve_uv() (the managed
$HERMES_HOME/bin/uv) before falling back to pip, so a uv installed via
`pkg install uv` lives on PATH but is invisible to the helper. Combined
with the cherry-picked wheel-only fallback, a Termux user with no managed
uv still hit `pip install uv`, which has no Android wheel and tried to
source-build the Rust crate, OOM-killing low-memory devices.

Probe shutil.which("uv") right after the Termux guard and reuse it before
pip. Add a regression test that keeps resolve_uv() returning None while a
uv exists on PATH and asserts pip is never invoked.

hermes_cli/main.py

@@ -7724,8 +7724,9 @@ def _ensure_uv_for_termux(pip_cmd: list[str]) -> str | None:
 
     The normal path (``ensure_uv()`` in managed_uv) installs the managed
     standalone uv into ``$HERMES_HOME/bin/uv``, but on Termux the official
-    installer may not work (glibc vs bionic).  Fall back to ``pip install uv``
-    which gets a Termux-compatible binary.
+    installer may not work (glibc vs bionic).  Prefer a uv already on PATH
+    (e.g. ``pkg install uv``); only if there is none do we fall back to a
+    wheel-only ``pip install uv`` so we never source-build the Rust crate.
     """
     from hermes_cli.managed_uv import resolve_uv
 
@@ -7734,6 +7735,12 @@ def _ensure_uv_for_termux(pip_cmd: list[str]) -> str | None:
         return existing
     if not _is_termux_env():
         return None
+    # A Termux-packaged uv lands on PATH but not in the managed bin dir, so
+    # resolve_uv() misses it. Use it before pip, which has no Android wheel and
+    # would otherwise build uv from source on a low-memory device.
+    system_uv = shutil.which("uv")
+    if system_uv:
+        return system_uv
     try:
         print("  → Termux detected: trying to install uv for faster dependency updates...")
         result = subprocess.run(

tests/hermes_cli/test_cmd_update.py

@@ -138,6 +138,23 @@ class TestCmdUpdateTermuxUvBootstrap:
         assert mock_run.call_args.kwargs["cwd"] == PROJECT_ROOT
         assert mock_run.call_args.kwargs["check"] is False
 
+    @patch("subprocess.run")
+    def test_termux_reuses_existing_path_uv_without_pip(self, mock_run, monkeypatch):
+        """A uv already on PATH (e.g. ``pkg install uv``) is reused before pip runs."""
+        from hermes_cli import main as hm
+
+        pkg_uv = "/data/data/com.termux/files/usr/bin/uv"
+        monkeypatch.setattr(hm, "_is_termux_env", lambda env=None: True)
+        # Production resolve_uv only checks $HERMES_HOME/bin/uv; model an empty
+        # managed dir so the PATH probe is what surfaces the packaged uv.
+        monkeypatch.setattr("hermes_cli.managed_uv.resolve_uv", lambda: None)
+        monkeypatch.setattr("shutil.which", lambda name: pkg_uv if name == "uv" else None)
+
+        uv_bin = hm._ensure_uv_for_termux(["/termux/python", "-m", "pip"])
+
+        assert uv_bin == pkg_uv
+        mock_run.assert_not_called()
+
 
 class TestCmdUpdateBranchFallback:
     """cmd_update falls back to main when current branch has no remote counterpart."""