Copilot review on PR #29703 flagged two issues with the `uv tool list`
fallback in `is_uv_tool_install`:
1. False positive: `uv tool list` returns the *machine*'s installed
tools, not the active install. A regular pip/venv Hermes on a host
that also has `uv tool install hermes-agent` available would be
misclassified as a uv-tool install, and `hermes update` would
upgrade the wrong copy.
2. Overhead: the subprocess call (up to a 15s timeout) was triggered
even from `recommended_update_command_for_method`, which just
computes a display string.
Restrict detection to properties of the running interpreter
(`sys.prefix` and `sys.executable` — both can carry the uv-tool layout
marker depending on entry point). Drop the `uv tool list` fallback and
the `uv_path` parameter entirely. `_cmd_update_pip` now also surfaces a
clear hint when the runtime looks like a uv-tool install but `uv` is
missing from PATH, instead of silently falling back to `python -m pip`.
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