fix(update): route the self-update by install kind (apt/pip/source) — 0.37.1

rigdoctor update assumed a pip/venv install and ran 'python -m pip install', which
fails on a .deb (system python has no pip; you can't pip-upgrade a dpkg package).
Add updates.install_kind() (dpkg ownership / venv / source-checkout detection,
cached) and route apply_update: pip self-updates in place; apt and source installs
return guidance instead. CLI and the GUI Update button show the apt/git command.
Adds tests/test_updates.py.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/rigdoctor/__init__.py

@@ -1,3 +1,3 @@
 """RigDoctor — modular hardware monitoring & crash diagnostics for Linux gamers."""
 
-__version__ = "0.37.0"
+__version__ = "0.37.1"

src/rigdoctor/cli.py

@@ -263,6 +263,10 @@ def cmd_update(args) -> int:
         print("\nWhat's new:\n" + "\n".join("  " + ln for ln in notes.splitlines()) + "\n")
     if args.check:
         return 0
+    kind = updates.install_kind()
+    if kind != "pip":  # apt/source installs aren't pip-updatable — show the right command
+        print(updates.update_hint(kind))
+        return 0
     print(f"Installing {tag}…")
     rc, out = updates.apply_update(tag)
     print(out[-2000:])

src/rigdoctor/core/updates.py

@@ -8,11 +8,14 @@ state for the UI; `apply_update` performs the no-root self-update.
 
 from __future__ import annotations
 
+import functools
 import json
+import shutil
 import subprocess
 import sys
 import urllib.error
 import urllib.request
+from pathlib import Path
 
 from .. import __version__
 from ..config import load_token
@@ -31,6 +34,50 @@ UP_TO_DATE = "up-to-date"
 AVAILABLE = "available"
 
 
+APT_PACKAGE = "rigdoctor"
+
+
+def _dpkg_owns(path: Path) -> bool:
+    """True if dpkg reports `path` belongs to a package (i.e. an apt/.deb install)."""
+    if not shutil.which("dpkg"):
+        return False
+    try:
+        r = subprocess.run(["dpkg", "-S", str(path)], capture_output=True, text=True, timeout=5)
+    except (subprocess.SubprocessError, OSError):
+        return False
+    return r.returncode == 0 and APT_PACKAGE in r.stdout
+
+
+@functools.lru_cache(maxsize=1)
+def install_kind() -> str:
+    """How RigDoctor was installed: 'apt' (.deb), 'pip' (venv/.run), or 'dev' (source checkout).
+
+    Decides which updater to use: only 'pip' can self-update in place; apt is root/dpkg-managed
+    and source is VCS-managed, so those are guided rather than auto-applied.
+    """
+    pkg = Path(__file__).resolve().parents[1]  # .../rigdoctor
+    if _dpkg_owns(pkg / "__init__.py"):
+        return "apt"
+    if sys.prefix != sys.base_prefix:  # inside a venv → the pip/.run install
+        return "pip"
+    if (pkg.parents[1] / "pyproject.toml").exists():  # repo checkout
+        return "dev"
+    if str(pkg).startswith("/usr/") or "/dist-packages/" in str(pkg):
+        return "apt"  # system-managed but no dpkg record — still don't pip
+    return "pip"
+
+
+def update_hint(kind: str | None = None) -> str:
+    """Human guidance for installs that can't self-update via pip (apt / source)."""
+    kind = kind or install_kind()
+    if kind == "apt":
+        return ("Installed via apt — update with:\n"
+                f"  sudo apt update && sudo apt install --only-upgrade {APT_PACKAGE}")
+    if kind == "dev":
+        return "Running from a source checkout — update with `git pull`."
+    return ""
+
+
 def _parse(version: str) -> tuple[int, ...]:
     return tuple(int(p) for p in version.lstrip("vV").split(".") if p.isdigit())
 
@@ -100,11 +147,16 @@ def list_releases(limit: int = 15, timeout: float = 6.0) -> tuple[list[tuple[str
 
 
 def apply_update(tag: str) -> tuple[int, str]:
-    """Self-update the current (user-local) install to `tag` via authenticated pip.
+    """Update to `tag` using the method matching how RigDoctor was installed.
 
-    Installs `rigdoctor[gui] @ git+https://oauth2:<token>@…/rigdoctor.git@<tag>` into
-    the running environment. Returns (exit_code, output) with the token scrubbed.
+    Only pip/venv installs are upgraded in place (authenticated pip install of
+    `rigdoctor[gui] @ git+https://oauth2:<token>@…/rigdoctor.git@<tag>`). apt and source
+    installs can't be (root/dpkg- or VCS-managed), so they return guidance instead of
+    attempting pip. Returns (exit_code, output) with the token scrubbed.
     """
+    kind = install_kind()
+    if kind != "pip":
+        return (1, update_hint(kind))
     token = load_token()
     if not token:
         return (1, "No update token configured. Run `rigdoctor login`.")

src/rigdoctor/gui/main_window.py

@@ -289,6 +289,9 @@ class MainWindow(QMainWindow):
     def _apply_update(self) -> None:
         if not self._latest_tag:
             return
+        if updates.install_kind() != "pip":  # apt/source: can't pip-update — show the command
+            QMessageBox.information(self, "Update RigDoctor", updates.update_hint())
+            return
         box = QMessageBox(self)
         box.setWindowTitle(f"Update to {self._latest_tag}")
         box.setText(f"Update RigDoctor to {self._latest_tag}?")
@@ -454,7 +457,7 @@ class MainWindow(QMainWindow):
             self._update_label.setText("update check unavailable")
         elif state == updates.AVAILABLE:
             self._update_label.setText(f'<span style="color:{GOOD};">{tag} available</span>')
-            self._update_btn.setText(f"Update to {tag}")
+            self._update_btn.setText(f"Update to {tag}" if updates.install_kind() == "pip" else "How to update")
             self._update_btn.setVisible(True)
             if self._alert_monitor.enabled and tag != self._notified_update_tag:
                 self._notified_update_tag = tag  # once per version, not every poll