*fix(nix): resolve nix profile conflicts without numeric indices and fix update pkgmgr system test*

* Switch conflict handling from index-based removal to token-based removal (*nix profile remove <name>*) for newer nix versions
* Add robust parsing of *nix profile list --json* with normalization and heuristics for output/name matching
* Detect at runtime whether numeric profile indices are supported and fall back automatically when they are not
* Ensure *pkgmgr* / *package-manager* flake outputs are correctly identified and cleaned up during reinstall
* Fix failing E2E test *test_update_pkgmgr_shallow_pkgmgr_with_system* by reliably removing conflicting profile entries before reinstall

https://chatgpt.com/share/693efae5-b8bc-800f-94e3-28c93b74ed7b

tests/integration/test_nix_profile_list_json.py

@@ -0,0 +1,63 @@
+from __future__ import annotations
+
+import json
+import unittest
+from dataclasses import dataclass
+
+
+@dataclass
+class FakeRunResult:
+    """
+    Mimics your runner returning a structured result object.
+    """
+    returncode: int
+    stdout: str
+    stderr: str = ""
+
+
+class FakeRunner:
+    """
+    Minimal runner stub: returns exactly what we configure.
+    """
+    def __init__(self, result):
+        self._result = result
+
+    def run(self, ctx, cmd: str, allow_failure: bool = False):
+        return self._result
+
+
+class TestE2ENixProfileListJsonParsing(unittest.TestCase):
+    """
+    This test verifies that NixProfileInspector can parse `nix profile list --json`
+    regardless of whether the CommandRunner returns:
+      - raw stdout string, OR
+      - a RunResult-like object with a `.stdout` attribute.
+    """
+
+    def test_list_json_accepts_raw_string(self) -> None:
+        from pkgmgr.actions.install.installers.nix.profile import NixProfileInspector
+
+        payload = {"elements": {"pkgmgr-1": {"attrPath": "packages.x86_64-linux.pkgmgr"}}}
+        raw = json.dumps(payload)
+
+        runner = FakeRunner(raw)
+        inspector = NixProfileInspector()
+
+        data = inspector.list_json(ctx=None, runner=runner)
+        self.assertEqual(data["elements"]["pkgmgr-1"]["attrPath"], "packages.x86_64-linux.pkgmgr")
+
+    def test_list_json_accepts_runresult_object(self) -> None:
+        from pkgmgr.actions.install.installers.nix.profile import NixProfileInspector
+
+        payload = {"elements": {"pkgmgr-1": {"attrPath": "packages.x86_64-linux.pkgmgr"}}}
+        raw = json.dumps(payload)
+
+        runner = FakeRunner(FakeRunResult(returncode=0, stdout=raw))
+        inspector = NixProfileInspector()
+
+        data = inspector.list_json(ctx=None, runner=runner)
+        self.assertEqual(data["elements"]["pkgmgr-1"]["attrPath"], "packages.x86_64-linux.pkgmgr")
+
+
+if __name__ == "__main__":
+    unittest.main()