fix(plugins): --install-deps probe imports from the synced environment

hermes plugins validate --install-deps synced the plugin's declared
dependencies into a newly committed environment, then ran the capability
probe with sys.executable, the pre-sync interpreter. Plugins importing a
non-core package at load time (evalroute: pyyaml, gone from core since the
ruamel move) failed the catalog gate with a masked ImportError.

Run the probe with the committed environment's interpreter and activation
env. A developer venv without a committed environment keeps the old path.

hermes_cli/plugin_validate.py

@@ -324,20 +324,25 @@ def _probe_options(manifest: dict) -> dict:
     }
 
 
-def _run_capability_probe(plugin_dir: Path, manifest: dict) -> Tuple[Optional[dict], str]:
+def _run_capability_probe(
+    plugin_dir: Path, manifest: dict, probe: Optional[Tuple[Path, Dict[str, str]]] = None,
+) -> Tuple[Optional[dict], str]:
     """Run the recording probe in a scratch subprocess.
 
+    *probe* is ``(interpreter, env)`` of the dependency environment to import the plugin from;
+    None probes this interpreter.
+
     Returns ``(recorded, error)`` — exactly one is meaningful: *recorded*
     is the ``{tools, hooks, middleware, commands, providers}`` dict on
     success, and *error* is a human-readable failure description otherwise.
     """
     with tempfile.TemporaryDirectory(prefix="hermes-validate-") as scratch:
-        env = dict(os.environ)
+        env = dict(probe[1] if probe else os.environ)
         env["HERMES_HOME"] = scratch
         try:
             result = subprocess.run(
                 [
-                    sys.executable,
+                    str(probe[0]) if probe else sys.executable,
                     "-c",
                     _PROBE_SCRIPT,
                     str(plugin_dir),
@@ -379,7 +384,8 @@ def _declared_list(manifest: dict, key: str) -> List[str]:
 
 
 def _check_capabilities(
-    report: ValidationReport, manifest: dict, plugin_dir: Path
+    report: ValidationReport, manifest: dict, plugin_dir: Path,
+    probe: Optional[Tuple[Path, Dict[str, str]]] = None,
 ) -> Optional[dict]:
     """Probe actual registrations and diff against declared capabilities.
 
@@ -393,7 +399,7 @@ def _check_capabilities(
         report.add("capability probe", True, "skipped (no __init__.py)")
         return None
 
-    recorded, error = _run_capability_probe(plugin_dir, manifest)
+    recorded, error = _run_capability_probe(plugin_dir, manifest, probe)
     if recorded is None:
         report.add("capability probe", False, error)
         return None
@@ -472,8 +478,11 @@ def _check_builtin_collisions(
 # ─── Entry point ─────────────────────────────────────────────────────────────
 
 
-def validate_plugin_dir(plugin_dir: Path) -> ValidationReport:
-    """Run every admission check against *plugin_dir* and return the report."""
+def validate_plugin_dir(
+    plugin_dir: Path, probe: Optional[Tuple[Path, Dict[str, str]]] = None,
+) -> ValidationReport:
+    """Run every admission check against *plugin_dir* and return the report. *probe* is
+    ``(interpreter, env)`` for the capability probe (see ``_run_capability_probe``)."""
     report = ValidationReport()
     plugin_dir = Path(plugin_dir)
 
@@ -520,7 +529,7 @@ def validate_plugin_dir(plugin_dir: Path) -> ValidationReport:
     _check_requires_env(report, manifest)
     _check_loadable(report, plugin_dir, manifest)
     _check_python_dependencies(report, plugin_dir)
-    recorded = _check_capabilities(report, manifest, plugin_dir)
+    recorded = _check_capabilities(report, manifest, plugin_dir, probe)
     _check_builtin_collisions(report, manifest, recorded)
     _check_trusted_inbound(report, recorded)
     _check_security_scan(report, plugin_dir)

hermes_cli/plugins_cmd_catalog.py

@@ -770,14 +770,22 @@ def cmd_validate(path: str, as_json: bool = False, install_deps: bool = False) -
     installs the declared Python deps first so the capability probe imports what an install would."""
     from hermes_cli.plugin_validate import validate_plugin_dir
     from hermes_cli.plugins_cmd import _console
+    probe = None
     if install_deps:
         import pm
+        from pm import paths
+        from pm.environments import activation_environment, project_python
         from pm.plugin_inputs import Candidates
         try:
             pm.sync_venv(plugins=Candidates([Path(path)]))
+            # The sync commits a NEW environment that this running process never switches to,
+            # so the probe must import the plugin from that environment's interpreter.
+            root = paths.repo_root()
+            if project_python(root).is_file():  # a developer venv has no committed environment
+                probe = (project_python(root), activation_environment(root))
         except Exception as exc:  # validation still runs; the probe reports what is missing
             print(f"dependency preparation failed: {exc}", file=sys.stderr)
-    report = validate_plugin_dir(Path(path))
+    report = validate_plugin_dir(Path(path), probe)
     if as_json:
         print(json.dumps(report.to_dict(), indent=2))
         sys.exit(report.exit_code)

tests/hermes_cli/test_plugin_validate.py

@@ -450,3 +450,31 @@ def test_core_override_through_a_method_patch_helper(tmp_path):
     from hermes_cli.plugin_validate_core_override import core_override_findings
 
     assert core_override_findings(bad) == ["bind(auxiliary_client, ...) (__init__.py:6)"]
+
+
+def test_install_deps_probe_imports_from_the_synced_environment(tmp_path: Path, monkeypatch, capsys) -> None:
+    """`--install-deps` commits a new dependency environment this process never switches to;
+    the probe must import the plugin from that environment, not the validator's own."""
+    import os
+    import sys
+
+    import pm
+    import pm.environments as environments
+    from hermes_cli.plugins_cmd_catalog import cmd_validate
+
+    deps = tmp_path / "synced-site-packages"
+    deps.mkdir()
+    (deps / "probe_only_dep.py").write_text("VALUE = 1\n", encoding="utf-8")
+    plugin = _make_plugin(tmp_path, manifest={"name": "needs-dep", "version": "1.0.0", "description": "d"},
+                          init_py="import probe_only_dep\n\ndef register(ctx):\n    pass\n")
+    synced_env = {**os.environ, "PYTHONPATH": os.pathsep.join([str(Path(__file__).resolve().parents[2]), str(deps)])}
+    monkeypatch.setattr(pm, "sync_venv", lambda **_kw: None)
+    monkeypatch.setattr(environments, "project_python", lambda _root: Path(sys.executable))
+    monkeypatch.setattr(environments, "activation_environment", lambda _root: synced_env)
+
+    try:
+        cmd_validate(str(plugin), as_json=True, install_deps=True)
+    except SystemExit:
+        pass
+    checks = {c["name"]: c for c in json.loads(capsys.readouterr().out)["checks"]}
+    assert checks["capability probe"]["ok"], checks["capability probe"]["detail"]