fix(cron): degrade to the caller's interpreter when selected_venv raises

_posix_cron_python_invocation called selected_venv(repo) unguarded; the
four RuntimeError cases it is documented to raise would escape through
_script_argv (which runs before _run_job_script's try), crash the tick,
and leave the execution row in running forever — the exact half-migrated
install the test docstring already claimed was supported. Mirror the
Windows bootstrap's degrade-don't-crash contract: warn and run on the
caller's interpreter. Adds the raising-selection case to the POSIX
invocation test (red on the previous head), a sealed-payload caveat on
the e2e test's hand-written .pth, and a pointer from the Windows
invocation docstring to its POSIX counterpart.

(cherry picked from commit 8d5b3b5e9727d612d91b2a7485e0f4bb245358f3)

cron/scheduler_script.py

@@ -126,7 +126,10 @@ def _posix_cron_python_invocation(python_exe: str) -> tuple[str, dict[str, str]]
     and crash (#123440). Lazy installs are disabled for script children so a script importing
     ``hermes_bootstrap`` off the store-record venv cannot republish launchers (#123440).
     Installs without a committed store (source checkouts, pre-PM venvs) keep the caller's
-    interpreter."""
+    interpreter. A broken committed selection degrades to the caller's interpreter too:
+    ``selected_venv`` is documented as a raising function, and this runs before
+    ``_run_job_script``'s ``try``, so an escaping error would crash the tick and leave the
+    execution row in ``running`` forever."""
     from hermes_cli._launchers import resolve_store_python
 
     repo = Path(__file__).resolve().parents[1]
@@ -135,7 +138,18 @@ def _posix_cron_python_invocation(python_exe: str) -> tuple[str, dict[str, str]]
 
     from pm.environments import selected_venv, venv_bin_dir
 
-    venv_python = venv_bin_dir(selected_venv(repo)) / "python"
+    try:
+        venv = selected_venv(repo)
+    except (RuntimeError, OSError) as exc:
+        # Degrade, don't crash — same contract as the Windows bootstrap's unresolvable-venv
+        # fallback below (a silent fallback would make the misconfiguration undiagnosable).
+        logger.warning(
+            "POSIX cron script: cannot select the dependency venv (%s); running on the "
+            "caller's interpreter",
+            exc,
+        )
+        return python_exe, {}
+    venv_python = venv_bin_dir(venv) / "python"
     if not venv_python.is_file():
         return python_exe, {}
     return str(venv_python), {"HERMES_DISABLE_LAZY_INSTALLS": "1"}
@@ -144,7 +158,9 @@ def _posix_cron_python_invocation(python_exe: str) -> tuple[str, dict[str, str]]
 def _windows_cron_python_invocation(python_exe: str) -> tuple[str, dict[str, str]]:
     """Hidden, output-capable Python invocation for Windows cron scripts. ``pythonw.exe`` loses
     captured output; uv venv launchers can re-exec the base console python and flash a window
-    even with CREATE_NO_WINDOW, so run the base python directly with venv paths overlaid in env."""
+    even with CREATE_NO_WINDOW, so run the base python directly with venv paths overlaid in env.
+    Off-Windows callers are routed to ``_posix_cron_python_invocation`` (venv interpreter
+    selection, no env overlay)."""
     if sys.platform != "win32":
         return _posix_cron_python_invocation(python_exe)
 
@@ -362,7 +378,10 @@ def _script_argv(path: Path) -> tuple[Optional[list[str]], dict[str, str], Optio
     python_exe, env_overlay = _windows_cron_python_invocation(sys.executable)
     if env_overlay.get("PYTHONPATH"):
         # The bootstrap exists to give PYTHONPATH overlays .pth processing (editable installs);
-        # non-PYTHONPATH overlays (the POSIX venv-interpreter path) pass through plain.
+        # non-PYTHONPATH overlays (the POSIX venv-interpreter path) pass through plain. Both
+        # overlay producers that exist today always set PYTHONPATH (the managed-store branch
+        # sets only it, the uv re-exec sets it alongside VIRTUAL_ENV); a future overlay-only
+        # producer must revisit this gate or it silently loses .pth processing.
         return _windows_cron_bootstrap_argv(python_exe, env_overlay, str(path)), env_overlay, None
     return [python_exe, str(path)], env_overlay, None
 

tests/cron/test_cron_script.py

@@ -313,7 +313,9 @@ class TestRunJobScript:
         inherited overlay makes foreign-interpreter children import the store's 3.14 extension
         modules first (#123440). No committed store → the caller's interpreter passes through
         untouched (pre-PM venvs, source checkouts), as does a store whose venv python
-        vanished (half-migrated install must not crash the scheduler)."""
+        vanished (half-migrated install must not crash the scheduler) or whose committed
+        selection record is broken (``selected_venv`` raises → degrade, not propagate — the
+        call site runs before ``_run_job_script``'s ``try``)."""
         from cron import scheduler_script
 
         venv = tmp_path / "selected-venv" / "bin"
@@ -337,6 +339,17 @@ class TestRunJobScript:
             {},
         )
 
+        def _broken_selection(repo):
+            raise RuntimeError(
+                "dependency environment is missing or outside this install"
+            )
+
+        monkeypatch.setattr("pm.environments.selected_venv", _broken_selection)
+        assert scheduler_script._posix_cron_python_invocation(sys.executable) == (
+            sys.executable,
+            {},
+        )
+
         monkeypatch.setattr(
             "hermes_cli._launchers.resolve_store_python", lambda repo: None
         )
@@ -398,7 +411,11 @@ class TestRunJobScript:
         deps = dependency_site(fake_venv)
         deps.mkdir(parents=True)
         (deps / "probe_pkg.py").write_text("VALUE = 42\n", encoding="utf-8")
-        # Editable-style repo exposure, as a real PM venv carries for the checkout.
+        # Editable-style repo exposure, as a real PM venv carries for the checkout. Caveat:
+        # a real generation venv gets its repo pointer from uv's editable install of the
+        # generated workspace (not a hand-written .pth), and sealed-payload installs prune
+        # editable .pth files outright because the payload wires the repo snapshot itself
+        # (pm/environment.py prune_site_pth) — do not generalize this .pth shape to payloads.
         repo = Path(__file__).resolve().parents[2]
         (deps / "zz_repo.pth").write_text(f"{repo}\n", encoding="utf-8")