fix(ci): permit audited caller-only permission inheritance

The stable-install smoke body is intentionally workflow_call-only so its read-only continuity caller and draft-capable release caller can supply different explicit token budgets. Treat that exact no-override shape as an auditable permission boundary while continuing to reject independent triggers and job permission overrides.

Validation: 41 workflow-trust tests, repository workflow audit, focused install-smoke contract tests, Python compilation and diff checks pass.

Change-source: pulse-maintainer

scripts/check_workflow_trust.py

@@ -833,6 +833,40 @@ def _has_trigger(lines: list[str], event: str) -> bool:
     return False
 
 
+def _is_workflow_call_only(lines: list[str]) -> bool:
+    """Return whether a workflow can run only with its caller's token budget."""
+    for index, line in enumerate(lines):
+        code = line.split("#", 1)[0]
+        match = re.match(rf"^{_yaml_key('on')}\s*:\s*(.*)$", code)
+        if not match:
+            continue
+
+        inline = match.group(1).strip()
+        if inline:
+            return inline in {"workflow_call", "[workflow_call]"}
+
+        direct_indent = _direct_mapping_indent(lines, index)
+        if direct_indent is None:
+            return False
+        trigger_re = re.compile(
+            rf"^(\s*)({_yaml_key('workflow_call')})\s*:"
+        )
+        direct_triggers = []
+        for trigger_line in lines[index + 1 :]:
+            trigger_code = trigger_line.split("#", 1)[0]
+            if not trigger_code.strip():
+                continue
+            indent = _indent(trigger_code)
+            if indent == 0:
+                break
+            if indent != direct_indent:
+                continue
+            trigger_match = trigger_re.match(trigger_code)
+            direct_triggers.append(bool(trigger_match))
+        return direct_triggers == [True]
+    return False
+
+
 def _is_hardened_closed_pr_cancellation(path: Path, lines: list[str]) -> bool:
     """Recognise the one metadata-only privileged PR automation we permit."""
     if path.name != SAFE_PULL_REQUEST_TARGET_WORKFLOW:
@@ -1404,12 +1438,16 @@ def audit_workflow(path: Path) -> list[Finding]:
         for index, match in permission_declarations
         if not match.group(1)
     ]
-    if len(top_level_permissions) != 1:
+    inherits_caller_permissions = (
+        not permission_declarations and _is_workflow_call_only(lines)
+    )
+    if len(top_level_permissions) != 1 and not inherits_caller_permissions:
         findings.append(
             Finding(
                 path,
                 1,
-                "workflow must declare top-level permissions explicitly exactly once",
+                "workflow must declare top-level permissions explicitly exactly once "
+                "unless it is workflow_call-only and inherits its caller budget",
             )
         )
     for index, match in permission_declarations:

scripts/tests/test_workflow_trust.py

@@ -645,6 +645,51 @@ steps:
         dynamic = self.audit("permissions: ${{ inputs.permissions }}\njobs: {}\n")
         self.assertTrue(any("scope mapping" in finding for finding in dynamic))
 
+    def test_workflow_call_only_may_inherit_caller_permissions(self) -> None:
+        inherited = self.audit(
+            """on:
+  workflow_call:
+jobs:
+  test:
+    runs-on: ubuntu-24.04
+    timeout-minutes: 5
+    steps:
+      - run: echo inherited
+"""
+        )
+        self.assertEqual(inherited, [])
+
+        independently_runnable = self.audit(
+            """on:
+  workflow_call:
+  workflow_dispatch:
+jobs:
+  test:
+    runs-on: ubuntu-24.04
+    timeout-minutes: 5
+    steps:
+      - run: echo independent
+"""
+        )
+        self.assertTrue(
+            any("top-level permissions" in finding for finding in independently_runnable)
+        )
+
+        job_override = self.audit(
+            """on:
+  workflow_call:
+jobs:
+  unsafe:
+    permissions:
+      contents: write
+    runs-on: ubuntu-24.04
+    timeout-minutes: 5
+    steps:
+      - run: echo unsafe
+"""
+        )
+        self.assertTrue(any("top-level permissions" in finding for finding in job_override))
+
     def test_rejects_broad_or_dynamic_job_permission_overrides(self) -> None:
         broad = self.audit(
             """permissions: