Order doctor's diagnostic references deterministically

changelog/870.fix.md

@@ -0,0 +1,2 @@
+Fixed `ref doctor` producing a different report on each run.
+Diagnostics that share a name were ordered by set iteration order, so two identical runs disagreed.

packages/climate-ref-core/src/climate_ref_core/summary.py

@@ -267,9 +267,9 @@ def label(self) -> str:
         return f"{self.name} ({self.provider_slug})"
 
     @property
-    def sort_key(self) -> str:
-        """Sort by provider then name."""
-        return f"{self.provider_slug}/{self.name}"
+    def sort_key(self) -> tuple[str, str, str]:
+        """Sort by provider, then name, then slug. Several diagnostics can share a name."""
+        return (self.provider_slug, self.name, self.slug)
 
 
 @frozen

packages/climate-ref-core/tests/unit/test_summary.py

@@ -451,6 +451,17 @@ def test_diagnostics_tracked_per_variable(self, simple_provider):
         assert ref.provider_slug == "test-provider"
         assert ref.label == "Simple Diagnostic (test-provider)"
 
+    def test_sort_key_breaks_ties_on_slug(self):
+        """Several diagnostics can share a name, so the slug has to settle the order."""
+        shared = [
+            DiagnosticReference(name="Ozone Diagnostics", slug=slug, provider_slug="esmvaltool")
+            for slug in ("ozone-sh-oct", "ozone-annual-cycle", "ozone-nh-mar")
+        ]
+
+        ordered = sorted(shared, key=lambda r: r.sort_key)
+
+        assert [r.slug for r in ordered] == ["ozone-annual-cycle", "ozone-nh-mar", "ozone-sh-oct"]
+
     def test_empty_providers(self):
         result = collect_by_source_type([])
         assert result == []

packages/climate-ref/src/climate_ref/doctor/registry.py

@@ -81,7 +81,7 @@ def register_check(registered: RegisteredCheck) -> None:
     ------
     ValueError
         If another check already claims the same slug. Two checks sharing a slug would be
-        indistinguishable in the output and in ``--only``.
+        indistinguishable in the report.
     """
     existing = _REGISTRY.get(registered.slug)
     if existing is not None: