feat: Allow normal format string behavior for cancelation mode Per review feedback on openjd-specifications PR #148, a format-string cancelation mode gets normal format string behavior: partial interpolation like "{{ 'NOTIFY' }}_THEN_TERMINATE" is valid, and the resolved value is checked against the two mode names at run time. Null semantics (dropping the cancelation object) now apply only when the mode is a whole-field "{{ ... }}" expression, per the Template Schemas 5.3 wording; a normal format string that resolves to the empty string is an invalid mode, matching the openjd-rs typed-resolution behavior.

Author: leongdl

src/openjd/sessions/_runner_base.py

@@ -151,8 +151,20 @@ def resolve_period(period: Any) -> Optional[int]:
     if cancelation is None:
         return (None, None)
     if isinstance(cancelation, CancelationMethodDeferred_2023_09):
+        # Null semantics apply only to a whole-field expression
+        # ("{{ ... }}" with no surrounding text, target type string? —
+        # Template Schemas 5.3). A normal format string that happens to
+        # resolve to the empty string is NOT null; it falls through to the
+        # "must resolve to..." error below.
+        raw = str(cancelation.mode).strip()
+        is_whole_field = (
+            raw.startswith("{{")
+            and raw.endswith("}}")
+            and raw.count("{{") == 1
+            and raw.count("}}") == 1
+        )
         mode = cancelation.mode.resolve(symtab=symtab)
-        if mode == "":
+        if mode == "" and is_whole_field:
             # Null mode drops the ENTIRE cancelation object: mode is the
             # object's required discriminator, so an "omitted" mode cannot
             # leave a partial object behind. The action behaves exactly as

test/openjd/sessions_v0/test_wrap_cancelation.py

@@ -258,8 +258,8 @@ def test_no_cancelation_renders_null_mode_as_empty(
 class TestResolveEffectiveCancelation:
     """Unit tests for the shared deferred-cancelation resolution helper.
 
-    A CancelationMethodDeferred carries a whole-field format-string mode
-    whose TERMINATE-vs-NOTIFY_THEN_TERMINATE decision is made at run time
+    A CancelationMethodDeferred carries a format-string mode whose
+    TERMINATE-vs-NOTIFY_THEN_TERMINATE decision is made at run time
     against the live symbol table (see resolve_effective_cancelation's
     docstring for the full story).
     """
@@ -319,6 +319,26 @@ def test_mode_resolving_garbage_raises(self) -> None:
         with pytest.raises(ValueError, match="must resolve to"):
             resolve_effective_cancelation(cancelation, self._symtab(X="SOMETHING_ELSE"))
 
+    def test_partial_interpolation_mode_resolves_normally(self) -> None:
+        # Normal format string behavior (Template Schemas 5.3): partial
+        # interpolation is permitted; the resolved value is checked
+        # against the two mode names.
+        from openjd.sessions._runner_base import resolve_effective_cancelation
+
+        cancelation = self._deferred("{{X}}_THEN_TERMINATE", "{{P}}")
+        result = resolve_effective_cancelation(cancelation, self._symtab(X="NOTIFY", P=45))
+        assert result == ("NOTIFY_THEN_TERMINATE", 45)
+
+    def test_partial_interpolation_mode_resolving_empty_raises(self) -> None:
+        # Null semantics (dropping the cancelation object) apply only to a
+        # whole-field expression. A normal format string that resolves to
+        # the empty string is not null — it is an invalid mode.
+        from openjd.sessions._runner_base import resolve_effective_cancelation
+
+        cancelation = self._deferred("{{X}}{{Y}}")
+        with pytest.raises(ValueError, match="must resolve to"):
+            resolve_effective_cancelation(cancelation, self._symtab(X=None, Y=None))
+
     def test_resolved_period_exceeding_cap_raises(self) -> None:
         # The static validator caps literal periods at 600 (Template
         # Schemas 5.3.2); format-string values could not be checked at