fix(python-cli): verify --templates enforces @requiredSlots/@requiredTags (#230)

Python's `verify --templates` never passed required_slots/required_tags to the render
verify() engine, so a `template.prompt` whose body omits a `@requiredTags` output tag
passed verify (exit 0) while TS/Java/C# failed it — a cross-port parity gap (surfaced
during the #193 review). The `if e.code == ERR_REQUIRED_SLOT_UNUSED: continue` branch
could never even fire.

Now the prompt path threads @requiredSlots/@requiredTags (resolving read, ADR-0039 — an
inherited value is honored) into render_verify: a missing required output tag →
ERR_OUTPUT_TAG_MISSING (drift, fails); an unused required slot → ERR_REQUIRED_SLOT_UNUSED
(warning). Kept prompt-only — the email/document output gate does not apply them per-part
(the #193 cross-port consensus). Error line generalized to `{code}: {path}` (was
payload-VO-specific, wrong for a missing-tag finding).

Regression tests: a @requiredTags prompt missing the tag fails; present passes.
verify-subverbs 14/14.

Closes #230.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XeGSV3StPCcJGZNNJ4ZfAb

Author: dmealing

server/python/src/metaobjects/cli.py

@@ -573,6 +573,16 @@ def _verify_codegen(args: argparse.Namespace) -> int:
 )
 
 
+def _attr_str_list(raw: object) -> list[str] | None:
+    """Coerce a string-array attr (a list, or a single string) to ``list[str]``; ``None``
+    when absent — the shape :func:`render.verify` expects for required_slots/required_tags."""
+    if isinstance(raw, str):
+        return [raw]
+    if isinstance(raw, (list, tuple)):
+        return [str(x) for x in raw]
+    return None
+
+
 def _verify_templates(args: argparse.Namespace) -> int:
     """``verify --templates`` — the template/prompt ``{{field}}`` ↔ payload drift gate.
 
@@ -659,6 +669,16 @@ def _verify_templates(args: argparse.Namespace) -> int:
             error_count += 1
             continue
 
+        # #193/#230: @requiredSlots/@requiredTags are a template.prompt concept — enforced ONLY on
+        # the prompt path (the email/document output gate does not apply them per-part; the #193
+        # cross-port consensus). A prompt whose body omits a required output tag →
+        # ERR_OUTPUT_TAG_MISSING (drift, fails); an unused required slot → ERR_REQUIRED_SLOT_UNUSED
+        # (warning). This brings Python to parity with TS/Java/C# (previously it enforced neither).
+        is_prompt = tmpl.sub_type == tc.TEMPLATE_SUBTYPE_PROMPT
+        # ADR-0039: resolving read — an inherited @requiredSlots/@requiredTags is honored.
+        req_slots = _attr_str_list(tmpl.get_meta_attr(tc.TEMPLATE_ATTR_REQUIRED_SLOTS)) if is_prompt else None
+        req_tags = _attr_str_list(tmpl.get_meta_attr(tc.TEMPLATE_ATTR_REQUIRED_TAGS)) if is_prompt else None
+
         for ref in refs:
             text = provider.resolve(ref)
             if text is None:
@@ -670,12 +690,14 @@ def _verify_templates(args: argparse.Namespace) -> int:
                 error_count += 1
                 continue
             checked += 1
-            for e in render_verify(text, fields, provider=provider):
+            for e in render_verify(
+                text, fields, provider=provider,
+                required_slots=req_slots, required_tags=req_tags,
+            ):
                 if e.code == ERR_REQUIRED_SLOT_UNUSED:
-                    continue  # warning, not drift
+                    continue  # an unused required slot is a warning, not drift
                 print(
-                    f"error: [{tmpl.name}] ref '{ref}' — {e.code}: "
-                    f"{{{{{e.path}}}}} not on payload VO '{payload_ref}'.",
+                    f"error: [{tmpl.name}] ref '{ref}' — {e.code}: {e.path}",
                     file=sys.stderr,
                 )
                 error_count += 1

server/python/tests/codegen/test_cli_verify_subverbs.py

@@ -196,6 +196,55 @@ def test_templates_email_body_drift_is_caught(tmp_path: Path, capsys) -> None:
     assert "WelcomeEmail" in err
 
 
+# --- #230: template.prompt @requiredTags / @requiredSlots enforcement (parity w/ TS/Java/C#) ---
+
+_META_PROMPT_TAGS = """\
+{
+  "metadata.root": {
+    "package": "acme::ai",
+    "children": [
+      {
+        "object.value": {
+          "name": "Welcome",
+          "children": [
+            { "field.string": { "name": "name", "@required": true } }
+          ]
+        }
+      },
+      {
+        "template.prompt": {
+          "name": "TaggedPrompt",
+          "@payloadRef": "Welcome",
+          "@textRef": "pages/welcome",
+          "@requiredTags": ["answer"]
+        }
+      }
+    ]
+  }
+}
+"""
+
+
+def test_templates_prompt_required_tag_missing_is_drift(tmp_path: Path, capsys) -> None:
+    # #230: a template.prompt @requiredTags whose rendered body omits the <answer> tag must FAIL
+    # verify. Python previously passed required_slots/required_tags to render_verify NOWHERE, so it
+    # enforced neither — a divergence from TS/Java/C#.
+    meta_dir = _meta_dir_with(tmp_path, _META_PROMPT_TAGS)
+    troot = _templates_dir(tmp_path, "Hello {{name}}")  # no <answer>…</answer> tag
+    rc = main(["verify", "--templates", meta_dir, "--templates-root", troot])
+    assert rc != 0
+    err = capsys.readouterr().err
+    assert "ERR_OUTPUT_TAG_MISSING" in err
+    assert "answer" in err
+
+
+def test_templates_prompt_required_tag_present_passes(tmp_path: Path) -> None:
+    meta_dir = _meta_dir_with(tmp_path, _META_PROMPT_TAGS)
+    troot = _templates_dir(tmp_path, "Hello {{name}} <answer>{{name}}</answer>")
+    rc = main(["verify", "--templates", meta_dir, "--templates-root", troot])
+    assert rc == 0
+
+
 # --- 3. bare verify = codegen (back-compat) + the subverb note --------------