Version answer display instructions and restrict unsupported payloads (#60904)

## What changed

- Replace free-form `AgentMessageDisplay` actions with a version `1` contract using `show`, `hide`, and `block` modes, with typed annotations, replacements, block reasons, and trusted-contact handling.
- Discard invalid or unsupported display instructions and set `moderated` to `true` when reading moderation data in Rust and the Python SDK.
- Update generated JSON schemas, TypeScript types, and Python SDK models to match the contract.

## Testing

Add coverage for display variants, tolerance of extra fields, and unsupported-version or unknown-mode fallback. Update the final-answer moderation test and add Python coverage for thread history and item notifications.

GitOrigin-RevId: ec64070002da67e8e377dccb3728806ac8b290e7

sdk/python/scripts/update_sdk_artifacts.py

@@ -612,6 +612,30 @@ def generate_v2_all(schema_dir: Path, *, format_output: bool = True) -> None:
     _preserve_thread_source_enum(out_path)
     _preserve_open_enum(out_path, "PlanType")
     _normalize_generated_timestamps(out_path)
+    _add_answer_display_fallback(out_path)
+
+
+def _add_answer_display_fallback(out_path: Path) -> None:
+    """Keep items readable and restricted when their display instruction is unsupported."""
+    source = out_path.read_text()
+    header = "class AgentMessageModeration(BaseModel):"
+    if source.count(header) != 1:
+        raise RuntimeError("Generated SDK is missing a unique AgentMessageModeration class")
+    source = source.replace(
+        "from pydantic import ", "from pydantic import ValidationError, model_validator, ", 1
+    )
+    validator = """
+    @model_validator(mode="before")
+    @classmethod
+    def _read_display(cls, data: Any) -> Any:
+        if not isinstance(data, dict) or "moderated" not in data or data.get("display") is None:
+            return data
+        try:
+            return {**data, "display": AgentMessageDisplay.model_validate(data["display"])}
+        except ValidationError:
+            return {**data, "moderated": True, "display": None}
+"""
+    out_path.write_text(source.replace(header, header + "\n" + validator, 1))
 
 
 def _preserve_inline_media_class_names(out_path: Path) -> None: