fix(agent-runner): package context for plugin execution

src/langbot/pkg/agent/runner/context_packager.py

@@ -0,0 +1,79 @@
+"""Agent context packaging helpers."""
+from __future__ import annotations
+
+import dataclasses
+import typing
+
+from langbot_plugin.api.entities.builtin.pipeline import query as pipeline_query
+
+
+DEFAULT_LEGACY_MAX_ROUND = 10
+
+
+@dataclasses.dataclass(frozen=True)
+class ContextPackagingResult:
+    """Packaged working context for one AgentRunner run."""
+
+    messages: list[typing.Any]
+    policy: dict[str, typing.Any]
+    history: dict[str, typing.Any]
+
+
+def get_legacy_max_round(runner_config: dict[str, typing.Any]) -> typing.Any:
+    """Return the configured legacy max-round value.
+
+    Keep the existing config semantics intact: callers are expected to pass the
+    already-resolved runner binding config, and invalid values fail the same way
+    the old truncator failed when comparing them with an integer round count.
+    """
+    return runner_config.get('max-round', DEFAULT_LEGACY_MAX_ROUND)
+
+
+def select_legacy_max_round_messages(
+    messages: list[typing.Any] | None,
+    max_round: typing.Any,
+) -> list[typing.Any]:
+    """Select the same message window as the legacy round truncator."""
+    if not messages:
+        return []
+
+    temp_messages: list[typing.Any] = []
+    current_round = 0
+
+    for msg in messages[::-1]:
+        if current_round < max_round:
+            temp_messages.append(msg)
+            if getattr(msg, 'role', None) == 'user':
+                current_round += 1
+        else:
+            break
+
+    return temp_messages[::-1]
+
+
+class AgentContextPackager:
+    """Build the bounded working context for AgentRunner execution."""
+
+    def package_messages(
+        self,
+        query: pipeline_query.Query,
+        runner_config: dict[str, typing.Any],
+    ) -> ContextPackagingResult:
+        """Package query messages using the current legacy max-round policy."""
+        source_messages = query.messages or []
+        max_round = get_legacy_max_round(runner_config)
+        packaged_messages = select_legacy_max_round_messages(source_messages, max_round)
+
+        return ContextPackagingResult(
+            messages=packaged_messages,
+            policy={
+                'mode': 'legacy_max_round',
+                'max_round': max_round,
+            },
+            history={
+                'source': 'query.messages',
+                'source_total_count': len(source_messages),
+                'delivered_count': len(packaged_messages),
+                'messages_complete': len(packaged_messages) == len(source_messages),
+            },
+        )