fix: preserve exploration tool history and cap context budget

artemis/agents/operator/operator.py

@@ -17,7 +17,7 @@ from collections.abc import Awaitable
 from typing import Any
 from uuid import uuid4
 
-from langchain_core.messages import SystemMessage, ToolMessage
+from langchain_core.messages import BaseMessage, SystemMessage, ToolMessage
 from langchain_core.tools import BaseTool
 
 from artemis.agents.validator.tool_declarations import normalize_coordinate_target
@@ -146,9 +146,9 @@ class OperatorNode:
                 from artemis.config.agent import MemoryTranscriptConfig
 
                 self._transcript_cfg = MemoryTranscriptConfig()
-        # Index into the rendered message list where this turn's tail begins;
-        # set by the transcript build and consumed after the tool loop.
-        self._transcript_turn_base: int | None = None
+        # Keep the actual observation, not an index: plugin/exploration context
+        # may be prepended after render, shifting every message's position.
+        self._transcript_turn_tail: BaseMessage | None = None
         self._turn_plan_baseline: str | None = None
         self._turn_ledger_streak: int = 0
         # Whether the previous turn's replies carried no visible reasoning text;
@@ -225,7 +225,7 @@ class OperatorNode:
         active_background_tasks: list[dict] = None,
         newly_finished_tasks: list[dict] = None,
     ) -> list:
-        self._transcript_turn_base = None
+        self._transcript_turn_tail = None
         if getattr(self._transcript_cfg, "enabled", False):
             try:
                 return await self._build_prompt_transcript(
@@ -243,7 +243,7 @@ class OperatorNode:
                     f"Transcript prompt path failed; falling back to the legacy"
                     f" 2-message build for this turn: {e}"
                 )
-                self._transcript_turn_base = None
+                self._transcript_turn_tail = None
 
         plan_and_history = self._build_plan_and_history(steps, task_plan)
 
@@ -468,18 +468,19 @@ class OperatorNode:
             mark_ephemeral(tail, builder.ephemeral_indices)
 
         messages = ledger.render([tail])
-        self._transcript_turn_base = len(messages) - 1
+        self._transcript_turn_tail = tail
         return messages
 
     def _stage_transcript_turn(self, messages: list) -> None:
         """Hand this turn's tail + tool-loop products to the ledger."""
-        base = self._transcript_turn_base
-        self._transcript_turn_base = None
-        if base is None:
+        tail = self._transcript_turn_tail
+        self._transcript_turn_tail = None
+        if tail is None:
             return
         try:
             ledger = getattr(self.ctx, "transcript_ledger", None)
             if ledger is not None:
+                base = next(i for i, message in enumerate(messages) if message is tail)
                 ledger.stage_turn(messages[base:])
         except Exception as e:
             logger.error(f"Failed to stage transcript turn: {e}")