fix: sanitize orphaned tool-call/result pairs in message compression

Enhance message compression by adding a method to clean up orphaned tool-call and tool-result pairs. This ensures that the API receives well-formed messages, preventing errors related to mismatched IDs. The new functionality includes removing orphaned results and adding stub results for missing calls, improving overall message integrity during compression.

agent/context_compressor.py

@@ -196,10 +196,111 @@ Write only the summary, starting with "[CONTEXT SUMMARY]:" prefix."""
             logger.debug("Could not build fallback auxiliary client: %s", exc)
             return None, None
 
+    # ------------------------------------------------------------------
+    # Tool-call / tool-result pair integrity helpers
+    # ------------------------------------------------------------------
+
+    @staticmethod
+    def _get_tool_call_id(tc) -> str:
+        """Extract the call ID from a tool_call entry (dict or SimpleNamespace)."""
+        if isinstance(tc, dict):
+            return tc.get("id", "")
+        return getattr(tc, "id", "") or ""
+
+    def _sanitize_tool_pairs(self, messages: List[Dict[str, Any]]) -> List[Dict[str, Any]]:
+        """Fix orphaned tool_call / tool_result pairs after compression.
+
+        Two failure modes:
+        1. A tool *result* references a call_id whose assistant tool_call was
+           removed (summarized/truncated).  The API rejects this with
+           "No tool call found for function call output with call_id ...".
+        2. An assistant message has tool_calls whose results were dropped.
+           The API rejects this because every tool_call must be followed by
+           a tool result with the matching call_id.
+
+        This method removes orphaned results and inserts stub results for
+        orphaned calls so the message list is always well-formed.
+        """
+        surviving_call_ids: set = set()
+        for msg in messages:
+            if msg.get("role") == "assistant":
+                for tc in msg.get("tool_calls") or []:
+                    cid = self._get_tool_call_id(tc)
+                    if cid:
+                        surviving_call_ids.add(cid)
+
+        result_call_ids: set = set()
+        for msg in messages:
+            if msg.get("role") == "tool":
+                cid = msg.get("tool_call_id")
+                if cid:
+                    result_call_ids.add(cid)
+
+        # 1. Remove tool results whose call_id has no matching assistant tool_call
+        orphaned_results = result_call_ids - surviving_call_ids
+        if orphaned_results:
+            messages = [
+                m for m in messages
+                if not (m.get("role") == "tool" and m.get("tool_call_id") in orphaned_results)
+            ]
+            if not self.quiet_mode:
+                logger.info("Compression sanitizer: removed %d orphaned tool result(s)", len(orphaned_results))
+
+        # 2. Add stub results for assistant tool_calls whose results were dropped
+        missing_results = surviving_call_ids - result_call_ids
+        if missing_results:
+            patched: List[Dict[str, Any]] = []
+            for msg in messages:
+                patched.append(msg)
+                if msg.get("role") == "assistant":
+                    for tc in msg.get("tool_calls") or []:
+                        cid = self._get_tool_call_id(tc)
+                        if cid in missing_results:
+                            patched.append({
+                                "role": "tool",
+                                "content": "[Result from earlier conversation — see context summary above]",
+                                "tool_call_id": cid,
+                            })
+            messages = patched
+            if not self.quiet_mode:
+                logger.info("Compression sanitizer: added %d stub tool result(s)", len(missing_results))
+
+        return messages
+
+    def _align_boundary_forward(self, messages: List[Dict[str, Any]], idx: int) -> int:
+        """Push a compress-start boundary forward past any orphan tool results.
+
+        If ``messages[idx]`` is a tool result, slide forward until we hit a
+        non-tool message so we don't start the summarised region mid-group.
+        """
+        while idx < len(messages) and messages[idx].get("role") == "tool":
+            idx += 1
+        return idx
+
+    def _align_boundary_backward(self, messages: List[Dict[str, Any]], idx: int) -> int:
+        """Pull a compress-end boundary backward to avoid splitting a
+        tool_call / result group.
+
+        If the message just before ``idx`` is an assistant message with
+        tool_calls, those tool results will start at ``idx`` and would be
+        separated from their parent.  Move backwards to include the whole
+        group in the summarised region.
+        """
+        if idx <= 0 or idx >= len(messages):
+            return idx
+        prev = messages[idx - 1]
+        if prev.get("role") == "assistant" and prev.get("tool_calls"):
+            # The results for this assistant turn sit at idx..idx+k.
+            # Include the assistant message in the summarised region too.
+            idx -= 1
+        return idx
+
     def compress(self, messages: List[Dict[str, Any]], current_tokens: int = None) -> List[Dict[str, Any]]:
         """Compress conversation messages by summarizing middle turns.
 
         Keeps first N + last N turns, summarizes everything in between.
+        After compression, orphaned tool_call / tool_result pairs are cleaned
+        up so the API never receives mismatched IDs.
         """
         n_messages = len(messages)
         if n_messages <= self.protect_first_n + self.protect_last_n + 1:
@@ -212,6 +313,12 @@ Write only the summary, starting with "[CONTEXT SUMMARY]:" prefix."""
         if compress_start >= compress_end:
             return messages
 
+        # Adjust boundaries to avoid splitting tool_call/result groups.
+        compress_start = self._align_boundary_forward(messages, compress_start)
+        compress_end = self._align_boundary_backward(messages, compress_end)
+        if compress_start >= compress_end:
+            return messages
+
         turns_to_summarize = messages[compress_start:compress_end]
         display_tokens = current_tokens if current_tokens else self.last_prompt_tokens or estimate_messages_tokens_rough(messages)
 
@@ -233,6 +340,7 @@ Write only the summary, starting with "[CONTEXT SUMMARY]:" prefix."""
             tail = messages[-self.protect_last_n:]
             kept.extend(m.copy() for m in tail)
             self.compression_count += 1
+            kept = self._sanitize_tool_pairs(kept)
             if not self.quiet_mode:
                 print(f"   ✂️  Truncated: {len(messages)} → {len(kept)} messages (dropped middle turns)")
             return kept
@@ -256,6 +364,8 @@ Write only the summary, starting with "[CONTEXT SUMMARY]:" prefix."""
 
         self.compression_count += 1
 
+        compressed = self._sanitize_tool_pairs(compressed)
+
         if not self.quiet_mode:
             new_estimate = estimate_messages_tokens_rough(compressed)
             saved_estimate = display_tokens - new_estimate