fix: preserve redacted_thinking blocks in multi-turn Bedrock conversations

src/agents/models/chatcmpl_converter.py

@@ -147,23 +147,39 @@ def message_to_output_items(
 
             # Store thinking blocks for Anthropic compatibility
             if hasattr(message, "thinking_blocks") and message.thinking_blocks:
-                # Store thinking text in content and signature in encrypted_content
-                reasoning_item.content = []
-                signatures: list[str] = []
-                for block in message.thinking_blocks:
-                    if isinstance(block, dict):
-                        thinking_text = block.get("thinking", "")
-                        if thinking_text:
-                            reasoning_item.content.append(
-                                Content(text=thinking_text, type="reasoning_text")
-                            )
-                        # Store the signature if present
-                        if signature := block.get("signature"):
-                            signatures.append(signature)
-
-                # Store the signatures in encrypted_content with newline delimiter
-                if signatures:
-                    reasoning_item.encrypted_content = "\n".join(signatures)
+                # Normalise blocks before serialisation.  The last-resort fallback
+                # in LitellmConverter can produce {"thinking": str(block)} dicts
+                # that are missing a "type" field.  Dropping them entirely would
+                # lose thinking content and could still cause Bedrock to reject the
+                # next turn; instead, inject "type": "thinking" so the block is
+                # valid and replayable.  Blocks that are not dicts or have neither
+                # "type" nor "thinking" are discarded as unrecoverable.
+                blocks_as_dicts = []
+                for b in message.thinking_blocks:
+                    if not isinstance(b, dict):
+                        continue
+                    if not b.get("type") and b.get("thinking"):
+                        b = {**b, "type": "thinking"}
+                    if b.get("type"):
+                        blocks_as_dicts.append(b)
+
+                # Serialise the full blocks as JSON so that both thinking and
+                # redacted_thinking blocks can be reconstructed verbatim on the
+                # next turn.  Providers like Bedrock reject requests where
+                # thinking/redacted_thinking blocks are modified or dropped
+                # between turns; redacted_thinking blocks carry a "data" field
+                # instead of "thinking"/"signature" and were silently lost with
+                # the previous signature-only serialisation.
+                if blocks_as_dicts:
+                    reasoning_item.encrypted_content = json.dumps(blocks_as_dicts)
+
+                # Populate content with the visible thinking text so it can be
+                # used for display and summary purposes.
+                reasoning_item.content = [
+                    Content(text=block.get("thinking", ""), type="reasoning_text")
+                    for block in blocks_as_dicts
+                    if block.get("thinking")
+                ]
 
             items.append(reasoning_item)
 
@@ -772,33 +788,53 @@ def ensure_assistant_message() -> ChatCompletionAssistantMessageParam:
                 if (
                     model
                     and ("claude" in model.lower() or "anthropic" in model.lower())
-                    and content_items
                     and preserve_thinking_blocks
+                    and (content_items or encrypted_content)
                     # Items may not all originate from Claude, so we need to check for model match.
                     # For backward compatibility, if provider_data is missing, we ignore the check.
                     and (model == item_model or item_provider_data == {})
                 ):
-                    signatures = encrypted_content.split("\n") if encrypted_content else []
-
-                    # Reconstruct thinking blocks from content and signature
-                    reconstructed_thinking_blocks = []
-                    for content_item in content_items:
-                        if (
-                            isinstance(content_item, dict)
-                            and content_item.get("type") == "reasoning_text"
-                        ):
-                            thinking_block = {
-                                "type": "thinking",
-                                "thinking": content_item.get("text", ""),
-                            }
-                            # Add signatures if available
-                            if signatures:
-                                thinking_block["signature"] = signatures.pop(0)
-                            reconstructed_thinking_blocks.append(thinking_block)
-
-                    # Store thinking blocks as pending for the next assistant message
-                    # This preserves the original behavior
-                    pending_thinking_blocks = reconstructed_thinking_blocks
+                    if encrypted_content:
+                        # Try the JSON format first (current serialisation, preserves
+                        # redacted_thinking verbatim).  Fall back to the legacy
+                        # "\n"-joined signatures format so existing in-flight sessions
+                        # with the old encoding are not broken.
+                        try:
+                            decoded = json.loads(encrypted_content)
+                            if not isinstance(decoded, list) or not all(
+                                isinstance(b, dict) and b.get("type") for b in decoded
+                            ):
+                                raise ValueError(
+                                    "expected a list of block dicts with a 'type' field"
+                                )
+                            pending_thinking_blocks = decoded
+                        except (json.JSONDecodeError, TypeError, ValueError):
+                            signatures = encrypted_content.split("\n")
+
+                            reconstructed_thinking_blocks = []
+                            for content_item in content_items:
+                                if (
+                                    isinstance(content_item, dict)
+                                    and content_item.get("type") == "reasoning_text"
+                                ):
+                                    thinking_block: dict[str, str] = {
+                                        "type": "thinking",
+                                        "thinking": content_item.get("text", ""),
+                                    }
+                                    if signatures:
+                                        thinking_block["signature"] = signatures.pop(0)
+                                    reconstructed_thinking_blocks.append(thinking_block)
+
+                            pending_thinking_blocks = reconstructed_thinking_blocks
+                    else:
+                        # No encrypted_content: older persisted turns where signatures
+                        # were absent.  Reconstruct thinking blocks from content text
+                        # only so multi-turn history is not silently dropped.
+                        pending_thinking_blocks = [
+                            {"type": "thinking", "thinking": item.get("text", "")}
+                            for item in content_items
+                            if isinstance(item, dict) and item.get("type") == "reasoning_text"
+                        ]
 
                 if model is not None:
                     replay_context = ReasoningContentReplayContext(

tests/test_anthropic_thinking_blocks.py

@@ -10,10 +10,12 @@
 
 from __future__ import annotations
 
+import json
 from typing import Any, cast
 
 from openai.types.chat import ChatCompletionMessageToolCall
 from openai.types.chat.chat_completion_message_tool_call import Function
+from openai.types.responses import ResponseReasoningItem
 
 from agents.extensions.models.litellm_model import InternalChatCompletionMessage
 from agents.models.chatcmpl_converter import Converter
@@ -160,12 +162,18 @@ def test_anthropic_thinking_blocks_with_tool_calls():
         "Content should be reasoning_text type"
     )
 
-    # Verify signature is stored in encrypted_content
-    assert hasattr(reasoning_item, "encrypted_content"), (
+    # Verify full blocks are stored as JSON in encrypted_content so that both
+    # thinking and redacted_thinking blocks survive the round-trip verbatim.
+    assert isinstance(reasoning_item, ResponseReasoningItem)
+    assert reasoning_item.encrypted_content is not None, (
         "Reasoning item should have encrypted_content"
     )
-    assert reasoning_item.encrypted_content == "TestSignature123\nTestSignature456", (
-        "Signature should be preserved"
+    stored_blocks = json.loads(reasoning_item.encrypted_content)
+    assert stored_blocks[0]["signature"] == "TestSignature123", (
+        "Signature of first block should be preserved"
+    )
+    assert stored_blocks[1]["signature"] == "TestSignature456", (
+        "Signature of second block should be preserved"
     )
 
     # Verify tool calls are present
@@ -349,11 +357,13 @@ def test_anthropic_thinking_blocks_without_tool_calls():
         "Thinking text should be preserved"
     )
 
-    # Verify signature is stored in encrypted_content
-    assert hasattr(reasoning_item, "encrypted_content"), (
+    # Verify full blocks are stored as JSON in encrypted_content.
+    assert isinstance(reasoning_item, ResponseReasoningItem)
+    assert reasoning_item.encrypted_content is not None, (
         "Reasoning item should have encrypted_content"
     )
-    assert reasoning_item.encrypted_content == "TestSignatureNoTools123", (
+    stored_blocks = json.loads(reasoning_item.encrypted_content)
+    assert stored_blocks[0]["signature"] == "TestSignatureNoTools123", (
         "Signature should be preserved"
     )
 
@@ -416,3 +426,157 @@ def test_anthropic_thinking_blocks_without_tool_calls():
     assert (
         second_content.get("text") == "The weather in Paris is sunny with a temperature of 22°C."
     ), "Text content should be preserved"
+
+
+def test_redacted_thinking_blocks_preserved_across_turns():
+    """
+    Regression test for Bedrock redacted_thinking blocks being dropped.
+
+    When Claude (via Bedrock) returns redacted_thinking blocks the previous
+    serialisation only stored thinking/signature pairs and silently discarded
+    any block whose type is "redacted_thinking" (they carry a "data" field
+    instead of "thinking"/"signature").  Bedrock then rejected the next turn
+    with: "thinking or redacted_thinking blocks in the latest assistant message
+    cannot be modified".
+
+    The fix serialises the complete block list as JSON so every block type
+    survives the round-trip verbatim.
+    """
+    redacted_data = "SGVsbG8gV29ybGQ="  # base64 stand-in for encrypted content
+    message = InternalChatCompletionMessage(
+        role="assistant",
+        content="I've investigated the cluster.",
+        reasoning_content="Thinking was redacted by the provider.",
+        thinking_blocks=[
+            {
+                "type": "redacted_thinking",
+                "data": redacted_data,
+            }
+        ],
+        tool_calls=None,
+    )
+
+    # Step 1: model response → output items
+    output_items = Converter.message_to_output_items(message)
+
+    reasoning_items = [i for i in output_items if getattr(i, "type", None) == "reasoning"]
+    assert len(reasoning_items) == 1
+
+    reasoning_item = cast(ResponseReasoningItem, reasoning_items[0])
+
+    # encrypted_content must be present (the block has no "thinking" text, so
+    # content will be empty — encrypted_content is the only carrier).
+    assert reasoning_item.encrypted_content is not None, (
+        "encrypted_content must be set even for redacted_thinking blocks"
+    )
+    stored_blocks = json.loads(reasoning_item.encrypted_content)
+    assert len(stored_blocks) == 1
+    assert stored_blocks[0]["type"] == "redacted_thinking", "Block type must be preserved verbatim"
+    assert stored_blocks[0]["data"] == redacted_data, "Encrypted data must be preserved verbatim"
+
+    # Step 2: output items → next-turn messages
+    items_as_dicts: list[dict[str, Any]] = [
+        i.model_dump() if hasattr(i, "model_dump") else cast(dict[str, Any], i)
+        for i in output_items
+    ]
+    messages = Converter.items_to_messages(
+        items_as_dicts,  # type: ignore[arg-type]
+        model="anthropic/claude-sonnet-4-5",
+        preserve_thinking_blocks=True,
+    )
+
+    assistant_messages = [m for m in messages if m.get("role") == "assistant"]
+    assert len(assistant_messages) == 1
+
+    content = assistant_messages[0].get("content")
+    assert isinstance(content, list) and len(content) >= 1, (
+        "Assistant message must contain the redacted_thinking block"
+    )
+
+    redacted_block = content[0]
+    assert redacted_block.get("type") == "redacted_thinking", (
+        f"Expected redacted_thinking block, got {redacted_block.get('type')}"
+    )
+    assert redacted_block.get("data") == redacted_data, (
+        "data field of redacted_thinking block must be preserved verbatim"
+    )
+
+
+def test_mixed_thinking_and_redacted_thinking_blocks_preserved():
+    """
+    When a response contains both thinking and redacted_thinking blocks,
+    all blocks must survive the round-trip in their original order and with
+    their original fields intact.
+    """
+    message = InternalChatCompletionMessage(
+        role="assistant",
+        content="Done.",
+        reasoning_content="Mixed thinking blocks.",
+        thinking_blocks=[
+            {
+                "type": "thinking",
+                "thinking": "First, let me check the pods.",
+                "signature": "SigAAA",
+            },
+            {
+                "type": "redacted_thinking",
+                "data": "cmVkYWN0ZWQ=",
+            },
+            {
+                "type": "thinking",
+                "thinking": "Now summarising findings.",
+                "signature": "SigBBB",
+            },
+        ],
+        tool_calls=None,
+    )
+
+    output_items = Converter.message_to_output_items(message)
+
+    reasoning_items = [i for i in output_items if getattr(i, "type", None) == "reasoning"]
+    assert len(reasoning_items) == 1
+
+    reasoning_item_mixed = cast(ResponseReasoningItem, reasoning_items[0])
+    assert reasoning_item_mixed.encrypted_content is not None
+    stored_blocks = json.loads(reasoning_item_mixed.encrypted_content)
+    assert len(stored_blocks) == 3
+    assert stored_blocks[0] == {
+        "type": "thinking",
+        "thinking": "First, let me check the pods.",
+        "signature": "SigAAA",
+    }
+    assert stored_blocks[1] == {"type": "redacted_thinking", "data": "cmVkYWN0ZWQ="}
+    assert stored_blocks[2] == {
+        "type": "thinking",
+        "thinking": "Now summarising findings.",
+        "signature": "SigBBB",
+    }
+
+    items_as_dicts: list[dict[str, Any]] = [
+        i.model_dump() if hasattr(i, "model_dump") else cast(dict[str, Any], i)
+        for i in output_items
+    ]
+    messages = Converter.items_to_messages(
+        items_as_dicts,  # type: ignore[arg-type]
+        model="bedrock/anthropic.claude-sonnet-4-5",
+        preserve_thinking_blocks=True,
+    )
+
+    assistant_messages = [m for m in messages if m.get("role") == "assistant"]
+    assert len(assistant_messages) == 1
+
+    content = assistant_messages[0].get("content")
+    assert isinstance(content, list)
+
+    # First three entries are the thinking blocks (in original order)
+    assert content[0] == {
+        "type": "thinking",
+        "thinking": "First, let me check the pods.",
+        "signature": "SigAAA",
+    }
+    assert content[1] == {"type": "redacted_thinking", "data": "cmVkYWN0ZWQ="}
+    assert content[2] == {
+        "type": "thinking",
+        "thinking": "Now summarising findings.",
+        "signature": "SigBBB",
+    }