fix(converters): prepend reasoningContent blocks in _openai_to_bedrock()

[cagataycali]

Summary

Fixes #416 — _openai_to_bedrock() appends reasoningContent blocks after text and toolUse, but Bedrock requires thinking blocks to come first.

3-line fix. No new dependencies. No behavioral change for messages without reasoning.

The Bug

# Before: reasoning appended LAST
content_items = [text, toolUse, reasoningContent]  # → ValidationException

# After: reasoning prepended FIRST  
content_items = [reasoningContent, text, toolUse]  # → Correct

Bedrock error:

ValidationException: If an assistant message contains any thinking blocks, the first block must be thinking. Found text

Changes

 content_items: list[dict[str, Any]] = []
+reasoning_items: list[dict[str, Any]] = []
 ...
     for rc in openai_msg.get("_strands_reasoning_content", []):
         if isinstance(rc, dict) and "reasoningContent" in rc:
-            content_items.append(rc)
+            reasoning_items.append(rc)
 ...
-    return {"role": bedrock_role, "content": content_items}
+    # Reasoning blocks MUST come first per Bedrock API:
+    # "If an assistant message contains any thinking blocks, the first block must be thinking."
+    return {"role": bedrock_role, "content": reasoning_items + content_items}

Verification

15 tests across 3 suites all pass:

Suite	Tests	Result
Strands SDK session managers	5/5	✅ (no bug here)
AgentCoreMemoryConverter (default)	5/5	✅ (no bug here)
OpenAIConverseConverter	5/5	✅ after fix (was 1/5)

Impact

• Fixes: Multi-turn conversations with extended thinking + OpenAIConverseConverter
• No impact: Messages without reasoningContent (empty list prepended = no change)
• No impact: Default AgentCoreMemoryConverter users (already works correctly)

I understand this repo's policy on external PRs — feel free to close if preferred and cherry-pick internally. The fix is also documented in the #416 comment thread.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #419   +/-   ##
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  Coverage        ?   91.24%           
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  Files           ?       58           
  Lines           ?     4970           
  Branches        ?      756           
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  Hits            ?     4535           
  Misses          ?      249           
  Partials        ?      186           

Flag	Coverage Δ
unittests	91.24% <100.00%> (?)

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[phongtran222]

Hi team, I also facing this error for toolUse, can you all help me fix? Appreciate it