Problem

Closes #9486

Bedrock and strict Anthropic-compatible endpoints reject messages where a text content block has an empty text field:

ValidationException: messages: text content blocks must be non-empty

This happens in multi-turn conversations when an assistant message contains an empty text block alongside tool_use blocks.

Root Cause

In convert_to_anthropic_messages(), user messages already had an empty-block guard. Assistant messages were missing it — converted_content blocks were extended into the final list without filtering empty text entries.

Fix

Skip text blocks with empty/whitespace text when building the assistant content block list:

for blk in converted_content:
    if (
        isinstance(blk, dict)
        and blk.get("type") == "text"
        and not blk.get("text", "").strip()
    ):
        continue  # drop empty text block
    blocks.append(blk)

Before / After

Before: Multi-turn chat with tool calls → empty text block in assistant message → Bedrock 400 error

After: Empty text blocks silently dropped → valid message sent → no error