fix: prevent IndexError when content is empty after tool recursion (#355)

[guoyangzhen]

Problem

When max_recursions is exhausted during the tool execution loop, the agent returns a ConversationMessage with either:

• content=None (Python AnthropicAgent)
• content containing tool_use blocks instead of text (Python/TypeScript BedrockLLMAgent)
• content=[] after filtering (Python AnthropicAgent streaming)

This causes IndexError: list index out of range when callers access response.output.content[0]['text'].

Issue #355 reports this happening intermittently with the SupervisorAgent, which delegates to lead agents that use tool recursion.

Root Cause

In the tool recursion loop:

while continue_with_tools and max_recursions > 0:
    # ... tool processing ...
    max_recursions -= 1

return ConversationMessage(content=llm_content)  # llm_content is None!

When max_recursions hits 0 inside the loop while processing tool calls, llm_content (or equivalent) never gets assigned a text response.

Fix

Added fallback handling in all 4 affected code paths:

Python:

• AnthropicAgent._handle_single_response_loop: Guard llm_content is None after loop
• AnthropicAgent._handle_streaming: Guard empty content_list after filtering
• BedrockLLMAgent._handle_single_response_loop: Detect tool_use content in final response
• BedrockLLMAgent._handle_streaming: Detect None final_response after loop

TypeScript:

• AnthropicAgent.processRequest: Safe optional chaining for message.content?.[0]?.["text"]
• BedrockLLMAgent.processRequest: Detect null/tool_use finalMessage after loop

All fallbacks return "Maximum tool recursion limit reached without a final response." instead of crashing.

Fixes #355