fix: Bedrock Converse API tool arguments silently dropped (#4972)

[guoyangzhen]

Problem

When using AWS Bedrock with native function calling, all tool arguments are silently dropped. Every tool call receives an empty dict {} instead of the actual arguments, causing pydantic validation failures on any tool with required parameters.

This affects ALL Bedrock models using native function calling (Claude, Llama, etc.) via the native tool loop code path.

Root Cause

In _parse_native_tool_call (crew_agent_executor.py), the dict-format branch has a truthy default:

func_args = func_info.get("arguments", "{}") or tool_call.get("input", {})

Bedrock Converse API returns {name, input, toolUseId} — no "function" key.

So func_info is {}, and func_info.get("arguments", "{}") returns the default "{}" — a truthy string. The or short-circuits and tool_call.get("input", {}) is never evaluated.

Fix

Remove the default so get() returns None (falsy), allowing the or to fall through:

func_args = func_info.get("arguments") or tool_call.get("input") or "{}"

Verification

Bedrock format: {"name": "search_tool", "input": {"search_query": "hello"}, "toolUseId": "abc"}
OLD: func_info.get("arguments", "{}") → "{}" (truthy!) → short-circuits → broken
NEW: func_info.get("arguments") → None (falsy) → falls through to tool_call["input"] ✓

OpenAI format: {"function": {"name": "t", "arguments": "{"x": 1}"}}
NEW: func_info.get("arguments") → "{"x": 1}" (truthy) → same as before ✓

Tests Added

• test_parse_native_tool_call_bedrock_format — verifies Bedrock input dict is correctly extracted
• test_parse_native_tool_call_openai_dict_format — verifies OpenAI format still works

Fixes #4972