fix: preserve Bedrock Converse API tool arguments in _parse_native_tool_call

[guoyangzhen]

Fix

Fixes #4972

Problem

When using AWS Bedrock (Converse API) with native function calling, all tool arguments are silently dropped — every tool call receives an empty dict {} instead of actual arguments.

Root Cause

In _parse_native_tool_call, the dict-handling branch has:

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

Bedrock returns tool calls as {"name": "...", "input": {...}, "toolUseId": "..."} — no "function" key. So func_info is {}, and func_info.get("arguments", "{}") returns the default string "{}". Since "{}" is truthy, the or short-circuits and tool_call["input"] is never evaluated.

Fix

Remove the default value from .get("arguments") so it returns None when the key is absent, allowing the or to fall through to tool_call.get("input"):

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

Behavior by provider:

Provider	tool_call structure	Before fix	After fix
OpenAI	{"function": {"arguments": "{...}"}}	"{...}" ✅	"{...}" ✅
Anthropic (direct)	{"input": {...}} (has attr)	Handled earlier	Handled earlier
Bedrock (dict)	{"name": "..", "input": {...}}	"{}" ❌	{...} ✅

Testing

The fix can be verified by running a crew with Bedrock and a tool that has required arguments. Before the fix, all tool calls fail with Field required [type=missing, input_value={}, input_type=dict]. After fix, arguments are correctly passed through.