refactor: remove stale ManagedModel message management and AgentGraphResult type #658

Job	Run time
server-ai-langchain-windows (3.13)	20s
server-ai-openai-linux (3.12)	23s
server-ai-openai-linux (3.13)	28s
server-ai-langchain-windows (3.14)	30s
server-ai-langchain-windows (3.10)	21s
server-ai-openai-linux (3.10)	27s
server-ai-linux (3.11)	19s
server-ai-openai-linux (3.11)	28s
server-ai-langchain-linux (3.14)	21s
server-ai-langchain-windows (3.11)	34s
server-ai-linux (3.13)	16s
server-ai-openai-linux (3.14)	30s
server-ai-linux (3.10)	17s
server-ai-openai-windows (3.12)	42s
server-ai-windows (3.12)	20s
server-ai-optimization-linux (3.11)	10s
server-ai-optimization-windows (3.11)	23s
server-ai-optimization-linux (3.14)	11s
server-ai-optimization-linux (3.10)	13s
server-ai-openai-windows (3.11)	20s
server-ai-windows (3.10)	40s
server-ai-optimization-windows (3.14)	32s
server-ai-optimization-linux (3.12)	9s
server-ai-openai-windows (3.14)	28s
server-ai-linux (3.14)	1m 13s
server-ai-openai-windows (3.13)	25s
server-ai-optimization-windows (3.12)	19s
server-ai-optimization-windows (3.13)	28s
server-ai-langchain-linux (3.11)	23s
server-ai-langchain-linux (3.13)	20s
server-ai-windows (3.11)	21s
server-ai-openai-windows (3.10)	37s
server-ai-windows (3.14)	34s
server-ai-linux (3.12)	17s
server-ai-windows (3.13)	22s
server-ai-langchain-windows (3.12)	27s
server-ai-optimization-windows (3.10)	20s
server-ai-optimization-linux (3.13)	13s
server-ai-langchain-linux (3.10)	19s
server-ai-langchain-linux (3.12)	23s
	16m 23s

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