feat!: narrow AgentGraphRunner.run input from Any to str

[jsonbailey]

Summary

Narrows the AgentGraphRunner.run input type from Any to str across the protocol (server-ai) and both concrete implementations (server-ai-openai, server-ai-langchain). Also narrows ManagedAgentGraph.run (which forwards directly to the runner) for type-consistency.

Brings AgentGraphRunner.run in line with Runner.run (narrowed in #165) and matches the JS AgentGraphRunner interface in feat/next-ai-release, which already accepts string. The spec is updated in parallel in sdk-specs#164.

Changes

• packages/sdk/server-ai/src/ldai/providers/agent_graph_runner.py — protocol declares run(input: str); dropped unused Any import.
• packages/sdk/server-ai/src/ldai/managed_agent_graph.py — ManagedAgentGraph.run(input: str) to match the underlying runner; dropped unused Any import.
• packages/ai-providers/server-ai-openai/src/ldai_openai/openai_agent_graph_runner.py — narrowed run signature; removed redundant str(input) coercion.
• packages/ai-providers/server-ai-langchain/src/ldai_langchain/langgraph_agent_graph_runner.py — narrowed run signature; removed redundant str(input) coercion in HumanMessage construction.

BREAKING CHANGE

AgentGraphRunner.run(input: Any) is now AgentGraphRunner.run(input: str). ManagedAgentGraph.run(input: Any) is now ManagedAgentGraph.run(input: str). Callers passing non-string inputs must coerce to str at the call site.

Test plan

• make test — 329 tests pass across server-ai, server-ai-langchain, server-ai-openai
• make lint — mypy, isort, pycodestyle clean across all three packages
• CI pipeline green on draft PR

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Note

Medium Risk
This is a breaking API change that will require downstream callers passing non-string inputs to update, but runtime behavior changes are minimal (removal of implicit str() coercion).

Overview
Narrows the agent-graph execution API to accept only string prompts by changing AgentGraphRunner.run and ManagedAgentGraph.run from input: Any to input: str.

Updates the OpenAI and LangGraph runner implementations to match the new signature and removes redundant str(input) coercions when constructing messages / invoking Runner.run.

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