Repair gateway's misplaced streamed tool-call id in assembly code

[alexkroman]

Problem

assembly code crashes on any tool-calling turn with:

✗ ValidationError: 1 validation error for ToolMessage
tool_call_id
  Input should be a valid string [type=string_type, input_value=None, input_type=NoneType]

Root cause (confirmed live against the production gateway)

The AssemblyAI LLM Gateway's streaming /v1/chat/completions nests the tool-call id inside function instead of at the tool-call's top level, where the OpenAI streaming spec — and langchain_openai (id=rtc.get("id")) — read it:

// actual (streaming first delta)
"tool_calls": [{ "index": 0, "function": { "id": "toolu_…", "name": "get_weather", "arguments": "" } }]

// expected (OpenAI spec)
"tool_calls": [{ "index": 0, "id": "toolu_…", "type": "function", "function": { "name": "get_weather", "arguments": "" } }]

function.name/function.arguments are in the right place, so the call assembles with a name and args but id=None. deepagents' ToolNode then builds ToolMessage(tool_call_id=None) → Pydantic rejects it → the whole turn errors out. The non-streaming endpoint places the id correctly, so only the streaming path (which the agent always uses) is affected.

The gateway bug is being reported upstream for a server-side fix; this keeps the CLI resilient regardless of that timeline.

Fix

Client-side, in the existing _GatewayChatOpenAI quirk-adapter (the same subclass that already flattens content arrays the gateway 500s on): override _convert_chunk_to_generation_chunk to hoist a function.id back to the tool-call top level before langchain converts the chunk. Split into small rank-A helpers for the complexity gate.

Idempotent once the gateway is fixed — a correct delta puts the id at the top level and leaves no function.id, so the move never fires.

Tests

• branch-by-branch coverage of the hoist logic (malformed variants skipped, only a function-nested id is hoisted)
• guard early-returns
• end-to-end: a real gateway-shaped chunk run through the override yields a tool call with its id intact

./scripts/check.sh → All checks passed (100% patch coverage, mutation gate, escape-hatch gate, build+twine all green).

🤖 Generated with Claude Code