The e2eURL() path used createOpenAI().responses() which produces a
Responses API format that the mock server's SSE stream can't correctly
convey tool calls through. Switch to createOpenAICompatible().chatModel()
which uses the chat completions format — matching what the mock was
designed for and what the integration tests use.
This only affects the OPENCODE_E2E_LLM_URL code path (e2e tests only).
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