fix: force streaming mode for string prompts with SDK MCP servers #492
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SDK MCP servers require bidirectional communication through stdin/stdout. When using a string prompt, stdin was being closed immediately, causing "ProcessTransport is not ready for writing" errors. This fix detects SDK MCP servers and converts string prompts to async iterables, enabling the streaming protocol required for MCP communication. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
This was referenced Jan 19, 2026
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Jan 19, 2026
Use forked branch to resolve ProcessTransport error when using SDK MCP servers with string prompts. - Add [tool.uv.sources] to use forked branch - Bump version from 0.0.3 to 0.0.4 Upstream PR: anthropics/claude-agent-sdk-python#492 Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
When SDK MCP servers are present, the transport converts string prompts to AsyncIterable for bidirectional communication. The client now: 1. Forces streaming mode when SDK MCP servers are configured, even for string prompts (they require bidirectional communication) 2. Uses the transport's potentially converted prompt (`_prompt` attribute) instead of the original prompt when starting the input stream This ensures proper streaming behavior when using string prompts with SDK MCP servers. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
When the CLI process exits immediately after processing the final message, the transport may close before we can send the control response. This caused unhandled CLIConnectionError exceptions. Wrap transport.write calls in _handle_control_request with try/except to gracefully handle the race condition when the transport is already closed. Other exceptions still propagate normally. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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Summary
Changes
_string_to_async_iterable()helper function to convert string prompts to stream-json format_has_sdk_mcp_servers()method to detect SDK MCP server presence__init__to force streaming mode when SDK MCP servers are configured with string promptsTest plan
_string_to_async_iterableoutput format validationFixes #386
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