fix(mcp): accept transport field as alias for type (#3238)

[18062706139fcz]

Summary

Fixes #3238 — A remote MCP server configured with only transport: sse was misidentified as stdio (the default for type) and failed at startup with:

Failed to configure MCP server: with stdio transport requires 'command' field

Root cause

McpServerConfig only honored type and defaulted it to "stdio". The official MCP configuration schema uses transport for the same concept, so configurations following the spec were treated as stdio.

Change

• McpServerConfig now has a model_validator(mode="before") that promotes transport to type when only transport is provided. type remains authoritative when both are set, so existing configurations are unaffected.
• Added regression tests covering the alias for sse/http and the precedence rule.

Test

cd backend && uv run pytest tests/test_mcp_client_config.py -q
# 13 passed

Closes #3238

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[18062706139fcz]

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DONE

[Copilot]

Pull request overview

Fixes #3238 by accepting the MCP spec's transport field as an alias for the project's type field on McpServerConfig, so remote SSE/HTTP servers configured with only transport: sse are no longer misidentified as stdio.

Changes:

• Add a Pydantic model_validator(mode="before") on McpServerConfig that promotes transport to type when only transport is set; type wins when both are present.
• Add regression tests covering the alias for sse/http and the precedence rule.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
backend/packages/harness/deerflow/config/extensions_config.py	Adds _accept_transport_alias before-validator to normalize transport → type.
backend/tests/test_mcp_client_config.py	Adds regression tests for the alias and precedence behavior.