refactor: extract transport mode selection

[zereight]

Summary

Part of #516.

This is a small behavior-preserving server refactor:

• moves TransportMode and transport selection priority into server/transport-mode.ts
• keeps all startup functions in index.ts
• preserves the existing priority: Streamable HTTP > SSE > stdio

Verification

• rtk npm run build
• rtk npm run test:remote-auth
• rtk npm run test:mcp-oauth
• node --import tsx/esm --test test/streamable-http-static-token-auth.test.ts

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Note

Low Risk
Behavior-preserving refactor with no changes to startup wiring or transport priority; only module boundaries moved.

Overview
Moves MCP transport mode selection out of index.ts into a new server/transport-mode.ts module.

The TransportMode enum and determineTransportMode() (priority: Streamable HTTP → SSE → stdio) are exported from there; index.ts imports them and still owns all startup paths (startStdioServer, SSE, Streamable HTTP). Selection logic is unchanged—only location and a slightly tighter determineTransportMode implementation.

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[coderabbitai]

📝 Walkthrough

Walkthrough

The TransportMode enum and determineTransportMode() function are extracted from index.ts into a new server/transport-mode.ts module. index.ts removes its inline definitions (−32 lines) and adds a single import from the new module.

Changes

Transport Mode Module Extraction

Layer / File(s)	Summary
New transport-mode module and index.ts import server/transport-mode.ts, index.ts	server/transport-mode.ts exports TransportMode enum (stdio, sse, streamable-http) and determineTransportMode() with streamable-http → sse → stdio priority fallback. index.ts removes the equivalent inline definitions and replaces them with an import from the new module.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'refactor: extract transport mode selection' clearly and concisely summarizes the main change - extracting transport mode logic into a separate module.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description check	✅ Passed	The PR description clearly relates to the changeset, explaining the refactor of transport mode selection into a new module while preserving behavior.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch refactor/transport-mode

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch refactor/transport-mode

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