Summary

• revert the MCP client SDK v2 migration from feat(mcp): upgrade client SDK to v2 #39247
• revert the v2-specific callback port and session recovery follow-ups from fix(mcp): honor callback port in debug #39259 and fix(mcp): recover expired SDK sessions #39265
• revert the final MCP client 2.0.0 upgrade from chore(mcp): upgrade client to 2.0.0 #39369
• restore @modelcontextprotocol/sdk 1.29.0 and its compatibility patch

Rationale

The MCP SDK v2 client is not quite ready for production use in OpenCode. It still has significant compatibility issues with legacy MCP servers, so we should remain on the established v1 SDK until those interoperability gaps are resolved.

This rollback addresses the reported Xcode MCP startup timeout, Atlassian OAuth issuer mismatch, Draft-07 schema rejection, ReUI OAuth authentication failure, and missing fallback after server/discover rejection. The numeric parameter conversion report in #39334 is not included because it appears unrelated to the SDK v2 migration.

Fixes #39315
Fixes #39332
Fixes #39333
Fixes #39343
Fixes #39354

Testing

• bun test test/mcp (from packages/opencode): 60 pass
• bun typecheck (from packages/opencode)
• git diff --check origin/dev...HEAD