[ENG-3258] feat: add providerWorkspaceRef support for multi-workspace providers

[dionlow]

Summary

• Add providerWorkspaceRef support to OAuth flow for multi-workspace providers
• Implement consistent fallback order prioritizing settings over parameters
• Add optional workspace reference parameter to MCP tools

Details

Multi-Workspace Provider Support

Some SaaS providers (e.g., Slack, Microsoft Teams) support multiple workspaces per user account. This PR adds support for specifying which workspace to connect to during OAuth:

• New parameter: providerWorkspaceRef (optional) added to start-oauth tool
• Settings support: Added to ClientSettings type for configuration
• Conditional inclusion: Only included in OAuth request when provided

Fallback Order Consistency

Implements a consistent fallback order across both SDK and mcp-server:

// Settings take precedence over parameters
const finalProviderWorkspaceRef = 
  settings?.providerWorkspaceRef || providerWorkspaceRef;

This ensures that:

1. Configuration settings are always prioritized
2. Tool parameters serve as runtime overrides when settings are not provided
3. Behavior is consistent with other configuration values (groupRef, projectId, etc.)

API Changes

MCP Server (mcp-server/src/oauth.ts)

• Added providerWorkspaceRef parameter to start-oauth tool
• Implements fallback logic for workspace reference

SDK (sdk/lib/adapters/mcp.ts)

• Added providerWorkspaceRef?: string to ClientSettings type
• Updated createStartOAuthTool to handle workspace references
• Conditionally includes workspace ref in OAuth API requests

Test plan

• Test OAuth flow without providerWorkspaceRef (existing behavior)
• Test OAuth flow with providerWorkspaceRef parameter
• Test OAuth flow with providerWorkspaceRef in settings
• Verify settings take precedence over parameters
• Test with multi-workspace providers (e.g., Slack)

🤖 Generated with Claude Code

[linear]

ENG-3258 [mcp] oAuth does not support workspace

[dionlow]

split this branch from the logger one that was reverted. merging to test build