fix: don't block stdio transport on cache warmup#249
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mark-liu wants to merge 3 commits intokorotovsky:masterfrom
Closed
fix: don't block stdio transport on cache warmup#249mark-liu wants to merge 3 commits intokorotovsky:masterfrom
mark-liu wants to merge 3 commits intokorotovsky:masterfrom
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The stdio transport blocks on IsReady() which requires both the users and channels caches to be fully populated before serving. On large workspaces (200k+ members like Kubernetes Slack), the user cache takes several seconds to load, causing MCP clients with tight startup timeouts to fail the connection. This brings stdio in line with the SSE and HTTP transports, which already serve immediately while caches warm in the background. Tools that depend on the user cache gracefully degrade (showing user IDs instead of display names) until the cache is ready. Signed-off-by: Mark Liu <mark@prove.com.au>
5 tasks
…AuthTest dedup Three fixes for running multiple MCP server instances concurrently: 1. Atomic cache writes — write to temp file then rename, prevents concurrent readers from seeing partial 400MB+ JSON files. 2. Startup jitter — random 0-3s delay before first API call, staggers concurrent instances to avoid Slack rate limit thundering herd. 3. AuthTest deduplication — validateAuthAndGetTeamID now returns the full AuthTestResponse which is passed to NewMCPSlackClient, eliminating a redundant AuthTest call per startup (was 2 per instance, now 1).
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Problem
The stdio transport blocks serving until
IsReady()returns true, which requires both the users and channels caches to be fully populated. On large workspaces (Kubernetes Slack has 225k+ members), the user cache load takes several seconds — long enough that MCP clients with startup timeouts (like Claude Code) fail the connection before the server is ready.The SSE and HTTP transports don't have this problem — they serve immediately and log "still warming up caches" while the background goroutine populates.
Fix
Remove the blocking
IsReady()loop for stdio and match the SSE/HTTP behaviour: serve immediately, let caches warm in the background.Tools that depend on the user cache (DM channel naming, user search, display name resolution in message history) gracefully degrade by showing user IDs until the cache is ready.
Testing
Tested against Kubernetes Slack (225,807 members, 555 channels):