listener: only ack data events, never lifecycle frames — fixes the 1006 disconnect loop

[vinodhalaharvi-claude]

The bug (deterministic, code-side — NOT environmental)

readLoop acked every event with a non-nil Request:

if evt.Request != nil { l.sm.Ack(*evt.Request) }

But slack-go creates the hello lifecycle frame WITH a Request (newEvent(EventTypeHello, nil, req)). So on every connect, loom acked the hello — sending a Socket Mode response with an empty envelope ID ({"envelope_id":""}, visible in debug logs). Slack rejects that and closes the socket: websocket close 1006 (abnormal closure). Then: reconnect → hello → ack → 1006 → forever. No app_mention is ever delivered because the socket never survives past the hello.

This reproduced identically on two different networks and two different Slack apps precisely because it's deterministic protocol misuse, not a middlebox. The earlier 'environmental WebSocket flap' diagnosis was wrong — the cross-network identical failure was the tell.

The fix

Gate the ack on the event type, not merely Request != nil. Only data events are acknowledgeable — EventsAPI, SlashCommand, Interactive. Lifecycle frames (hello, connecting, connected, disconnect, errors) are never acked and never dispatched. Extracted into a pure ackable(EventType) bool so the rule is explicit and regression-tested. Matches slack-go's own handler, which dispatches only those three types.

Tests (listener_ack_test.go)

• ackable() true only for EventsAPI/SlashCommand/Interactive; false for all lifecycle frames
• explicit guard: ackable(Hello) must be false — acking hello is what killed the socket

Step	Result
go vet / gofmt / staticcheck	✅
go test -race ./...	✅
go build ./...	✅

Note on branch contents

This branch is stacked on claude/loom-claude-code-llm (PR #6, Claude Code default LLM), so it also contains that change. Both are wanted loom changes; merge #6 first if you want this to reduce to just the ack fix, or merge this and it carries both.

This unblocks the live Slack demo

With the socket no longer self-terminating on every hello, app_mention events are finally delivered. @loom say hello from slack round-trips: 👀 + 'Working on it…' → echoed result in the thread.