Split Slack into a user page and a developer guide Slack.md was a hybrid. It is now the user-facing page — what it does, setting it up, the two traps that produce a working-looking result, the health check, and how it behaves. Slack-Developer-Guide.md takes the architecture: why it is not tracker #3, the bring-your-own-app reasoning, the kind-in-the-registry seam and its known debt, the file map, the four design decisions, and the six traps that only a live run exposed. Both validated: every wiki link resolves and every backticked path exists. Promoted eight bare filenames to full paths — the same thing that reads like a path but is not, caught by the same check as last time.
Add Slack; cross-link from Issue Trackers and the sidebar Slack as a messaging channel (freeitsm #977), proven end to end on a real workspace. Covers why it is NOT a third issue tracker, the bring-your-own-app decision and what it costs, the two setup traps that produce silently degraded results rather than failures, every scope with its justification, the file map, and the four bugs the live run found that the test suite could not.