ADR-0016: Followers start on open¶

Status: Accepted Date: 2026-10-12 Deciders: Alex Nodeland Amends: stackr RFC-0002's start of a workspace's follower, and its template's: followers start through the libraries' on_open hook, not their authorize hook.

Context¶

RFC-0002 starts a workspace's follower "the first time a workspace is used, through the libraries' authorize hook, as the template's Mirrors does for feedback", and its template section wires "followers started through the authorize hook". Lattice RFC-0001 has since moved the hooks onto Workspaces(authorize=, on_open=) in both libraries. authorize is asked for every command and read, so it must have no side effects; on_open is called on every allowed open, after the check, and its callees are idempotent. The template's mirrors moved to on_open in that RFC's phase 1.

Decision¶

• Followers.watch(tenant_id, workspace_id) is an OnOpen. It starts the workspace's follower unless it runs already, so it does nothing on every open after the first, the follower's own included.
• The application gives it to both libraries' Workspaces. Each takes one on_open, so the template composes watch with the mirrors' into one function. Opening a workspace in either library then starts its follower.
• At startup, Followers.resume() follows every workspace the ledger knows (ADR-0015). A workspace used for the first time since the bridge was installed is followed once someone opens it, until artifactr can list a tenant's workspaces (lattice #5).
• A follower that stopped starts again the next time its workspace is opened, as a mirror does.

Options considered¶

Consequences¶

• Easier: a permission check stays a check, and a follower starts exactly where a mirror does.
• Harder: the template's on_open has two callees, each of which must stay idempotent.