turn loop: pin to haiku 4.5 (todo: per-agent override)

CLAUDE.md

@@ -407,6 +407,14 @@ with `./agent.nix` plus an inline module that sets
   claude-code's `--allowedTools` extended grammar. Likely lives in
   `agent.nix` so each agent can scope its own shell surface.
 
+## Per-agent settings backlog
+
+- **Model override.** Hard-coded to `claude-haiku-4-5-20251001` in the turn
+  loop right now. Surface it as a per-agent override: operator via
+  dashboard, manager via `request_apply_commit` setting an attr on the
+  agent's flake (most natural place since the flake already carries
+  per-agent env/identity).
+
 ## Polish backlog
 
 Not phased — pick when relevant: