Development record

The brief at .abcd/development/brief/04-surfaces/11-history.md:216-219 says: The session-start hook that carries the notice channel 'always exits successfully, because a notice is not a failure and a failing session-start hook shows the user an empty error banner'. The shipped surface differs: The shipped SessionStart hook (hooks/hooks.json -> hooks/session-start.sh) exits 2 when the plugin binary is not installed or when both ~/.abcd and ~/.abcd.noindex exist, and otherwise propagates the non-zero exit of bootstrap.sh or of `abcd hook session-start`/`prompt-router-reset`; only the Go entrypoint itself is the always-exit-0 path. The chapter states the property for 'the hook' without that scope. (v0.14.2 release crosscheck, false-claim, raised by opus in a10.)