Spec: latest scans notes by branch and round

docs/superpowers/specs/2026-10-02-review-notes-design.md

@@ -62,9 +62,11 @@ Bash, git plumbing only. Subcommands:
   proper re-review targets a new commit, so overwriting is always deliberate.
   Validates that `branch`, `round`, and `verdict` are present and that
   `verdict` uses the vocabulary above. No other validation.
-- `review-note latest [branch]` — print the newest note for a branch: start at
-  the branch tip (default: current branch), and walk back through `previous`
-  until a note is found. Exit 1 if the chain is exhausted without a note.
+- `review-note latest [branch]` — print the note with the highest `round` for
+  a branch (default: current branch), scanning the notes ref and matching
+  notes on their `branch:` header. Exit 1 if there is no note for the branch.
+  (A `previous`-chain walk cannot bootstrap from an unreviewed tip, so the
+  scan uses the `branch:` header as the index instead.)
 - `review-note push` — `git push origin refs/notes/review`. Plain `git push`
   ignores notes, so this is the only way results travel.
 
@@ -73,8 +75,7 @@ the user decide.
 
 ## Lifecycle
 
-1. Reviewer reads `review-note latest <branch>` (nothing printed means first
-   review).
+1. Reviewer reads `review-note latest <branch>` (exit 1 means first review).
 2. Reviewer reviews the branch tip per `REVIEW.md`.
 3. Reviewer writes the note with `review-note write` and runs
    `review-note push`.