Version-bump detection in .hooks/pre-commit should compare old vs new value

[vivek7405]

Problem

.hooks/pre-commit detects a staged version bump by scanning git diff --cached --unified=0 for an ADDED "version": "..." line in any packages/*/package.json (the STAGED_PKG_BUMPS awk, ~L54-63). With --unified=0, an edit ADJACENT to the version line (e.g. adding a sibling field right after "version") re-emits the version line as a + line even when the version did NOT change. That spuriously registers a "bump", which then:

• (gate 2, pre-existing) fires the changelog generator, which finds no version-bump commit and blocks with "the generator did not produce the expected files", and
• (gate 3, added in Enforce worktree-per-task to stop concurrent-agent branch collisions #590/feat: enforce worktree-per-task to stop concurrent-agent branch collisions #591) blocks the commit as a wrong-branch library release.

So a legit non-version edit to a published package's package.json, made immediately adjacent to the version line on a feature branch, is rejected. Escape is --no-verify, but it is a surprising false-positive.

Design / approach

Make the detection compare the NEW version value against the committed (HEAD) value, and treat it as a bump only when they differ. Roughly: for each packages/<dir>/package.json in the staged diff, read the new staged version (git show :<path> or the working file) and the old (git show HEAD:<path>), and emit <pkg>@<newver> only if old != new. This fixes BOTH gate 2 (changelog) and gate 3 (release-branch guard) since both read STAGED_PKG_BUMPS.

Implementation notes (for the implementing agent)

• Where: .hooks/pre-commit, the STAGED_PKG_BUMPS awk block (~L54-63). Replace the "any added version line" heuristic with an old-vs-new comparison per changed package.json. Keep the output shape (<dir>@<version>) so gate 2 + gate 3 are unchanged downstream.
• Map dirs the same way the current awk does (packages/editors/intellisense -> intellisense, etc.).
• Landmines: a NEWLY-ADDED package.json has no HEAD:<path> (treat as a bump or skip, decide deliberately). Preserve the $GITHUB_ACTIONS bot-skip and main-block. Invariant 11 in any new comments.
• Tests: extend test/hooks/release-branch-guard.test.mjs with a case that stages a non-version edit adjacent to the version line on a feature branch and asserts the hook does NOT block (currently it would). Counterfactual: a real version change still registers.

Acceptance criteria

• A non-version edit to a published package's package.json (even adjacent to the version line) on a feature branch is NOT blocked.
• A real version change is still detected (gate 2 generates the changelog; gate 3 still guards off release branches).
• Test covers both, with a counterfactual.