fix(hunkHeader): use per-side total count in the fallback @@ header

[YuriNachos]

Summary

formatHunkHeader's fallback branch emitted a malformed @@ -l,s +l,s @@ header for any hunk carrying context lines, because it used the changed-lines count (*Lines) instead of the per-side total count (*Count).

Root cause

The fallback built the header from hunk.deletionLines /hunk.additionLines, which count only the changed +/- lines. The unified-diff @@ count is the per-side total (context + changed), so any hunk with context was undercounted and malformed.

Fix

Use hunk.deletionCount /hunk.additionCount (the per-side totals). Hunks with no context are unchanged.

Tests

New hunkHeader.test.ts covers the context-carrying case (was malformed, now correct) and the no-context case (unchanged).

[greptile-apps]

PR author is not in the allowed authors list.

[vercel]

@YuriNachos is attempting to deploy a commit to the Modem Team on Vercel.

A member of the Team first needs to authorize it.

[YuriNachos]

Heads-up on the red check, so it doesn't read as a problem with this branch: the failing Vercel job is the fork-deployment authorization gate, not a build or test failure. Its status text is:

Authorization required to deploy.

and the target URL is vercel.com/git/authorize?team=Modem&…, i.e. a request for someone on the Modem team to authorize a deployment from a fork. It is red on every open fork PR in this repo right now, mine and other people's alike — sampled just now: #696, #695, #689 (mine) and #686, #682, #678, #676 (not mine), all with the identical message.

Every check a fork PR can actually influence is green here: Socket Security: Project Report and Socket Security: Pull Request Alerts both pass.

Nothing on this branch can turn Vercel green — it needs the authorize link clicked on your side. Happy to rebase or re-trigger if that helps.