docs(sc-gh-stack): prohibit git reset --hard in workflow guidance

Hard rule 2 and the convert playbook's do-not list now name git reset --hard
explicitly, with the sanctioned alternatives (rebase --abort/--continue,
script-driven fast-forward). Scripts never used it; test fixtures keep it only
to manufacture behind-remote states.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: randlee

packages/sc-gh-stack/skills/managing-gh-stacks/SKILL.md

@@ -79,8 +79,11 @@ installed — **do not reproduce the rebase chain or preflight checks by hand.**
 1. Never run bare `view`, `submit`, `init`, `add`, `checkout`, `switch`, or `modify` — they
    prompt or open a TUI and block forever. Use `view --json`, `submit --auto`, `init <b>...`,
    `add <b>`, `checkout <target>`, `up/down/top/bottom`. `modify` has no non-interactive form.
-2. Never `gh pr merge` a stacked PR; never `git push --force`; never merge layers into each
-   other by hand. `gh stack` owns pushing (`push`, `submit`, `sync`) and merging (`merge --yes`).
+2. Never `gh pr merge` a stacked PR; never `git push --force`; never `git reset --hard` as
+   part of a workflow (it discards commits and rerere state — recover with `git rebase
+   --abort`, `git rebase --continue`, or a fast-forward instead); never merge layers into
+   each other by hand. `gh stack` owns pushing (`push`, `submit`, `sync`) and merging
+   (`merge --yes`).
 3. Never restructure with metadata. Rechain with `git rebase --onto`, then `unstack` + `init`
    (`references/troubleshooting.md`, "Restructuring a stack").
 4. A change belongs to the layer that owns the concern: check out that layer, commit, then

packages/sc-gh-stack/skills/managing-gh-stacks/references/playbook-convert.md

@@ -4,8 +4,10 @@
 Merging them one at a time costs n(n+1)/2 CI runs and forces every remaining branch to rebase
 after each merge. As a stack they cost n CI runs and land atomically.
 
-**Do not:** force-push, merge branches into each other by hand, `gh pr merge`, use `gh stack add`
-(it only appends to a stack's top), or try to "fix" order with metadata. Ancestry first.
+**Do not:** force-push, `git reset --hard` (to abandon a conflicted rebase use
+`git rebase --abort`; to move a branch to its remote let the script fast-forward it), merge
+branches into each other by hand, `gh pr merge`, use `gh stack add` (it only appends to a
+stack's top), or try to "fix" order with metadata. Ancestry first.
 
 ## Inputs