* fix(#1772): read full multi-line command in graphify-update hook Gate 2
The PostToolUse hook joined tool_name + newline + tool_input.command and
extracted the command with sed -n '2p' — line 2 only. Agent runtimes
(Claude Code's Bash tool among them) routinely emit HEAD-advancing commits
as multi-line scripts ('cd /path', then 'git add', then 'git commit …'), so
line 2 is the 'cd', Gate 2's *"git commit"* match failed, and the rebuild
silently no-op'd on real commits despite graphify.auto_update: true.
Capture line 2 through EOF (sed -n '2,$p') so the case glob sees the full
multi-line command string. Single-line behavior is unchanged (the match
only widens); non-HEAD-advancing multi-line commands still no-op cleanly.
Regression tests cover multi-line commit/merge/pull dispatch plus a
multi-line no-op no-regression guard.
* docs(#1772): add changeset fragment for graphify-update multi-line fix
* test(#1772): regenerate golden-install-parity fixtures for hook change
gsd-graphify-update.sh ships to 9 graphify-aware runtimes; widening the
sed range (2p -> 2,$p) shifts its shipped hash. Recapture the 9 affected
fixtures via UPDATE_GOLDEN=1 — each changes exactly one line (the hook hash).
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