fix(#1772): read full multi-line command in graphify-update hook Gate 2 (#1815)

* 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).

hooks/gsd-graphify-update.sh

@@ -45,7 +45,13 @@ process.stdin.on("end", () => {
 });
 ' 2>/dev/null || printf '\n')
 TOOL_NAME=$(printf '%s\n' "$TOOL_INFO" | sed -n '1p')
-COMMAND=$(printf '%s\n' "$TOOL_INFO" | sed -n '2p')
+# Capture the FULL command (line 2 through EOF). Agent runtimes routinely emit
+# HEAD-advancing commits as multi-line scripts (`cd /path` then `git add` then
+# `git commit …`); reading only line 2 (`sed -n '2p'`) missed a `git commit`
+# that was not on the first command line and silently no-op'd the rebuild
+# (#1772). Line 2..EOF preserves embedded newlines; the `case` glob below
+# matches the substring anywhere in the multi-line string.
+COMMAND=$(printf '%s\n' "$TOOL_INFO" | sed -n '2,$p')
 
 [ "$TOOL_NAME" = "Bash" ] || exit 0