diff --git a/scripts/check-shell-portability.test.sh b/scripts/check-shell-portability.test.sh
index 44143605d9..0a2397d41b 100755
--- a/scripts/check-shell-portability.test.sh
+++ b/scripts/check-shell-portability.test.sh
@@ -24,6 +24,7 @@ SELF_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 REPO_ROOT="$(cd "$SELF_DIR/.." && pwd)"
 SCRIPT="$SELF_DIR/check-shell-portability.sh"
 REAL_TOKENS="$REPO_ROOT/scripts/shell-portability-tokens.txt"
+. "$SELF_DIR/test-git-helpers.sh"
 
 PASS=0
 FAIL=0
@@ -1543,9 +1544,7 @@ mkdir -p "$fx/scripts" "$fx/plugins/alpha/skills/demo/context"
 cp "$SCRIPT" "$fx/scripts/"
 out="$(
   cd "$fx" &&
-    git -C "$fx" init -q &&
-    git -C "$fx" config user.email test@example.com &&
-    git -C "$fx" config user.name test &&
+    git_init_test_repo "$fx" &&
     git -C "$fx" commit -q --allow-empty -m base &&
     base="$(git -C "$fx" rev-parse HEAD)" &&
     printf '%s\n' 'stat -c %Y "$f"' >'plugins/alpha/skills/demo/context/mtime.md' &&
@@ -1639,9 +1638,7 @@ cp "$SCRIPT" "$fx/scripts/"
 quoted_name="$(printf 'quoted-\303\251.sh')" # trailing U+00E9 byte -- non-ASCII, triggers Git quoting
 out="$(
   cd "$fx" &&
-    git -C "$fx" init -q &&
-    git -C "$fx" config user.email test@example.com &&
-    git -C "$fx" config user.name test &&
+    git_init_test_repo "$fx" &&
     git -C "$fx" commit -q --allow-empty -m base &&
     base="$(git -C "$fx" rev-parse HEAD)" &&
     printf '%s\n' 'grep -Eq "\\bfoo\\b" "$file"' >'plain.sh' &&
diff --git a/scripts/check-skill-portability.test.sh b/scripts/check-skill-portability.test.sh
index 9d0ee0bdbb..6684b6bede 100755
--- a/scripts/check-skill-portability.test.sh
+++ b/scripts/check-skill-portability.test.sh
@@ -16,6 +16,7 @@ SELF_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 REPO_ROOT="$(cd "$SELF_DIR/.." && pwd)"
 SCRIPT="$SELF_DIR/check-skill-portability.sh"
 REAL_TOKENS="$REPO_ROOT/scripts/skill-portability-tokens.txt"
+. "$SELF_DIR/test-git-helpers.sh"
 
 # Minimal token list: just the active branch class, so a synthetic case is not
 # coupled to the shipping list's staged entries.
@@ -669,9 +670,7 @@ cp "$SCRIPT" "$fx/scripts/"
 quoted_name="$(printf 'quoted-\303\251.md')" # trailing U+00E9 byte — non-ASCII, triggers Git quoting
 out="$(
   cd "$fx" &&
-    git -C "$fx" init -q &&
-    git -C "$fx" config user.email test@example.com &&
-    git -C "$fx" config user.name test &&
+    git_init_test_repo "$fx" &&
     git -C "$fx" commit -q --allow-empty -m base &&
     base="$(git -C "$fx" rev-parse HEAD)" &&
     mkdir -p 'plugins/p/skills/s' &&
diff --git a/scripts/fixture-git-isolation-baseline.txt b/scripts/fixture-git-isolation-baseline.txt
index e980c8b0c8..e977a9a458 100644
--- a/scripts/fixture-git-isolation-baseline.txt
+++ b/scripts/fixture-git-isolation-baseline.txt
@@ -61,7 +61,4 @@ plugins/testing/skills/audit/scripts/cant-fail-scan.test.sh
 plugins/typos-format/hooks/typos-format.test.sh
 plugins/work-items/skills/work/scripts/preflight.test.sh
 scripts/check-contract-slice-prune.test.sh
-scripts/check-shell-portability.test.sh
-scripts/check-skill-portability.test.sh
 scripts/check-stale-base-overlap.test.sh
-scripts/sync-standards-contract.test.sh
diff --git a/scripts/sync-standards-contract.test.sh b/scripts/sync-standards-contract.test.sh
index 5ca82dd9e3..7e1f14bc3a 100755
--- a/scripts/sync-standards-contract.test.sh
+++ b/scripts/sync-standards-contract.test.sh
@@ -8,6 +8,7 @@ set -uo pipefail
 
 SELF_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 SCRIPT="$SELF_DIR/sync-standards-contract.sh"
+. "$SELF_DIR/test-git-helpers.sh"
 
 PASS=0
 FAIL=0
@@ -76,10 +77,9 @@ base_fixture() {
 # git_fixture <fixture> → init repo + commit everything as the base ref; prints base sha
 git_fixture() {
   local fixture="$1"
-  git -C "$fixture" init -q
-  git -C "$fixture" config core.autocrlf false
-  git -C "$fixture" config user.email test@example.com
-  git -C "$fixture" config user.name test
+  # On refusal (e.g. TMPDIR inside the checkout) stop before add/commit can
+  # resolve to the enclosing real repository.
+  git_init_test_repo "$fixture" || return 1
   git -C "$fixture" add -A
   git -C "$fixture" commit -qm base
   git -C "$fixture" rev-parse HEAD