diff --git a/tests/unit/test-pr-creation-log.sh b/tests/unit/test-pr-creation-log.sh
index 408a0db..86ba5f6 100644
--- a/tests/unit/test-pr-creation-log.sh
+++ b/tests/unit/test-pr-creation-log.sh
@@ -44,14 +44,44 @@ else
   fail "pr-creation-log: hook should use external script with tool_response schema"
 fi
 
+# Select this feature's entry by its command, never by matcher.
+# `.hooks.PostToolUse[] | select(.matcher == "Bash")` emits one output per
+# matching entry and `jq -e` derives its exit code from the LAST one, so a
+# second Bash-matcher PostToolUse hook would silently decide the verdict — and
+# for the negated legacy checks it would decide it as a PASS, masking exactly
+# the regression they exist to catch. Collect first, then assert on the whole
+# set: `length == 1` pins the entry and `all(...)` is the correct collapse for
+# a negated condition (`any(...)` would still pass on a regressed first entry).
+# Selection walks the PARENT PostToolUse entries (not the inner hooks) so the
+# matcher stays visible: this feature must remain bound to matcher "Bash".
+_pr_entries='[.hooks.PostToolUse[]?
+  | select(any(.hooks[]?; (.command? // "") | contains("pr-creation-log/log-pr.sh")))]'
+
+_pr_modern_hook_ok() { # <settings-file>
+  jq -e "$_pr_entries
+    | length == 1
+      and all(.matcher == \"Bash\"
+              and (.hooks | length == 1)
+              and all(.hooks[]; .if == \"Bash(gh pr create *)\" and .async == true))" \
+    "$1" >/dev/null 2>&1
+}
+
+_pr_legacy_hook_ok() { # <settings-file>
+  jq -e "$_pr_entries
+    | length == 1
+      and all(.matcher == \"Bash\"
+              and (.hooks | length == 1)
+              and all(.hooks[]; (has(\"if\") | not) and (has(\"async\") | not)))" \
+    "$1" >/dev/null 2>&1
+}
+
 build_settings_json \
   "$PROJECT_DIR/config/settings-base.json" \
   "$PROJECT_DIR/config/permissions.json" \
   "$_pr_settings" \
   "$_pr_hooks" >/dev/null
 
-if jq -e '.hooks.PostToolUse[] | select(.matcher == "Bash") | .hooks[0].if == "Bash(gh pr create *)"' "$_pr_settings" >/dev/null 2>&1 \
-  && jq -e '.hooks.PostToolUse[] | select(.matcher == "Bash") | .hooks[0].async == true' "$_pr_settings" >/dev/null 2>&1; then
+if _pr_modern_hook_ok "$_pr_settings"; then
   pass "pr-creation-log: merged settings keep if condition and async execution"
 else
   fail "pr-creation-log: merged settings should keep if condition and async execution"
@@ -70,8 +100,7 @@ _CLAUDE_SEMVER_CACHE=""
 _CLAUDE_SEMVER_CACHE_SET=false
 PATH="$_pr_tmp/claude-current-bin:$PATH" build_settings_file "$_pr_supported_settings" >/dev/null
 
-if jq -e '.hooks.PostToolUse[] | select(.matcher == "Bash") | .hooks[0].if == "Bash(gh pr create *)"' "$_pr_supported_settings" >/dev/null 2>&1 \
-  && jq -e '.hooks.PostToolUse[] | select(.matcher == "Bash") | .hooks[0].async == true' "$_pr_supported_settings" >/dev/null 2>&1; then
+if _pr_modern_hook_ok "$_pr_supported_settings"; then
   pass "pr-creation-log: supported Claude Code gets if/async hook"
 else
   fail "pr-creation-log: supported Claude Code should get if/async hook"
@@ -90,13 +119,34 @@ _CLAUDE_SEMVER_CACHE=""
 _CLAUDE_SEMVER_CACHE_SET=false
 PATH="$_pr_tmp/claude-legacy-bin:$PATH" build_settings_file "$_pr_legacy_settings" >/dev/null
 
-if jq -e '.hooks.PostToolUse[] | select(.matcher == "Bash") | .hooks[0] | has("if") | not' "$_pr_legacy_settings" >/dev/null 2>&1 \
-  && jq -e '.hooks.PostToolUse[] | select(.matcher == "Bash") | .hooks[0] | has("async") | not' "$_pr_legacy_settings" >/dev/null 2>&1; then
+if _pr_legacy_hook_ok "$_pr_legacy_settings"; then
   pass "pr-creation-log: legacy Claude Code falls back to legacy hook fragment"
 else
   fail "pr-creation-log: legacy Claude Code should fall back to legacy hook fragment"
 fi
 
+# The arity guard itself. Append a second Bash-matcher PostToolUse entry and
+# regress the pr-creation-log one to the modern shape: the legacy assertion
+# must now fail. The old `select(.matcher == "Bash") | .hooks[0] | has("if") |
+# not` filter returns 0 here (the appended entry is the last output), and so
+# does an `any(...)` rewrite — only selecting by command and collapsing with
+# `all(...)` reports the regression.
+_pr_arity_settings="$_pr_tmp/settings-two-bash.json"
+jq '.hooks.PostToolUse = [
+      {"matcher":"Bash","hooks":[{"type":"command",
+        "command":"__HOME__/.claude/hooks/pr-creation-log/log-pr.sh",
+        "if":"Bash(gh pr create *)","async":true}]},
+      {"matcher":"Bash","hooks":[{"type":"command",
+        "command":"/somewhere/future-hook.sh"}]}
+    ]' "$_pr_legacy_settings" > "$_pr_arity_settings"
+
+if ! _pr_legacy_hook_ok "$_pr_arity_settings" \
+  && _pr_modern_hook_ok "$_pr_arity_settings"; then
+  pass "pr-creation-log: a second Bash-matcher hook cannot decide the verdict"
+else
+  fail "pr-creation-log: assertions must select this feature's entry by command"
+fi
+
 _pr_script="$_pr_tmp/pr-hook.sh"
 _pr_input="$_pr_tmp/input.json"
 _pr_out="$_pr_tmp/out.json"