diff --git a/tests/run-bats.sh b/tests/run-bats.sh
index 9cf171e..4fd0ff7 100755
--- a/tests/run-bats.sh
+++ b/tests/run-bats.sh
@@ -46,6 +46,17 @@ fi
 # which is ADR-0024 consequence 2 arriving here. Keeping the exclusion now is
 # what stops that landing as a mystery double-run on the merge that enables it.
 #
+# build/ is excluded for the same reason again, one layer further out: `apm
+# pack` stages a full copy of a package's tree (including its skills' tests/
+# directories) under build/<package>-<version>/ before archiving it. Those
+# staged .bats files carry the same six-levels-up REPO_ROOT walk-up as any
+# other copy, which resolves past this repo's actual root and fails on a
+# missing bats-support helper -- the same failure mode apm_modules/ and
+# .claude/skills/ above already guard against, just from a different apm
+# subcommand. build/ is gitignored and regenerated on demand, so nothing here
+# depends on its contents; the exclusion only stops a stray local `apm pack`
+# output from being discovered and double-run.
+#
 # The walk runs from inside REPO_ROOT so the exclusions match paths RELATIVE to
 # it, the same universe the `git ls-files` grep below sees. Matched against
 # absolute paths, `*/.claude/worktrees/*` excluded every file whenever the
@@ -61,6 +72,7 @@ done < <(
         -not -path "*/.claude/worktrees/*" \
         -not -path "*/apm_modules/*" \
         -not -path "*/.claude/skills/*" \
+        -not -path "*/build/*" \
         | sort
 )
 
@@ -99,7 +111,7 @@ if [[ -n "$GIT_TOPLEVEL" && "$GIT_TOPLEVEL" == "$REPO_ROOT" ]]; then
         [[ -n "$f" ]] && EXPECTED_FILES+=("$REPO_ROOT/$f")
     done < <(
         git -C "$REPO_ROOT" ls-files -- '*.bats' \
-            | grep -Ev '(^|/)tests/bats/|(^|/)test_helper/|(^|/)\.claude/worktrees/|(^|/)apm_modules/|(^|/)\.claude/skills/' \
+            | grep -Ev '(^|/)tests/bats/|(^|/)test_helper/|(^|/)\.claude/worktrees/|(^|/)apm_modules/|(^|/)\.claude/skills/|(^|/)build/' \
             | sort || true
     )
 else
diff --git a/tests/test-run-bats.sh b/tests/test-run-bats.sh
index e28eedf..c60906c 100644
--- a/tests/test-run-bats.sh
+++ b/tests/test-run-bats.sh
@@ -476,6 +476,40 @@ else
   fail "the plan-shortfall run failed with the wrong count: $FAKE_OUT"
 fi
 
+# --- 12. A build/ directory (apm pack's staging output) is excluded, the same
+# way apm_modules/ and .claude/skills/ above are. A stray local `apm pack` run
+# leaves build/<pkg>-<version>/ on disk holding a full copy of every packaged
+# skill's tests/ directory, gitignored and regenerable, but discoverable by a
+# bare `find` all the same. Those staged .bats files carry the same
+# several-levels-up REPO_ROOT walk-up as any other copy, which overshoots this
+# fixture's root, so an unexcluded build/ turns into the same
+# bats-support-not-found failure apm_modules/ and .claude/skills/ already guard
+# against -- this was caught live with 423 duplicate failures against a real
+# checkout holding a stray build/holocron-*/ from an earlier `apm pack`.
+echo ""
+echo "--- a build/ directory holding staged .bats copies is excluded ---"
+DIR12="$(make_fake_repo)"
+FIXTURES+=("$DIR12")
+seed_bats_files "$DIR12"
+mkdir -p "$DIR12/build/some-pkg-1.0.0/tests"
+printf '@test "staged" { false; }\n' > "$DIR12/build/some-pkg-1.0.0/tests/staged.bats"
+install_stub_bats "$DIR12" <<'EOF'
+#!/usr/bin/env bash
+echo "1..1"
+echo "ok 1 first"
+exit 0
+EOF
+run_fake "$DIR12"
+if [[ $FAKE_RC -ne 0 ]]; then
+  fail "a tree holding a build/ directory failed the run: $FAKE_OUT"
+elif grep -q "build/some-pkg-1.0.0" <<< "$FAKE_OUT"; then
+  fail "a .bats file staged under build/ was discovered and run: $FAKE_OUT"
+elif grep -q "^2 tests, 0 failures$" <<< "$FAKE_OUT"; then
+  pass "a build/ directory's staged .bats copies are excluded from discovery"
+else
+  fail "the build/-exclusion run passed with an unexpected count: $FAKE_OUT"
+fi
+
 echo ""
 echo "Results: $PASS passed, $FAIL failed"
 [[ $FAIL -eq 0 ]]