diff --git a/.github/workflows/check-tools.yml b/.github/workflows/check-tools.yml
index de1f2f0f..7be9aaa8 100644
--- a/.github/workflows/check-tools.yml
+++ b/.github/workflows/check-tools.yml
@@ -44,3 +44,6 @@ jobs:
 
       - name: Validate shared destinations for detected tools
         run: bash scripts/test-install-all-path-collision.sh
+
+      - name: Validate complete selected installs
+        run: bash scripts/test-install-selection-completeness.sh
diff --git a/scripts/install.sh b/scripts/install.sh
index 5150b190..179d41aa 100755
--- a/scripts/install.sh
+++ b/scripts/install.sh
@@ -235,7 +235,9 @@ build_selection() {
 slug_allowed() {
   $SELECTION_ACTIVE || return 0
   local s="${1#agency-}"
-  printf '%s\n' "$_ALLOWED_SLUGS" | grep -qxF "$s"
+  # grep -q closes a pipe as soon as it finds an early match. With pipefail,
+  # printf may then get SIGPIPE and make a valid slug look unselected.
+  grep -qxF "$s" <<< "$_ALLOWED_SLUGS"
 }
 
 # selected_agent_count — how many agents the current selection installs.
diff --git a/scripts/test-install-selection-completeness.sh b/scripts/test-install-selection-completeness.sh
new file mode 100644
index 00000000..2973dd78
--- /dev/null
+++ b/scripts/test-install-selection-completeness.sh
@@ -0,0 +1,39 @@
+#!/usr/bin/env bash
+# grep -q must not make an early selected slug fail under pipefail/SIGPIPE.
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_ROOT="$(cd "$SCRIPT_DIR/.." && pwd)"
+tmp="$(mktemp -d "${TMPDIR:-/tmp}/agency-selection.XXXXXX")"
+trap 'rm -rf "$tmp"' EXIT
+
+# Exercise the installer's actual slug predicate with a list beyond the pipe
+# buffer. An early grep -q match can close its input before printf finishes.
+eval "$(sed -n '/^slug_allowed() {/,/^}/p' "$SCRIPT_DIR/install.sh")"
+SELECTION_ACTIVE=true
+_ALLOWED_SLUGS="$(awk 'BEGIN { print "first"; for (i = 0; i < 20000; i++) print "other-" i }')"
+if ! slug_allowed first; then
+  echo 'FAIL: an allowed early slug was rejected after grep closed the pipe' >&2
+  exit 1
+fi
+slug_allowed other-19999 || {
+  echo 'FAIL: an allowed final slug was rejected' >&2
+  exit 1
+}
+echo 'PASS: early and final slugs remain selectable in a large roster'
+
+# Confirm the real division install copies every source agent, not a variable
+# subset that happens to survive the pipeline race.
+source "$SCRIPT_DIR/lib.sh"
+expected=0
+while IFS= read -r -d '' file; do
+  is_agent_file "$file" && expected=$((expected + 1))
+done < <(find "$REPO_ROOT/engineering" -name '*.md' -type f -print0)
+HOME="$tmp/home" bash "$SCRIPT_DIR/install.sh" --no-interactive --tool claude-code \
+  --division engineering --path "$tmp/agents" > "$tmp/output" 2>&1
+actual="$(find "$tmp/agents" -maxdepth 1 -name '*.md' -type f | wc -l | tr -d ' ')"
+if [[ "$actual" != "$expected" ]]; then
+  printf 'FAIL: engineering install copied %s of %s source agents\n' "$actual" "$expected" >&2
+  exit 1
+fi
+echo "PASS: engineering install copies all $expected selected agents"