diff --git a/scripts/install.sh b/scripts/install.sh
index 1ff20c47..a3c13dc6 100755
--- a/scripts/install.sh
+++ b/scripts/install.sh
@@ -176,6 +176,19 @@ division_files() {
 # division_count <division> — number of agents in a division.
 division_count() { division_files "$1" | grep -c . ; }
 
+# agent_slug_exists <slug> — verify a requested agent against the source roster.
+# Selection filters should fail before installation when they name nothing that
+# can be installed; otherwise dry-run counts and completion messages lie.
+agent_slug_exists() {
+  local target="$1" div f
+  for div in "${ALL_DIVISIONS[@]}"; do
+    while IFS= read -r f; do
+      [[ "$(agent_slug "$f")" == "$target" ]] && return 0
+    done < <(division_files "$div")
+  done
+  return 1
+}
+
 # build_selection — compute the allowed slug set from --division/--agent/--agents-file.
 # With no filter flags, SELECTION_ACTIVE stays false (install everything).
 build_selection() {
@@ -184,20 +197,32 @@ build_selection() {
     return
   fi
   SELECTION_ACTIVE=true
-  local slugs="" div f s line
+  local slugs="" div f s line requested
   for div in ${FILTER_DIVISIONS[@]+"${FILTER_DIVISIONS[@]}"}; do
     while IFS= read -r f; do
       s="$(agent_slug "$f")"; [[ -n "$s" ]] && slugs+="$s"$'\n'
     done < <(division_files "$div")
   done
-  for s in ${FILTER_AGENTS[@]+"${FILTER_AGENTS[@]}"}; do slugs+="$(slugify "$s")"$'\n'; done
+  for s in ${FILTER_AGENTS[@]+"${FILTER_AGENTS[@]}"}; do
+    requested="$(slugify "$s")"
+    if ! agent_slug_exists "$requested"; then
+      err "Unknown agent '$s'. Use --list agents to see the available roster."
+      exit 1
+    fi
+    slugs+="$requested"$'\n'
+  done
   if [[ -n "$AGENTS_FILE" ]]; then
     [[ -f "$AGENTS_FILE" ]] || { err "agents-file not found: $AGENTS_FILE"; exit 1; }
     while IFS= read -r line || [[ -n "$line" ]]; do
       line="${line%%#*}"                              # strip trailing comment
       line="$(printf '%s' "$line" | xargs 2>/dev/null)" # trim
       [[ -z "$line" ]] && continue
-      slugs+="$(slugify "$line")"$'\n'
+      requested="$(slugify "$line")"
+      if ! agent_slug_exists "$requested"; then
+        err "Unknown agent '$line' in agents-file '$AGENTS_FILE'."
+        exit 1
+      fi
+      slugs+="$requested"$'\n'
     done < "$AGENTS_FILE"
   fi
   _ALLOWED_SLUGS="$(printf '%s' "$slugs" | sort -u | sed '/^$/d')"
diff --git a/scripts/test-agent-selection.sh b/scripts/test-agent-selection.sh
new file mode 100755
index 00000000..5ce0561c
--- /dev/null
+++ b/scripts/test-agent-selection.sh
@@ -0,0 +1,44 @@
+#!/usr/bin/env bash
+# Regression coverage for install.sh agent-selection validation.
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+INSTALLER="$SCRIPT_DIR/install.sh"
+AGENTS_FILE="$(mktemp "${TMPDIR:-/tmp}/agency-agent-selection.XXXXXX")"
+trap 'rm -f "$AGENTS_FILE"' EXIT
+
+set +e
+output="$($INSTALLER --tool claude-code --agent definitely-not-an-agent --dry-run 2>&1)"
+status=$?
+set -e
+[[ "$status" -ne 0 ]] || {
+  printf 'Unknown --agent selection unexpectedly succeeded:\n%s\n' "$output" >&2
+  exit 1
+}
+[[ "$output" == *"Unknown agent"* ]] || {
+  printf 'Unknown --agent selection did not explain the error:\n%s\n' "$output" >&2
+  exit 1
+}
+
+printf '%s\n' 'definitely-not-an-agent' > "$AGENTS_FILE"
+set +e
+output="$($INSTALLER --tool claude-code --agents-file "$AGENTS_FILE" --dry-run 2>&1)"
+status=$?
+set -e
+[[ "$status" -ne 0 ]] || {
+  printf 'Unknown agents-file entry unexpectedly succeeded:\n%s\n' "$output" >&2
+  exit 1
+}
+[[ "$output" == *"in agents-file"* ]] || {
+  printf 'Unknown agents-file entry did not identify its source:\n%s\n' "$output" >&2
+  exit 1
+}
+
+output="$($INSTALLER --tool claude-code --agent 'Developer Tooling Engineer' --dry-run 2>&1)"
+[[ "$output" == *"Agents:  1"* ]] || {
+  printf 'Valid display-name selection did not resolve to one agent:\n%s\n' "$output" >&2
+  exit 1
+}
+
+echo "PASS: install.sh rejects unknown agent selections and accepts display names"