fix(install): preserve list-item indent when adding the Hermes plugin; regression test + CI (#714)

ensure_hermes_plugin_enabled() hardcoded a 2-space indent for the inserted `- agency-agents-router` line. Hermes writes plugins.enabled items at 4 spaces, so the new line and the next existing item collapsed into one plain scalar ("agency-agents-router - disk-cleanup") and every previously enabled plugin silently dropped (#839, and #689 diagnosed the same in July). The inserter now matches the existing item indent (default 4), appends after existing entries so order is preserved, and is idempotent on re-run. scripts/check-hermes-config-rewrite.{sh,py} runs seven regression cases; a small workflow runs it on every PR.

Reproduced on main with a 4-space config and verified fixed with this patch; installer suite 36/0; the regression script passes 7/7.

Fixes #839. Closes #689 (same fix, proposed first by @harshsinghmp).

Co-Authored-By: Harsh Singh <32476777+harshsinghmp@users.noreply.github.com>
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

scripts/check-hermes-config-rewrite.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+#
+# check-hermes-config-rewrite.sh — regression test for the
+# ensure_hermes_plugin_enabled() heredoc in scripts/install.sh.
+#
+# Reproduces and guards against the indent bug: the previous heredoc hardcoded
+# a 2-space indent when inserting into plugins.enabled, which broke any
+# config that used a different list-item indent (Hermes' default is 4 spaces).
+# Symptom: plugins.enabled collapses onto one line as a plain scalar string
+# when re-parsed, and the script's idempotency check fails to detect that
+# the plugin is already there.
+#
+# Usage: ./scripts/check-hermes-config-rewrite.sh
+# Exits non-zero on any failure. Mirrors scripts/check-X.sh style.
+
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+python3 scripts/check-hermes-config-rewrite.py