feat(2): Q4.6 discourse — recipe_meta + postgres P4 overlays + health (WIP, §4.3 create-topic next)

discourse (forum: postgres+redis+sidekiq). HEALTH_PATH=/srv/status (slow Rails boot, DEPLOY_TIMEOUT=1800).
P4 via postgres ci_marker (db service, pg_dump backupbot — matrix-synapse pattern). Health functional
test. §4.3 create-a-topic + PARITY.md to follow after smoke discovers the admin/API bootstrap path.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/discourse/test_backup.py

@@ -0,0 +1,26 @@
+"""discourse — BACKUP overlay (Phase 1e HC3 / Phase 2 P4): assertion-only + additive.
+
+ops.pre_backup seeded ci_marker='original' into the discourse postgres DB (which the recipe's
+backupbot pre-hook pg_dumps). This overlay ADDS: the seeded row is intact at backup time. The
+backup→restore divergence (dropping the table) is in ops.pre_restore.
+"""
+
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "runner"))
+from harness import lifecycle  # noqa: E402
+
+
+def _psql(domain, sql):
+    cmd = (
+        'PGPASSWORD=$(cat /run/secrets/db_password) '
+        f'psql -U discourse -d discourse -tAc "{sql}"'
+    )
+    return lifecycle.exec_in_app(domain, ["sh", "-c", cmd], service="db").strip()
+
+
+def test_backup_captures_state(live_app):
+    assert _psql(live_app, "SELECT v FROM ci_marker;") == "original", (
+        "the seeded discourse postgres state was not present at backup time"
+    )