Add support for multiple PostgreSQL DSN candidates

This update introduces `PG_DSN_CANDIDATES` for specifying multiple DSN options, improving compatibility and CI portability. The script now attempts connections sequentially using the provided candidates before falling back to single DSN or raising an error. Relevant updates to documentation and workflow configuration have also been made.

.github/workflows/pg-compat-matrix.yml

@@ -43,5 +43,5 @@ jobs:
 
       - name: Run PostgreSQL compatibility smoke checks
         env:
-          PG_DSN: postgresql://postgres:postgres@127.0.0.1:5432/compatdb?sslmode=disable
+          PG_DSN_CANDIDATES: postgresql://postgres:postgres@postgres:5432/compatdb?sslmode=disable,postgresql://postgres:postgres@127.0.0.1:5432/compatdb?sslmode=disable
         run: python backend/scripts/pg_compat_smoke.py

README.md

@@ -106,6 +106,13 @@ PG_DSN='postgresql://postgres:postgres@127.0.0.1:5432/compatdb?sslmode=disable'
 python backend/scripts/pg_compat_smoke.py
 ```
 
+CI/runner-safe variant (tries multiple hosts):
+
+```bash
+PG_DSN_CANDIDATES='postgresql://postgres:postgres@postgres:5432/compatdb?sslmode=disable,postgresql://postgres:postgres@127.0.0.1:5432/compatdb?sslmode=disable' \
+python backend/scripts/pg_compat_smoke.py
+```
+
 ## Environment variables reference
 
 All variables are defined in `.env.example`.

backend/scripts/pg_compat_smoke.py

@@ -31,13 +31,39 @@ async def _fetchrow_required(conn: asyncpg.Connection, query: str, label: str) -
     return dict(row)
 
 
+def _dsn_candidates() -> list[str]:
+    # Preferred: explicit candidate list for CI portability (Gitea/GitHub runners).
+    raw_candidates = os.getenv("PG_DSN_CANDIDATES", "").strip()
+    if raw_candidates:
+        values = [item.strip() for item in raw_candidates.split(",") if item.strip()]
+        if values:
+            return values
+    # Backward compatible single DSN.
+    raw_single = os.getenv("PG_DSN", "").strip()
+    if raw_single:
+        return [raw_single]
+    raise RuntimeError("Missing PG_DSN or PG_DSN_CANDIDATES")
+
+
 async def run() -> None:
-    dsn = _required_env("PG_DSN")
+    candidates = _dsn_candidates()
+    last_error: Exception | None = None
+    conn: asyncpg.Connection | None = None
+    used_dsn = ""
+    for dsn in candidates:
+        try:
             conn = await _connect_with_retry(dsn)
+            used_dsn = dsn
+            break
+        except Exception as exc:
+            last_error = exc
+    if conn is None:
+        raise RuntimeError(f"Could not connect to PostgreSQL using candidates: {last_error}")
+
     try:
         version = await conn.fetchval("SHOW server_version")
         current_db = await conn.fetchval("SELECT current_database()")
-        print(f"[compat] Connected: version={version} db={current_db}")
+        print(f"[compat] Connected: version={version} db={current_db} dsn={used_dsn}")
 
         # Core collector queries
         await _fetchrow_required(