fix(db): prevent POSTGRES_HOST env var leakage between tests

resetEnv() conditionally set POSTGRES_HOST only when empty. When
TestConnect_InvalidCredentials explicitly set it to 'localhost' and
then called resetEnv(), the value was preserved because it wasn't
empty. This leaked into TestConcurrentQueries, which then tried to
connect to localhost:5432 instead of the workflow-configured postgres
hostname.

Fix: capture the POSTGRES_HOST value at init() time in a package-level
variable (savedPOSTGRESHost) and always restore it in resetEnv(), so
the correct value is always used regardless of which tests ran before.

.gitea/workflows/backend-tests.yaml

@@ -60,9 +60,7 @@ jobs:
 
       - name: Test (all packages)
         working-directory: backend
-        run: |
-          echo "POSTGRES_HOST=$POSTGRES_HOST TEST_DB_HOST=$TEST_DB_HOST"
-          go test -tags "test,dev" -count=1 -v -timeout 120s ./handlers/... ./auth/... ./mw/... ./internal/... ./db/...
+        run: go test -tags "test,dev" -count=1 -v -timeout 120s ./handlers/... ./auth/... ./mw/... ./internal/... ./db/...
         env:
           POSTGRES_HOST: postgres
           TEST_DB_HOST: postgres

backend/db/db_test.go

@@ -14,9 +14,7 @@ import (
 func resetEnv() {
 	os.Setenv("POSTGRES_USER", "myuser")
 	os.Setenv("POSTGRES_PASSWORD", "mypassword")
-	if os.Getenv("POSTGRES_HOST") == "" {
-		os.Setenv("POSTGRES_HOST", "localhost")
-	}
+	os.Setenv("POSTGRES_HOST", savedPOSTGRESHost)
 	os.Setenv("POSTGRES_DB", "crussell_test_db")
 }
 

backend/db/db_test_init.go

@@ -9,11 +9,16 @@ import (
 
 // DB is a compatibility alias for Conn, for tests not yet migrated from db.Conn to db.Conn.
 
+// savedPOSTGRESHost captures the env value at init time so resetEnv() can
+// always restore it, even after a test temporarily overrides it.
+var savedPOSTGRESHost string
+
 func init() {
 	// Set defaults for test environment if not already set
 	if os.Getenv("POSTGRES_HOST") == "" {
 		os.Setenv("POSTGRES_HOST", "localhost")
 	}
+	savedPOSTGRESHost = os.Getenv("POSTGRES_HOST")
 	if os.Getenv("POSTGRES_USER") == "" {
 		os.Setenv("POSTGRES_USER", "myuser")
 	}