test: match tests to canonical "does not exist" absent-collection error

Update expected error substrings from the legacy "not found" / "unknown
table" wording to the canonical "does not exist" (SQLSTATE 42P01), still
accepting the older wordings where cross-tenant isolation semantics
require it.

Author: farhan-syah

nodedb/tests/database_boundary.rs

@@ -234,9 +234,12 @@ async fn cross_database_collection_looks_absent() {
     server
         .expect_error(
             "SELECT * FROM cross_secret",
-            // The error must match the "not found" family; it must NOT
-            // mention a distinct "database boundary" code.
-            "not found",
+            // Must surface as the canonical absent-collection error
+            // (`does not exist`, SQLSTATE 42P01) — indistinguishable from a
+            // truly-absent collection. It must NOT mention a distinct
+            // "database boundary" code that would leak the collection's
+            // existence in another database.
+            "does not exist",
         )
         .await;
 }

nodedb/tests/pgwire_returning_dml.rs

@@ -252,7 +252,7 @@ async fn unicode_identifier_before_returning_preserves_connection() {
     let server = TestServer::start().await;
 
     server
-        .expect_error("DELETE FROM missingffff RETURNING *", "not found")
+        .expect_error("DELETE FROM missingffff RETURNING *", "does not exist")
         .await;
     let rows = server
         .query_text("SELECT 1")

nodedb/tests/pgwire_tenant_scoping.rs

@@ -196,12 +196,15 @@ async fn tenant_user_cannot_see_other_tenants_collection_as_empty() {
     let result = query_as(&server, "svc_xtn", "SELECT secret FROM t1_only").await;
     match result {
         Err(msg) => {
-            // Accept both legacy "unknown table" and the canonical
-            // "table not found" wording — semantics are identical
-            // (cross-tenant isolation enforced via lookup failure).
+            // Cross-tenant isolation is enforced via lookup failure: the
+            // collection must appear absent. Accept the legacy "unknown table"
+            // / "table not found" wordings and the now-canonical
+            // "does not exist" (SQLSTATE 42P01) — semantics are identical.
             let lower = msg.to_lowercase();
             assert!(
-                lower.contains("unknown table") || lower.contains("table not found"),
+                lower.contains("unknown table")
+                    || lower.contains("table not found")
+                    || lower.contains("does not exist"),
                 "expected isolation error, got: {msg}"
             );
         }