ADR-0027: existing-cases sweep + docs (step F)

Sweep: input_verdict tests confirm the schema-existence check
fires across the identifier-taking commands — unknown table
on drop / show / add column, unknown column on drop column /
update — and that known references stay clean. The Step B
check is grammar-generic, so this is verification + coverage
rather than new code.

Docs: requirements.md S6 -> [x], baseline 1096; CLAUDE.md
deferred list reconciled (C5a and S6 are done — removed);
ADR-0026's as-built note updated (step 5 shipped via
ADR-0027); ADR-0027 gains an As-built notes section
recording the post-walk diagnostics realization, the
pre-rendered message, the timeout-based debounce, coarse
WARNING spans, and the deferred highlight/hint wiring.

src/dsl/walker/mod.rs

@@ -1679,6 +1679,63 @@ mod tests {
         );
     }
 
+    // ---- Existing-cases sweep (ADR-0027 §6) -------------------
+
+    #[test]
+    fn input_verdict_sweep_unknown_table_across_commands() {
+        let schema = schema_with("Customers", &[("id", Type::Int)]);
+        for input in [
+            "drop table NoSuchTable",
+            "show table NoSuchTable",
+            "show data NoSuchTable",
+            "add column to NoSuchTable: x (int)",
+        ] {
+            assert_eq!(
+                super::input_verdict(input, Some(&schema)),
+                Some(super::Severity::Error),
+                "unknown table in {input:?} should be flagged",
+            );
+        }
+    }
+
+    #[test]
+    fn input_verdict_sweep_unknown_column_across_commands() {
+        let schema = schema_with(
+            "Customers",
+            &[("id", Type::Int), ("Name", Type::Text)],
+        );
+        for input in [
+            "drop column from table Customers: NoSuchCol",
+            "update Customers set NoSuchCol = 1 where id = 1",
+        ] {
+            assert_eq!(
+                super::input_verdict(input, Some(&schema)),
+                Some(super::Severity::Error),
+                "unknown column in {input:?} should be flagged",
+            );
+        }
+    }
+
+    #[test]
+    fn input_verdict_known_entities_across_commands_are_clean() {
+        let schema = schema_with(
+            "Customers",
+            &[("id", Type::Int), ("Name", Type::Text)],
+        );
+        for input in [
+            "show table Customers",
+            "drop table Customers",
+            "add column to Customers: Email (text)",
+            "drop column from table Customers: Name",
+        ] {
+            assert_eq!(
+                super::input_verdict(input, Some(&schema)),
+                None,
+                "{input:?} references only known entities — clean",
+            );
+        }
+    }
+
     #[test]
     fn walker_parses_insert_with_explicit_column_list() {
         assert_eq!(