feat: V5a show relationship/index <name> detail views

Fold the singular per-item forms into Command::ShowList { kind,
name: Option<String> } (name: Some = one item). Two grammar
branches reuse the relationship/index completion sources; worker
do_show_one renders a labelled detail block or a friendly
"No ... named X." line, reusing the V5 render path. Help +
parse-usage entries, two ADR-0042 near-miss rows, 5 integration
tests. Mark V5a [x] — V5's [<name>] clause now complete.

tests/it/parse_error_pedagogy.rs

@@ -168,6 +168,8 @@ fn near_miss_matrix_committed_multiforms() {
         ("drop index on T", false, &["after `drop index on T`, expected `(`", "drop index on <Table>"]),
         ("drop relationship", false, &["after `drop relationship`, expected `from` or relationship name", "drop relationship <Name>"]),
         ("show table", false, &["after `show table`, expected table name", "show table <Table>"]),
+        ("show relationship", false, &["after `show relationship`, expected relationship name", "show relationship <name>"]),
+        ("show index", false, &["after `show index`, expected index name", "show index <name>"]),
         ("change column in table T: c", false, &["after `change column in table T: c`, expected `(`", "change column [in] [table]"]),
         // advanced committed multi-forms
         ("create index on", true, &["after `create index on`, expected table name", "create [unique] index"]),

tests/it/show_list.rs

@@ -33,7 +33,8 @@ fn show_tables_parses_as_show_list_tables() {
     assert_eq!(
         parse_command("show tables").expect("parses"),
         Command::ShowList {
-            kind: ShowListKind::Tables
+            kind: ShowListKind::Tables,
+            name: None,
         },
     );
 }
@@ -43,7 +44,8 @@ fn show_relationships_parses_as_show_list_relationships() {
     assert_eq!(
         parse_command("show relationships").expect("parses"),
         Command::ShowList {
-            kind: ShowListKind::Relationships
+            kind: ShowListKind::Relationships,
+            name: None,
         },
     );
 }
@@ -53,7 +55,30 @@ fn show_indexes_parses_as_show_list_indexes() {
     assert_eq!(
         parse_command("show indexes").expect("parses"),
         Command::ShowList {
-            kind: ShowListKind::Indexes
+            kind: ShowListKind::Indexes,
+            name: None,
+        },
+    );
+}
+
+#[test]
+fn show_relationship_singular_parses_with_name() {
+    assert_eq!(
+        parse_command("show relationship orders_customer").expect("parses"),
+        Command::ShowList {
+            kind: ShowListKind::Relationships,
+            name: Some("orders_customer".to_string()),
+        },
+    );
+}
+
+#[test]
+fn show_index_singular_parses_with_name() {
+    assert_eq!(
+        parse_command("show index idx_orders_customer").expect("parses"),
+        Command::ShowList {
+            kind: ShowListKind::Indexes,
+            name: Some("idx_orders_customer".to_string()),
         },
     );
 }
@@ -145,7 +170,7 @@ fn show_tables_lists_all_user_tables_with_count_header() {
     let rt = rt();
     rt.block_on(seed_schema(&db));
     let lines = rt
-        .block_on(db.show_list(ShowListKind::Tables))
+        .block_on(db.show_list(ShowListKind::Tables, None))
         .expect("show tables");
     assert_eq!(lines[0], "Tables (2):", "count header");
     assert!(
@@ -164,7 +189,7 @@ fn show_relationships_lists_name_endpoints_and_nondefault_action() {
     let rt = rt();
     rt.block_on(seed_schema(&db));
     let lines = rt
-        .block_on(db.show_list(ShowListKind::Relationships))
+        .block_on(db.show_list(ShowListKind::Relationships, None))
         .expect("show relationships");
     assert_eq!(lines[0], "Relationships (1):");
     // Name, both endpoints, and the non-default ON DELETE CASCADE
@@ -182,7 +207,7 @@ fn show_indexes_lists_qualified_name_and_columns() {
     let rt = rt();
     rt.block_on(seed_schema(&db));
     let lines = rt
-        .block_on(db.show_list(ShowListKind::Indexes))
+        .block_on(db.show_list(ShowListKind::Indexes, None))
         .expect("show indexes");
     assert_eq!(lines[0], "Indexes (1):");
     assert_eq!(
@@ -197,20 +222,76 @@ fn show_lists_report_empty_collections_with_friendly_lines() {
     let rt = rt();
     // No schema seeded — every kind is empty.
     assert_eq!(
-        rt.block_on(db.show_list(ShowListKind::Tables)).unwrap(),
+        rt.block_on(db.show_list(ShowListKind::Tables, None)).unwrap(),
         vec!["No tables in this project yet.".to_string()],
     );
     assert_eq!(
-        rt.block_on(db.show_list(ShowListKind::Relationships))
+        rt.block_on(db.show_list(ShowListKind::Relationships, None))
             .unwrap(),
         vec!["No relationships in this project yet.".to_string()],
     );
     assert_eq!(
-        rt.block_on(db.show_list(ShowListKind::Indexes)).unwrap(),
+        rt.block_on(db.show_list(ShowListKind::Indexes, None)).unwrap(),
         vec!["No indexes in this project yet.".to_string()],
     );
 }
 
+// =================================================================
+// V5a — singular per-item detail
+// =================================================================
+
+#[test]
+fn show_one_relationship_renders_detail_block() {
+    let (_p, db, _dir) = open_project_db();
+    let rt = rt();
+    rt.block_on(seed_schema(&db));
+    let lines = rt
+        .block_on(db.show_list(ShowListKind::Relationships, Some("orders_customer".to_string())))
+        .expect("show relationship");
+    assert_eq!(lines[0], "Relationship `orders_customer`:");
+    assert_eq!(lines[1], "  Customers.id → Orders.customer_id");
+    assert!(
+        lines.iter().any(|l| l == "  on delete cascade"),
+        "on-delete shown: {lines:?}",
+    );
+}
+
+#[test]
+fn show_one_index_renders_detail_block() {
+    let (_p, db, _dir) = open_project_db();
+    let rt = rt();
+    rt.block_on(seed_schema(&db));
+    let lines = rt
+        .block_on(db.show_list(ShowListKind::Indexes, Some("idx_orders_customer".to_string())))
+        .expect("show index");
+    assert_eq!(lines[0], "Index `idx_orders_customer` on Orders:");
+    assert!(
+        lines.iter().any(|l| l == "  columns: customer_id"),
+        "columns shown: {lines:?}",
+    );
+    assert!(
+        lines.iter().any(|l| l == "  unique: no"),
+        "uniqueness shown: {lines:?}",
+    );
+}
+
+#[test]
+fn show_one_unknown_name_reports_friendly_not_found() {
+    let (_p, db, _dir) = open_project_db();
+    let rt = rt();
+    rt.block_on(seed_schema(&db));
+    assert_eq!(
+        rt.block_on(db.show_list(ShowListKind::Relationships, Some("nope".to_string())))
+            .unwrap(),
+        vec!["No relationship named `nope`.".to_string()],
+    );
+    assert_eq!(
+        rt.block_on(db.show_list(ShowListKind::Indexes, Some("nope".to_string())))
+            .unwrap(),
+        vec!["No index named `nope`.".to_string()],
+    );
+}
+
 // =================================================================
 // App end-to-end
 // =================================================================
@@ -241,7 +322,8 @@ fn app_show_tables_dispatches_show_list_command() {
             a,
             Action::ExecuteDsl {
                 command: Command::ShowList {
-                    kind: ShowListKind::Tables
+                    kind: ShowListKind::Tables,
+                    name: None,
                 },
                 ..
             }
@@ -262,6 +344,7 @@ fn app_renders_show_list_lines_as_system_output() {
     app.update(AppEvent::DslShowListSucceeded {
         command: Command::ShowList {
             kind: ShowListKind::Tables,
+            name: None,
         },
         lines: vec!["Tables (1):".to_string(), "  Customers".to_string()],
     });

tests/typing_surface/mod.rs

@@ -233,7 +233,7 @@ fn command_kind_label(cmd: &rdbms_playground::dsl::Command) -> String {
         AddConstraint { .. } => "AddConstraint".into(),
         DropConstraint { .. } => "DropConstraint".into(),
         ShowTable { .. } => "ShowTable".into(),
-        ShowList { kind } => format!("ShowList({kind:?})"),
+        ShowList { kind, name } => format!("ShowList({kind:?}, {})", name.is_some()),
         Insert { .. } => "Insert".into(),
         Update { .. } => "Update".into(),
         Delete { .. } => "Delete".into(),