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.

docs/requirements.md

@@ -463,16 +463,21 @@ since ADR-0027.)
   per-item detail for relationships/indexes — is split out as
   **V5a** below so it has a tracked home rather than living as a
   footnote here.)*
-- [ ] **V5a** Singular per-item detail views `show relationship
+- [x] **V5a** Singular per-item detail views `show relationship
   <name>` / `show index <name>` — the `[<name>]` half of V5 for
   the relationship and index kinds (the table kind already has
-  `show table <name>`). Each names one item and renders its
-  detail (a relationship's endpoints + ON DELETE/UPDATE actions; an
-  index's table, columns, and uniqueness). Small follow-up on the
-  V5 machinery: a name slot after the `relationship` / `index`
-  keyword in `SHOW_CHOICES`, a lookup-one in the worker, and a
-  detail render. Not yet built; raised 2026-06-07 when V5's
-  list-all family shipped.
+  `show table <name>`).
+  *(Done 2026-06-07: folded into `Command::ShowList { kind, name:
+  Option<String> }` — `name: Some(_)` is the singular form. Two
+  grammar branches (`relationship <name>` / `index <name>`,
+  reusing the `Relationships`/`Indexes` completion sources for the
+  name slot), a worker `do_show_one` rendering a labelled detail
+  block (endpoints + ON DELETE/UPDATE for a relationship; table,
+  columns, uniqueness for an index) or a friendly "No relationship/
+  index named `X`." line, reusing the V5 `ShowList` render path.
+  Help + parse-usage entries + two ADR-0042 near-miss matrix rows;
+  5 added integration tests. V5's `[<name>]` clause is now
+  complete across all three kinds.)*
 - [x] **V6** Copy the output panel to the system clipboard
   (issue #11, ADR-0041). `copy` / `copy all` copy the whole
   panel; `copy last` copies the most recent command's output.

src/app.rs

@@ -2890,6 +2890,8 @@ mod tests {
             "show tables",
             "show relationships",
             "show indexes",
+            "show relationship",
+            "show index",
         ] {
             app.update(key(KeyCode::Tab));
             assert_eq!(app.input, expected);
@@ -2903,8 +2905,9 @@ mod tests {
     fn shift_tab_cycles_backward_starting_from_last() {
         let mut app = App::new();
         type_str(&mut app, "show ");
-        // Backward starts from the last candidate (`indexes`).
-        for expected in ["show indexes", "show relationships", "show tables"] {
+        // Backward starts from the last candidate (`index`, the
+        // V5a singular form).
+        for expected in ["show index", "show relationship", "show indexes"] {
             app.update(key(KeyCode::BackTab));
             assert_eq!(app.input, expected);
         }

src/completion.rs

@@ -1674,6 +1674,8 @@ mod tests {
                 "tables".to_string(),
                 "relationships".to_string(),
                 "indexes".to_string(),
+                "relationship".to_string(),
+                "index".to_string(),
             ],
         );
     }

src/db.rs

@@ -560,6 +560,9 @@ enum Request {
     /// from the same helpers the items panel and describe view use.
     ShowList {
         kind: crate::dsl::command::ShowListKind,
+        /// `None` lists all items of the kind; `Some(name)` shows
+        /// one named relationship/index's detail (V5a).
+        name: Option<String>,
         reply: oneshot::Sender<Result<Vec<String>, DbError>>,
     },
     DescribeTable {
@@ -1330,9 +1333,10 @@ impl Database {
     pub async fn show_list(
         &self,
         kind: crate::dsl::command::ShowListKind,
+        name: Option<String>,
     ) -> Result<Vec<String>, DbError> {
         let (reply, recv) = oneshot::channel();
-        self.send(Request::ShowList { kind, reply }).await?;
+        self.send(Request::ShowList { kind, name, reply }).await?;
         recv.await.map_err(|_| DbError::WorkerGone)?
     }
 
@@ -2264,8 +2268,8 @@ fn handle_request(
         Request::ListTables { reply } => {
             let _ = reply.send(do_list_tables(conn));
         }
-        Request::ShowList { kind, reply } => {
-            let _ = reply.send(do_show_list(conn, kind));
+        Request::ShowList { kind, name, reply } => {
+            let _ = reply.send(do_show_list(conn, kind, name.as_deref()));
         }
         Request::DescribeTable {
             name,
@@ -5865,8 +5869,13 @@ fn do_list_tables(conn: &Connection) -> Result<Vec<String>, DbError> {
 fn do_show_list(
     conn: &Connection,
     kind: crate::dsl::command::ShowListKind,
+    name: Option<&str>,
 ) -> Result<Vec<String>, DbError> {
     use crate::dsl::command::ShowListKind;
+    // V5a: a named item shows one relationship/index's detail.
+    if let Some(name) = name {
+        return do_show_one(conn, kind, name);
+    }
     let mut lines = Vec::new();
     match kind {
         ShowListKind::Tables => {
@@ -5929,6 +5938,64 @@ fn do_show_list(
     Ok(lines)
 }
 
+/// Detail lines for one named relationship or index (V5a): a
+/// labelled block, or a friendly "no such item" line. `Tables` is
+/// never routed here (the table singular is `ShowTable`); the
+/// defensive arm keeps the match total without a panic.
+fn do_show_one(
+    conn: &Connection,
+    kind: crate::dsl::command::ShowListKind,
+    name: &str,
+) -> Result<Vec<String>, DbError> {
+    use crate::dsl::command::ShowListKind;
+    let mut lines = Vec::new();
+    match kind {
+        ShowListKind::Relationships => match read_all_relationships(conn)?
+            .into_iter()
+            .find(|r| r.name == name)
+        {
+            None => lines.push(format!("No relationship named `{name}`.")),
+            Some(r) => {
+                lines.push(format!("Relationship `{}`:", r.name));
+                lines.push(format!(
+                    "  {}.{} → {}.{}",
+                    r.parent_table, r.parent_column, r.child_table, r.child_column
+                ));
+                lines.push(format!("  on delete {}", r.on_delete.keyword()));
+                lines.push(format!("  on update {}", r.on_update.keyword()));
+            }
+        },
+        ShowListKind::Indexes => {
+            // Find the user-created index by name across all tables.
+            let mut found = None;
+            for table in do_list_tables(conn)? {
+                if let Some(ix) = read_table_indexes(conn, &table)?
+                    .into_iter()
+                    .find(|ix| ix.name == name)
+                {
+                    found = Some((table, ix));
+                    break;
+                }
+            }
+            match found {
+                None => lines.push(format!("No index named `{name}`.")),
+                Some((table, ix)) => {
+                    lines.push(format!("Index `{}` on {table}:", ix.name));
+                    lines.push(format!("  columns: {}", ix.columns.join(", ")));
+                    lines.push(format!(
+                        "  unique: {}",
+                        if ix.unique { "yes" } else { "no" }
+                    ));
+                }
+            }
+        }
+        ShowListKind::Tables => {
+            lines.push(format!("No relationship or index named `{name}`."));
+        }
+    }
+    Ok(lines)
+}
+
 /// Internal full schema of a table, sufficient to regenerate
 /// its `CREATE TABLE` statement during the rebuild dance.
 #[derive(Debug, Clone)]

src/dsl/command.rs

@@ -332,12 +332,16 @@ pub enum Command {
     ShowTable {
         name: String,
     },
-    /// Re-display a whole schema collection — every table,
-    /// relationship, or index — as a list in the output (V5). The
-    /// read-only "all items" sibling of `ShowTable`; pure display,
-    /// no schema change.
+    /// Re-display a schema collection in the output (V5/V5a). With
+    /// `name: None`, the whole collection — every table,
+    /// relationship, or index (the list-all forms). With
+    /// `name: Some(_)`, one named item's detail — `show
+    /// relationship <name>` / `show index <name>` (V5a); the table
+    /// singular is the separate `ShowTable`, so a named `Tables`
+    /// never occurs. Read-only; pure display, no schema change.
     ShowList {
         kind: ShowListKind,
+        name: Option<String>,
     },
     /// Insert a single row. `columns` is `None` for the natural-
     /// order short form (`insert into T values (...)`); the
@@ -903,7 +907,17 @@ impl Command {
             Self::AddConstraint { .. } => "add constraint",
             Self::DropConstraint { .. } => "drop constraint",
             Self::ShowTable { .. } => "show table",
-            Self::ShowList { kind } => kind.command_name(),
+            // A named item reports the singular verb; the list-all
+            // forms report the plural (`kind.command_name()`).
+            Self::ShowList {
+                kind: ShowListKind::Relationships,
+                name: Some(_),
+            } => "show relationship",
+            Self::ShowList {
+                kind: ShowListKind::Indexes,
+                name: Some(_),
+            } => "show index",
+            Self::ShowList { kind, .. } => kind.command_name(),
             Self::Insert { .. } => "insert into",
             Self::Update { .. } => "update",
             Self::Delete { .. } => "delete from",

src/dsl/grammar/data.rs

@@ -107,12 +107,53 @@ const SHOW_TABLES: Node = Node::Word(Word::keyword("tables"));
 const SHOW_RELATIONSHIPS: Node = Node::Word(Word::keyword("relationships"));
 const SHOW_INDEXES: Node = Node::Word(Word::keyword("indexes"));
 
+// `show relationship <name>` / `show index <name>` — singular
+// per-item detail (V5a). The name slot reuses the existing
+// completion sources (relationship / index names). Distinct
+// keyword tokens from the plurals (`relationship` ≠
+// `relationships`), so Choice ordering is irrelevant.
+const SHOW_RELATIONSHIP_NAME: Node = Node::Ident {
+    source: IdentSource::Relationships,
+    role: "relationship_name",
+    validator: None,
+    highlight_override: None,
+    writes_table: false,
+    writes_column: false,
+    writes_user_listed_column: false,
+    writes_table_alias: false,
+    writes_cte_name: false,
+    writes_projection_alias: false,
+};
+const SHOW_RELATIONSHIP_NODES: &[Node] = &[
+    Node::Word(Word::keyword("relationship")),
+    SHOW_RELATIONSHIP_NAME,
+];
+const SHOW_RELATIONSHIP: Node = Node::Seq(SHOW_RELATIONSHIP_NODES);
+
+const SHOW_INDEX_NAME: Node = Node::Ident {
+    source: IdentSource::Indexes,
+    role: "index_name",
+    validator: None,
+    highlight_override: None,
+    writes_table: false,
+    writes_column: false,
+    writes_user_listed_column: false,
+    writes_table_alias: false,
+    writes_cte_name: false,
+    writes_projection_alias: false,
+};
+const SHOW_INDEX_NODES: &[Node] =
+    &[Node::Word(Word::keyword("index")), SHOW_INDEX_NAME];
+const SHOW_INDEX: Node = Node::Seq(SHOW_INDEX_NODES);
+
 const SHOW_CHOICES: &[Node] = &[
     SHOW_DATA,
     SHOW_TABLE,
     SHOW_TABLES,
     SHOW_RELATIONSHIPS,
     SHOW_INDEXES,
+    SHOW_RELATIONSHIP,
+    SHOW_INDEX,
 ];
 const SHOW_SHAPE: Node = Node::Choice(SHOW_CHOICES);
 
@@ -576,12 +617,24 @@ fn build_show(path: &MatchedPath, _source: &str) -> Result<Command, ValidationEr
         }),
         Some("tables") => Ok(Command::ShowList {
             kind: ShowListKind::Tables,
+            name: None,
         }),
         Some("relationships") => Ok(Command::ShowList {
             kind: ShowListKind::Relationships,
+            name: None,
         }),
         Some("indexes") => Ok(Command::ShowList {
             kind: ShowListKind::Indexes,
+            name: None,
+        }),
+        // V5a singular per-item detail — carry the named item.
+        Some("relationship") => Ok(Command::ShowList {
+            kind: ShowListKind::Relationships,
+            name: Some(require_ident(path, "relationship_name")?),
+        }),
+        Some("index") => Ok(Command::ShowList {
+            kind: ShowListKind::Indexes,
+            name: Some(require_ident(path, "index_name")?),
         }),
         _ => Err(ValidationError {
             message_key: "parse.error_wrapper",
@@ -1395,6 +1448,8 @@ pub static SHOW: CommandNode = CommandNode {
         "parse.usage.show_tables",
         "parse.usage.show_relationships",
         "parse.usage.show_indexes",
+        "parse.usage.show_relationship",
+        "parse.usage.show_index",
     ],};
 
 pub static INSERT: CommandNode = CommandNode {

src/friendly/keys.rs

@@ -311,6 +311,8 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
     ("parse.usage.show_tables", &[]),
     ("parse.usage.show_relationships", &[]),
     ("parse.usage.show_indexes", &[]),
+    ("parse.usage.show_relationship", &[]),
+    ("parse.usage.show_index", &[]),
     ("parse.usage.update", &[]),
     ("parse.usage.with", &[]),
     ("parse.expect.select_projection", &[]),

src/friendly/strings/en-US.yaml

@@ -325,6 +325,8 @@ help:
         show tables                — list all tables
         show relationships         — list all relationships
         show indexes               — list all indexes
+        show relationship <name>   — show one relationship's detail
+        show index <name>          — show one index's detail
     insert: |-
         insert into <T> [(cols)] [values] (vals)        — add a row
     update: |-
@@ -565,6 +567,8 @@ parse:
     show_tables: "show tables"
     show_relationships: "show relationships"
     show_indexes: "show indexes"
+    show_relationship: "show relationship <name>"
+    show_index: "show index <name>"
     insert: "insert into <Table> [(<col>[, ...])] [values] (<value>[, ...])"
     update: "update <Table> set <col>=<value>[, ...] (where <col>=<value> | --all-rows)"
     delete: "delete from <Table> (where <col>=<value> | --all-rows)"

src/input_render.rs

@@ -2061,6 +2061,8 @@ mod tests {
                 "tables".to_string(),
                 "relationships".to_string(),
                 "indexes".to_string(),
+                "relationship".to_string(),
+                "index".to_string(),
             ],
         );
     }

src/runtime.rs

@@ -2774,9 +2774,10 @@ async fn execute_command_typed(
             .describe_table(name, src)
             .await
             .map(|d| CommandOutcome::Schema(Some(d))),
-        Command::ShowList { kind } => {
-            database.show_list(kind).await.map(CommandOutcome::ShowList)
-        }
+        Command::ShowList { kind, name } => database
+            .show_list(kind, name)
+            .await
+            .map(CommandOutcome::ShowList),
         Command::Insert {
             table,
             columns,

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(),