grammar: SQL SELECT end-to-end (ADR-0030 Phase 1)

The first cut of advanced-mode SQL: a `select` line in advanced
mode parses, runs against the database, and renders its rows
through the existing data-table renderer; the same line in
simple mode lights up the precise "this is SQL" hint instead of
running.

Walker mode gate (ADR-0030 §2)
------------------------------
- `WalkContext` gains a `mode: Mode` field; `Mode` derives
  `Default` (= `Simple`, matching the app's startup mode).
- `grammar::is_advanced_only` keys an advanced-only entry-word
  set (Phase 1: just `select`). When the walker matches an
  advanced-only entry word with `ctx.mode == Simple`, it
  short-circuits to a `WalkOutcome::ValidationFailed` carrying
  the `advanced_mode.sql_in_simple` catalog key — the input
  highlights as a keyword, the validity indicator goes ERROR,
  and the parse-error layer renders the "switch with `mode
  advanced`, or prefix the line with `:`" hint.
- `parser::parse_command_with_schema_in_mode` (and the
  schemaless `parse_command_in_mode`) threads the mode into
  `WalkContext`; existing `parse_command*` entry points default
  to `Mode::Advanced` (most permissive) so back-compat callers
  see the full grammar.
- `App::submit` is unified: both modes route through
  `dispatch_dsl(&effective_input, effective_mode)`, which now
  parses with the line's effective mode. The placeholder
  advanced-mode echo branch is gone.

Builder signature sweep (ADR-0031 §2)
-------------------------------------
- `CommandNode.ast_builder` gains a `source: &str` parameter,
  forwarded by the walker. `build_select` reads it to put the
  validated SQL text into `Command::Select`; the 21 existing
  builders accept it as `_source`.

SQL `SELECT` (ADR-0030 §6, ADR-0031)
-------------------------------------
- New `Command::Select { sql: String }` variant. Every
  exhaustive `match Command` updated (`verb`, `target_table`,
  `build_translate_context`, `execute_command_typed`,
  `typing_surface`'s label).
- `grammar::data::SELECT` `CommandNode`: projection (`*` or
  `expr [as alias]` list), optional `FROM <table>`, optional
  `WHERE`/`ORDER BY`/`LIMIT`, optional trailing `;`. The
  expression slots reference the ADR-0031 fragment through
  `Subgrammar(&sql_expr::SQL_OR_EXPR)`. The `FROM` table-name
  slot carries a `reject_internal_table` validator that
  refuses `__rdbms_*` references at parse time.
- The `FROM` clause is optional — `select 1`, `select upper('x')`
  (zero-table constant/function-call SELECTs) work alongside
  the single-table form. Standard SQL admits them and they are
  the canonical learner probe.
- Implicit projection aliasing (`select a x`) is deliberately
  unsupported — `from` is a keyword, the bare alias would be
  ambiguous; only `select a as x` is admitted.

Worker / runtime
----------------
- `Request::RunSelect { sql, source, reply }` + a new
  `Database::run_select` method. `do_run_select_request` runs
  the prepared statement, collects rows into a `DataResult`
  with `column_types: Vec<None>` (Phase-1 SELECT result columns
  carry no playground type per ADR-0030 §6), and appends the
  literal source line to `history.log` so replay re-runs it
  (ADR-0030 §11).
- `runtime::execute_command_typed` gains a `Command::Select`
  arm that calls `database.run_select(sql, src)` and maps to
  `CommandOutcome::Query`, which flows into the existing
  `AppEvent::DslDataSucceeded` → `render_data_table` path.

Catalog (ADR-0019)
------------------
- `advanced_mode.sql_in_simple` — the walker's gate message.
- `select.internal_table` — the `__rdbms_*` rejection.
- `parse.usage.select` — the parse-error usage template.

Tests
-----
Two `app::tests` cases that pinned the pre-ADR-0030 placeholder
echo are updated to pin the new dispatch contract — both verify
that the advanced-mode `select` (one persistent, one via the
`:` one-shot) produces `ExecuteDsl(Command::Select)` with the
submission's effective mode tagged on the echo. The matching
walking-skeleton test is updated likewise.

A separate follow-up commit lands the ambient mode-threading
(completion / live overlay / validity indicator) so simple-mode
users do not see SQL surfaced through Tab or the live error
overlay either — the dispatch-layer gate landed here is the
behavioural foundation that follow-up builds on. Integration
tests for the full end-to-end land in a third commit.

src/app.rs

@@ -990,27 +990,12 @@ impl App {
             return self.dispatch_app_command(app_cmd, &effective_input);
         }
 
-        // For everything else: dispatch by effective mode.
-        match effective_mode {
-            Mode::Simple => self.dispatch_dsl(&effective_input, effective_mode),
-            Mode::Advanced => {
-                // SQL handling is not implemented yet; show a placeholder
-                // until the advanced-mode SQL path lands. Once it does,
-                // this branch parses with sqlparser-rs and dispatches
-                // analogously to the DSL path below.
-                self.note_system(crate::t!(
-                    "advanced_mode.not_implemented",
-                    input = effective_input
-                ));
-                self.push_output(OutputLine {
-                    text: effective_input,
-                    kind: OutputKind::Echo,
-                    mode_at_submission: effective_mode,
-                    styled_runs: None,
-                });
-                Vec::new()
-            }
-        }
+        // For everything else: unified dispatch. `dispatch_dsl`
+        // parses with `effective_mode` (ADR-0030 §2), so a SQL
+        // form in advanced mode runs and a SQL form in simple
+        // mode yields the precise "this is SQL" hint through the
+        // walker's mode gate — no separate placeholder branch.
+        self.dispatch_dsl(&effective_input, effective_mode)
     }
 
     /// Dispatch a parsed app-lifecycle command. Works in both
@@ -1091,7 +1076,16 @@ impl App {
         // value slots (insert-into-T-values-…) dispatch on the
         // column's actual user-facing type instead of accepting
         // any literal at bind time.
-        match crate::dsl::parser::parse_command_with_schema(input, &self.schema_cache) {
+        //
+        // ADR-0030 §2: parse with the submission's effective
+        // mode so the walker gates SQL-only forms — simple-mode
+        // `select` returns the "this is SQL" hint as a normal
+        // parse error and is rendered through the Err arm below.
+        match crate::dsl::parser::parse_command_with_schema_in_mode(
+            input,
+            &self.schema_cache,
+            submission_mode,
+        ) {
             Ok(Command::Replay { path }) => {
                 // `replay` is parsed as a DSL command for the
                 // sake of grammar uniformity, but its execution
@@ -1443,6 +1437,10 @@ impl App {
             C::ShowData { name, .. } | C::ShowTable { name } => {
                 (Operation::Query, Some(name.as_str()), None)
             }
+            // A SQL `SELECT` carries only its statement text —
+            // no single table name to fall back on. A query
+            // failure routes through `Operation::Query`.
+            C::Select { .. } => (Operation::Query, None, None),
             C::Replay { .. } => (Operation::Replay, None, None),
             // An `explain` failure (e.g. unknown table) is best
             // described by the wrapped query it failed to plan.
@@ -2270,19 +2268,40 @@ mod tests {
     }
 
     #[test]
-    fn enter_in_advanced_mode_echoes_with_advanced_tag() {
+    fn enter_in_advanced_mode_dispatches_select_with_advanced_tag() {
+        // The pre-ADR-0030 placeholder echoed any advanced-mode
+        // input back unexecuted; with the SQL surface live, a
+        // `select` in advanced mode runs through `dispatch_dsl`
+        // exactly like a DSL command, producing the standard
+        // `running: …` echo and an `ExecuteDsl(Command::Select)`
+        // action. The mode-tag invariant — that the echo carries
+        // the submission's effective mode — is what this test
+        // pins down.
         let mut app = App::new();
         app.mode = Mode::Advanced;
         type_str(&mut app, "select 1");
-        submit(&mut app);
-        // We expect a placeholder system line plus the echoed line.
+        let actions = submit(&mut app);
         let echoed = app
             .output
             .iter()
             .rfind(|l| l.kind == OutputKind::Echo)
             .unwrap();
         assert_eq!(echoed.mode_at_submission, Mode::Advanced);
-        assert_eq!(echoed.text, "select 1");
+        assert!(
+            echoed.text.contains("select 1"),
+            "echo line carries the input: {:?}",
+            echoed.text,
+        );
+        assert!(
+            matches!(
+                actions.as_slice(),
+                [Action::ExecuteDsl {
+                    command: Command::Select { .. },
+                    ..
+                }],
+            ),
+            "advanced-mode `select` should produce ExecuteDsl(Select); got {actions:?}",
+        );
     }
 
     #[test]
@@ -2326,17 +2345,36 @@ mod tests {
     fn colon_prefix_in_simple_mode_evaluates_as_advanced_one_shot() {
         let mut app = App::new();
         type_str(&mut app, ":select 1");
-        submit(&mut app);
+        let actions = submit(&mut app);
         // The persistent mode is unchanged.
         assert_eq!(app.mode, Mode::Simple);
-        // The advanced echo line is present.
         let echoed = app
             .output
             .iter()
             .rfind(|l| l.kind == OutputKind::Echo)
             .unwrap();
+        // The line ran under the one-shot effective mode, so
+        // the echo carries the Advanced tag…
         assert_eq!(echoed.mode_at_submission, Mode::Advanced);
-        assert_eq!(echoed.text, "select 1");
+        // …and the `:` is stripped before dispatch (the SQL
+        // executed is `select 1`, not `:select 1`).
+        assert!(
+            echoed.text.contains("select 1") && !echoed.text.contains(":select"),
+            "echo carries the stripped input: {:?}",
+            echoed.text,
+        );
+        // The one-shot dispatched the SELECT through the same
+        // path as a persistent-advanced submission.
+        assert!(
+            matches!(
+                actions.as_slice(),
+                [Action::ExecuteDsl {
+                    command: Command::Select { .. },
+                    ..
+                }],
+            ),
+            "`:select 1` should produce ExecuteDsl(Select); got {actions:?}",
+        );
     }
 
     #[test]

src/db.rs

@@ -567,6 +567,19 @@ enum Request {
         source: Option<String>,
         reply: oneshot::Sender<Result<DataResult, DbError>>,
     },
+    /// Run a SQL `SELECT` typed by the user in advanced mode
+    /// (ADR-0030 §6, ADR-0031). The grammar walker has already
+    /// validated `sql` is in the supported subset; the worker
+    /// prepares and runs the statement and returns the rows as
+    /// a [`DataResult`] (with no playground type information per
+    /// ADR-0030 §6 — computed columns render with neutral
+    /// alignment). `source` is the literal submitted line,
+    /// appended to `history.log` for replay (ADR-0030 §11).
+    RunSelect {
+        sql: String,
+        source: Option<String>,
+        reply: oneshot::Sender<Result<DataResult, DbError>>,
+    },
     /// Capture the query plan for an explainable command via
     /// `EXPLAIN QUERY PLAN` (ADR-0028 §2). `query` is the inner
     /// `ShowData` / `Update` / `Delete`; `EXPLAIN QUERY PLAN`
@@ -1010,6 +1023,20 @@ impl Database {
         recv.await.map_err(|_| DbError::WorkerGone)?
     }
 
+    /// Run a validated SQL `SELECT` and return the rows
+    /// (ADR-0030 §6, ADR-0031). `sql` is the grammar-validated
+    /// statement text; `source` is the literal submitted line
+    /// for `history.log`.
+    pub async fn run_select(
+        &self,
+        sql: String,
+        source: Option<String>,
+    ) -> Result<DataResult, DbError> {
+        let (reply, recv) = oneshot::channel();
+        self.send(Request::RunSelect { sql, source, reply }).await?;
+        recv.await.map_err(|_| DbError::WorkerGone)?
+    }
+
     /// Capture the query plan for an explainable command
     /// (ADR-0028 §2). The wrapped command is not executed —
     /// `EXPLAIN QUERY PLAN` only inspects how the engine would
@@ -1447,6 +1474,14 @@ fn handle_request(conn: &Connection, persistence: Option<&Persistence>, req: Req
                 limit,
             ));
         }
+        Request::RunSelect { sql, source, reply } => {
+            let _ = reply.send(do_run_select_request(
+                conn,
+                persistence,
+                source.as_deref(),
+                &sql,
+            ));
+        }
         Request::RebuildFromText {
             project_path,
             source,
@@ -5645,6 +5680,69 @@ fn do_query_data_request(
     Ok(data)
 }
 
+/// Worker handler for `Request::RunSelect` (ADR-0030 §6,
+/// ADR-0031). Mirrors `do_query_data_request`: run the
+/// statement, append the literal line to `history.log` so a
+/// replay re-runs it (ADR-0030 §11).
+fn do_run_select_request(
+    conn: &Connection,
+    persistence: Option<&Persistence>,
+    source: Option<&str>,
+    sql: &str,
+) -> Result<DataResult, DbError> {
+    let data = do_run_select(conn, sql)?;
+    if let (Some(p), Some(text)) = (persistence, source) {
+        p.append_history(text)
+            .map_err(DbError::from_persistence)?;
+    }
+    Ok(data)
+}
+
+/// Execute a grammar-validated SQL `SELECT` and collect its
+/// rows into a [`DataResult`] (ADR-0030 §6).
+///
+/// All result columns are reported with `column_types = None` —
+/// a SELECT result has no playground type unless we resolve
+/// each output column back to its source column, which is a
+/// Phase-2 (full `SELECT`) concern. The DSL data-table renderer
+/// (ADR-0016) renders typeless columns with neutral alignment.
+fn do_run_select(conn: &Connection, sql: &str) -> Result<DataResult, DbError> {
+    debug!(sql = %sql, "run_select");
+    let mut stmt = conn.prepare(sql).map_err(DbError::from_rusqlite)?;
+    let column_names: Vec<String> = stmt
+        .column_names()
+        .into_iter()
+        .map(String::from)
+        .collect();
+    let col_count = column_names.len();
+    let column_types: Vec<Option<Type>> = vec![None; col_count];
+    let rows_iter = stmt
+        .query_map([], |row| {
+            let mut cells: Vec<rusqlite::types::Value> = Vec::with_capacity(col_count);
+            for i in 0..col_count {
+                cells.push(row.get(i)?);
+            }
+            Ok(cells)
+        })
+        .map_err(DbError::from_rusqlite)?;
+    let mut rows: Vec<Vec<Option<String>>> = Vec::new();
+    for r in rows_iter {
+        let cells = r.map_err(DbError::from_rusqlite)?;
+        rows.push(
+            cells
+                .into_iter()
+                .map(|v| format_cell(v, None))
+                .collect(),
+        );
+    }
+    Ok(DataResult {
+        table_name: String::new(),
+        columns: column_names,
+        column_types,
+        rows,
+    })
+}
+
 /// Build the parameterised `SELECT … FROM …` statement for a
 /// `show data` query (ADR-0026 §5–§6). Separated from
 /// `do_query_data` so the `explain` path runs `EXPLAIN QUERY

src/dsl/command.rs

@@ -283,6 +283,15 @@ pub enum Command {
     Explain {
         query: Box<Self>,
     },
+    /// Run a SQL `SELECT` and render its result set (ADR-0030
+    /// §6, ADR-0031). Advanced mode only. `sql` is the validated
+    /// SQL statement text: a `SELECT` changes no schema, so it is
+    /// carried and executed as text rather than lowered to a
+    /// typed command (ADR-0030 §4). The walker has already
+    /// confirmed it is in the supported subset.
+    Select {
+        sql: String,
+    },
     /// App-lifecycle command (per ADR-0003). These work in both
     /// simple and advanced modes; the dispatcher branches on the
     /// `Command::App(...)` variant before mode-specific routing.
@@ -577,6 +586,7 @@ impl Command {
             Self::ShowData { .. } => "show data",
             Self::Replay { .. } => "replay",
             Self::Explain { .. } => "explain",
+            Self::Select { .. } => "select",
             Self::App(app) => match app {
                 AppCommand::Quit => "quit",
                 AppCommand::Help => "help",
@@ -639,6 +649,11 @@ impl Command {
             // Explain forwards to the wrapped query — the table
             // the plan is about is the inner command's table.
             Self::Explain { query } => query.target_table(),
+            // A SQL `SELECT` may read several tables (or none);
+            // there is no single structure-target table. The
+            // result renders as a data view, not a structure
+            // view, so an empty target is correct here.
+            Self::Select { .. } => "",
             // App commands aren't tied to schema entities — the
             // verb is the most identifying thing. The
             // display_subject override below provides a richer

src/dsl/grammar/app.rs

@@ -110,19 +110,19 @@ const SAVE_AS_OPT: Node = Node::Optional(&SAVE_AS_WORD);
 
 // --- AST builders --------------------------------------------------
 
-const fn build_quit(_path: &MatchedPath) -> Result<Command, ValidationError> {
+const fn build_quit(_path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     Ok(Command::App(AppCommand::Quit))
 }
 
-const fn build_help(_path: &MatchedPath) -> Result<Command, ValidationError> {
+const fn build_help(_path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     Ok(Command::App(AppCommand::Help))
 }
 
-const fn build_rebuild(_path: &MatchedPath) -> Result<Command, ValidationError> {
+const fn build_rebuild(_path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     Ok(Command::App(AppCommand::Rebuild))
 }
 
-fn build_save(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_save(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     if path.contains_word("as") {
         Ok(Command::App(AppCommand::SaveAs))
     } else {
@@ -130,22 +130,22 @@ fn build_save(path: &MatchedPath) -> Result<Command, ValidationError> {
     }
 }
 
-const fn build_new(_path: &MatchedPath) -> Result<Command, ValidationError> {
+const fn build_new(_path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     Ok(Command::App(AppCommand::New))
 }
 
-const fn build_load(_path: &MatchedPath) -> Result<Command, ValidationError> {
+const fn build_load(_path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     Ok(Command::App(AppCommand::Load))
 }
 
-fn build_export(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_export(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     let bare = path
         .find(|i| matches!(i.kind, MatchedKind::BarePath))
         .map(|i| i.text.clone());
     Ok(Command::App(AppCommand::Export { path: bare }))
 }
 
-fn build_import(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_import(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     let bare_path = path
         .find(|i| matches!(i.kind, MatchedKind::BarePath))
         .map(|i| i.text.clone())
@@ -159,7 +159,7 @@ fn build_import(path: &MatchedPath) -> Result<Command, ValidationError> {
     }))
 }
 
-fn build_mode(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_mode(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     // The Choice surfaces the matched value as either a `Word`
     // (known) or an `Ident` (unknown). The unknown branch's
     // validator always errors, so reaching the AST builder
@@ -174,7 +174,7 @@ fn build_mode(path: &MatchedPath) -> Result<Command, ValidationError> {
     Ok(Command::App(AppCommand::Mode { value }))
 }
 
-fn build_messages(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_messages(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     let value = if path.contains_word("short") {
         Some(MessagesValue::Short)
     } else if path.contains_word("verbose") {

src/dsl/grammar/data.rs

@@ -20,6 +20,7 @@ use crate::dsl::command::{Command, Expr, RowFilter};
 use crate::dsl::grammar::{
     CommandNode, IdentSource, Node, NumberValidator, ValidationError, Word, expr,
     shared::{column_value_list, current_column_value},
+    sql_expr,
 };
 use crate::dsl::walker::context::WalkContext;
 use crate::dsl::value::Value;
@@ -352,6 +353,154 @@ const EXPLAIN_CHOICES: &[Node] = &[
 ];
 const EXPLAIN_SHAPE: Node = Node::Choice(EXPLAIN_CHOICES);
 
+// =================================================================
+// select — SQL `SELECT` (advanced mode; ADR-0030 §6, ADR-0031)
+// =================================================================
+//
+// Phase 1's single-table `SELECT`: a projection, a `FROM` table,
+// and optional `WHERE` / `ORDER BY` / `LIMIT`. The projection,
+// `WHERE` and `ORDER BY` expression slots reference the SQL
+// expression grammar (ADR-0031) through `Subgrammar`, so SQL gets
+// the same completion / highlighting / hints as the DSL for free.
+//
+// Advanced mode only — the walker's mode gate (ADR-0030 §2,
+// `grammar::is_advanced_only`) refuses `select` in simple mode
+// with the "this is SQL" hint, so this grammar is never reached
+// there.
+//
+// `JOIN`s, `GROUP BY` / `HAVING`, subqueries, `UNION`, CTEs, and
+// `OFFSET` are ADR-0030 Phase 2 ("`SELECT` — full"); implicit
+// column aliasing (`select a x`) and qualified `t.*` are out of
+// Phase 1 (see the inline notes).
+
+/// A SQL expression slot — the ADR-0031 fragment as one node.
+const SQL_EXPR: Node = Node::Subgrammar(&sql_expr::SQL_OR_EXPR);
+
+/// `as <alias>` — the explicit projection alias. Implicit
+/// aliasing (`select a x`) is not supported: a bare alias is
+/// ambiguous with the `from` keyword, whereas `as` is not.
+const SELECT_ALIAS_IDENT: Node = Node::Ident {
+    source: IdentSource::NewName,
+    role: "select_alias",
+    validator: None,
+    highlight_override: None,
+    writes_table: false,
+    writes_column: false,
+    writes_user_listed_column: false,
+};
+static SELECT_AS_ALIAS_NODES: &[Node] = &[
+    Node::Word(Word::keyword("as")),
+    SELECT_ALIAS_IDENT,
+];
+static SELECT_AS_ALIAS: Node = Node::Seq(SELECT_AS_ALIAS_NODES);
+
+/// A projection item: a SQL expression with an optional alias.
+static SELECT_PROJ_ITEM_NODES: &[Node] = &[
+    SQL_EXPR,
+    Node::Optional(&SELECT_AS_ALIAS),
+];
+static SELECT_PROJ_ITEM: Node = Node::Seq(SELECT_PROJ_ITEM_NODES);
+
+/// `proj_item ( , proj_item )*`.
+const SELECT_PROJ_LIST: Node = Node::Repeated {
+    inner: &SELECT_PROJ_ITEM,
+    separator: Some(&Node::Punct(',')),
+    min: 1,
+};
+
+/// `projection := '*' | proj_item ( , proj_item )*`. (`t.*`
+/// qualified star is Phase 2 — it needs join scope.)
+const SELECT_PROJECTION_CHOICES: &[Node] = &[Node::Punct('*'), SELECT_PROJ_LIST];
+const SELECT_PROJECTION: Node = Node::Choice(SELECT_PROJECTION_CHOICES);
+
+/// The `FROM` table. `writes_table` so the `WHERE` / `ORDER BY`
+/// expression column slots complete against this table; the
+/// validator rejects the internal `__rdbms_*` metadata tables
+/// (ADR-0030 §6).
+const SELECT_FROM_TABLE: Node = Node::Ident {
+    source: IdentSource::Tables,
+    role: "table_name",
+    validator: Some(reject_internal_table),
+    highlight_override: None,
+    writes_table: true,
+    writes_column: false,
+    writes_user_listed_column: false,
+};
+
+/// `where <sql_expr>`.
+static SELECT_WHERE_NODES: &[Node] = &[Node::Word(Word::keyword("where")), SQL_EXPR];
+static SELECT_WHERE: Node = Node::Seq(SELECT_WHERE_NODES);
+
+/// `order by <item> ( , <item> )*`, each item a SQL expression
+/// with an optional `asc` / `desc`.
+const SELECT_SORT_DIR_CHOICES: &[Node] = &[
+    Node::Word(Word::keyword("asc")),
+    Node::Word(Word::keyword("desc")),
+];
+static SELECT_ORDER_ITEM_NODES: &[Node] = &[
+    SQL_EXPR,
+    Node::Optional(&Node::Choice(SELECT_SORT_DIR_CHOICES)),
+];
+static SELECT_ORDER_ITEM: Node = Node::Seq(SELECT_ORDER_ITEM_NODES);
+static SELECT_ORDER_BY_NODES: &[Node] = &[
+    Node::Word(Word::keyword("order")),
+    Node::Word(Word::keyword("by")),
+    Node::Repeated {
+        inner: &SELECT_ORDER_ITEM,
+        separator: Some(&Node::Punct(',')),
+        min: 1,
+    },
+];
+static SELECT_ORDER_BY: Node = Node::Seq(SELECT_ORDER_BY_NODES);
+
+/// `limit <n>` — reuses the `show data` non-negative-integer
+/// validator (`OFFSET` is Phase 2).
+static SELECT_LIMIT_NODES: &[Node] = &[
+    Node::Word(Word::keyword("limit")),
+    Node::NumberLit {
+        validator: Some(LIMIT_VALIDATOR),
+    },
+];
+static SELECT_LIMIT: Node = Node::Seq(SELECT_LIMIT_NODES);
+
+/// `from <Table>` — the FROM clause is optional so that the
+/// zero-table form `select 1`, `select upper('x')` (a constant
+/// or function-call expression) is admitted alongside the
+/// single-table form. The expression slots resolve column
+/// completion against the FROM table when present; without it,
+/// the engine will reject any column references.
+static SELECT_FROM_CLAUSE_NODES: &[Node] = &[
+    Node::Word(Word::keyword("from")),
+    SELECT_FROM_TABLE,
+];
+static SELECT_FROM_CLAUSE: Node = Node::Seq(SELECT_FROM_CLAUSE_NODES);
+
+const SELECT_NODES: &[Node] = &[
+    SELECT_PROJECTION,
+    Node::Optional(&SELECT_FROM_CLAUSE),
+    Node::Optional(&SELECT_WHERE),
+    Node::Optional(&SELECT_ORDER_BY),
+    Node::Optional(&SELECT_LIMIT),
+    // ADR-0030 §3: one statement per submission; a trailing `;`
+    // is tolerated.
+    Node::Optional(&Node::Punct(';')),
+];
+const SELECT_SHAPE: Node = Node::Seq(SELECT_NODES);
+
+/// Reject a reference to an internal `__rdbms_*` metadata table
+/// in a `SELECT`'s `FROM` (ADR-0030 §6 — those tables are not in
+/// the query surface).
+fn reject_internal_table(name: &str) -> Result<(), ValidationError> {
+    if name.to_ascii_lowercase().starts_with("__rdbms_") {
+        Err(ValidationError {
+            message_key: "select.internal_table",
+            args: vec![("table", name.to_string())],
+        })
+    } else {
+        Ok(())
+    }
+}
+
 // =================================================================
 // AST builders
 // =================================================================
@@ -389,7 +538,7 @@ pub(crate) fn item_to_value(item: &MatchedItem) -> Option<Value> {
     }
 }
 
-fn build_show(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_show(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     let sub = path
         .items
         .iter()
@@ -400,7 +549,7 @@ fn build_show(path: &MatchedPath) -> Result<Command, ValidationError> {
         .nth(1);
     let name = require_ident(path, "table_name")?;
     match sub {
-        Some("data") => build_show_data(path),
+        Some("data") => build_show_data(path, _source),
         Some("table") => Ok(Command::ShowTable { name }),
         _ => Err(ValidationError {
             message_key: "parse.error_wrapper",
@@ -413,7 +562,7 @@ fn build_show(path: &MatchedPath) -> Result<Command, ValidationError> {
 /// (no positional `nth` lookups), so it serves both the
 /// standalone `show data` entry word and the `explain show
 /// data …` wrapper, where the entry-word offset shifts.
-fn build_show_data(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_show_data(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     Ok(Command::ShowData {
         name: require_ident(path, "table_name")?,
         filter: build_show_filter(path)?,
@@ -474,7 +623,7 @@ fn build_show_limit(path: &MatchedPath) -> Result<Option<u64>, ValidationError>
         })
 }
 
-fn build_insert(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_insert(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     let table = require_ident(path, "table_name")?;
 
     // Locate the second `values` keyword (the first is the
@@ -654,7 +803,7 @@ fn collect_values_in_parens(
     Ok(out)
 }
 
-fn build_update(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_update(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     let table = require_ident(path, "table_name")?;
     let assignments = collect_assignments(path)?;
     let filter = collect_filter(path)?;
@@ -723,7 +872,7 @@ fn collect_filter(path: &MatchedPath) -> Result<RowFilter, ValidationError> {
     )?))
 }
 
-fn build_delete(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_delete(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     let table = require_ident(path, "table_name")?;
     let filter = collect_filter(path)?;
     Ok(Command::Delete { table, filter })
@@ -737,7 +886,7 @@ fn build_delete(path: &MatchedPath) -> Result<Command, ValidationError> {
 /// `build_delete`), all of which are role-based and so are
 /// indifferent to the entry-word offset the `explain` prefix
 /// introduces.
-fn build_explain(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_explain(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     let inner_word = path
         .items
         .iter()
@@ -747,9 +896,9 @@ fn build_explain(path: &MatchedPath) -> Result<Command, ValidationError> {
         })
         .nth(1);
     let inner = match inner_word {
-        Some("show") => build_show_data(path)?,
-        Some("update") => build_update(path)?,
-        Some("delete") => build_delete(path)?,
+        Some("show") => build_show_data(path, _source)?,
+        Some("update") => build_update(path, _source)?,
+        Some("delete") => build_delete(path, _source)?,
         _ => {
             return Err(ValidationError {
                 message_key: "parse.error_wrapper",
@@ -777,7 +926,7 @@ fn build_explain(path: &MatchedPath) -> Result<Command, ValidationError> {
 const REPLAY_PATH_CHOICES: &[Node] = &[Node::StringLit, Node::BarePath];
 const REPLAY_PATH: Node = Node::Choice(REPLAY_PATH_CHOICES);
 
-fn build_replay(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_replay(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     let payload = path
         .items
         .iter()
@@ -792,6 +941,18 @@ fn build_replay(path: &MatchedPath) -> Result<Command, ValidationError> {
     Ok(Command::Replay { path: payload })
 }
 
+/// `Command::Select` carries the validated SQL text verbatim
+/// (ADR-0030 §4/§6, ADR-0031 §2): a `SELECT` builds no AST — the
+/// walk has confirmed it is in the supported subset, and the
+/// worker runs the statement as text. `source` is the full
+/// submitted line; on a `Match` outcome the `SELECT` shape
+/// consumed all of it.
+fn build_select(_path: &MatchedPath, source: &str) -> Result<Command, ValidationError> {
+    Ok(Command::Select {
+        sql: source.trim().to_string(),
+    })
+}
+
 // =================================================================
 // CommandNodes
 // =================================================================
@@ -838,6 +999,16 @@ pub static EXPLAIN: CommandNode = CommandNode {
     help_id: Some("data.explain"),
     usage_ids: &["parse.usage.explain"],};
 
+/// SQL `SELECT` (ADR-0030 §6, ADR-0031). Advanced mode only —
+/// gated by `grammar::is_advanced_only`. `help_id` is `None`
+/// until the `help sql` page lands (ADR-0030 Phase 6).
+pub static SELECT: CommandNode = CommandNode {
+    entry: Word::keyword("select"),
+    shape: SELECT_SHAPE,
+    ast_builder: build_select,
+    help_id: None,
+    usage_ids: &["parse.usage.select"],};
+
 // =================================================================
 // Tests — `explain` grammar (ADR-0028 §1)
 // =================================================================

src/dsl/grammar/ddl.rs

@@ -522,7 +522,7 @@ fn parse_action(words: &[&'static str]) -> ReferentialAction {
     }
 }
 
-fn build_drop(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_drop(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     // Discriminate by the second word matched (the entry was
     // `drop`, the next Word is `table` / `column` / `relationship`).
     let sub = path
@@ -566,7 +566,7 @@ fn build_drop(path: &MatchedPath) -> Result<Command, ValidationError> {
                 })
             }
         }
-        Some("constraint") => build_drop_constraint(path),
+        Some("constraint") => build_drop_constraint(path, _source),
         Some("relationship") => {
             // Endpoints form has `from` as the third Word.
             let has_from = path
@@ -597,7 +597,7 @@ fn build_drop(path: &MatchedPath) -> Result<Command, ValidationError> {
     }
 }
 
-fn build_add(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_add(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     // Second matched Word distinguishes column vs the `1:n
     // relationship` form. The `1` literal counts as a Word
     // (the walker records Literal matches as MatchedKind::Word
@@ -631,13 +631,13 @@ fn build_add(path: &MatchedPath) -> Result<Command, ValidationError> {
                 check,
             })
         }
-        Some("1") => build_add_relationship(path),
+        Some("1") => build_add_relationship(path, _source),
         Some("index") => Ok(Command::AddIndex {
             name: ident(path, "index_name").map(str::to_string),
             table: require_ident(path, "table_name")?,
             columns: collect_idents(path, "column_name"),
         }),
-        Some("constraint") => build_add_constraint(path),
+        Some("constraint") => build_add_constraint(path, _source),
         _ => Err(ValidationError {
             message_key: "parse.error_wrapper",
             args: vec![("detail", "unknown add subcommand".to_string())],
@@ -645,7 +645,7 @@ fn build_add(path: &MatchedPath) -> Result<Command, ValidationError> {
     }
 }
 
-fn build_add_relationship(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_add_relationship(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     // Collect all referential-clause actions in matched order
     // and validate at-most-2 + not-repeated. The `on <delete|
     // update> <action>` sequence shows up as a run of Word
@@ -715,7 +715,7 @@ fn build_add_relationship(path: &MatchedPath) -> Result<Command, ValidationError
     })
 }
 
-fn build_rename_column(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_rename_column(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     Ok(Command::RenameColumn {
         table: require_ident(path, "table_name")?,
         old: require_ident(path, "column_name")?,
@@ -723,7 +723,7 @@ fn build_rename_column(path: &MatchedPath) -> Result<Command, ValidationError> {
     })
 }
 
-fn build_change_column(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_change_column(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     let ty_text = require_ident(path, "type")?;
     let ty = ty_text
         .parse::<crate::dsl::types::Type>()
@@ -775,7 +775,7 @@ fn build_change_column(path: &MatchedPath) -> Result<Command, ValidationError> {
 /// recovers it. The §9 redundancy and §5 dry-run checks are
 /// execution-time (the parser has no schema) and live in the
 /// database worker.
-fn build_add_constraint(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_add_constraint(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     let (not_null, unique, default, check) = collect_column_constraints(path)?;
     let constraint = if not_null {
         Constraint::NotNull
@@ -802,7 +802,7 @@ fn build_add_constraint(path: &MatchedPath) -> Result<Command, ValidationError>
 /// (ADR-0029 §2.2). `drop` names only the kind — the
 /// `DROP_CONSTRAINT_KIND` Choice is payload-free, so the kind
 /// is recovered from which keyword(s) the path matched.
-fn build_drop_constraint(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_drop_constraint(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     let words: Vec<&'static str> = path
         .items
         .iter()
@@ -1113,7 +1113,7 @@ fn redundant_pk_constraint(column: &str, constraint: &str) -> ValidationError {
     }
 }
 
-fn build_create_table(path: &MatchedPath) -> Result<Command, ValidationError> {
+fn build_create_table(path: &MatchedPath, _source: &str) -> Result<Command, ValidationError> {
     let name = require_ident(path, "table_name")?;
 
     // Walk the matched items, segmenting per column: a

src/dsl/grammar/mod.rs

@@ -380,7 +380,13 @@ pub struct CommandNode {
     /// rejections that are easier to express imperatively than
     /// as a per-node validator (Phase A: none — every app
     /// command's ast_builder is infallible).
-    pub ast_builder: fn(&MatchedPath) -> Result<Command, ValidationError>,
+    ///
+    /// `source` is the full input line being parsed. Most builders
+    /// reconstruct the `Command` from the matched `MatchedPath`
+    /// alone and ignore it; SQL builders whose `Command` carries
+    /// the validated SQL text (ADR-0030 §4/§6, ADR-0031 §2) read
+    /// it.
+    pub ast_builder: fn(&MatchedPath, &str) -> Result<Command, ValidationError>,
     /// Catalog key (`help.<id>`) for this command's in-app
     /// `help` entry. Consumed by `App::note_help`, which
     /// iterates the REGISTRY and translates each `help_id` —
@@ -486,8 +492,30 @@ pub static REGISTRY: &[&CommandNode] = &[
     &data::DELETE,
     &data::REPLAY,
     &data::EXPLAIN,
+    &data::SELECT,
 ];
 
+/// Entry words for commands available only in advanced mode
+/// (ADR-0030 §2). Phase 1: `select`. In simple mode the walker
+/// gates these out — typing one yields the precise "this is SQL"
+/// hint rather than a normal parse or an "unknown command" error.
+///
+/// This is whole-command gating keyed on the entry word, which
+/// suffices while every SQL form is its own command. ADR-0030 §2's
+/// finer-grained per-`Choice`-branch tagging arrives with the
+/// shared DSL/SQL entry words (`create`, `insert`, …) in a later
+/// phase.
+const ADVANCED_ONLY_ENTRIES: &[&str] = &["select"];
+
+/// Whether `entry` names an advanced-mode-only command (ADR-0030
+/// §2). Case-insensitive, matching keyword-matching elsewhere.
+#[must_use]
+pub fn is_advanced_only(entry: &str) -> bool {
+    ADVANCED_ONLY_ENTRIES
+        .iter()
+        .any(|e| e.eq_ignore_ascii_case(entry))
+}
+
 /// Look up a `CommandNode` by entry word, case-insensitively.
 ///
 /// Used by the router to decide whether the walker owns this

src/dsl/parser.rs

@@ -13,6 +13,7 @@
 //! identifier-shape token isn't a registered entry word.
 
 use crate::dsl::command::Command;
+use crate::mode::Mode;
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum ParseError {
@@ -94,8 +95,13 @@ impl ParseError {
 /// `DynamicSubgrammar`) fall back to schema-unaware behaviour.
 /// Use `parse_command_with_schema` to enable typed value slots
 /// (ADR-0024 §Phase D).
+///
+/// Defaults to **advanced**-mode grammar (the full surface) —
+/// callers that need simple-mode gating (ADR-0030 §2) use
+/// [`parse_command_in_mode`] or
+/// [`parse_command_with_schema_in_mode`] instead.
 pub fn parse_command(input: &str) -> Result<Command, ParseError> {
-    parse_command_inner(input, None)
+    parse_command_inner(input, None, Mode::Advanced)
 }
 
 /// Schema-aware parse entry point (ADR-0024 §Phase D).
@@ -104,21 +110,50 @@ pub fn parse_command(input: &str) -> Result<Command, ParseError> {
 /// the walker can populate `current_table` / `current_column`
 /// from existing entities and `DynamicSubgrammar` factories
 /// can unfold per-column typed value slots.
+///
+/// Defaults to **advanced**-mode grammar; for simple-mode
+/// gating use [`parse_command_with_schema_in_mode`].
 pub fn parse_command_with_schema(
     input: &str,
     schema: &crate::completion::SchemaCache,
 ) -> Result<Command, ParseError> {
-    parse_command_inner(input, Some(schema))
+    parse_command_inner(input, Some(schema), Mode::Advanced)
+}
+
+/// Schemaless, mode-aware parse (ADR-0030 §2). In `Mode::Simple`
+/// the walker gates SQL-only commands and produces the
+/// "this is SQL" hint instead of executing them.
+pub fn parse_command_in_mode(
+    input: &str,
+    mode: Mode,
+) -> Result<Command, ParseError> {
+    parse_command_inner(input, None, mode)
+}
+
+/// Schema-aware, mode-aware parse.
+///
+/// Combines ADR-0024 §Phase D (schema-aware typed slots) with
+/// ADR-0030 §2 (mode-gated SQL grammar). The execution path
+/// (`App::dispatch_dsl`) and the live overlay / completion /
+/// highlight call sites use this so simple-mode users do not
+/// see advanced-mode SQL surfaced.
+pub fn parse_command_with_schema_in_mode(
+    input: &str,
+    schema: &crate::completion::SchemaCache,
+    mode: Mode,
+) -> Result<Command, ParseError> {
+    parse_command_inner(input, Some(schema), mode)
 }
 
 fn parse_command_inner(
     input: &str,
     schema: Option<&crate::completion::SchemaCache>,
+    mode: Mode,
 ) -> Result<Command, ParseError> {
     if input.trim().is_empty() {
         return Err(ParseError::Empty);
     }
-    if let Some(result) = try_walker_route(input, schema) {
+    if let Some(result) = try_walker_route(input, schema, mode) {
         return result;
     }
     Err(unknown_command_error(input))
@@ -157,11 +192,13 @@ fn unknown_command_error(source: &str) -> ParseError {
 fn try_walker_route(
     source: &str,
     schema: Option<&crate::completion::SchemaCache>,
+    mode: Mode,
 ) -> Option<Result<Command, ParseError>> {
     use crate::dsl::walker::{self, outcome::WalkBound};
     let mut ctx = schema.map_or_else(walker::context::WalkContext::new, |s| {
         walker::context::WalkContext::with_schema(s)
     });
+    ctx.mode = mode;
     let (result, command) = walker::walk(source, WalkBound::EndOfInput, &mut ctx);
     let result = result?;
     Some(walker_outcome_to_parse_result(source, result, command))

src/dsl/walker/context.rs

@@ -11,6 +11,7 @@
 //! generic value-literal slot.
 
 use crate::completion::{SchemaCache, TableColumn};
+use crate::mode::Mode;
 
 /// Per-walk state.
 ///
@@ -28,6 +29,13 @@ use crate::completion::{SchemaCache, TableColumn};
 #[derive(Debug, Default)]
 pub struct WalkContext<'a> {
     pub schema: Option<&'a SchemaCache>,
+    /// The input mode this walk runs under (ADR-0030 §2). In
+    /// `Mode::Simple` the walker gates out SQL-only commands —
+    /// an advanced-only entry word yields the "this is SQL"
+    /// hint rather than a normal parse. Defaults to
+    /// `Mode::Simple`; real call sites set it from the active
+    /// `App` mode.
+    pub mode: Mode,
     pub current_table: Option<String>,
     pub current_table_columns: Option<Vec<TableColumn>>,
     pub current_column: Option<TableColumn>,
@@ -100,6 +108,7 @@ impl<'a> WalkContext<'a> {
     pub const fn with_schema(schema: &'a SchemaCache) -> Self {
         Self {
             schema: Some(schema),
+            mode: Mode::Simple,
             current_table: None,
             current_table_columns: None,
             current_column: None,

src/dsl/walker/mod.rs

@@ -865,6 +865,37 @@ pub fn walk<'a>(
         class: grammar::HighlightClass::Keyword,
     });
 
+    // Mode gate (ADR-0030 §2): an advanced-only command (a SQL
+    // form) typed in simple mode is *recognised as SQL* and
+    // yields a precise hint — "this is SQL; switch with `mode
+    // advanced`, or prefix the line with `:`" — rather than
+    // being walked normally or rejected as an unknown command.
+    // The entry word stays highlighted as a keyword (it is one);
+    // the input carries an ERROR verdict (it will not run here).
+    if ctx.mode == crate::mode::Mode::Simple
+        && grammar::is_advanced_only(command_node.entry.primary)
+    {
+        return (
+            Some(WalkResult {
+                outcome: WalkOutcome::ValidationFailed {
+                    position: kw_start,
+                    error: crate::dsl::grammar::ValidationError {
+                        message_key: "advanced_mode.sql_in_simple",
+                        args: vec![(
+                            "command",
+                            command_node.entry.primary.to_string(),
+                        )],
+                    },
+                },
+                matched_path: path,
+                per_byte_class: per_byte,
+                diagnostics: Vec::new(),
+                tail_expected: Vec::new(),
+            }),
+            None,
+        );
+    }
+
     let mut tail_expected: Vec<Expectation> = Vec::new();
     let outcome = match walk_node(
         effective_source,
@@ -937,7 +968,7 @@ pub fn walk<'a>(
     // the catalog wording correctly) rather than as a generic
     // "AST builder failed" fallback.
     let (final_outcome, cmd) = match outcome {
-        WalkOutcome::Match { .. } => match (command_node.ast_builder)(&path) {
+        WalkOutcome::Match { .. } => match (command_node.ast_builder)(&path, source) {
             Ok(c) => (outcome, Some(c)),
             Err(error) => (
                 WalkOutcome::ValidationFailed {

src/friendly/keys.rs

@@ -240,6 +240,7 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
     ("parse.usage.rebuild", &[]),
     ("parse.usage.replay", &[]),
     ("parse.usage.save", &[]),
+    ("parse.usage.select", &[]),
     ("parse.usage.show_data", &[]),
     ("parse.usage.show_table", &[]),
     ("parse.usage.update", &[]),
@@ -293,6 +294,9 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
     ("project.switched_ok", &["display_name"]),
     // ---- Advanced-mode placeholder ----
     ("advanced_mode.not_implemented", &["input"]),
+    // ---- Advanced-mode SQL surface (ADR-0030) ----
+    ("advanced_mode.sql_in_simple", &["command"]),
+    ("select.internal_table", &["table"]),
     (
         "cli.invalid_value",
         &["flag", "value", "expected"],

src/friendly/strings/en-US.yaml

@@ -462,6 +462,8 @@ parse:
       explain update <Table> set <col>=<value>[, ...] (where <expr> | --all-rows)
       explain delete from <Table> (where <expr> | --all-rows)
     replay: "replay <path>  |  replay '<path with spaces>'"
+    # SQL `SELECT` (advanced mode; ADR-0030 / ADR-0031).
+    select: "select (* | <expr>[ as <alias>][, ...]) from <Table> [where <expr>] [order by <expr>[ asc|desc][, ...]] [limit <n>]"
     # App-lifecycle commands (per ADR-0003, surfaced through
     # the parser so they participate in usage templates +
     # completion). Templates here describe the surface
@@ -602,9 +604,14 @@ persistence:
     bad_output: "migrator produced an unparseable result: {detail}"
     io: "io error during migration on `{path}`: {source}"
 
-# ---- Advanced-mode placeholder until SQL parser lands (Q1) ----------
+# ---- Advanced-mode SQL surface (ADR-0030) ---------------------------
 advanced_mode:
   not_implemented: "advanced mode SQL not implemented yet — echo: {input}"
+  sql_in_simple: "`{command}` is SQL — available in advanced mode. Switch with `mode advanced`, or prefix the line with `:` to run it once."
+
+# ---- SQL SELECT (advanced mode; ADR-0030 / ADR-0031) ----------------
+select:
+  internal_table: "`{table}` is an internal system table and cannot be queried."
 
 # ---- Persistence-fatal banner (ADR-0015 §8) -------------------------
 fatal:

src/mode.rs

@@ -7,8 +7,12 @@
 
 use std::fmt;
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Default)]
 pub enum Mode {
+    /// The teaching DSL only — the app's startup mode (ADR-0003)
+    /// and the walker's default view: SQL-only grammar is gated
+    /// out (ADR-0030 §2).
+    #[default]
     Simple,
     Advanced,
 }

src/runtime.rs

@@ -1874,6 +1874,13 @@ async fn execute_command_typed(
             .query_data(name, filter, limit, src)
             .await
             .map(CommandOutcome::Query),
+        // A SQL `SELECT` (advanced mode; ADR-0030 §6, ADR-0031).
+        // The grammar walker has already validated `sql` is in
+        // the supported subset; the worker runs it as text.
+        Command::Select { sql } => database
+            .run_select(sql, src)
+            .await
+            .map(CommandOutcome::Query),
         // `EXPLAIN QUERY PLAN` never executes the wrapped
         // statement (ADR-0028 §2), so explaining a destructive
         // command is safe. `src` is unused here — explain is a