fix(hint): labelled tier-3 block format + snapshot (ADR-0053 /runda)

Final /runda found the rendered block was three bare unlabelled lines,
deviating from the approved exemplar format. Fix:
- emit_tier3_block now renders a `Hint` heading + aligned `What:` /
  `Example:` / `Concept:` lines (hint.block.* labels); concept stays muted
- lock the format with an insta snapshot (hint_block_insert)
- amend ADR-0053 D2/D4 + exemplars: drop the `Next:` line (tier-2 ambient
  already owns live position-awareness — user-confirmed), align exemplars
  to the shipped format

2499 pass / 1 ignored, clippy clean.

src/app.rs

@@ -3205,17 +3205,32 @@ impl App {
     /// polish (the framed block) lands with the corpus.
     fn emit_tier3_block(&mut self, stem: &str) -> bool {
         let cat = crate::friendly::catalog();
-        if cat.get(&format!("{stem}.what")).is_none() {
+        let what_key = format!("{stem}.what");
+        if cat.get(&what_key).is_none() {
             return false;
         }
-        self.note_system(crate::friendly::translate(&format!("{stem}.what"), &[]));
+        // Labelled block (ADR-0053 D4): a `Hint` heading, then aligned
+        // `What:` / `Example:` / `Concept:` lines. `concept` renders
+        // muted (`OutputStyleClass::Hint`); the rest are plain system.
+        let labelled = |label: &str, value: &str| {
+            // Pad `<Label>:` to a common width so the values align.
+            format!("  {:<9}{value}", format!("{label}:"))
+        };
+        self.note_system(crate::t!("hint.block.heading"));
+        self.note_system(labelled(
+            &crate::t!("hint.block.what"),
+            &crate::friendly::translate(&what_key, &[]),
+        ));
         if cat.get(&format!("{stem}.example")).is_some() {
-            self.note_system(crate::friendly::translate(&format!("{stem}.example"), &[]));
+            self.note_system(labelled(
+                &crate::t!("hint.block.example"),
+                &crate::friendly::translate(&format!("{stem}.example"), &[]),
+            ));
         }
         if cat.get(&format!("{stem}.concept")).is_some() {
-            self.push_category_three_prose(crate::friendly::translate(
-                &format!("{stem}.concept"),
-                &[],
+            self.push_category_three_prose(labelled(
+                &crate::t!("hint.block.concept"),
+                &crate::friendly::translate(&format!("{stem}.concept"), &[]),
             ));
         }
         true
@@ -5813,6 +5828,22 @@ mod tests {
         );
     }
 
+    /// Locks the rendered tier-3 block format (ADR-0053 D4): a `Hint`
+    /// heading + aligned `What:` / `Example:` / `Concept:` lines.
+    #[test]
+    fn insert_hint_block_renders_in_the_labelled_format() {
+        let mut app = App::new();
+        type_str(&mut app, "insert into Customers ");
+        f1(&mut app);
+        let block = app
+            .output
+            .iter()
+            .map(|l| l.text.as_str())
+            .collect::<Vec<_>>()
+            .join("\n");
+        insta::assert_snapshot!("hint_block_insert", block);
+    }
+
     #[test]
     fn f1_on_add_relationship_renders_the_relationship_block() {
         let mut app = App::new();

src/friendly/keys.rs

@@ -224,6 +224,10 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
     ),
     ("hint.ambient_expected", &["expected"]),
     ("hint.getting_started", &[]),
+    ("hint.block.heading", &[]),
+    ("hint.block.what", &[]),
+    ("hint.block.example", &[]),
+    ("hint.block.concept", &[]),
     // Tier-3 teaching blocks (ADR-0053 D3) — Phase-B exemplars.
     ("hint.cmd.insert.what", &[]),
     ("hint.cmd.insert.example", &[]),

src/friendly/strings/en-US.yaml

@@ -391,6 +391,13 @@ hint:
   # H2 / ADR-0053: shown by `hint` / F1 when there is nothing specific
   # to expand on (no recent error, empty input).
   getting_started: "Start typing a command and press F1 for a hint, or type `help` for the full command list."
+  # Tier-3 block scaffolding (ADR-0053 D4): the heading + the labels the
+  # `what` / `example` / `concept` parts render under.
+  block:
+    heading: "Hint"
+    what: "What"
+    example: "Example"
+    concept: "Concept"
   # ── Tier-3 teaching blocks (ADR-0053 D3) ──────────────────────────
   # Per-form command hints (`hint.cmd.<form>`) and per-class error
   # hints (`hint.err.<class>`), each a `what` (1–2 sentences) / `example`

src/snapshots/rdbms_playground__app__tests__hint_block_insert.snap

@@ -0,0 +1,9 @@
+---
+source: src/app.rs
+assertion_line: 5844
+expression: block
+---
+Hint
+  What:    Add one or more rows to a table.
+  Example: insert into Customers values ('Ann', 'ann@example.io')
+  Concept: A row is one record; each value lines up with a column, in order. Columns typed `serial`/`shortid` fill themselves — leave them out.