fix(hint): correct H2 corpus errors + add parse guard (handoff-71)

Semantic verification pass over the tier-3 `hint` corpus (ADR-0053).
Four content errors corrected in src/friendly/strings/en-US.yaml:

- cmd.create_table: the example `with pk id(serial), name(text),
  email(text)` declares a 3-column COMPOUND primary key, not a PK
  plus regular columns (every `with pk` column is a key member,
  ADR-0005). Rewritten to a single-column PK + `add column` for the
  rest; what/concept aligned.
- cmd.save: `save as my-shop` does not parse — `save as` takes no
  inline name, it opens a path-entry prompt. Example -> `save as`;
  what no longer implies inline naming; added a temp-vs-named concept.
- cmd.import: target `shop-copy` does not parse — the `as <target>`
  slot is a NewName ident that rejects hyphens. -> `shop_copy`.
- err.foreign_key.child_side: dropped the bogus `on delete set
  null/cascade` remedy — that governs the parent direction; a
  child-side violation is fixed by inserting the parent first
  (matches the tier-1 hint).

Adds every_cmd_hint_example_parses_in_its_mode — a catalog-driven
guard that parses every hint.cmd.* example in its taught mode,
backstopping syntactic drift (it caught the save and import errors).
Registers the new hint.cmd.save.concept key.

docs: drop two stale "deferred" entries from CLAUDE.md — project
storage (export/import, --resume, input history, migration scaffold)
and m:n convenience (C4) are all implemented (ADR-0015/0045); record
the verification pass on requirements.md H2.

src/dsl/grammar/mod.rs

@@ -1012,6 +1012,75 @@ mod hint_key_tests {
             assert!(cat.get(&key).is_some(), "missing tier-3 error block `{key}`");
         }
     }
+
+    /// Semantic-verification guard (handoff-71): every `hint.cmd.<form>`
+    /// **example** must parse in the mode the form is taught for. This
+    /// backstops the bug class found in the H2 corpus pass — an example
+    /// that drifts out of the real grammar (a typo, a removed clause, or
+    /// an argument the command never accepted, e.g. an inline name on
+    /// `save as` which opens a modal instead). It cannot police the
+    /// *semantics* of an example that happens to parse (that is the
+    /// manual pass), but it locks the syntactic floor so future edits
+    /// can't ship an unparseable teaching line.
+    ///
+    /// The mode per form mirrors `hint_key_for_input_in_mode`: the
+    /// advanced-SQL forms are taught in advanced mode; everything else
+    /// (DSL + app commands) in simple mode.
+    #[test]
+    fn every_cmd_hint_example_parses_in_its_mode() {
+        use crate::dsl::parser::parse_command_in_mode;
+        use crate::mode::Mode;
+
+        // Advanced-mode forms — the SQL surface (ADR-0030–0039). Every
+        // other form (DSL + app commands) is taught in simple mode. This
+        // mirrors the mode split `hint_key_for_input_in_mode` resolves.
+        const ADVANCED: &[&str] = &[
+            "sql_create_table",
+            "sql_alter_table",
+            "sql_create_index",
+            "sql_drop_index",
+            "sql_drop_table",
+            "sql_insert",
+            "sql_update",
+            "sql_delete",
+            "select",
+            "with",
+            "explain_sql",
+        ];
+
+        // Iterate the *catalog* (the corpus is the source of truth), not the
+        // REGISTRY: this reaches every `hint.cmd.<id>` block including any
+        // not owned by a command node, so an orphaned or mis-keyed example
+        // can't slip past the guard.
+        let cat = crate::friendly::catalog();
+        let mut checked = 0usize;
+        for key in cat.keys() {
+            let Some(id) = key
+                .strip_prefix("hint.cmd.")
+                .and_then(|rest| rest.strip_suffix(".example"))
+            else {
+                continue;
+            };
+            let example = cat.get(key).expect("key came from the catalog");
+            let mode = if ADVANCED.contains(&id) {
+                Mode::Advanced
+            } else {
+                Mode::Simple
+            };
+            assert!(
+                parse_command_in_mode(example, mode).is_ok(),
+                "hint.cmd.{id}.example does not parse in {mode:?} mode: {example:?}",
+            );
+            checked += 1;
+        }
+        // Floor guard: the corpus had 49 command forms at the time of
+        // writing (ADR-0053). If this drops, a block (and its example
+        // coverage) silently vanished.
+        assert!(
+            checked >= 49,
+            "expected at least 49 hint.cmd.* examples, checked {checked}",
+        );
+    }
 }
 
 #[cfg(test)]

src/friendly/keys.rs

@@ -277,6 +277,7 @@ pub const KEYS_AND_PLACEHOLDERS: &[(&str, &[&str])] = &[
     ("hint.cmd.rebuild.concept", &[]),
     ("hint.cmd.save.what", &[]),
     ("hint.cmd.save.example", &[]),
+    ("hint.cmd.save.concept", &[]),
     ("hint.cmd.new.what", &[]),
     ("hint.cmd.new.example", &[]),
     ("hint.cmd.load.what", &[]),

src/friendly/strings/en-US.yaml

@@ -430,8 +430,9 @@ hint:
       example: "rebuild"
       concept: "The text files (project.yaml + the data folder) are the source of truth; the database is derived and can always be rebuilt from them."
     save:
-      what: "Save the current project under a name; `save as` copies it to a new one."
-      example: "save as my-shop"
+      what: "Save the current project; `save as` copies it to a new name or location."
+      example: "save as"
+      concept: "On a temporary project, `save` opens a prompt to give it a permanent name; a named project auto-saves as you work, so `save` on one is already done. `save as` always prompts for a new name or path — use it to copy a project."
     new:
       what: "Close the current project and start a fresh temporary one."
       example: "new"
@@ -444,7 +445,7 @@ hint:
       concept: "The zip carries the schema and data as text, so anyone can rebuild the very same database from it."
     import:
       what: "Unpack a project zip into a new project and switch to it."
-      example: "import my-shop.zip as shop-copy"
+      example: "import my-shop.zip as shop_copy"
     mode:
       what: "Switch between simple mode (the guided teaching commands) and advanced mode (raw SQL)."
       example: "mode advanced"
@@ -465,9 +466,9 @@ hint:
       example: "copy last"
     # DDL — schema-shaping commands (Phase C batch 2).
     create_table:
-      what: "Create a new table — its columns, their types, and a primary key."
-      example: "create table Customers with pk id(serial), name(text), email(text)"
-      concept: "A table is a set of rows that share the same columns. The primary key uniquely identifies each row; a `serial` key numbers the rows for you."
+      what: "Create a new table and declare its primary key."
+      example: "create table Customers with pk id(serial)"
+      concept: "A table is a set of rows sharing the same columns. `with pk` declares the primary key — one column, or several for a compound key; add the other columns afterwards with `add column`. A `serial` key numbers the rows for you."
     create_m2n:
       what: "Create a junction table linking two tables many-to-many."
       example: "create m:n relationship from Students to Courses"
@@ -606,7 +607,7 @@ hint:
       child_side:
         what: "The value you gave for the child column doesn't match any parent row, so the foreign key has nothing to point at."
         example: "First insert the parent (insert into Customers …), then the child that references it."
-        concept: "A foreign key is a promise that every child points at a real parent, so the parent must exist first. To allow orphans on delete instead, set the relationship's `on delete` to `set null` or `cascade`."
+        concept: "A foreign key is a promise that every child points at a real parent, so the parent must exist before a child can reference it. (`on delete` actions like `cascade` or `set null` govern the other direction — what happens to children when their parent is removed — not this one.)"
       parent_side:
         what: "You're deleting or changing a row that other rows point at, which would orphan those children."
         example: "Delete the child rows first, or set the relationship's `on delete` to `cascade` (remove them too) or `set null` (keep them, unlinked)."