diff --git a/course/cards/bramble-wall.json b/course/10-spellgrid/cards/bramble-wall.json
similarity index 100%
rename from course/cards/bramble-wall.json
rename to course/10-spellgrid/cards/bramble-wall.json
diff --git a/course/cards/ember-moth.json b/course/10-spellgrid/cards/ember-moth.json
similarity index 100%
rename from course/cards/ember-moth.json
rename to course/10-spellgrid/cards/ember-moth.json
diff --git a/course/cards/graft.json b/course/10-spellgrid/cards/graft.json
similarity index 100%
rename from course/cards/graft.json
rename to course/10-spellgrid/cards/graft.json
diff --git a/course/cards/grave-warden.json b/course/10-spellgrid/cards/grave-warden.json
similarity index 100%
rename from course/cards/grave-warden.json
rename to course/10-spellgrid/cards/grave-warden.json
diff --git a/course/cards/powder-keg.json b/course/10-spellgrid/cards/powder-keg.json
similarity index 100%
rename from course/cards/powder-keg.json
rename to course/10-spellgrid/cards/powder-keg.json
diff --git a/course/cards/rune-scribe.json b/course/10-spellgrid/cards/rune-scribe.json
similarity index 100%
rename from course/cards/rune-scribe.json
rename to course/10-spellgrid/cards/rune-scribe.json
diff --git a/course/cards/spark.json b/course/10-spellgrid/cards/spark.json
similarity index 100%
rename from course/cards/spark.json
rename to course/10-spellgrid/cards/spark.json
diff --git a/course/cards/thorn-hedge.json b/course/10-spellgrid/cards/thorn-hedge.json
similarity index 100%
rename from course/cards/thorn-hedge.json
rename to course/10-spellgrid/cards/thorn-hedge.json
diff --git a/course/cards/tin-knight.json b/course/10-spellgrid/cards/tin-knight.json
similarity index 100%
rename from course/cards/tin-knight.json
rename to course/10-spellgrid/cards/tin-knight.json
diff --git a/course/cards/town-crier.json b/course/10-spellgrid/cards/town-crier.json
similarity index 100%
rename from course/cards/town-crier.json
rename to course/10-spellgrid/cards/town-crier.json
diff --git a/course/10-spellgrid/expansion/README.md b/course/10-spellgrid/expansion/README.md
index 980020d..f1ecbd3 100644
--- a/course/10-spellgrid/expansion/README.md
+++ b/course/10-spellgrid/expansion/README.md
@@ -3,7 +3,7 @@
 The lesson's [Expansion Drop](../lesson.md#expansion-drop) beat explains the task. This file holds the scenario, the test locations and the check.
 
 - Word: `BATTLECRY`, a noun that names a trigger, as `DEATHRATTLE` does. With it, `BATTLECRY IS DOUBLE` written on the grid makes every Battlecry trigger twice, like Brann Bronzebeard ("Your Battlecries trigger twice.", Module 4).
-- Card: Town Crier, a SpellGrid card that is already in `course/cards/` (`"game": "spellgrid"`): a 1-cost 1/1 minion, noun `CRIER`, "Battlecry: Deal 1 damage to the enemy hero."
+- Card: Town Crier, a SpellGrid card that is already in `course/10-spellgrid/cards/`, the module's own cards (`"game": "spellgrid"`): a 1-cost 1/1 minion, noun `CRIER`, "Battlecry: Deal 1 damage to the enemy hero."
 - Tests: `tests/rust/test_10x.rs` and `tests/ts/test_10x.test.ts`. Copy the one for your track into your workspace's `tests/`.
 - Reference answer, two data files and no code:
   - `solution/words.json`: the Module 10 reference's `src/content/words.json` with one entry added, `{ "name": "BATTLECRY", "role": "noun" }`.
diff --git a/course/10-spellgrid/expansion/solution/words.json b/course/10-spellgrid/expansion/solution/words.json
index e147957..ff78552 100644
--- a/course/10-spellgrid/expansion/solution/words.json
+++ b/course/10-spellgrid/expansion/solution/words.json
@@ -15,6 +15,7 @@
   { "name": "MOTH", "role": "noun" },
   { "name": "SCRIBE", "role": "noun" },
   { "name": "KNIGHT", "role": "noun" },
+  { "name": "CRIER", "role": "noun" },
   { "name": "DEATHRATTLE", "role": "noun" },
   { "name": "BATTLECRY", "role": "noun" },
   { "name": "YOU", "role": "property" },
diff --git a/course/10-spellgrid/lesson.md b/course/10-spellgrid/lesson.md
index 96ada4b..3b2cc34 100644
--- a/course/10-spellgrid/lesson.md
+++ b/course/10-spellgrid/lesson.md
@@ -61,7 +61,7 @@ From the course repository, copy the module's tests and levels into your workspa
 node tools/start-module.mjs 10 ~/my-engine
 ```
 
-It copies `tests/test_10.*` and the three levels into `levels/`. The tests load them from there.
+It copies `tests/test_10.*`, SpellGrid's cards into `cards/`, and the three levels into `levels/`. The tests load them from there.
 
 ### The harness
 
@@ -90,7 +90,7 @@ The three seams:
 2. **Hazards mark, the death step removes.** A minion that a turn destroys (a hazard, `OPEN`/`SHUT`, `X IS NOT X`) is marked pending destroy, in one Sequence, and Module 3's Death Creation Step removes it. Its Deathrattle resolves.
 3. **Grid changes reparse.** When a Sequence ends, the text its effects asked for is written (`spawnText`: "write the word on this minion's tile"), the minions that died leave the grid, and the rules are parsed again, before anything else.
 
-SpellGrid's cards, all in `course/cards/`:
+SpellGrid's cards, in `course/10-spellgrid/cards/`. `start-module 10` copies them into your `cards/` with the course's other cards; earlier modules never see them.
 
 | Card | Type | Stats | Noun | Text |
 |---|---|---|---|---|
@@ -121,6 +121,7 @@ The full statements are in `course/10-spellgrid/scenarios.md`.
 - `test_10_grid_and_card_doublers_take_max`: Predict question 1. Two, not four.
 - `test_10_hazard_feeds_death_step`: seam 2. The log is exactly `Destroyed`, `DeathPhase`, `Triggered`, `Damaged`.
 - `test_10_spawned_text_triggers_reparse`: seam 3. `BABA IS WIN` is a rule straight after the cast.
+- `test_10_targeted_spell_needs_target`: Spark without a target is an error, and the card stays in the hand.
 - `test_10_level_1_solution`, `test_10_level_2_solution`, `test_10_level_3_solution`: each level, played from a script to `won()`.
 - `test_10_level_3_naive_would_differ`: level 3 with `withNaiveAuraTiming()`. Same inputs, and the knight dies.
 
@@ -164,7 +165,7 @@ knight .      .      .      hedge  flag   #
 
 ## Build
 
-Make the nine tests pass, and keep Modules 1–9 green. The shape to aim for:
+Make the ten tests pass, and keep Modules 1–9 green. The shape to aim for:
 
 ```text
         Part I: the card engine                     Part II: the grid engine
@@ -341,10 +342,11 @@ export const END_OF_PHASE: readonly EndOfPhaseStep[] = ["deathCreation", "auraUp
 > - Baba Is You reparses "when any parsable object changes position or is destroyed" ([Rule](https://babaiswiki.fandom.com/wiki/Rule)). SpellGrid reparses after each Sequence whether or not it changed the grid. That is cheaper to reason about and gives the same rules.
 > - A minion that a conversion turns into something else (`KEG IS ROCK`) keeps its card in the reference: the object changes kind, the minion stays in play. No test or level does this, and a real design would have to decide.
 > - A minion that a card effect summons (Harvest Golem's Damaged Golem) enters play but not the grid. No SpellGrid card summons.
+> - Module 8 planned every `YOU` object's move "under the rules in force before the first". In SpellGrid, a minion destroyed during movement (`OPEN`/`SHUT`) dies in a Sequence on the spot, and seam 3 reparses when it ends, so the `YOU` objects that move after it use the new rules. The reference accepts this on purpose: a Sequence's grid changes always reparse at once, wherever the Sequence runs, and no level or test depends on the difference. A design that wanted Module 8's rule exactly would hold the reparse until movement ends.
 
 ## Expansion Drop
 
-A new trigger word: `BATTLECRY`. With it, `BATTLECRY IS DOUBLE` on the grid does what Brann Bronzebeard's "Your Battlecries trigger twice." does ([Brann Bronzebeard](https://hearthstone.wiki.gg/wiki/Brann_Bronzebeard)), the Module 4 Expansion Drop. The test plays a Town Crier ("Battlecry: Deal 1 damage to the enemy hero.", already in `course/cards/`) under the rule.
+A new trigger word: `BATTLECRY`. With it, `BATTLECRY IS DOUBLE` on the grid does what Brann Bronzebeard's "Your Battlecries trigger twice." does ([Brann Bronzebeard](https://hearthstone.wiki.gg/wiki/Brann_Bronzebeard)), the Module 4 Expansion Drop. The test plays a Town Crier ("Battlecry: Deal 1 damage to the enemy hero.", already in your `cards/`) under the rule.
 
 The constraint, as always: **do not edit anything under `src/engine/`**. The harness doesn't change either.
 
diff --git a/course/10-spellgrid/reference/rust/README.md b/course/10-spellgrid/reference/rust/README.md
index ef5cd41..e09bbeb 100644
--- a/course/10-spellgrid/reference/rust/README.md
+++ b/course/10-spellgrid/reference/rust/README.md
@@ -2,7 +2,7 @@
 
 The course's own engine as of the end of Module 10: Part I's card engine and Part II's grid engine, joined by SpellGrid. Every test from Modules 1–9 still passes. Module 9's reference was the starting point, so a diff between the two shows what this module adds.
 
-- `cards/` and `levels/` (at the crate root; not in this directory): copies of `course/cards/` and `course/10-spellgrid/levels/`, staged by `tools/verify-references.mjs`.
+- `cards/` and `levels/` (at the crate root; not in this directory): copies of `course/cards/` plus `course/10-spellgrid/cards/` (SpellGrid's own cards, which only Module 10 on receives), and of `course/10-spellgrid/levels/`, staged by `tools/verify-references.mjs`.
 - `src/engine/spellgrid.rs` (new): the only module that uses both engines. `SpellGrid` keeps a `World` and a `puzzle::Level` in step through the three seams: `rule_auras` (rules in force → auras), `CardSide::destroy` (hazard victims → one `Destroy` Sequence → the Death Creation Step), and `CardSide::sequence` (after each Sequence: write `TextSpawned` text, take dead minions off the grid, reparse). It also keeps one id space: a minion's id is its grid object's id.
 - Part I (`src/engine/`, outside `puzzle/`):
   - `queue.rs`: `END_OF_PHASE` (`[DeathCreation, AuraUpdate]`) is the list of steps at the end of the outermost Phase, read from the world. `Action::SpawnText` records a `TextSpawned` event.
diff --git a/course/10-spellgrid/reference/rust/src/cli.rs b/course/10-spellgrid/reference/rust/src/cli.rs
index ceb235c..1caad8f 100644
--- a/course/10-spellgrid/reference/rust/src/cli.rs
+++ b/course/10-spellgrid/reference/rust/src/cli.rs
@@ -14,7 +14,6 @@
 
 use std::cell::RefCell;
 use std::io::{BufRead, Write};
-use std::panic::{self, AssertUnwindSafe};
 use std::rc::Rc;
 
 use crate::harness::{new_spell_grid, Dir, LevelDef, SpellGrid};
@@ -138,13 +137,7 @@ pub fn run(level_text: &str, input: Box<dyn BufRead>, output: Box<dyn Write>) ->
             .and_then(|n| options.get(n.wrapping_sub(1)));
         picked.unwrap_or(&options[0]).clone()
     });
-    // The harness panics on a move the rules don't allow (a card not in the hand, a
-    // full tile). The CLI reports the message instead of stopping.
-    let hook = panic::take_hook();
-    panic::set_hook(Box::new(|_| {}));
-    let outcome = play(&mut g, &level, &io);
-    panic::set_hook(hook);
-    outcome
+    play(&mut g, &level, &io)
 }
 
 /// Draw, read a command, do it; until the level is won or lost, or the player quits.
@@ -172,27 +165,26 @@ fn play(g: &mut SpellGrid, level: &LevelDef, io: &Rc<RefCell<Io>>) -> Outcome {
             Some(&"d") => Some(Dir::Right),
             _ => None,
         };
-        let result = panic::catch_unwind(AssertUnwindSafe(|| match (dir, words.as_slice()) {
-            (Some(dir), _) => g.step(dir),
+        // The harness panics on a move the rules don't allow (a card not in the hand, a
+        // full tile). The CLI asks first, and reports the reason instead.
+        let done = match (dir, words.as_slice()) {
+            (Some(dir), _) => Ok(g.step(dir)),
             (None, ["c", args @ ..]) if !args.is_empty() => match parse_cast(args) {
-                (card, None) => g.cast(&card, None),
+                (card, None) => g.check_cast(&card, None).map(|()| g.cast(&card, None)),
                 (card, Some((x, y))) => match g.minion_at(x, y) {
-                    Some(target) => g.cast(&card, Some(target)),
-                    None => {
+                    Some(target) => g
+                        .check_cast(&card, Some(target))
+                        .map(|()| g.cast(&card, Some(target))),
+                    None => g.check_play(&card, x, y).map(|()| {
                         g.play(&card, x, y);
-                    }
+                    }),
                 },
             },
-            _ => io
-                .borrow_mut()
-                .write("Commands: w a s d (move), c <card> [x y] (cast or play), q (quit)\n"),
-        }));
-        if let Err(payload) = result {
-            let message = payload
-                .downcast_ref::<String>()
-                .cloned()
-                .or_else(|| payload.downcast_ref::<&str>().map(|s| s.to_string()))
-                .unwrap_or_else(|| "that can't be done".to_string());
+            _ => {
+                Err("Commands: w a s d (move), c <card> [x y] (cast or play), q (quit)".to_string())
+            }
+        };
+        if let Err(message) = done {
             io.borrow_mut().write(&format!("{message}\n"));
         }
     }
diff --git a/course/10-spellgrid/reference/rust/src/content/words.json b/course/10-spellgrid/reference/rust/src/content/words.json
index 5c49029..bb7c86c 100644
--- a/course/10-spellgrid/reference/rust/src/content/words.json
+++ b/course/10-spellgrid/reference/rust/src/content/words.json
@@ -15,6 +15,7 @@
   { "name": "MOTH", "role": "noun" },
   { "name": "SCRIBE", "role": "noun" },
   { "name": "KNIGHT", "role": "noun" },
+  { "name": "CRIER", "role": "noun" },
   { "name": "DEATHRATTLE", "role": "noun" },
   { "name": "YOU", "role": "property" },
   { "name": "WIN", "role": "property" },
diff --git a/course/10-spellgrid/reference/rust/src/engine/spellgrid.rs b/course/10-spellgrid/reference/rust/src/engine/spellgrid.rs
index 37a6974..1c4e9e9 100644
--- a/course/10-spellgrid/reference/rust/src/engine/spellgrid.rs
+++ b/course/10-spellgrid/reference/rust/src/engine/spellgrid.rs
@@ -24,7 +24,7 @@ use std::collections::{HashMap, HashSet};
 use serde::Deserialize;
 
 use super::aura::aura_update_other;
-use super::card::{Aura, CardLibrary, CardType, Stacking, TriggerOn};
+use super::card::{Aura, CardLibrary, CardType, Effect, Stacking, Target, TriggerOn};
 use super::event::Event;
 use super::puzzle::{Dir, Hazard, Kind, Level, LevelDef, ObjectId, Response, Rule, WordDef};
 use super::queue::{run_sequence, Action};
@@ -180,9 +180,62 @@ impl SpellGrid {
         self.side.grid_changed(&mut self.level);
     }
 
+    /// Why `cast(card, target)` can't be done now, or `Ok` if it can: the card must be a
+    /// spell in player 0's hand, and a spell that hits a chosen minion needs a target
+    /// minion on the grid. Nothing changes either way.
+    pub fn check_cast(&self, card: &str, target: Option<ObjectId>) -> Result<(), String> {
+        self.side.check_hand(card, CardType::Spell)?;
+        let chooses = self.side.world.card(card).on_cast.iter().any(|e| {
+            matches!(
+                e,
+                Effect::DealDamage {
+                    target: Target::Chosen,
+                    ..
+                } | Effect::GainAttack {
+                    target: Target::Chosen,
+                    ..
+                } | Effect::Destroy {
+                    target: Target::Chosen
+                }
+            )
+        });
+        match target {
+            None if chooses => Err(format!("{card:?} needs a target minion")),
+            None => Ok(()),
+            Some(id) => {
+                // Every id in `entities` was issued by the board, so `find` may ask about it.
+                let card = self.side.entities.contains_key(&id);
+                if card && self.level.board().find(id).is_some() {
+                    Ok(())
+                } else {
+                    Err(format!("{id} is not a minion on the grid"))
+                }
+            }
+        }
+    }
+
+    /// Why `play(card, x, y)` can't be done now, or `Ok` if it can.
+    pub fn check_play(&self, card: &str, x: i32, y: i32) -> Result<(), String> {
+        self.side.check_hand(card, CardType::Minion)?;
+        if self.side.world.card(card).def.noun.is_none() {
+            return Err(format!("{card:?} has no noun: it can't stand on the grid"));
+        }
+        if !self.level.board().in_bounds(x, y) {
+            return Err(format!("({x}, {y}) is off the grid"));
+        }
+        if self.level.board().at(x, y).next().is_some() {
+            return Err(format!("({x}, {y}) is not empty"));
+        }
+        Ok(())
+    }
+
     /// Cast a spell from player 0's hand, as one Sequence. `target` is a minion's id.
+    /// Panics if `check_cast` says no.
     pub fn cast(&mut self, card: &str, target: Option<ObjectId>) {
-        let in_hand = self.side.from_hand(card, CardType::Spell);
+        if let Err(problem) = self.check_cast(card, target) {
+            panic!("{problem}");
+        }
+        let in_hand = self.side.in_hand(card).expect("checked");
         self.side.world.move_to(in_hand, Zone::Graveyard);
         let target = target.map(|id| self.side.entity(id));
         let action = Action::Cast {
@@ -194,13 +247,12 @@ impl SpellGrid {
     }
 
     /// Play a minion from player 0's hand onto the empty tile (x, y), as one Sequence.
-    /// Returns its new id.
+    /// Returns its new id. Panics if `check_play` says no.
     pub fn play(&mut self, card: &str, x: i32, y: i32) -> ObjectId {
-        let in_hand = self.side.from_hand(card, CardType::Minion);
-        assert!(
-            self.level.board().at(x, y).next().is_none(),
-            "({x}, {y}) is not empty"
-        );
+        if let Err(problem) = self.check_play(card, x, y) {
+            panic!("{problem}");
+        }
+        let in_hand = self.side.in_hand(card).expect("checked");
         let kind = self.side.noun_of(card);
         let id = self.level.board_mut().place(kind, x, y);
         self.side.link(in_hand, id);
@@ -241,19 +293,26 @@ impl CardSide {
         }
     }
 
-    fn from_hand(&self, card: &str, card_type: CardType) -> EntityId {
-        let in_hand = self
-            .world
+    fn in_hand(&self, card: &str) -> Option<EntityId> {
+        self.world
             .zone(0, Zone::Hand)
             .iter()
             .copied()
             .find(|&id| self.world.card_name(id) == card)
-            .unwrap_or_else(|| panic!("{card:?} is not in the hand"));
-        assert!(
-            self.world.card(card).def.card_type == card_type,
-            "{card:?} is not a {card_type:?}"
-        );
-        in_hand
+    }
+
+    fn check_hand(&self, card: &str, card_type: CardType) -> Result<(), String> {
+        if self.in_hand(card).is_none() {
+            return Err(format!("{card:?} is not in the hand"));
+        }
+        if self.world.card(card).def.card_type != card_type {
+            let kind = match card_type {
+                CardType::Minion => "minion",
+                CardType::Spell => "spell",
+            };
+            return Err(format!("{card:?} is not a {kind}"));
+        }
+        Ok(())
     }
 
     /// Seam 2. Objects that aren't cards leave the board. Minions are marked pending
diff --git a/course/10-spellgrid/reference/rust/src/harness.rs b/course/10-spellgrid/reference/rust/src/harness.rs
index 651fbb2..cd362fa 100644
--- a/course/10-spellgrid/reference/rust/src/harness.rs
+++ b/course/10-spellgrid/reference/rust/src/harness.rs
@@ -436,6 +436,14 @@ impl SpellGrid {
     pub fn set_chooser(&mut self, chooser: impl FnMut(&str, &[String]) -> String + 'static) {
         self.grid.world_mut().set_chooser(Box::new(chooser));
     }
+    /// For the command line: why `cast` would panic, or `Ok` if it wouldn't.
+    pub fn check_cast(&self, card: &str, target: Option<Id>) -> Result<(), String> {
+        self.grid.check_cast(card, target)
+    }
+    /// For the command line: why `play` would panic, or `Ok` if it wouldn't.
+    pub fn check_play(&self, card: &str, x: i32, y: i32) -> Result<(), String> {
+        self.grid.check_play(card, x, y)
+    }
     /// Test hook: the naive engine reads the auras before the dead leave play, the
     /// same end-of-Phase steps reversed.
     pub fn with_naive_aura_timing(&mut self) {
diff --git a/course/10-spellgrid/reference/ts/README.md b/course/10-spellgrid/reference/ts/README.md
index 12687b6..3bc05c4 100644
--- a/course/10-spellgrid/reference/ts/README.md
+++ b/course/10-spellgrid/reference/ts/README.md
@@ -2,7 +2,7 @@
 
 The course's own engine as of the end of Module 10: Part I's card engine and Part II's grid engine, joined by SpellGrid. Every test from Modules 1–9 still passes. Module 9's reference was the starting point, so a diff between the two shows what this module adds.
 
-- `cards/` and `levels/` (at the package root; not in this directory): copies of `course/cards/` and `course/10-spellgrid/levels/`, staged by `tools/verify-references.mjs`.
+- `cards/` and `levels/` (at the package root; not in this directory): copies of `course/cards/` plus `course/10-spellgrid/cards/` (SpellGrid's own cards, which only Module 10 on receives), and of `course/10-spellgrid/levels/`, staged by `tools/verify-references.mjs`.
 - `src/engine/spellgrid.ts` (new): the only file that imports both engines. `SpellGrid` keeps a `World` and a `puzzle.Level` in step through the three seams: `ruleAuras` (rules in force → auras), the destroy function (hazard victims → one `destroy` Sequence → the Death Creation Step), and `sequence` (after each Sequence: write `TextSpawned` text, take dead minions off the grid, reparse). It also keeps one id space: a minion's id is its grid object's id.
 - Part I (`src/engine/`, outside `puzzle/`):
   - `queue.ts`: `END_OF_PHASE` (`["deathCreation", "auraUpdate"]`) is the list of steps at the end of the outermost Phase, read from the world. The `spawnText` action records a `TextSpawned` event.
diff --git a/course/10-spellgrid/reference/ts/src/content/words.json b/course/10-spellgrid/reference/ts/src/content/words.json
index 5c49029..bb7c86c 100644
--- a/course/10-spellgrid/reference/ts/src/content/words.json
+++ b/course/10-spellgrid/reference/ts/src/content/words.json
@@ -15,6 +15,7 @@
   { "name": "MOTH", "role": "noun" },
   { "name": "SCRIBE", "role": "noun" },
   { "name": "KNIGHT", "role": "noun" },
+  { "name": "CRIER", "role": "noun" },
   { "name": "DEATHRATTLE", "role": "noun" },
   { "name": "YOU", "role": "property" },
   { "name": "WIN", "role": "property" },
diff --git a/course/10-spellgrid/reference/ts/src/engine/spellgrid.ts b/course/10-spellgrid/reference/ts/src/engine/spellgrid.ts
index 9a5e29b..4e2e0ca 100644
--- a/course/10-spellgrid/reference/ts/src/engine/spellgrid.ts
+++ b/course/10-spellgrid/reference/ts/src/engine/spellgrid.ts
@@ -150,29 +150,62 @@ export class SpellGrid {
     this.gridChanged();
   }
 
-  /** Cast a spell from player 0's hand, as one Sequence. `target` is a minion's id. */
+  /**
+   * Why `cast(card, target)` can't be done now, or `undefined` if it can: the card must
+   * be a spell in player 0's hand, and a spell that hits a chosen minion needs a target
+   * minion on the grid. Nothing changes when the answer is no.
+   */
+  checkCast(card: string, target?: puzzle.ObjectId): string | undefined {
+    const problem = this.checkHand(card, "spell");
+    if (problem !== undefined) return problem;
+    const chooses = this.world.card(card).onCast.some((e) => "target" in e && e.target === "chosen");
+    if (target === undefined) return chooses ? `"${card}" needs a target minion` : undefined;
+    const object = this.level.board.find(target);
+    if (object === undefined || !this.entities.has(target)) return `${target} is not a minion on the grid`;
+    return undefined;
+  }
+
+  /** Why `play(card, x, y)` can't be done now, or `undefined` if it can. */
+  checkPlay(card: string, x: number, y: number): string | undefined {
+    const problem = this.checkHand(card, "minion");
+    if (problem !== undefined) return problem;
+    if (this.world.card(card).def.noun === undefined) return `"${card}" has no noun: it can't stand on the grid`;
+    if (!this.level.board.inBounds(x, y)) return `(${x}, ${y}) is off the grid`;
+    if (this.level.board.at(x, y).length > 0) return `(${x}, ${y}) is not empty`;
+    return undefined;
+  }
+
+  /** Cast a spell from player 0's hand, as one Sequence. `target` is a minion's id. Throws if `checkCast` says no. */
   cast(card: string, target?: puzzle.ObjectId): void {
-    const inHand = this.fromHand(card, "spell");
-    this.world.moveTo(inHand, "graveyard");
+    const problem = this.checkCast(card, target);
+    if (problem !== undefined) throw new Error(problem);
+    this.world.moveTo(this.inHand(card)!, "graveyard");
     const chosen = target === undefined ? undefined : this.entity(target);
     this.sequence({ type: "cast", card, player: 0, target: chosen });
   }
 
-  /** Play a minion from player 0's hand onto the empty tile (x, y), as one Sequence. Returns its new id. */
+  /**
+   * Play a minion from player 0's hand onto the empty tile (x, y), as one Sequence.
+   * Returns its new id. Throws if `checkPlay` says no.
+   */
   play(card: string, x: number, y: number): puzzle.ObjectId {
-    const inHand = this.fromHand(card, "minion");
-    if (this.level.board.at(x, y).length > 0) throw new Error(`(${x}, ${y}) is not empty`);
+    const problem = this.checkPlay(card, x, y);
+    if (problem !== undefined) throw new Error(problem);
+    const inHand = this.inHand(card)!;
     const id = this.level.board.place(this.nounOf(card), x, y);
     this.link(inHand, id);
     this.sequence({ type: "play", id: inHand });
     return id;
   }
 
-  private fromHand(card: string, type: "minion" | "spell"): EntityId {
-    const inHand = this.world.zone(0, "hand").find((id) => this.world.cardName(id) === card);
-    if (inHand === undefined) throw new Error(`"${card}" is not in the hand`);
-    if (this.world.card(card).def.type !== type) throw new Error(`"${card}" is not a ${type}`);
-    return inHand;
+  private inHand(card: string): EntityId | undefined {
+    return this.world.zone(0, "hand").find((id) => this.world.cardName(id) === card);
+  }
+
+  private checkHand(card: string, type: "minion" | "spell"): string | undefined {
+    if (this.inHand(card) === undefined) return `"${card}" is not in the hand`;
+    if (this.world.card(card).def.type !== type) return `"${card}" is not a ${type}`;
+    return undefined;
   }
 
   // ---- The seams ----
diff --git a/course/10-spellgrid/reference/ts/src/harness.ts b/course/10-spellgrid/reference/ts/src/harness.ts
index 15db9cf..90a4172 100644
--- a/course/10-spellgrid/reference/ts/src/harness.ts
+++ b/course/10-spellgrid/reference/ts/src/harness.ts
@@ -187,6 +187,9 @@ export interface SpellGrid extends Baba {
   clearLog(): void;
   setChooser(choose: Chooser): void; // makes Assemble's choices
   withNaiveAuraTiming(): void; // test hook: Aura Update before the Death Creation Step
+  // For the command line: why `cast`/`play` would fail, or null if they wouldn't
+  checkCast(card: string, target?: Id): string | null;
+  checkPlay(card: string, x: number, y: number): string | null;
 }
 
 /** A SpellGrid level; `extra` cards are added to the course's cards, replacing any with the same name. */
@@ -246,5 +249,7 @@ export function newSpellGrid(level: puzzle.LevelDef, extra: CardDef[]): SpellGri
     setChooser: (choose) => g.world.setChooser(choose),
     // The naive engine reads the auras before the dead leave play: the same steps, reversed.
     withNaiveAuraTiming: () => g.world.setEndOfPhase([...END_OF_PHASE].reverse()),
+    checkCast: (card, target) => g.checkCast(card, target) ?? null,
+    checkPlay: (card, x, y) => g.checkPlay(card, x, y) ?? null,
   };
 }
diff --git a/course/10-spellgrid/scenarios.md b/course/10-spellgrid/scenarios.md
index 3c34930..beced89 100644
--- a/course/10-spellgrid/scenarios.md
+++ b/course/10-spellgrid/scenarios.md
@@ -8,7 +8,7 @@ SpellGrid is the course's own small game: Part I's card engine and Part II's gri
 - The level format gains two optional fields (`course/schema/level.schema.json`): `cards`, a list of `{ card, x, y }`, and `hand`, a list of card names. Each entry of `cards` is a minion in play for player 0 **and** a grid object at (x, y) whose noun is the card's `"noun"` field (`"noun": "KEG"` makes an object of kind `"keg"`). Each name in `hand` is a card in player 0's hand.
 - `cards` (the constructor's second argument) is a list of extra card definitions, added to the course's cards. Every test here passes an empty list.
 - One id space: a minion's id is its grid object's id. `place`, `posOf`, `hasProperty` and `health` all take it, and `log()` reports it. A hero, or a card that isn't on the grid, gets an id no grid object has.
-- `cast(card, target?)` (Rust: `cast(card, Some(target))` or `None`) casts a spell from player 0's hand, as one Sequence. The card leaves the hand. Casting a card that isn't in the hand is an error.
+- `cast(card, target?)` (Rust: `cast(card, Some(target))` or `None`) casts a spell from player 0's hand, as one Sequence. The card leaves the hand. Casting a card that isn't in the hand is an error, and so is casting a spell that hits a chosen minion (Spark) without a target; neither changes anything.
 - `play(card, x, y)` plays a minion from player 0's hand onto the empty tile (x, y), as one Sequence (Module 4's `play`: it enters the board, then its Battlecry resolves), and returns its id. Playing onto a tile that holds anything is an error.
 - `setChooser(choose)` is Module 5's: it makes Assemble's choices (`"base"`, `"donor"`, `"half"`).
 - `health(id)`, `hero(player)`, `nameOf(id)`, `log()` and `clearLog()` are Part I's, with ids translated as above. `minionAt(x, y)` is the id of the minion on that tile, or `null` (Rust: `Option<Id>`). `hand()` lists the card names in player 0's hand, in order.
@@ -92,6 +92,14 @@ New words: the nouns `KEG`, `BRAMBLE`, `HEDGE`, `WARDEN`, `MOTH`, `SCRIBE`, `KNI
 - Action 2: `step("left")`.
 - Assertions 3: `won()` is true.
 
+### test_10_targeted_spell_needs_target
+
+- Setup: a level 3 wide and 1 high with card Bramble Wall at (0,0); hand `["Spark"]`.
+- Action 1: `cast("Spark")`, with no target.
+- Assertions 1: it is an error (Rust: a panic; TypeScript: it throws), and nothing changed: `hand()` is still `["Spark"]` and `health(bramble)` is 3. Spark's effect hits a chosen minion, so a cast without one would waste the card.
+- Action 2: `cast("Spark", bramble)`.
+- Assertions 2: `health(bramble)` is 2 and `hand()` is empty.
+
 ### test_10_level_1_solution
 
 Level `levels/l1-double-tap.json`. The Bramble Wall (3 Health) is `STOP` and blocks the only way to the flag. Whirlwind and one Powder Keg Deathrattle do 2 damage, one short.
diff --git a/course/10-spellgrid/tests/rust/test_10.rs b/course/10-spellgrid/tests/rust/test_10.rs
index 85a1142..9bd0e25 100644
--- a/course/10-spellgrid/tests/rust/test_10.rs
+++ b/course/10-spellgrid/tests/rust/test_10.rs
@@ -243,6 +243,26 @@ fn test_10_spawned_text_triggers_reparse() {
     assert!(g.won());
 }
 
+#[test]
+fn test_10_targeted_spell_needs_target() {
+    let mut g = new_spell_grid(
+        level(3, 1, &[], &[], &[("Bramble Wall", 0, 0)], &["Spark"]),
+        vec![],
+    );
+    let bramble = minion(&g, 0, 0);
+
+    let cast = std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| g.cast("Spark", None)));
+    assert!(cast.is_err());
+
+    assert_eq!(g.hand(), vec!["Spark"]);
+    assert_eq!(g.health(bramble), 3);
+
+    g.cast("Spark", Some(bramble));
+
+    assert_eq!(g.health(bramble), 2);
+    assert_eq!(g.hand(), Vec::<String>::new());
+}
+
 #[test]
 fn test_10_level_1_solution() {
     let mut g = new_spell_grid(
diff --git a/course/10-spellgrid/tests/ts/test_10.test.ts b/course/10-spellgrid/tests/ts/test_10.test.ts
index c49673d..f9c63fa 100644
--- a/course/10-spellgrid/tests/ts/test_10.test.ts
+++ b/course/10-spellgrid/tests/ts/test_10.test.ts
@@ -206,6 +206,21 @@ test("test_10_spawned_text_triggers_reparse", () => {
   expect(g.won()).toBe(true);
 });
 
+test("test_10_targeted_spell_needs_target", () => {
+  const g = newSpellGrid(level(3, 1, { cards: [["Bramble Wall", 0, 0]], hand: ["Spark"] }), []);
+  const bramble = minion(g, 0, 0);
+
+  expect(() => g.cast("Spark")).toThrow();
+
+  expect(g.hand()).toEqual(["Spark"]);
+  expect(g.health(bramble)).toBe(3);
+
+  g.cast("Spark", bramble);
+
+  expect(g.health(bramble)).toBe(2);
+  expect(g.hand()).toEqual([]);
+});
+
 test("test_10_level_1_solution", () => {
   const g = newSpellGrid(l1 as LevelDef, []);
   const keg = minion(g, 0, 4);
diff --git a/course/catalog.json b/course/catalog.json
index 675666c..848fbc1 100644
--- a/course/catalog.json
+++ b/course/catalog.json
@@ -411,7 +411,8 @@
     "role": "meta",
     "text": "a trigger type, so DEATHRATTLE IS DOUBLE doubles deathrattles",
     "source": "https://github.com/utilForever/baba-is-auto/blob/main/Documents/rule-language.md",
-    "game": "spellgrid"
+    "game": "spellgrid",
+    "note": "Lexicon role: SpellGrid's words.json lists it as a noun, so it can be the subject of a rule. The catalog keeps role meta: it names the engine's own trigger, which the coupling audit must not flag (only role-noun words are audited)."
   },
   {
     "name": "Powder Keg",
@@ -548,6 +549,13 @@
     "text": "Tin Knight's noun (a SpellGrid minion on the grid)",
     "game": "spellgrid"
   },
+  {
+    "name": "CRIER",
+    "kind": "word",
+    "role": "noun",
+    "text": "Town Crier's noun (a SpellGrid minion on the grid)",
+    "game": "spellgrid"
+  },
   {
     "name": "Town Crier",
     "kind": "card",
@@ -563,6 +571,7 @@
     "kind": "word",
     "role": "meta",
     "text": "a trigger type, so BATTLECRY IS DOUBLE doubles battlecries (the Module 10 Expansion Drop)",
-    "game": "spellgrid"
+    "game": "spellgrid",
+    "note": "Lexicon role: SpellGrid's words.json lists it as a noun, so it can be the subject of a rule. The catalog keeps role meta: it names the engine's own trigger, which the coupling audit must not flag (only role-noun words are audited)."
   }
 ]
diff --git a/course/harness.md b/course/harness.md
index aa1d79b..b1d4429 100644
--- a/course/harness.md
+++ b/course/harness.md
@@ -152,4 +152,4 @@ From M10, `LevelDef` has two more optional fields, `cards: { card, x, y }[]` and
 
 SpellGrid has one id space: a minion's id is its grid object's id, so `posOf`, `hasProperty` and `health` take the same id, and `log()` reports it. A hero or a card in hand gets an id that no grid object has; a card played from hand gets its grid object's id (returned by `play`). `cast(card, target?)` casts a spell from player 0's hand as one Sequence (target: a minion's id); `play(card, x, y)` plays a minion from player 0's hand onto an empty tile as one Sequence (it enters the board, then its Battlecry). Both are errors for a card not in the hand, and `play` for a tile that holds anything. Casting is not a turn: `won()` changes only in `step`.
 
-The three seams: (1) a rule in force `<TRIGGER> IS <MULTIPLIER>` (`DEATHRATTLE IS DOUBLE`) is an aura like Baron Rivendare's for both players (`DOUBLE`: twice, `stacking: "max"`), and `<TRIGGER> IS NOT <MULTIPLIER>` caps that trigger at one activation, whatever multiplies it; rule auras join the snapshot at the next Aura Update. (2) A minion that a turn destroys (hazards, `OPEN`/`SHUT`, `X IS NOT X`) is marked pending destroy in one Sequence, and the Death Creation Step removes it. (3) When a Sequence ends, text its effects asked for (`spawnText`) is written on the minion's tile, minions that died leave the grid, and the rules are reparsed. `withNaiveAuraTiming()` reverses the two end-of-Phase steps (Aura Update, then Death Creation Step) for that game; only `test_10_level_3_naive_would_differ` uses it.
+The three seams: (1) a rule in force `<TRIGGER> IS <MULTIPLIER>` (`DEATHRATTLE IS DOUBLE`) is an aura like Baron Rivendare's for both players (`DOUBLE`: twice, `stacking: "max"`), and `<TRIGGER> IS NOT <MULTIPLIER>` caps that trigger at one activation, whatever multiplies it; rule auras join the snapshot at the next Aura Update. (2) A minion that a turn destroys (hazards, `OPEN`/`SHUT`, `X IS NOT X`) is marked pending destroy in one Sequence, and the Death Creation Step removes it. (3) When a Sequence ends, text its effects asked for (`spawnText`) is written on the minion's tile, minions that died leave the grid, and the rules are reparsed. Trigger words (`DEATHRATTLE`, and `BATTLECRY` after the Expansion Drop) are nouns in the lexicon (`words.json`), so they can be the subject of a rule, but `role: "meta"` in `course/catalog.json`: they name the engine's own triggers, and the coupling audit checks only role-noun words. `checkCast(card, target?)` and `checkPlay(card, x, y)` (Rust: `check_cast`, `check_play`, returning `Result<(), String>`) say why `cast`/`play` would fail, or `null`/`Ok`; the command line uses them, the tests don't. `withNaiveAuraTiming()` reverses the two end-of-Phase steps (Aura Update, then Death Creation Step) for that game; only `test_10_level_3_naive_would_differ` uses it.
diff --git a/tools/lib.mjs b/tools/lib.mjs
index cb47d6c..2d9e91d 100644
--- a/tools/lib.mjs
+++ b/tools/lib.mjs
@@ -48,6 +48,19 @@ export function scenarioNames(path, file = "scenarios.md") {
   return [...names].sort();
 }
 
+/**
+ * The card data a workspace at module `upTo` has: course/cards (every module's, from
+ * Module 5), then the cards/ of each module up to `upTo` that has its own (Module 10's
+ * SpellGrid cards), so earlier modules never see later modules' cards.
+ */
+export function cardDirs(upTo) {
+  const shared = join(courseRoot(), "cards");
+  const local = moduleDirs()
+    .filter((m) => Number(m.num) <= Number(upTo))
+    .map((m) => join(m.path, "cards"));
+  return [shared, ...local].filter((d) => existsSync(d));
+}
+
 export function loadCatalog() {
   const f = join(courseRoot(), "catalog.json");
   if (!existsSync(f)) throw new Error(`catalog not found: ${f}`);
diff --git a/tools/start-module.mjs b/tools/start-module.mjs
index 5842725..276a895 100644
--- a/tools/start-module.mjs
+++ b/tools/start-module.mjs
@@ -2,7 +2,7 @@
 // Copies module NN's tests for the learner's track into <workspace>/tests/.
 import { cpSync, existsSync, mkdirSync, readFileSync } from "node:fs";
 import { basename, join } from "node:path";
-import { moduleDirs, courseRoot, testFiles, fail } from "./lib.mjs";
+import { cardDirs, moduleDirs, courseRoot, testFiles, fail } from "./lib.mjs";
 
 const [num, ws] = process.argv.slice(2);
 if (!/^\d\d$/.test(num || "") || !ws) fail("usage: start-module.mjs <NN> <workspaceDir>");
@@ -32,13 +32,12 @@ mkdirSync(join(ws, "tests"), { recursive: true });
 for (const f of files) cpSync(f, join(ws, "tests", basename(f)));
 console.log(`Copied ${files.length} test file(s) for module ${num} into ${join(ws, "tests")}`);
 
-// The course's card data (read by your content from Module 5). Refreshed on every start;
-// card files you add yourself are kept.
-const cards = join(courseRoot(), "cards");
-if (existsSync(cards)) {
-  cpSync(cards, join(ws, "cards"), { recursive: true });
-  console.log(`Copied the course card data into ${join(ws, "cards")}`);
-}
+// The course's card data (read by your content from Module 5): course/cards, plus the cards
+// of each module up to this one that has its own (Module 10's SpellGrid cards). Refreshed on
+// every start; card files you add yourself are kept.
+const cardSources = cardDirs(num);
+for (const cards of cardSources) cpSync(cards, join(ws, "cards"), { recursive: true });
+if (cardSources.length) console.log(`Copied the course card data into ${join(ws, "cards")}`);
 
 // The module's puzzle levels (Module 10's tests load them from levels/).
 const levels = join(mod.path, "levels");
diff --git a/tools/test/fixtures/course/02-m02/cards/module-fixture.json b/tools/test/fixtures/course/02-m02/cards/module-fixture.json
new file mode 100644
index 0000000..5295c43
--- /dev/null
+++ b/tools/test/fixtures/course/02-m02/cards/module-fixture.json
@@ -0,0 +1,9 @@
+{
+  "name": "Module Fixture",
+  "type": "minion",
+  "cost": 1,
+  "attack": 1,
+  "health": 1,
+  "split": 0,
+  "text": []
+}
\ No newline at end of file
diff --git a/tools/test/schema.test.mjs b/tools/test/schema.test.mjs
index 77c8708..376ac1c 100644
--- a/tools/test/schema.test.mjs
+++ b/tools/test/schema.test.mjs
@@ -55,14 +55,17 @@ test("card_schema_accepts_fixtures", () => {
   }
 });
 
-// Card data the course ships: course/cards (every card the references load) and the
+// Card data the course ships: course/cards (every module's cards), module-local cards in
+// course/NN-*/cards (Module 10's SpellGrid cards, staged from that module on), and the
 // Expansion Drop answers in course/NN-*/expansion/solution/cards.
 function courseCardFiles() {
   const courseDir = join(here, "../../course");
   const dirs = [join(courseDir, "cards")];
   for (const m of readdirSync(courseDir).filter((d) => /^\d\d-/.test(d))) {
-    const d = join(courseDir, m, "expansion/solution/cards");
-    if (existsSync(d)) dirs.push(d);
+    for (const sub of ["cards", "expansion/solution/cards"]) {
+      const d = join(courseDir, m, sub);
+      if (existsSync(d)) dirs.push(d);
+    }
   }
   return dirs.flatMap((d) => readdirSync(d).filter((f) => f.endsWith(".json")).map((f) => join(d, f)));
 }
@@ -141,3 +144,12 @@ test("course_levels_valid", () => {
     for (const card of level.hand ?? []) assert.ok(cards.has(card), `${f}: no card data for ${card}`);
   }
 });
+
+test("spellgrid_cards_are_module_local", () => {
+  // course/cards reaches every workspace from Module 5; SpellGrid's cards must not reach
+  // Modules 5-9 (their spawnText effect and their place in Assemble pools are Module 10's).
+  const shared = join(here, "../../course/cards");
+  for (const f of readdirSync(shared).filter((f) => f.endsWith(".json"))) {
+    assert.notEqual(json(join(shared, f)).game, "spellgrid", `${f} belongs in course/10-spellgrid/cards`);
+  }
+});
diff --git a/tools/test/start-module.test.mjs b/tools/test/start-module.test.mjs
index f2bfe6e..77c717e 100644
--- a/tools/test/start-module.test.mjs
+++ b/tools/test/start-module.test.mjs
@@ -21,6 +21,20 @@ test("start_module_copies_course_cards", () => {
   assert.ok(existsSync(join(ws, "cards/test-fixture.json")));
 });
 
+test("start_module_copies_module_cards_up_to_the_module", () => {
+  const early = copyFixture("ws-start");
+  assert.equal(run("start-module.mjs", ["01", early], env).code, 0);
+  assert.ok(existsSync(join(early, "cards/test-fixture.json")));
+  assert.ok(!existsSync(join(early, "cards/module-fixture.json")));
+  const later = copyFixture("ws-start");
+  mkdirSync(join(later, "tests"), { recursive: true });
+  writeFileSync(join(later, "tests/m02.rs"), "");
+  const r = run("start-module.mjs", ["03", later], env);
+  assert.equal(r.code, 0, r.out);
+  assert.ok(existsSync(join(later, "cards/test-fixture.json")));
+  assert.ok(existsSync(join(later, "cards/module-fixture.json")));
+});
+
 test("start_module_copies_module_levels", () => {
   const ws = copyFixture("ws-start");
   mkdirSync(join(ws, "tests"), { recursive: true });
diff --git a/tools/test/verify-references.test.mjs b/tools/test/verify-references.test.mjs
index b4fb2d9..5ca0eea 100644
--- a/tools/test/verify-references.test.mjs
+++ b/tools/test/verify-references.test.mjs
@@ -76,3 +76,18 @@ test("verify_stage_copies_module_levels", async () => {
   assert.ok(existsSync(join(stage(plans[2], "ts"), "levels", "fixture-level.json")));
   assert.ok(!existsSync(join(stage(plans[1], "ts"), "levels")));
 });
+
+test("verify_stage_copies_module_cards_up_to_the_module", async () => {
+  // Module-local cards (Module 10's SpellGrid cards) reach that module and later ones only.
+  process.env.COURSE_ROOT = root;
+  const { planVerification, stage } = await import("../verify-references.mjs");
+  const { existsSync } = await import("node:fs");
+  const plans = planVerification(moduleDirs(), 3);
+  for (const lang of ["rust", "ts"]) {
+    assert.ok(!existsSync(join(stage(plans[0], lang), "cards", "module-fixture.json")), lang);
+    assert.ok(existsSync(join(stage(plans[1], lang), "cards", "module-fixture.json")), lang);
+    const later = stage(plans[2], lang);
+    assert.ok(existsSync(join(later, "cards", "module-fixture.json")), lang);
+    assert.ok(existsSync(join(later, "cards", "test-fixture.json")), lang);
+  }
+});
diff --git a/tools/verify-references.mjs b/tools/verify-references.mjs
index b02e46a..1937878 100644
--- a/tools/verify-references.mjs
+++ b/tools/verify-references.mjs
@@ -1,12 +1,13 @@
 #!/usr/bin/env node
 // For each module <= N with a reference/: copy reference + tests of modules 01..module into a temp dir, run tests.
-// course/cards (the card data, loaded by the references from Module 5) is staged as <dir>/cards,
-// and each tested module's levels/ (the puzzle levels its tests load, from Module 10) as <dir>/levels.
+// The card data (loaded by the references from Module 5) is staged as <dir>/cards: course/cards
+// plus the cards/ of each module up to the one verified. Each tested module's levels/ (the
+// puzzle levels its tests load, from Module 10) is staged as <dir>/levels.
 import { cpSync, existsSync, mkdirSync, mkdtempSync, rmSync } from "node:fs";
 import { spawnSync } from "node:child_process";
 import { tmpdir } from "node:os";
 import { basename, join } from "node:path";
-import { courseRoot, moduleDirs, testFiles, fail } from "./lib.mjs";
+import { cardDirs, moduleDirs, testFiles, fail } from "./lib.mjs";
 
 // A staged reference has no node_modules, so TS installs the reference's own
 // pinned devDependencies first (a bare `npx vitest` would fetch an unrelated version).
@@ -38,8 +39,7 @@ export function stage(plan, lang) {
     for (const f of testFiles(t.path, lang)) cpSync(f, join(dir, "tests", basename(f)));
     if (existsSync(join(t.path, "levels"))) cpSync(join(t.path, "levels"), join(dir, "levels"), { recursive: true });
   }
-  const cards = join(courseRoot(), "cards");
-  if (existsSync(cards)) cpSync(cards, join(dir, "cards"), { recursive: true });
+  for (const cards of cardDirs(plan.num)) cpSync(cards, join(dir, "cards"), { recursive: true });
   return dir;
 }