feat: robustness in Module 5 (nesting guard, Death Phase limit, well-formed Assemble, multi-summon order)

A trigger is never queued while that same (minion, trigger) is resolving;
more than DEATH_PHASE_LIMIT = 64 Death Phases is an error ('Death Phase
limit'); Assemble refuses and never offers ill-formed text (wellFormed /
well_formed); summon count > 1 places tokens in summon order. Modules 05-10,
both tracks. Four new Module 5 tests, a tools test that every shipped card
is well-formed, lessons 2, 3, 5, 13 and harness.md updated.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

course/07-rule-resolution/reference/rust/src/engine/mod.rs

@@ -18,7 +18,9 @@
 //!
 //! Module 5: behaviour as data. Cards are definitions in the course's card format,
 //! loaded from JSON; one interpreter turns their effects into actions. Assemble
-//! builds a new card by swapping half of one card's text for half of another's.
+//! builds a new card by swapping half of one card's text for half of another's, and
+//! offers only results that are well-formed. A Sequence is bounded: a trigger never
+//! nests inside itself, and more than `DEATH_PHASE_LIMIT` Death Phases is an error.
 //!
 //! Part II lives in `puzzle`: a second engine, for the rule-writing puzzle game,
 //! beside the first.
@@ -35,11 +37,11 @@ pub mod puzzle;
 mod queue;
 mod world;
 
-pub use assemble::{assemble, register_assembled, AssembleError, Half};
+pub use assemble::{assemble, register_assembled, AssembleError, AssembleFailure, Half};
 pub use card::{
-    Aura, Card, CardDef, CardLibrary, CardType, Clause, Effect, PoolFilter, RedirectFrom,
-    RedirectTo, Stacking, Target, Trigger, TriggerOn,
+    well_formed, Aura, Card, CardDef, CardLibrary, CardType, Clause, Effect, PoolFilter,
+    RedirectFrom, RedirectTo, Stacking, Target, Trigger, TriggerOn,
 };
 pub use event::Event;
-pub use queue::{run_sequence, summon, Action, Ctx, DamageStep, DAMAGE_STEPS};
+pub use queue::{run_sequence, summon, Action, Ctx, DamageStep, DAMAGE_STEPS, DEATH_PHASE_LIMIT};
 pub use world::{Chooser, EntityId, PlayerId, World, Zone, HERO_HEALTH};