feat: log tree from Module 2 (logTree / log_tree); SpellGrid CLIs print Log:

Engine events carry the nesting depth they were recorded at; the harness
prints the log as an indented tree. New tests test_02_log_tree_shows_nesting
and test_03_log_tree_death_phase; both SpellGrid CLIs print the tree of the
last command's Sequences under a Log: line.

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

course/06-parser/reference/ts/src/engine/event.ts

@@ -1,4 +1,5 @@
 // What happened, in order. The engine records an event each time it changes the game.
+// The world also keeps the nesting depth each event was recorded at (`World.logDepths`).
 
 import type { TriggerOn } from "./card";
 import type { EntityId, PlayerId } from "./world";

course/06-parser/reference/ts/src/engine/queue.ts

@@ -192,7 +192,10 @@ function react(world: World, events: Event[]): void {
         event.type === "Destroyed" && event.id === source
           ? positionLeftOf(world, world.ownerOf(source), event.before)
           : world.boardIndex(source);
+      // The trigger's consequences are one level deeper in the log tree.
+      world.openBlock();
       runEffects(world, trigger.effects, new Ctx(world, world.ownerOf(source), source, undefined, position));
+      world.closeBlock();
     }
   }
 }

course/06-parser/reference/ts/src/engine/world.ts

@@ -46,6 +46,10 @@ export class World {
   private readonly sides: [Side, Side];
   private nextOrderOfPlay = 0;
   private events: Event[] = [];
+  /** The nesting depth at which each event in `events` was recorded, index for index. */
+  private depths: number[] = [];
+  /** How many triggers are resolving right now, one inside another. */
+  private depth = 0;
   /** The auras in force as of the last Aura Update. Changes only there (see `aura.ts`). */
   private auras: ActiveAura[] = [];
   /** Until a chooser is set, take the first option. */
@@ -212,10 +216,26 @@ export class World {
     return this.events;
   }
 
+  /** The nesting depth of each event in `log()`, index for index: 0 for the outermost action's own events. */
+  logDepths(): readonly number[] {
+    return this.depths;
+  }
+
   // ---- Changes: each one records its event ----
 
   record(event: Event): void {
     this.events.push(event);
+    this.depths.push(this.depth);
+  }
+
+  /** A trigger starts resolving: the events it causes are recorded one level deeper. */
+  openBlock(): void {
+    this.depth++;
+  }
+
+  /** The trigger that last opened a block has finished resolving. */
+  closeBlock(): void {
+    this.depth--;
   }
 
   /** Add a card to the library, or replace the card with the same name. */
@@ -248,6 +268,7 @@ export class World {
 
   clearLog(): void {
     this.events = [];
+    this.depths = [];
   }
 
   damage(target: EntityId, amount: number): void {

course/06-parser/reference/ts/src/harness.ts

@@ -46,6 +46,27 @@ function toGameEvent(event: Event): GameEvent | undefined {
   return { ...event };
 }
 
+/** One event as `scenarios.md` writes it, such as `Triggered{source: 3, trigger: "deathrattle"}`. */
+function eventText(event: GameEvent): string {
+  const { type, ...fields } = event;
+  const shown = Object.entries(fields).map(
+    ([key, value]) => `${key}: ${typeof value === "string" ? JSON.stringify(value) : value}`,
+  );
+  return `${type}{${shown.join(", ")}}`;
+}
+
+/** The log as a tree: one event per line, two spaces of indent per level of nesting. */
+function logTree(world: World, view: (event: Event) => GameEvent | undefined): string {
+  const depths = world.logDepths();
+  return world
+    .log()
+    .map((event, i) => {
+      const shown = view(event);
+      return shown === undefined ? "" : `${"  ".repeat(depths[i])}${eventText(shown)}\n`;
+    })
+    .join("");
+}
+
 export interface Game {
   summon(card: string, player?: Player): Id; // to right end of board
   addToHand(card: string, player?: Player): Id;
@@ -65,6 +86,7 @@ export interface Game {
   armor(player: Player): number;
   log(): GameEvent[];
   clearLog(): void;
+  logTree(): string; // the log as an indented tree
   // Module 3
   destroy(target: Id): void; // marks pending destroy, one Sequence
   // Module 5
@@ -104,6 +126,7 @@ export function newGame(opts?: { decks?: [string[], string[]] }): Game {
     armor: (player) => world.armor(player),
     log: () => world.log().flatMap((event) => toGameEvent(event) ?? []),
     clearLog: () => world.clearLog(),
+    logTree: () => logTree(world, toGameEvent),
 
     destroy: (target) => runSequence(world, { type: "destroy", targets: [target] }),