W120 — One Campaign Can Include Another

design/20-contract.md

@@ -2247,8 +2247,8 @@ const BASE_REASON_CODES = [
 > boundary's two, host persistence's four, session lifecycle's one, the audit vocabulary's
 > one, content-pack resolution's six, and campaign composition's seven. That is the intended
 > shape: a code is registered when a real caller produces it, not pre-declared from this list.
-> Composition's seven are the one batch this contract names before their caller exists; they
-> were specified with that caller (§10.4) and are not in `reasons.ts` until W120 builds it. Because `ReasonCode` is *additive, never
+> Composition's seven were the one batch this contract named before their caller existed; they
+> were specified with that caller (§10.4), and W120 shipped them in `reasons.ts`. Because `ReasonCode` is *additive, never
 > renamed* (above), growth costs nothing — a client switching on a code it has never seen
 > falls through to the localized message, which the core ships for every base code. Expect
 > this list to keep growing, and keep it in step with

design/30-slices.md

@@ -5292,7 +5292,7 @@ pack attachments ([11 §3a](11-content-packs.md#3a-attachments--reaching-into-a-
 It is one unit because no part of it can be played without the others. An include with no merge
 composes nothing, and a merge with no core envelope has nothing to call it.
 
-### [ ] W120 — One Campaign Can Include Another {#w120}
+### [x] W120 — One Campaign Can Include Another {#w120}
 
 **Delivers:** As a campaign author, I can include another story-graph campaign as a module.
 I name its exits and bind its inputs and outputs. As a pack author, I can attach a module to a
@@ -5316,7 +5316,7 @@ session, and the save format does not change.
       story-graph kind's campaign and source types, source builder, consequences, interpolation,
       validator and reason codes; their tests and synthetic fixtures; the regenerated human docs.
 - **Depends on:** none.
-- **Status:** Not started.
+- **Status:** Done — [PR #568](https://github.com/The-Running-Dev/SubZeroDev.GameEngine/pull/568).
 - **Done when:**
   - W120.1 These types are declared as 04 §10.4, 11 §3a and 03 §1.1 state:
         - `CampaignRef`, `CampaignInclude`, `CampaignAttachment`, `ComposedModule` and

design/90-decisions.md

@@ -2289,3 +2289,19 @@ Context: 12 §4.2 names the only canonical orders: runtime entity ids by prefix
 Chosen: Runtime-entity projections sort with `compareRuntimeEntityId`; every definition-id sort uses `compareDefinitionId`. Path and reason compare by ordinal code unit, now stated in 12 §12. The determinism lint block bans `localeCompare` with fewer than two arguments; a call naming its locale (the simulation kind's contracted `"en-US-POSIX"`, 10 §2.2) stays allowed.
 Rejected: **Numeric-aware path order** (`buildings.building:10` after `building:2`) — paths are not ids, and a path comparator that parses ids out of paths is a second canonical order to keep in step with §4.2. **Fix the call sites without a lint rule** — the same defect would return with the next sort.
 Reversibility: cheap. No fixture or golden changed order, because no shipped campaign has ten instances under one prefix.
+
+### 2026-10-07 — W120: composition is built as contracted; seven implementation calls recorded
+Context: W120 built campaign composition against the contract from #561 (04 §10.4, 11 §3a, 03 §1.1, §5, §8.3). Building it forced calls that the contract leaves open.
+Chosen:
+- **Validation stops at composition.** When `composeCampaigns` rejects, no Tier 1 or Tier 2 check runs, because they would run against content that was never assembled.
+- **Binding host variables check against the host's own `variables`**, not against anything merged in from other modules. A binding names the host's state, and no other module's.
+- **A composed-shaped authored id (`a::x`) is rejected twice.** `composeContent` rejects any `:` in a host's own ids, and `validateCampaign` accepts a `:` only under a synthesized entry node's alias.
+- **The entry node interpolates in the host's scope.** It is the host's node, and only nodes inside the module read `{x}` as `alias::x`.
+- **Module strings come first in the validation union**, so a host's own key wins.
+- **`duplicate_id` and `dangling_reference` from a merge are raised by `composeContent`**, with the composed path. They are not raised later by `validateCampaign` against the merged content.
+- **`ComposedModule`, `ComposedAttachment` and `CampaignInclude` are exported from `/authoring`**, beside the campaign types an author already imports.
+Rejected:
+- **Run Tier 1 over a failed composition.** It would report the same defect again as a dangling reference.
+- **Check bindings against the content merged so far.** That makes a binding's validity depend on the order of includes.
+- **Raise merge collisions in Tier 1.** The path would name the merged node, not the include that caused it.
+Reversibility: cheap. Each call is internal to the build, and no published campaign composes yet.

design/TODO.md

@@ -314,6 +314,6 @@
 
 ### Depth: Campaign Composition
 
-### [ ] W120 — One Campaign Can Include Another {#w120}
+### [x] W120 — One Campaign Can Include Another {#w120}
 
 ## Landed

docs/docs/engine/04-core.md

@@ -2109,8 +2109,8 @@ const BASE_REASON_CODES = [
 > boundary's two, host persistence's four, session lifecycle's one, the audit vocabulary's
 > one, content-pack resolution's six, and campaign composition's seven. That is the intended
 > shape: a code is registered when a real caller produces it, not pre-declared from this list.
-> Composition's seven are the one batch this contract names before their caller exists; they
-> were specified with that caller (§10.4) and are not in `reasons.ts` until W120 builds it. Because `ReasonCode` is *additive, never
+> Composition's seven were the one batch this contract named before their caller existed; they
+> were specified with that caller (§10.4), and W120 shipped them in `reasons.ts`. Because `ReasonCode` is *additive, never
 > renamed* (above), growth costs nothing — a client switching on a code it has never seen
 > falls through to the localized message, which the core ships for every base code. Expect
 > this list to keep growing, and keep it in step with

docs/docs/engine/TODO.md

@@ -5287,7 +5287,7 @@ pack attachments ([11 §3a](11-content-packs.md#3a-attachments--reaching-into-a-
 It is one unit because no part of it can be played without the others. An include with no merge
 composes nothing, and a merge with no core envelope has nothing to call it.
 
-### [ ] W120 — One Campaign Can Include Another {#w120}
+### [x] W120 — One Campaign Can Include Another {#w120}
 
 **Delivers:** As a campaign author, I can include another story-graph campaign as a module.
 I name its exits and bind its inputs and outputs. As a pack author, I can attach a module to a
@@ -5311,7 +5311,7 @@ session, and the save format does not change.
       story-graph kind's campaign and source types, source builder, consequences, interpolation,
       validator and reason codes; their tests and synthetic fixtures; the regenerated human docs.
 - **Depends on:** none.
-- **Status:** Not started.
+- **Status:** Done — [PR #568](https://github.com/The-Running-Dev/SubZeroDev.GameEngine/pull/568).
 - **Done when:**
   - W120.1 These types are declared as 04 §10.4, 11 §3a and 03 §1.1 state:
         - `CampaignRef`, `CampaignInclude`, `CampaignAttachment`, `ComposedModule` and

docs/docs/guide.md

@@ -3,7 +3,7 @@ sidebar_position: 1
 sidebar_label: Developer Guide
 ---
 
-<!-- design-digest: 2d57fa0f064f1dc036bff5fa5f994d51ba65e473d57a4f5e3f73fb9fdd9a76f3 -->
+<!-- design-digest: 8824e3253442ab556eabc039f74225a7ecc342397c7781157575885660bc312a -->
 
 > Generated from `design/` by `/make-human-docs`. Do not edit by hand — edit the
 > design docs and regenerate. `/reconcile` reports when this has gone stale.
@@ -678,7 +678,7 @@ imposes no relationship or currency model of its own; a campaign that wants a me
 declares an int and advances it itself, since the built-in turn counter is deliberately just a
 transition count.
 
-**Campaign composition is contracted, not yet built (W120).** Content never crosses a campaign
+**Campaign composition is built (W120).** Content never crosses a campaign
 boundary at runtime: the session's `campaignId` is singular and the save format has no frames.
 Instead, a host campaign *includes* another story-graph campaign as a module, pinned by its
 authored `{id, version}`. Registry build then merges the module into the host before validation

src/engine/src/authoring.test.ts

@@ -70,6 +70,7 @@ const AUTHORING_TYPE_EXPORTS = [
   "ItemDefinitionSource",
   "JobDefinitionSource",
   "LocationDefinitionSource",
+  "ModuleInterface",
   "NPCDefinitionSource",
   "NodeSource",
   "OpportunityDefinitionSource",
@@ -91,8 +92,10 @@ const AUTHORING_TYPE_EXPORTS = [
   "SimulationActionLabelKeysSource",
   "SimulationCampaignSource",
   "SkillDefinitionSource",
+  "StoryGraphAttachment",
   "StoryGraphCampaign",
   "StoryGraphCampaignSource",
+  "StoryGraphIncludeBinding",
   "StoryGraphKindState",
   "Submission",
   "TraitDefinitionSource",

src/engine/src/authoring.ts

@@ -35,7 +35,12 @@ export type {
   VariableDeclSource,
   VariableSchemaSource,
 } from "./kinds/story-graph/source.js";
-export type { StoryGraphCampaign } from "./kinds/story-graph/campaign.js";
+export type {
+  ModuleInterface,
+  StoryGraphAttachment,
+  StoryGraphCampaign,
+  StoryGraphIncludeBinding,
+} from "./kinds/story-graph/campaign.js";
 export type { StoryGraphKindState } from "./kinds/story-graph/state.js";
 export type {
   AchievementDefinitionSource as SimulationAchievementDefinitionSource,

src/engine/src/campaigns/stable-life-packs.test.ts

@@ -18,7 +18,7 @@ import { simulationKind } from "../kinds/simulation/kind.js";
 import type { LocKey } from "../core/localization/types.js";
 import { resolvePacks, type ContentPack } from "../core/registry/packs.js";
 import type { ContentRegistry } from "../core/registry/types.js";
-import { bulgariaCulturePack, resolveStableLifeRegistry, stableLifeBasePack } from "./stable-life-packs.js";
+import { bulgariaCulturePack, packVersion, resolveStableLifeRegistry, stableLifeBasePack } from "./stable-life-packs.js";
 import { STABLE_LIFE_CAMPAIGN_ID } from "./stable-life.js";
 
 const kinds = { simulation: simulationKind } as unknown as KindRegistry;
@@ -185,6 +185,24 @@ describe("W71 — Stable Life Bulgaria culture pack", () => {
    * from `stable-life.ts` — so both versions are derived from a digest of what they ship.
    * Two packs shipping different strings must therefore carry different versions.
    */
+  // W120.9 — 11 §6: includes and attachments change what plays, so they move the digest, but
+  // only when present; a pack carrying neither keeps the version it already had.
+  it("moves the digest for an attachment or an include, and only then", () => {
+    const { campaigns, strings } = stableLifeBasePack;
+    expect(packVersion(campaigns, strings)).toBe(stableLifeBasePack.version);
+    expect(packVersion(campaigns, strings, [])).toBe(stableLifeBasePack.version);
+
+    const include = { alias: "m", ref: { id: "module", version: "1.0.0" }, binding: {} };
+    const attached = packVersion(campaigns, strings, [{ hostCampaignId: STABLE_LIFE_CAMPAIGN_ID, include, payload: {} }]);
+    expect(attached).toMatch(/^1\.0\.0\+[0-9a-f]{12}$/);
+    expect(attached).not.toBe(stableLifeBasePack.version);
+
+    const including = campaigns.map((c) => ({ ...c, campaign: { ...c.campaign, includes: [include] } }));
+    expect(packVersion(including, strings)).not.toBe(stableLifeBasePack.version);
+    const emptyIncludes = campaigns.map((c) => ({ ...c, campaign: { ...c.campaign, includes: [] } }));
+    expect(packVersion(emptyIncludes, strings)).toBe(stableLifeBasePack.version);
+  });
+
   it("derives each pack's version from the content it ships", () => {
     expect(stableLifeBasePack.version).toMatch(/^1\.0\.0\+[0-9a-f]{12}$/);
     expect(bulgariaCulturePack.version).toMatch(/^1\.0\.0\+[0-9a-f]{12}$/);

src/engine/src/campaigns/stable-life-packs.ts

@@ -12,7 +12,7 @@
  */
 
 import type { ContentPack } from "../core/registry/packs.js";
-import type { BuiltCampaign, ContentRegistry } from "../core/registry/types.js";
+import type { BuiltCampaign, CampaignAttachment, ContentRegistry } from "../core/registry/types.js";
 import type { LocKey } from "../core/localization/types.js";
 import type { KindRegistry } from "../core/kernel/types.js";
 import type { CommandResult } from "../core/kernel/reasons.js";
@@ -50,8 +50,14 @@ const bulgarianCampaign = built(buildBulgariaStableLifeCampaign);
  * The campaign fields are listed rather than digested whole: `Campaign.migrateState` (04
  * §10.1) is an optional *function*, and `canonicalStringify` rejects one outright, so a
  * campaign that ever gains a migration must not take this module down at import time.
+ *
+ * Exported for the test that holds 11 §6's composition clause (W120.9), not as engine API.
  */
-function packVersion(campaigns: readonly BuiltCampaign[], strings: ReadonlyMap<LocKey, string>): string {
+export function packVersion(
+  campaigns: readonly BuiltCampaign[],
+  strings: ReadonlyMap<LocKey, string>,
+  attachments: readonly CampaignAttachment[] = [],
+): string {
   const digest = sha256Hex(
     canonicalStringify({
       campaigns: campaigns.map(({ campaign }) => ({
@@ -60,10 +66,14 @@ function packVersion(campaigns: readonly BuiltCampaign[], strings: ReadonlyMap<L
         version: campaign.version,
         titleKey: campaign.titleKey,
         content: campaign.content,
+        ...(campaign.includes && campaign.includes.length > 0 ? { includes: campaign.includes } : {}),
       })),
       // Sorted by key, not left in insertion order: the digest names what a pack ships, and
       // reordering an authoring file ships the same content.
       strings: [...strings].sort(([a], [b]) => (a < b ? -1 : a > b ? 1 : 0)),
+      // Includes and attachments change what plays, so they move the version — but only when
+      // present, which leaves every pack that has none exactly where it was (11 §6).
+      ...(attachments.length > 0 ? { attachments } : {}),
     }),
   );
   return `1.0.0+${digest.slice(0, 12)}`;

src/engine/src/core/kernel/reasons.ts

@@ -95,6 +95,12 @@ export type ReasonCode = string;
  * (`Kind.profileData`, 04 §7.1): a version mismatch with no migration (or one that fails)
  * drops a kind's profile slice for the session, and a throwing/oversized `fold` result is
  * refused, in both cases only ever surfacing as a warning.
+ *
+ * `include_missing`, `include_version_mismatch`, `include_kind_mismatch`, `include_cycle`,
+ * `include_alias_collision`, `attachment_host_missing` and `compose_unsupported` were added
+ * during W120 — campaign composition (04 §10.4, `registry/compose.ts`) checks an include's
+ * envelope before any kind merges content, at registry build. Base rather than kind-owned
+ * because the include, its pin and the cycle are core-owned; only the merge is the kind's.
  */
 export const BASE_REASON_CODES = [
   "action_not_available",
@@ -133,6 +139,14 @@ export const BASE_REASON_CODES = [
   "pack_override_unexpected",
   "profile_kind_data_unreadable",
   "profile_kind_data_rejected",
+  // campaign composition (04 §10.4) — registry build, before validation
+  "include_missing",
+  "include_version_mismatch",
+  "include_kind_mismatch",
+  "include_cycle",
+  "include_alias_collision",
+  "attachment_host_missing",
+  "compose_unsupported",
 ] as const;
 
 export type BaseReasonCode = (typeof BASE_REASON_CODES)[number];
@@ -180,6 +194,13 @@ const CORE_REASON_TEXT: Readonly<Record<BaseReasonCode, string>> = {
   pack_override_unexpected: "This pack overrides content no earlier pack supplied.",
   profile_kind_data_unreadable: "This kind's saved cross-game data couldn't be read for this session; it starts with none.",
   profile_kind_data_rejected: "This kind's cross-game data couldn't be updated. Your game progress was not affected.",
+  include_missing: "This campaign includes a campaign that isn't available.",
+  include_version_mismatch: "This campaign includes a different version of a campaign than the one available.",
+  include_kind_mismatch: "A campaign can only include a campaign of its own kind.",
+  include_cycle: "Campaigns can't include each other in a cycle.",
+  include_alias_collision: "This campaign uses the same include name twice.",
+  attachment_host_missing: "A pack attaches content to a campaign that isn't available.",
+  compose_unsupported: "This kind of campaign can't include other campaigns.",
 };
 
 /** `core.reason.<code>` → its shipped default-English message, for every base code. */

src/engine/src/core/kernel/types.ts

@@ -9,7 +9,7 @@ import type { LocKey } from "../localization/types.js";
 import type { RngHandle, StreamId } from "../determinism/types.js";
 import type { ProjectionAudience, PlayerView } from "../projection/types.js";
 import type { ValidationError, ValidationResult } from "../validation/types.js";
-import type { Campaign, ContentRegistry } from "../registry/types.js";
+import type { Campaign, ComposedAttachment, ComposedModule, ContentRegistry } from "../registry/types.js";
 import type { Emitter, EventName, ResolutionEmitter } from "../observability/types.js";
 import type {
   CommandResult,
@@ -180,6 +180,20 @@ export interface Kind<KState> {
    * is the state every kind is in until it declares this member.
    */
   readonly profileData?: KindProfileData;
+
+  /**
+   * Merges included modules and pack attachments into a host campaign's content (04 §10.4).
+   * Optional: a kind without it cannot host an include or receive an attachment, and a
+   * campaign of that kind that declares either fails with `compose_unsupported`. Called by
+   * registry assembly **before** `validateCampaign`, once per host, with every module
+   * already composed depth-first — so it only ever merges one level. Pure over content: the
+   * result replaces `host.content` in the registry and is what validation and play both see.
+   */
+  composeContent?(
+    host: Campaign,
+    modules: readonly ComposedModule[],
+    attachments: readonly ComposedAttachment[],
+  ): CommandResult<unknown>;
 }
 
 /**