@@ -0,0 +1,57 @@
+---
+'@objectstack/spec': minor
+---
+
+feat(spec): every `composeStacks` conflict refusal carries an ADR-0112 envelope — six new `STACK_COMPOSE_*` codes beside the `defineStack` family
+
+`composeStacks` refuses six authored-entity conflicts, and until now every one of them threw
+`new Error(message)` with `code` and `status` both `undefined`. The `defineStack` family in the
+same file has carried the envelope since #15963, so `packages/spec/src/stack.zod.ts` held two
+refusal families that are the same thing to an author — a stack refused at authoring time,
+through the same callers — and two different things to a consumer branching on `error.code`.
+
+Every message in the family carries the literal `composeStacks conflict:` prefix, which is how it
+is located: FIVE of the six raise inside helper functions 300-800 lines above `composeStacks`'
+own body, so reading the function the defect is named after finds one of them.
+
+| refusal | raised by | code |
+| :--- | :--- | :--- |
+| a single-valued top-level key declared with different values by two stacks | `composeSingleValue` | `STACK_COMPOSE_KEY_CONFLICT` |
+| `functions` authored in the map form by one stack, the array form by another | `composeFunctions` | `STACK_COMPOSE_FUNCTIONS_SHAPE_CONFLICT` |
+| two stacks defining one handler name | `composeFunctions` | `STACK_COMPOSE_FUNCTION_CONFLICT` |
+| under `objectConflict: 'merge'`, an object-level collection other than `fields` declared differently | `refuseUnmergeableCollections` | `STACK_COMPOSE_COLLECTION_CONFLICT` |
+| the same object name in two stacks under the default `objectConflict: 'error'` | `mergeObjects` | `STACK_COMPOSE_OBJECT_CONFLICT` |
+| a cross-stack action key collision | `collectComposedActionKeyCollisions` | `STACK_COMPOSE_ACTION_KEY_COLLISION` |
+
+Each carries `status: 422` — an unprocessable authored entity, not a server fault — and the
+findings the site collected in `issues`, one entry per finding. **Message text is byte-for-byte
+unchanged at every site**: this adds the machine-readable half, it rewords no sentence, and the
+message pins across the repo read the prose they always did.
+
+One code per refusal site rather than a shared `STACK_COMPOSE_CONFLICT` catch-all — the
+granularity the `defineStack` family landed with, and the granularity the ADR-0112 ledger's
+boot-refusal class already had before it. The `STACK_COMPOSE_*` spelling says what the
+per-stack family's spellings cannot: the defect is a disagreement BETWEEN stacks, each of which
+is legal on its own, so the fix is in the composition rather than in one malformed stack.
+`STACK_CROSS_REFERENCE_INVALID` stays the deliberate exception in the other direction — its
+per-stack and artifact passes share one code because they are one rule family over two scopes.
+
+All six are registered in `ERROR_CODE_LEDGER` under `@objectstack/spec`, under the ruling that
+every code shipped in `dist` is the published face, door or no door. No wire door raises them:
+`composeStacks` runs at authoring and boot time, and the reading was re-measured here — zero
+`composeStacks` call sites under `packages/runtime/src` + `packages/rest/src` (7 non-test
+occurrences, all doc comments or message prose in one file), with `defineStack` lighting the
+same probe 31 times across 8 files as the positive control.
+
+Not narrowed: `composeStacks` accepts and refuses exactly the inputs it did before, and no export
+changes — the error classes stay module-local, as every member of the `defineStack` family is,
+because `packages/spec/src/index.ts` re-exports the module with `export *` and the ADR-0112
+contract is the `code` / `status` pair read structurally.
+
+⛔ The seventh bare `Error` in that file is deliberately untouched:
+`composeStacks internal error: no source stack recorded for composed object …` is the code
+discovering its own bookkeeping is inconsistent, not an authored entity being refused. Filing it
+at 422 would tell an author their stack is invalid when the defect is ours. Whether it takes a
+500-class envelope of its own is a separate decision.
+
+Clause-②: yes
@@ -27,7 +27,7 @@ const result = ApiErrorSchema.parse(data);
 
 | Property | Type | Required | Description |
 | :--- | :--- | :--- | :--- |
-| **code** | `Enum<'VALIDATION_ERROR' \| 'INVALID_FIELD' \| 'MISSING_REQUIRED_FIELD' \| 'INVALID_FORMAT' \| 'VALUE_TOO_LONG' \| 'VALUE_TOO_SHORT' \| 'VALUE_OUT_OF_RANGE' \| … +325 more>` | ✅ | Error code (e.g. VALIDATION_ERROR; StandardErrorCode ∪ the ledger the serving side registers — ERROR_CODE_LEDGER for framework packages) |
+| **code** | `Enum<'VALIDATION_ERROR' \| 'INVALID_FIELD' \| 'MISSING_REQUIRED_FIELD' \| 'INVALID_FORMAT' \| 'VALUE_TOO_LONG' \| 'VALUE_TOO_SHORT' \| 'VALUE_OUT_OF_RANGE' \| … +331 more>` | ✅ | Error code (e.g. VALIDATION_ERROR; StandardErrorCode ∪ the ledger the serving side registers — ERROR_CODE_LEDGER for framework packages) |
 | **declaredCode** | `string` | optional | The producer-declared code, verbatim, when it is not a member of the closed `code` vocabulary — the open, author-authored channel (app-specific spellings; ADR-0112) |
 | **message** | `string` | ✅ | Readable error message |
 | **userMessage** | `string` | optional | Producer-marked user-facing refusal text, verbatim. Present exactly when the producer opted in at throw time; consumers render it to end users and keep their generic substitution for anything unmarked. Status-agnostic; never replaces `message`. |
@@ -335,6 +335,12 @@ const result = ApiErrorSchema.parse(data);
 * `SSO_REGISTER_FAILED`
 * `SSO_REGISTER_FORBIDDEN`
 * `STACK_CAPABILITY_UNKNOWN`
+* `STACK_COMPOSE_ACTION_KEY_COLLISION`
+* `STACK_COMPOSE_COLLECTION_CONFLICT`
+* `STACK_COMPOSE_FUNCTIONS_SHAPE_CONFLICT`
+* `STACK_COMPOSE_FUNCTION_CONFLICT`
+* `STACK_COMPOSE_KEY_CONFLICT`
+* `STACK_COMPOSE_OBJECT_CONFLICT`
 * `STACK_CROSS_REFERENCE_INVALID`
 * `STACK_HIERARCHY_SCOPE_CAPABILITY_REQUIRED`
 * `STACK_NAMESPACE_PREFIX_INVALID`
 
@@ -503,6 +503,12 @@ const result = ErrorCode.parse(data);
 * `SSO_REGISTER_FAILED`
 * `SSO_REGISTER_FORBIDDEN`
 * `STACK_CAPABILITY_UNKNOWN`
+* `STACK_COMPOSE_ACTION_KEY_COLLISION`
+* `STACK_COMPOSE_COLLECTION_CONFLICT`
+* `STACK_COMPOSE_FUNCTIONS_SHAPE_CONFLICT`
+* `STACK_COMPOSE_FUNCTION_CONFLICT`
+* `STACK_COMPOSE_KEY_CONFLICT`
+* `STACK_COMPOSE_OBJECT_CONFLICT`
 * `STACK_CROSS_REFERENCE_INVALID`
 * `STACK_HIERARCHY_SCOPE_CAPABILITY_REQUIRED`
 * `STACK_NAMESPACE_PREFIX_INVALID`
 
@@ -1279,7 +1279,8 @@ export const ERROR_CODE_LEDGER = {
     'EXTERNAL_SCHEMA_MISMATCH',
     'EXTERNAL_SCHEMA_MODE_VIOLATION',
     'EXTERNAL_WRITE_FORBIDDEN',
-    // [#16449] The eight rows below are `door: 'none'` codes — raised at
+    // [#16449] The eight rows below — through `STACK_TRIGGER_CAPABILITY_REQUIRED`
+    // — are `door: 'none'` codes — raised at
     // authoring / boot, before any HTTP boundary exists — registered under the
     // #16404 ruling (door or no door; see the header). Each ships in this
     // package's `dist`, so its spelling is the face a consumer's
@@ -1308,6 +1309,29 @@ export const ERROR_CODE_LEDGER = {
     'STACK_SCHEMA_INVALID',                      // `ObjectStackDefinitionSchema.safeParse` failed; `issues` carries the zod issues structurally
     'STACK_SINGLE_APP_VIOLATION',                // an `app` package declares more than one app (ADR-0019 D3)
     'STACK_TRIGGER_CAPABILITY_REQUIRED',         // an auto-launched flow while `requires` omits `triggers`
+    // [#16348] The COMPOSITION half of the same family, and `door: 'none'` on
+    // the same reading: the six `composeStacks` refusals, one code per raise
+    // site, every one `status: 422` (`StackRefusalError`, `stack.zod.ts`), the
+    // findings the site collected on `issues`. Every message carries the
+    // literal `composeStacks conflict:` prefix, which is how the family is
+    // located — five of the six raise inside helper functions, not in
+    // `composeStacks`' own body. Raised where `defineStack` is: `os validate` /
+    // `os build` and a hand-written `objectstack.config.ts`, before any HTTP
+    // boundary exists (measured: zero `composeStacks` CALL sites under
+    // `packages/runtime/src` + `packages/rest/src` — 7 non-test occurrences,
+    // all doc comments or message prose in one file; positive control
+    // `defineStack`, same two trees, 31 occurrences across 8 files).
+    // ⛔ NOT registered, and the absence is load-bearing: the seventh bare
+    // `Error` in that file, `composeStacks internal error: no source stack
+    // recorded for composed object …`, is an internal-bookkeeping invariant
+    // rather than an authored-entity refusal — a 422 would blame the author
+    // for our defect. Its disposition is its own decision.
+    'STACK_COMPOSE_ACTION_KEY_COLLISION',        // two stacks declare the same action key — the collision `defineStack` refuses within one stack, one composition step later
+    'STACK_COMPOSE_COLLECTION_CONFLICT',         // under `objectConflict: 'merge'`, an object-level collection other than `fields` is declared with different values by two stacks
+    'STACK_COMPOSE_FUNCTION_CONFLICT',           // two stacks define a handler under the same name; handlers resolve by name at boot
+    'STACK_COMPOSE_FUNCTIONS_SHAPE_CONFLICT',    // `functions` authored in the map form by one stack and the array form by another
+    'STACK_COMPOSE_KEY_CONFLICT',                // a single-valued top-level key is declared with different values by two stacks
+    'STACK_COMPOSE_OBJECT_CONFLICT',             // the same object name is defined by more than one stack under the default `objectConflict: 'error'`
   ],
 } as const satisfies Record<string, readonly string[]>;