@@ -0,0 +1,24 @@
+---
+'@objectstack/spec': minor
+'@objectstack/formula': minor
+'@objectstack/platform-objects': minor
+---
+
+fix(spec)!: a `fixed` currency config needs its code — `currencyConfig.defaultCurrency` loses its `'CNY'` default, and a `dynamic` config parses with no code
+
+Clause-②: no (narrowing)
+Metadata-protocol: narrowed
+
+<!-- adr-0087: registered currency-config-fixed-default-currency-required, currency-config-dynamic-default-currency-removed -->
+
+**BREAKING** for one shape: a `currencyConfig` with `currencyMode: 'fixed'` and no `defaultCurrency`, on a currency field or on a formula field whose `returnType` is `currency`. Ruling X on #27119: an amount whose currency is not known takes the tenant default, and nothing guesses.
+
+- **Before.** `defaultCurrency` was `.default('CNY')`. `{ currencyMode: 'fixed' }` parsed to `{ currencyMode: 'fixed', defaultCurrency: 'CNY' }`, so the field silently became a yuan field and showed `¥` in a dollar or euro app. Every `dynamic` config's parse output carried that `'CNY'` too, though nothing reads a `dynamic` config's code.
+- **Now.** A `fixed` config without a code is refused at every door that parses a field (`defineStack`, `os validate`, the object save door), with one `custom` issue at `currencyConfig.defaultCurrency`: "`currencyConfig.currencyMode: 'fixed'` needs `defaultCurrency`, the field's one currency: give its ISO 4217 code (e.g. `defaultCurrency: 'USD'`), or use `currencyMode: 'dynamic'` to display amounts in the tenant default currency (the `localization.currency` setting)." A `dynamic` config (and an empty one) parses to `{ currencyMode: 'dynamic' }`: no code is materialized. An authored code under `dynamic` is still accepted and still unread.
+- **FROM → TO.** `currencyConfig: { currencyMode: 'fixed' }` → `currencyConfig: { currencyMode: 'fixed', defaultCurrency: 'USD' }` (the code the field is in; until now it displayed CNY), or `currencyMode: 'dynamic'` / no `currencyConfig` for the tenant default currency.
+- **The one-line fix.** Write the code next to `currencyMode: 'fixed'`.
+- **Stored rows and built artifacts (ADR-0087).** A built artifact holds the parsed stack, so its `fixed` configs carry the code the old parse filled in and keep it. A `sys_metadata` object row is stored as authored, so a row saved as `{ currencyMode: 'fixed' }` (Studio's Fixed mode with the code left blank, or a `/meta` write) has no code, and nothing converts one in: guessing `'CNY'` is what the ruling forbids. Such a row still loads and is registered unchanged; boot counts it `invalid` and prints `[metadata_spec_invalid] stored object/NAME fails the current spec schema even after conversion (fields.FIELD.currencyConfig.defaultCurrency: …)`, and the next save of that object is refused (422 `INVALID_METADATA` at `fields.FIELD.currencyConfig.defaultCurrency`) until the code is written. Its display does not change: the registry already held the row as stored, and the console reads a `fixed` code only when there is one, so it showed the tenant default before and still does. `@objectstack/formula` now reads a formula over that field as an unproven currency instead of fixed CNY. The D2 conversion `currency-config-dynamic-default-currency-removed` strips the unread code from `dynamic` configs (and configs with no mode) on stored-row rehydration and inside a built artifact's declared-floor window, on objects and object extensions; no display changes. It is retired from the load path, so an authored source is never rewritten. The upgrade guide entry is `currency-config-fixed-default-currency-required`.
+- **Readers.** None changes what it displays. The console's `resolveFieldCurrency` and the analytics field-currency relay already read the code only under `fixed`. `@objectstack/formula`'s return-type inference reads a field's currency through `CurrencyConfigSchema`; a `fixed` config without a code no longer parses there, so it reads as an unproven currency instead of CNY.
+- **`@objectstack/platform-objects`.** The field form's `defaultCurrency` help text says the code is required in fixed mode instead of "Defaults to CNY", in en, zh-CN, ja-JP and es-ES.
+
+Survey at the change: 11 `fixed` currency configs across `examples/**`, `packages/platform-objects/**`, `packages/qa/**`, seeds and fixtures, none without a code.
@@ -215,7 +215,7 @@ code lives in `currencyConfig`, never in the value.
 | `min` | `number` | — | Minimum value |
 | `max` | `number` | — | Maximum value |
 | `currencyConfig.currencyMode` | `'dynamic' \| 'fixed'` | `'dynamic'` | Whether the column is pinned to `defaultCurrency` (`fixed`) or displays in the tenant default currency, the `localization.currency` setting (`dynamic`); the value is a bare number either way |
-| `currencyConfig.defaultCurrency` | `string` | `'CNY'` | The column's currency code under `fixed`; not the displayed currency under `dynamic` |
+| `currencyConfig.defaultCurrency` | `string` | — | The column's currency code under `fixed`, where it is required; not the displayed currency under `dynamic` |
 
 ```typescript
 { name: 'price', label: 'Price', type: 'currency', currencyConfig: { currencyMode: 'fixed', defaultCurrency: 'USD' } }
 
@@ -153,7 +153,7 @@ These properties apply to **all** field types and are validated by the base `Fie
 | `min` | `number` | — | Minimum monetary value |
 | `max` | `number` | — | Maximum monetary value |
 | `currencyConfig.currencyMode` | `enum` | `dynamic` | `fixed` pins the field to `defaultCurrency`; `dynamic` displays the tenant default currency (the `localization.currency` setting). Not a per-record choice |
-| `currencyConfig.defaultCurrency` | `string` | `CNY` | 3-character currency code (ISO 4217 or crypto): the field's currency under `fixed`; not the displayed currency under `dynamic` |
+| `currencyConfig.defaultCurrency` | `string` | — | 3-character currency code (ISO 4217 or crypto): the field's currency under `fixed`, where it is required (a `fixed` config without one is refused); not the displayed currency under `dynamic` |
 
 **Default constraints:** Stored as a **bare number** (a finite numeric scalar — `valueSchemaFor` routes `currency` to `z.number().finite()`); there is no `{ value, currency }` envelope on the value path. The currency **code** is never stored per record: it is field configuration, carried by `currencyConfig` above. Decimal places are the currency's ISO 4217 minor unit (2 for USD, 0 for JPY, 3 for KWD) and are declared nowhere — `currencyConfig` has no decimal-places key (`currencyConfig.precision` is refused, with a prescription to delete it), and the field-level `precision` is the total digit count, never compared with the currency.
 
 
@@ -29,7 +29,7 @@ const result = CurrencyConfigSchema.parse(data);
 | Property | Type | Required | Description |
 | :--- | :--- | :--- | :--- |
 | **currencyMode** | `Enum<'dynamic' \| 'fixed'>` | optional (default: `"dynamic"`) | Currency mode. `fixed`: the field has one currency, `defaultCurrency`. `dynamic` (the default): the field has no currency of its own — amounts display in the tenant default currency (the `localization.currency` setting; a plain number when none is set) and `defaultCurrency` is not read. Neither mode is a per-record choice: the value is a bare number either way. |
-| **defaultCurrency** | `string` | optional (default: `"CNY"`) | The currency code (ISO 4217, e.g. USD, CNY, EUR) of a `fixed`-mode field: its one currency. Not read under `dynamic` (the default), where amounts display in the tenant default currency. |
+| **defaultCurrency** | `string` | optional | The currency code (ISO 4217, e.g. USD, CNY, EUR) of a `fixed`-mode field: its one currency, required under `fixed`. Not read under `dynamic` (the default), where amounts display in the tenant default currency. |
 
 
 ---
@@ -249,7 +249,7 @@ const result = CurrencyConfigSchema.parse(data);
 | Property | Type | Required | Description |
 | :--- | :--- | :--- | :--- |
 | **currencyMode** | `Enum<'dynamic' \| 'fixed'>` | optional (default: `"dynamic"`) | Currency mode. `fixed`: the field has one currency, `defaultCurrency`. `dynamic` (the default): the field has no currency of its own — amounts display in the tenant default currency (the `localization.currency` setting; a plain number when none is set) and `defaultCurrency` is not read. Neither mode is a per-record choice: the value is a bare number either way. |
-| **defaultCurrency** | `string` | optional (default: `"CNY"`) | The currency code (ISO 4217, e.g. USD, CNY, EUR) of a `fixed`-mode field: its one currency. Not read under `dynamic` (the default), where amounts display in the tenant default currency. |
+| **defaultCurrency** | `string` | optional | The currency code (ISO 4217, e.g. USD, CNY, EUR) of a `fixed`-mode field: its one currency, required under `fixed`. Not read under `dynamic` (the default), where amounts display in the tenant default currency. |
 
 ### Nested Shape: `Field.conditionalFormatting[number]`
 
 
@@ -38,6 +38,8 @@ const FIELDS: Readonly<Record<string, FormulaSourceField>> = {
   weighted: { type: 'formula', returnType: 'currency', currencyConfig: USD },
   count_formula: { type: 'formula', returnType: 'number' },
   broken: { type: 'currency', currencyConfig: { currencyMode: 'fixed', defaultCurrency: 'US' } },
+  // `fixed` with no code: the spec refuses it rather than filling in CNY (#27157).
+  fixed_no_code: { type: 'currency', currencyConfig: { currencyMode: 'fixed' } },
 };
 
 const NAMES = Object.keys(FIELDS);
@@ -127,6 +129,8 @@ describe('CONTROL — a numeric formula stays `number`', () => {
       'record.flag ? record.amount : record.fee_eur',
       // A source whose currency does not parse names no currency.
       'record.broken * 2',
+      // Nor does a fixed source with no code: it is never read as CNY (#27157).
+      'record.fixed_no_code * 2',
       // A roll-up's unit is its child field's, not readable here.
       'record.rollup * 2',
       'record.amount % 3',
 
@@ -129,13 +129,16 @@ function sameCurrency(a: MoneyCurrency, b: MoneyCurrency): boolean {
   return a.code === b.code;
 }
 
-/** A field's currency, read through the schema a currency field is parsed with — or `null` when it does not parse. */
+/**
+ * A field's currency, read through the schema a currency field is parsed with — or `null` when it does not parse.
+ * A `fixed` config with no code does not parse (the schema refuses it rather than filling in a code), so the
+ * `defaultCurrency` guard below only narrows the type the refinement already guarantees.
+ */
 function currencyOf(config: unknown): MoneyCurrency | null {
   const parsed = CurrencyConfigSchema.safeParse(config ?? {});
   if (!parsed.success) return null;
-  return parsed.data.currencyMode === 'fixed'
-    ? { mode: 'fixed', code: parsed.data.defaultCurrency }
-    : { mode: 'dynamic' };
+  if (parsed.data.currencyMode !== 'fixed') return { mode: 'dynamic' };
+  return parsed.data.defaultCurrency === undefined ? null : { mode: 'fixed', code: parsed.data.defaultCurrency };
 }
 
 /** Is `d` a number that is not an amount (a quantity or a constant)? */
 
@@ -618,7 +618,7 @@ export const enMetadataForms: NonNullable<TranslationData['metadataForms']> = {
       },
       "currencyConfig.defaultCurrency": {
         label: "Default Currency",
-        helpText: "The one currency of a fixed-mode field, as a three-character ISO 4217 code (e.g. USD, EUR). Defaults to CNY. Not read in dynamic mode."
+        helpText: "The one currency of a fixed-mode field, as a three-character ISO 4217 code (e.g. USD, EUR). Required in fixed mode; nothing fills one in. Not read in dynamic mode."
       },
       step: {
         label: "Step",
 
@@ -618,7 +618,7 @@ export const esESMetadataForms: NonNullable<TranslationData['metadataForms']> =
       },
       "currencyConfig.defaultCurrency": {
         label: "Moneda predeterminada",
-        helpText: "La única moneda de un campo en modo fixed, como código ISO 4217 de tres caracteres (p. ej., USD, EUR). Por defecto, CNY. No se lee en modo dynamic."
+        helpText: "La única moneda de un campo en modo fixed, como código ISO 4217 de tres caracteres (p. ej., USD, EUR). Obligatorio en modo fixed; no se rellena automáticamente. No se lee en modo dynamic."
       },
       step: {
         label: "Incremento",
 
@@ -618,7 +618,7 @@ export const jaJPMetadataForms: NonNullable<TranslationData['metadataForms']> =
       },
       "currencyConfig.defaultCurrency": {
         label: "既定の通貨",
-        helpText: "fixed モードのフィールドの通貨。3 文字の ISO 4217 コード（例：USD、EUR）で指定します。既定は CNY です。dynamic モードでは参照されません。"
+        helpText: "fixed モードのフィールドの通貨。3 文字の ISO 4217 コード（例：USD、EUR）で指定します。fixed モードでは必須で、自動では補われません。dynamic モードでは参照されません。"
       },
       step: {
         label: "ステップ値",
 
@@ -618,7 +618,7 @@ export const zhCNMetadataForms: NonNullable<TranslationData['metadataForms']> =
       },
       "currencyConfig.defaultCurrency": {
         label: "默认货币",
-        helpText: "fixed 模式字段的唯一货币，使用三个字符的 ISO 4217 代码（例如 USD、EUR）。默认为 CNY。dynamic 模式下不读取。"
+        helpText: "fixed 模式字段的唯一货币，使用三个字符的 ISO 4217 代码（例如 USD、EUR）。fixed 模式下必填，不会自动填入。dynamic 模式下不读取。"
       },
       step: {
         label: "步进值",