docs(spec): stop the translation @example blocks teaching an unresolvable messages id

`messages` is a flat `Record<string, string>` while `t()` resolves a key by
walking its dot path, so an id that merely contains a dot is unreachable.
Both docblock `@example` blocks on `TranslationDataSchema` and
`TranslationItemSchema` demonstrated exactly such an id (`'common.save'`);
they now author `commonSave` and state the rule.

Claude-Session: https://claude.ai/code/session_01JbZnqu8bt6YqfJsr9vaFb3
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

.changeset/18190-translation-messages-example-single-segment.md

@@ -0,0 +1,19 @@
+---
+'@objectstack/spec': patch
+---
+
+docs(translation): the two `TranslationData` / `TranslationItem` `@example` blocks stop teaching a `messages` id that cannot resolve (#18190)
+
+`messages` is declared a flat `Record<string, string>` (`translation.zod.ts` — `messages: z.record(z.string(), z.string())`), while `t()` resolves a key by walking its dot path segment by segment. Both implementations do this, identically:
+
+- `packages/core/src/fallbacks/memory-i18n.ts` — `resolveKey()`, `key.split('.')`, walked by `t()`;
+- `packages/services/service-i18n/src/file-i18n-adapter.ts` — a second `resolveKey()` with the same body, walked by `t()` through `resolveFromLocale()`.
+
+So an id that merely *contains* a dot is one flat key named `common.save`, and `t('messages.common.save', …)` looks for a nested `common` object, finds a string or nothing at the first hop, and returns the key itself. Both docblock `@example` blocks on this schema demonstrated exactly that id — the doorway an author (or an authoring agent) copies from.
+
+- The JSON example on `TranslationDataSchema` and the TypeScript example on `TranslationItemSchema` now author `commonSave`, the single-segment spelling `content/docs/protocol/kernel/i18n-standard.mdx` already prescribes and `packages/plugins/plugin-audit/src/translations/messages.ts` already applies to its own bundle.
+- Both docblocks now state the rule, so the counter-example is named as one rather than demonstrated.
+
+⚠️ **The schema still accepts a dotted id** — nothing is narrowed here and no key is retired. Whether the door should refuse a dotted `messages` key narrows a published accept set and rides its own card; this change is the doorway half only.
+
+For authors: a `messages` id containing a dot never resolved, so re-spelling one single-segment (`'common.save'` → `commonSave`, looked up as `messages.commonSave`) turns a key that was returning itself into one that translates. No key that resolved before stops resolving.

packages/spec/src/system/translation.zod.ts

@@ -574,9 +574,16 @@ const TRANSLATION_KEY_GUIDANCE: Record<LegacyObjectFirstKey | 'validationMessage
  * {
  *   "objects": { "account": { "label": "Account" } },
  *   "apps": { "crm": { "label": "CRM" } },
- *   "messages": { "common.save": "Save" }
+ *   "messages": { "commonSave": "Save" }
  * }
  * ```
+ *
+ * `messages` ids are single-segment. `t()` resolves a key by walking its dot
+ * path into this structure, and `messages` is a flat `Record<string, string>`,
+ * so an id that itself contains a dot (`'common.save'`) is looked up as a
+ * nested `common` object and resolves to nothing; `messages.commonSave`
+ * resolves. Both implementations walk identically — see
+ * `content/docs/protocol/kernel/i18n-standard.mdx`.
  */
 /**
  * The translation groups, as a shape rather than a schema.
@@ -1414,6 +1421,10 @@ export type TranslationConfig = z.input<typeof TranslationConfigSchema>;
  * sync skips an item whose locale it cannot resolve, and a skip is invisible
  * to whoever — or whatever — authored it.
  *
+ * `messages` ids are single-segment, for the reason spelled out on
+ * {@link TranslationDataSchema}: `t()` walks the dot path, so an id containing
+ * a dot resolves to nothing.
+ *
  * @example
  * ```typescript
  * const zhCN = defineTranslation({
@@ -1427,7 +1438,7 @@ export type TranslationConfig = z.input<typeof TranslationConfigSchema>;
  *     },
  *   },
  *   apps: { crm: { label: '客户关系管理' } },
- *   messages: { 'common.save': '保存' },
+ *   messages: { commonSave: '保存' },
  * });
  * ```
  */