@@ -0,0 +1,23 @@
+---
+'@objectstack/lint': minor
+'@objectstack/spec': patch
+---
+
+fix(lint)!: a `lookup` or `master_detail` field whose `reference` is a stored-metadata-body table is refused where it is declared
+
+Clause-②: no (narrowing)
+
+<!-- adr-0087: not-required (no-migration-prescription) No spec key, stored shape or authorable spelling is added, removed or renamed. The expression rule's object pass now refuses one field declaration it accepted before: a `lookup` or `master_detail` whose `reference` is `sys_metadata` or `sys_metadata_history`, which the engine never hydrates. Nothing stored is rewritten, so there is nothing for `objectstack migrate meta` to convert; the `@objectstack/spec` change is the text of the `reference` describe only. -->
+
+**BREAKING** (an authoring narrowing), shipped as `minor` under the launch-window convention for breaking changes.
+
+A `lookup` or `master_detail` whose `reference` names a table of the stored-metadata-body family (`STORED_METADATA_BODY_OBJECTS`: `sys_metadata`, `sys_metadata_history`) is an error. The engine never hydrates such a field: `$expand` keeps the stored id and never nests the row, a formula or a validation rule never reads through it, and a master-detail child's `parent` root stays unbound, so every write a `parent` rule judges is refused. `os validate`, `os build` and the object save door (`PUT /api/v1/meta/object/:name`, and a draft's promotion) run the same pass, under the existing `EXPRESSION_INVALID` rule, located at the field's `reference`.
+
+- FROM: `meta: { type: 'lookup', reference: 'sys_metadata' }` (or a `master_detail`, or `sys_metadata_history`) saved with a 200 and built with exit 0, and then only ever showed an id. TO: refused, with `422 INVALID_METADATA` at the save door and an error at `os validate` / `os build`. The message names the field, its type and the target, and ends on the family's one prescription.
+- A reference to any other table, platform tables such as `sys_user` included, is unchanged.
+- A `user` field whose authored `reference` names a family table is refused the same way: the parse accepts an authored `reference` on a `user` field, and it is the target every reader resolves.
+- The refusal of a formula or a validation rule that reads through such a field is unchanged, and is still reported at that expression.
+- A stored object row that already declares such a field keeps loading: no authoring rule runs when a stored row is rehydrated, and the engine guards keep refusing every relationship read into the family. Its next active save, or a draft's promotion, through the metadata API is refused until the field is removed or retargeted. The engine guards stay, for every path that runs no authoring rule.
+- `@objectstack/spec` (`patch`): the `reference` describe states the convention, so the generated field reference says it too.
+
+What to do. Remove the field, or retarget it. To point a record at a metadata item, store the item's type and name in `text` fields and read the item through the metadata API (`GET /api/v1/meta/:type/:name`), where its body is projected.
@@ -307,7 +307,7 @@ Reference to a record in another object (foreign key).
 
 | Property | Type | Default | Description |
 |:---|:---|:---|:---|
-| `reference` | `string` | **required** | Target object name (snake_case) |
+| `reference` | `string` | **required** | Target object name (snake_case). A stored-metadata table (`sys_metadata`, `sys_metadata_history`) is refused — see [below](#a-relationship-never-targets-a-stored-metadata-table) |
 | `referenceFilters` | `string[]` | — | **Removed** (#2377, ADR-0049) — no longer a recognized field property. `FieldSchema` is a strict object, so an unknown key is **rejected with guidance**, not silently stripped (ADR-0078): the error echoes the offending key and prescribes the replacement. Use structured `lookupFilters` + `dependsOn` instead; see [Relationships](/docs/data-modeling/relationships) |
 | `deleteBehavior` | `'restrict' \| 'cascade' \| 'set_null'` | `'set_null'` | Behavior when referenced record is deleted. On a *required* lookup `set_null` is escalated to `restrict`, since a NOT NULL foreign key cannot be cleared — **whether the `set_null` was defaulted or written out explicitly**. On a `multiple: true` required lookup the escalation is judged per referencing row: only a row the member removal would leave EMPTY is refused. `cascade` and `restrict` are the values honored as written. Where `set_null` does run, a `multiple: true` lookup loses only the deleted **member** — the other members are kept, and a set emptied that way is stored as `[]`, never `null` |
 
@@ -329,7 +329,7 @@ Parent-child relationship (cascading delete by default).
 
 | Property | Type | Default | Description |
 |:---|:---|:---|:---|
-| `reference` | `string` | **required** | Target (master) object name |
+| `reference` | `string` | **required** | Target (master) object name. A stored-metadata table is refused — see [below](#a-relationship-never-targets-a-stored-metadata-table) |
 | `referenceFilters` | `string[]` | — | **Removed** (#2377, ADR-0049) — no longer a recognized field property. `FieldSchema` is a strict object, so an unknown key is **rejected with guidance**, not silently stripped (ADR-0078): the error echoes the offending key and prescribes the replacement. Use structured `lookupFilters` + `dependsOn` instead; see [Relationships](/docs/data-modeling/relationships) |
 | `deleteBehavior` | `'restrict' \| 'cascade'` | `'cascade'` | Behavior when parent is deleted. `restrict` refuses the parent delete while children exist; `cascade` (and omitting the key) deletes the children with the parent. An explicit `set_null` is a **parse-time rejection** on this type (#9689) — a detail row cannot outlive its master; use a `lookup` if children must survive the parent |
 | `inlineEdit` | `boolean \| 'grid' \| 'form'` | — | Edit child records inline on the parent create/edit form (`true` = auto-pick, `'grid'`, or `'form'`) |
@@ -347,6 +347,10 @@ Parent-child relationship (cascading delete by default).
 }
 ```
 
+#### A relationship never targets a stored-metadata table
+
+A `lookup` or `master_detail` whose `reference` is `sys_metadata` or `sys_metadata_history` is refused by `os validate`, `os build` and the object save door alike. Those rows carry serialized metadata bodies, which are served only through the metadata API (`GET /api/v1/meta/:type/:name`), where the body is projected; the engine never hydrates a reference into them, so `$expand` would keep the stored id and never nest the row, and a master-detail child's `parent` root would stay unbound, refusing every write a `parent` rule judges. To point a record at a metadata item, store its type and name in `text` fields and read the item through the metadata API.
+
 ### `tree`
 Self-referential hierarchy (e.g., categories, org chart).
 
 
@@ -76,7 +76,7 @@ const result = CurrencyConfigSchema.parse(data);
 | **maxSize** | `integer` | optional | Maximum permitted file size in BYTES for media fields. Enforced on write against the stored file size, not just checked in the browser. |
 | **options** | `{ label: string; value: string; description?: string; color?: string; … }[]` | optional | Static options for the option types. A `select` / `radio` field needs a non-empty list here or a `picklist` — with neither (or `options: []`) it is refused at parse. |
 | **picklist** | `string` | optional | Name of a shared `picklist` whose options this field offers — instead of `options`, never with it. Option types only (select, radio, multiselect, checkboxes, tags). A select / radio declares this or a non-empty `options`; with neither it is refused at parse. |
-| **reference** | `string` | optional | Target object name (snake_case) for lookup/master_detail fields. Required for relationship types. Used by $expand to resolve foreign key IDs into full objects. On a `tree` field it is optional and, if given, must be the declaring object's own name — the object schema refuses any other target, and writes the own name when it is left out. |
+| **reference** | `string` | optional | Target object name (snake_case) for lookup/master_detail fields. Required for relationship types. Used by $expand to resolve foreign key IDs into full objects. Never a stored-metadata table (`sys_metadata`, `sys_metadata_history`): their rows are served only through the metadata API, so the engine never hydrates a reference into one, and `os validate`, `os build` and the object save door refuse it. On a `tree` field it is optional and, if given, must be the declaring object's own name — the object schema refuses any other target, and writes the own name when it is left out. |
 | **referenceVia** | `string` | optional | Declares this text field as the id half of a polymorphic pointer pair (ADR-0052 §5 ActivityPointer): the value is a record id of the object named by the SIBLING FIELD this key names — e.g. `record_id` with `referenceVia: 'object_name'`. The sibling must be a declared field on the same object holding an object machine name. Text fields only; mutually exclusive with `reference` (a static and a per-record target contradict). Enforced today at seed load: the value resolves as a natural key against the object the sibling column names, and an unresolvable pointer is refused loudly instead of stored verbatim. Adds no referential integrity or $expand behavior. |
 | **referenceDeletedWhen** | `{ field: string; value: string }` | optional | Marks the record a `referenceVia` pointer names as PLATFORM-DELETED on rows where a sibling `select` field holds one declared option — e.g. `record_id` with `{ field: 'cancel_reason', value: 'record_deleted' }`. A renderer then draws a tombstone from that option's own label, reads nothing and links nothing. Valid only beside `referenceVia`; `field` must be a single-value `select` on the same object declaring inline `options`, and `value` one of its option values — any other shape is refused at parse. |
 | **mailAssociation** | `boolean` | optional | Inbound mail association (`email` fields only): TRUE marks this field as identifying a correspondent. When a mailbox service ingests a message, it associates the message with every record of this object whose value in this field equals one of the message's participant addresses (From, Sender, Reply-To, To and Cc, plus those of a forwarded message it carries; ASCII case-insensitive; the receiving mailbox's own addresses excluded; only within the mailbox's organization). A message no record matches waits in the mailbox's unassociated pool. Refused on any other type. Takes effect only where a mailbox service is composed. |
 
@@ -242,7 +242,7 @@ const result = ApiMethod.parse(data);
 | **maxSize** | `integer` | optional | Maximum permitted file size in BYTES for media fields. Enforced on write against the stored file size, not just checked in the browser. |
 | **options** | `{ label: string; value: string; description?: string; color?: string; … }[]` | optional | Static options for the option types. A `select` / `radio` field needs a non-empty list here or a `picklist` — with neither (or `options: []`) it is refused at parse. |
 | **picklist** | `string` | optional | Name of a shared `picklist` whose options this field offers — instead of `options`, never with it. Option types only (select, radio, multiselect, checkboxes, tags). A select / radio declares this or a non-empty `options`; with neither it is refused at parse. |
-| **reference** | `string` | optional | Target object name (snake_case) for lookup/master_detail fields. Required for relationship types. Used by $expand to resolve foreign key IDs into full objects. On a `tree` field it is optional and, if given, must be the declaring object's own name — the object schema refuses any other target, and writes the own name when it is left out. |
+| **reference** | `string` | optional | Target object name (snake_case) for lookup/master_detail fields. Required for relationship types. Used by $expand to resolve foreign key IDs into full objects. Never a stored-metadata table (`sys_metadata`, `sys_metadata_history`): their rows are served only through the metadata API, so the engine never hydrates a reference into one, and `os validate`, `os build` and the object save door refuse it. On a `tree` field it is optional and, if given, must be the declaring object's own name — the object schema refuses any other target, and writes the own name when it is left out. |
 | **referenceVia** | `string` | optional | Declares this text field as the id half of a polymorphic pointer pair (ADR-0052 §5 ActivityPointer): the value is a record id of the object named by the SIBLING FIELD this key names — e.g. `record_id` with `referenceVia: 'object_name'`. The sibling must be a declared field on the same object holding an object machine name. Text fields only; mutually exclusive with `reference` (a static and a per-record target contradict). Enforced today at seed load: the value resolves as a natural key against the object the sibling column names, and an unresolvable pointer is refused loudly instead of stored verbatim. Adds no referential integrity or $expand behavior. |
 | **referenceDeletedWhen** | `{ field: string; value: string }` | optional | Marks the record a `referenceVia` pointer names as PLATFORM-DELETED on rows where a sibling `select` field holds one declared option — e.g. `record_id` with `{ field: 'cancel_reason', value: 'record_deleted' }`. A renderer then draws a tombstone from that option's own label, reads nothing and links nothing. Valid only beside `referenceVia`; `field` must be a single-value `select` on the same object declaring inline `options`, and `value` one of its option values — any other shape is refused at parse. |
 | **mailAssociation** | `boolean` | optional | Inbound mail association (`email` fields only): TRUE marks this field as identifying a correspondent. When a mailbox service ingests a message, it associates the message with every record of this object whose value in this field equals one of the message's participant addresses (From, Sender, Reply-To, To and Cc, plus those of a forwarded message it carries; ASCII case-insensitive; the receiving mailbox's own addresses excluded; only within the mailbox's organization). A message no record matches waits in the mailbox's unassociated pool. Refused on any other type. Takes effect only where a mailbox service is composed. |
@@ -598,7 +598,7 @@ const result = ApiMethod.parse(data);
 | **maxSize** | `integer` | optional | Maximum permitted file size in BYTES for media fields. Enforced on write against the stored file size, not just checked in the browser. |
 | **options** | `{ label: string; value: string; description?: string; color?: string; … }[]` | optional | Static options for the option types. A `select` / `radio` field needs a non-empty list here or a `picklist` — with neither (or `options: []`) it is refused at parse. |
 | **picklist** | `string` | optional | Name of a shared `picklist` whose options this field offers — instead of `options`, never with it. Option types only (select, radio, multiselect, checkboxes, tags). A select / radio declares this or a non-empty `options`; with neither it is refused at parse. |
-| **reference** | `string` | optional | Target object name (snake_case) for lookup/master_detail fields. Required for relationship types. Used by $expand to resolve foreign key IDs into full objects. On a `tree` field it is optional and, if given, must be the declaring object's own name — the object schema refuses any other target, and writes the own name when it is left out. |
+| **reference** | `string` | optional | Target object name (snake_case) for lookup/master_detail fields. Required for relationship types. Used by $expand to resolve foreign key IDs into full objects. Never a stored-metadata table (`sys_metadata`, `sys_metadata_history`): their rows are served only through the metadata API, so the engine never hydrates a reference into one, and `os validate`, `os build` and the object save door refuse it. On a `tree` field it is optional and, if given, must be the declaring object's own name — the object schema refuses any other target, and writes the own name when it is left out. |
 | **referenceVia** | `string` | optional | Declares this text field as the id half of a polymorphic pointer pair (ADR-0052 §5 ActivityPointer): the value is a record id of the object named by the SIBLING FIELD this key names — e.g. `record_id` with `referenceVia: 'object_name'`. The sibling must be a declared field on the same object holding an object machine name. Text fields only; mutually exclusive with `reference` (a static and a per-record target contradict). Enforced today at seed load: the value resolves as a natural key against the object the sibling column names, and an unresolvable pointer is refused loudly instead of stored verbatim. Adds no referential integrity or $expand behavior. |
 | **referenceDeletedWhen** | `{ field: string; value: string }` | optional | Marks the record a `referenceVia` pointer names as PLATFORM-DELETED on rows where a sibling `select` field holds one declared option — e.g. `record_id` with `{ field: 'cancel_reason', value: 'record_deleted' }`. A renderer then draws a tombstone from that option's own label, reads nothing and links nothing. Valid only beside `referenceVia`; `field` must be a single-value `select` on the same object declaring inline `options`, and `value` one of its option values — any other shape is refused at parse. |
 | **mailAssociation** | `boolean` | optional | Inbound mail association (`email` fields only): TRUE marks this field as identifying a correspondent. When a mailbox service ingests a message, it associates the message with every record of this object whose value in this field equals one of the message's participant addresses (From, Sender, Reply-To, To and Cc, plus those of a forwarded message it carries; ASCII case-insensitive; the receiving mailbox's own addresses excluded; only within the mailbox's organization). A message no record matches waits in the mailbox's unassociated pool. Refused on any other type. Takes effect only where a mailbox service is composed. |