@@ -0,0 +1,16 @@
+---
+'@objectstack/lint': patch
+---
+
+feat(lint): `security-external-owner-unmapped` warns when a writable external object refuses every member write (#27332)
+
+Clause-②: no (a warning narrows nothing; no accepted metadata shape moves)
+Metadata-protocol: none
+
+An external object (ADR-0015) on an owner-keyed sharing model (`private`, `public_read`, or none on a custom object) refuses every member edit and delete with 403 `PERMISSION_DENIED`, even for a member whose permission set grants `allowEdit`, unless an app-authored row-level policy admits the row. Before the write, record sharing reads the row's `owner_id` and the platform ownership floor reads `created_by` equal to the caller, and no remote row carries either column. `os validate`, `os build` and `os lint` now say so with a warning on the object.
+
+- The warning names two ways out. One: declare `sharingModel: 'public_read_write'` and decide who may edit in a `beforeUpdate` hook. Two: declare `owner_id` in `fields` and have the driver return the remote owner under that name. A built-in SQL driver does that through `external.columnMap`; `columnMap` is not applied by the engine, so a plugin driver must return the field itself.
+- A `columnMap` entry for `owner_id` without the declared field still warns, worded for it: it works on a built-in SQL driver only, and leaves reads unscoped by owner there.
+- `ownership: 'none'` (or `'org'` / `'business_unit'`) is not a way out. It drops `owner_id`, and the floor's `created_by` check refuses the same write, so the warning still fires and names `created_by`. Declaring `created_by` (served by the driver) silences it.
+- It skips a read-only binding (`external.writable` not `true`, or a datasource the stack declares with `external.allowWrites: false`), `public_read_write`, `controlled_by_parent`, and an object that declares the column its check reads.
+- It is a warning, never an error: `defineStack` and every publish door accept the same stacks as before. `os explain security-external-owner-unmapped` explains the two checks, and why `public_read_write` opens edits but not deletes.
@@ -758,7 +758,7 @@ os compile --json                    # JSON output for CI pipelines
   → Normalizing stack definition...
   → Lowering inline handlers...
   → Validating protocol compliance...
-  → Running author-time rules (55)...
+  → Running author-time rules (56)...
   → Checking that every required capability has a provider installable in this edition...
   → Collecting package docs (ADR-0046)... 0 collected
   → Writing artifact...
 
@@ -752,7 +752,7 @@ A clean run walks the registry and reports timing:
   Config: /path/to/support-desk/objectstack.config.ts
   Load time: 21ms
   → Validating against ObjectStack Protocol...
-  → Running author-time rules (55)...
+  → Running author-time rules (56)...
   → Checking that every required capability has a provider installable in this edition...
   → Checking package docs (ADR-0046)...
 
 
@@ -305,7 +305,7 @@ visible: 'status != "resolved"'
 ◆ Validate
 ────────────────────────────────────────
   → Validating against ObjectStack Protocol...
-  → Running author-time rules (55)...
+  → Running author-time rules (56)...
 
   ✗ Author-time rules failed (1 issue)
   • stack · action 'resolve_ticket' visible: bare reference `status` — a
 
@@ -404,7 +404,7 @@ objectstack validate
 ────────────────────────────────────────
   → Loading configuration...
   → Validating against ObjectStack Protocol...
-  → Running author-time rules (55)...
+  → Running author-time rules (56)...
   → Checking that every required capability has a provider installable in this edition...
   → Checking package docs (ADR-0046)...
 
 
@@ -137,6 +137,7 @@ import { validatePredicatePathRefs } from './validate-predicate-path-refs.js';
 import { validateSecurityPosture, validateSecurityRoleWord } from './validate-security-posture.js';
 import { validateOrgAxisRedLines } from './validate-org-axis-red-lines.js';
 import { validateSharingRuleEnforceability } from './validate-sharing-rule-enforceability.js';
+import { validateExternalOwnerSharing } from './validate-external-owner-sharing.js';
 import { validateRlsPredicateEnforceability } from './validate-rls-predicate-enforceability.js';
 import {
   validateMembershipKeyDeclarations,
@@ -2330,6 +2331,22 @@ export const AUTHORING_RULES: readonly AuthoringRule[] = [
       + 'never run at a door should not claim it.',
     run: (stack) => validateSharingRuleEnforceability(stack),
   },
+  // A writable ADR-0015 external object on an owner-keyed sharing model whose
+  // owner column no remote row serves: record sharing reads `owner_id`, the
+  // platform ownership floor reads `created_by == caller`, neither has storage,
+  // so every member edit and delete is refused (403). Advisory: the stack is
+  // valid and an administrator still writes; a refusal would narrow the
+  // published accept set.
+  {
+    name: 'validateExternalOwnerSharing',
+    tier: 'advisory',
+    input: 'parsed',
+    commands: ALL,
+    source: 'packages/lint/src/validate-external-owner-sharing.ts',
+    surfaces: CLI_ONLY,
+    surfaceReason: RUNTIME_OBJECT_ADVISORY_VOLUME,
+    run: (stack) => validateExternalOwnerSharing(stack),
+  },
   // #4983 — the sibling surface of the rule above, and ADR-0056 D4's gate,
   // which had never been wired to anything: `isSupportedRlsExpression` existed
   // solely so an authoring command could reject a predicate the runtime drops,
 
@@ -380,6 +380,17 @@ export type {
   SharingRuleEnforceabilitySeverity,
 } from './validate-sharing-rule-enforceability.js';
 
+// A writable external object on an owner-keyed sharing model whose owner column
+// no remote row serves refuses every member edit and delete (403).
+export {
+  validateExternalOwnerSharing,
+  SECURITY_EXTERNAL_OWNER_UNMAPPED,
+} from './validate-external-owner-sharing.js';
+export type {
+  ExternalOwnerSharingFinding,
+  ExternalOwnerSharingSeverity,
+} from './validate-external-owner-sharing.js';
+
 // #4983 — the sibling surface, and ADR-0056 D4's gate finally wired. An RLS
 // `using` / `check` the runtime cannot compile is DROPPED (and, when it is the
 // only applicable policy, replaced by the deny sentinel), so the policy reads
 
@@ -730,6 +730,49 @@ const SECURITY_CBP_OWNER_POLICY_WITHOUT_OPT_IN_EXPLANATION: RuleExplanation = {
   ],
 };
 
+const SECURITY_EXTERNAL_OWNER_UNMAPPED_EXPLANATION: RuleExplanation = {
+  rule: 'security-external-owner-unmapped',
+  covers: 'why members cannot write an external object',
+  paragraphs: [
+    'Before a member updates or deletes one record, the platform runs two row-level checks. Record ' +
+      'sharing, on a `private` or `public_read` object that carries an `owner_id` column, asks for the ' +
+      'row\'s `owner_id` and admits the owner (widened by write depth, an `edit` share or Modify All ' +
+      'Data). The platform ownership floor, `created_by` equal to the caller, stays in force unless record ' +
+      'sharing admits the write or the object declares `sharingModel: \'public_read_write\'`.',
+    'The registry adds `owner_id` and `created_by` to an external object as it does to every object, but ' +
+      'the remote database owns the table and the platform creates no column for either. So the remote row ' +
+      'answers no `owner_id` (record sharing refuses) and no `created_by` equal to the caller (the floor ' +
+      'refuses). A member whose permission set grants `allowEdit` is refused every edit and every delete ' +
+      'with 403 `PERMISSION_DENIED`, unless an app-authored row-level policy admits the row; otherwise only ' +
+      'an administrator can write. An object with no `sharingModel` is ' +
+      'judged as \'private\', the value the runtime falls back to.',
+    '`ownership: \'none\'` (or `\'org\'`, `\'business_unit\'`) is not a way out: without `owner_id` record ' +
+      'sharing stops judging the row, and the floor\'s `created_by` check refuses the same write. Turning ' +
+      'the audit columns off (`systemFields.audit: false`) does not help either: the floor then has no ' +
+      'column to compare and refuses every row.',
+    'There are two ways out. Declare `sharingModel: \'public_read_write\'`: every member who holds ' +
+      '`allowEdit` may then edit, and a `beforeUpdate` hook decides who really may. Or serve the column ' +
+      'the check reads: declare `owner_id` in `fields` and have the driver return the remote owner under ' +
+      'that name, so the owner edits and deletes the row and other members are refused. A built-in SQL ' +
+      'driver does that through `external.columnMap` (remote column to `owner_id`); `columnMap` is applied ' +
+      'by those drivers, not by the engine, so a plugin driver must return the field itself. Declaring ' +
+      'the field matters for reads too: the platform\'s own `owner_id` is treated as unstored, and reads ' +
+      'are not scoped by owner. On an object without `owner_id`, declare `created_by` the same way instead, ' +
+      'so the creator writes the row.',
+    'A `columnMap` entry for the column without a declared field is reported too, with its own wording: ' +
+      'it serves the check on a built-in SQL driver and does nothing on a plugin driver, and the ' +
+      'declaration is what holds on both.',
+    'Deletes are not opened by `public_read_write`: that model opens edits, and the floor keeps deletes ' +
+      'to the row\'s `created_by`. On an external object that column has no storage either, so member ' +
+      'deletes stay refused unless the driver returns `created_by` or an authored policy or share grants them.',
+    'The rule judges only a writable binding (`external.writable: true`, on a datasource this stack does ' +
+      'not declare with `external.allowWrites: false`) on a model that keys writes to ' +
+      'an owner (`private`, `public_read`, or none on a custom object). `controlled_by_parent` is not judged: ' +
+      'the master record\'s gate decides its writes. It is a warning, not an error: the stack is valid and ' +
+      'an administrator can still write.',
+  ],
+};
+
 const SECURITY_FLS_UNKNOWN_FIELD_EXPLANATION: RuleExplanation = {
   rule: 'security-fls-unknown-field',
   covers: 'how the runtime resolves a field-permission key',
@@ -5150,6 +5193,7 @@ export const RULE_EXPLANATIONS: Readonly<Record<string, RuleExplanation>> = Obje
   [SECURITY_CBP_AMBIGUOUS_RELATION_EXPLANATION.rule]: SECURITY_CBP_AMBIGUOUS_RELATION_EXPLANATION,
   [SECURITY_CBP_NO_RELATION_EXPLANATION.rule]: SECURITY_CBP_NO_RELATION_EXPLANATION,
   [SECURITY_CBP_OWNER_POLICY_WITHOUT_OPT_IN_EXPLANATION.rule]: SECURITY_CBP_OWNER_POLICY_WITHOUT_OPT_IN_EXPLANATION,
+  [SECURITY_EXTERNAL_OWNER_UNMAPPED_EXPLANATION.rule]: SECURITY_EXTERNAL_OWNER_UNMAPPED_EXPLANATION,
   [SECURITY_FLS_UNKNOWN_FIELD_EXPLANATION.rule]: SECURITY_FLS_UNKNOWN_FIELD_EXPLANATION,
   [SECURITY_MASTER_DETAIL_UNGRANTED_EXPLANATION.rule]: SECURITY_MASTER_DETAIL_UNGRANTED_EXPLANATION,
   [SECURITY_WILDCARD_VAMA_EXPLANATION.rule]: SECURITY_WILDCARD_VAMA_EXPLANATION,