diff --git a/.changeset/owd-alias-fix-provenance-split.md b/.changeset/owd-alias-fix-provenance-split.md
new file mode 100644
index 0000000000..0608f31b76
--- /dev/null
+++ b/.changeset/owd-alias-fix-provenance-split.md
@@ -0,0 +1,13 @@
+---
+"@objectstack/lint": patch
+---
+
+`security-owd-alias` no longer tells authors that `sharingModel: 'public'` is a retired ADR-0090 D4 alias. It never was one — no shipped schema ever accepted it — and the map that said so is now split along the two histories it was conflating.
+
+`OWD_ALIAS_FIX` carried four keys under one comment, `[ADR-0090 D4] Legacy alias → canonical fix-it mapping`, while D4 names three: "The legacy aliases `read`, `read_write`, `full` are **removed from the zod enum**". Those three have a retirement behind them — the `owd-legacy-read-aliases` ADR-0087 stored-row conversion for the two `read*` spellings, the `13.owd-full-alias-removed` semantic entry for `full`. `public` has neither, and correctly so: a conversion rewrites a spelling some shipped schema once took, and this one never was taken, so its stored population is zero by construction. The missing conversion was the mislabel's shadow, not a gap.
+
+- **Two maps, one union.** `OWD_RETIRED_ALIAS_FIX` holds the three D4 aliases; `OWD_WRONG_LAYER_FIX` holds `public`; `OWD_ALIAS_FIX` stays as their union, so every key still earns the same rule id, the same path and the same fix-it. No accept set moves and no value starts or stops being reported.
+- **The `public` fix-it is KEPT.** It catches a real authoring mistake: three neighbouring keys on the same `ObjectSchema` take `'public'` legally — `access.default` (`z.enum(['public', 'private'])`, ADR-0066) and `publicSharing.allowedAudiences` (`z.enum(['public', 'link_only', 'signed_in', 'email'])`) — and off-schema so does the sharing runtime's own internal vocabulary, `effectiveSharingModel(): 'private' | 'read' | 'public'`. `sharingModel` is the one neighbour that refuses it, and it fails CLOSED to `private` with no notice on the read path, so this fix-it is the author's only signal.
+- **The message says which group it is in.** One shared clause, used by both the `sharingModel` and the `externalSharingModel` branch. A retired alias still reads `is a retired alias (ADR-0090 D4)`; `public` now reads that it is not an OWD value and never was, and names the neighbouring keys that do take it. The fix-it text, severity, rule id and path are byte-identical either way.
+
+Why the wording mattered enough to change: a diagnostic that credits `public` to D4 sends its reader looking for the conversion and the semantic entry that would exist if the acceptance had happened, and finding them absent reads as a data-fidelity defect in the conversion registry. It is not one.
diff --git a/packages/cli/test/serve-mcp-capability-collision.e2e.test.ts b/packages/cli/test/serve-mcp-capability-collision.e2e.test.ts
index 7a007fd1e9..73b67a0327 100644
--- a/packages/cli/test/serve-mcp-capability-collision.e2e.test.ts
+++ b/packages/cli/test/serve-mcp-capability-collision.e2e.test.ts
@@ -122,7 +122,7 @@ export default {
   objects: [{
     name: 'mcpcollision_task',
     label: 'Task',
-    sharingModel: 'public',
+    sharingModel: 'private',
     fields: { title: { type: 'text', label: 'Title' } },
   }],
   // NOTE: \`mcp\` is deliberately NOT declared. The banner advertises the MCP
diff --git a/packages/cli/test/serve-mcp-stdio-answers.e2e.test.ts b/packages/cli/test/serve-mcp-stdio-answers.e2e.test.ts
index df61d29125..b77f5093f0 100644
--- a/packages/cli/test/serve-mcp-stdio-answers.e2e.test.ts
+++ b/packages/cli/test/serve-mcp-stdio-answers.e2e.test.ts
@@ -105,7 +105,7 @@ export default {
   objects: [{
     name: 'stdioprobe_task',
     label: 'Task',
-    sharingModel: 'public',
+    sharingModel: 'private',
     fields: { title: { type: 'text', label: 'Title' } },
   }],
 };
diff --git a/packages/cli/test/serve-node-env-production-default.e2e.test.ts b/packages/cli/test/serve-node-env-production-default.e2e.test.ts
index 9350089f47..b74f5d127e 100644
--- a/packages/cli/test/serve-node-env-production-default.e2e.test.ts
+++ b/packages/cli/test/serve-node-env-production-default.e2e.test.ts
@@ -270,7 +270,7 @@ export default {
   objects: [{
     name: 'nodeenvdefault_task',
     label: 'Task',
-    sharingModel: 'public',
+    sharingModel: 'private',
     fields: { title: { type: 'text', label: 'Title' } },
   }],
   // Constructed here, by the HOST — not left to os serve's own auto-inject.
diff --git a/packages/cli/test/serve-process-child-env.e2e.test.ts b/packages/cli/test/serve-process-child-env.e2e.test.ts
index 4578f8d23b..d4ca502140 100644
--- a/packages/cli/test/serve-process-child-env.e2e.test.ts
+++ b/packages/cli/test/serve-process-child-env.e2e.test.ts
@@ -145,7 +145,7 @@ export default {
   objects: [{
     name: 'childenv_task',
     label: 'Task',
-    sharingModel: 'public',
+    sharingModel: 'private',
     fields: { title: { type: 'text', label: 'Title' } },
   }],
 };
diff --git a/packages/cli/test/serve-stdio-stdout-purity.e2e.test.ts b/packages/cli/test/serve-stdio-stdout-purity.e2e.test.ts
index da773c2e7c..feced02b1c 100644
--- a/packages/cli/test/serve-stdio-stdout-purity.e2e.test.ts
+++ b/packages/cli/test/serve-stdio-stdout-purity.e2e.test.ts
@@ -102,7 +102,7 @@ export default {
   objects: [{
     name: 'stdoutpurity_task',
     label: 'Task',
-    sharingModel: 'public',
+    sharingModel: 'private',
     fields: { title: { type: 'text', label: 'Title' } },
   }],
 };
diff --git a/packages/lint/src/validate-security-posture.ts b/packages/lint/src/validate-security-posture.ts
index d616b72f1d..00069e9f36 100644
--- a/packages/lint/src/validate-security-posture.ts
+++ b/packages/lint/src/validate-security-posture.ts
@@ -79,7 +79,9 @@
  * ## Intake — which doors can reach `security-owd-alias` at all (#16109)
  *
  * `sharingModel` and `externalSharingModel` are CLOSED enums on `ObjectSchema`
- * (ADR-0090 D4 / D11): every value `OWD_ALIAS_FIX` names, and every
+ * (ADR-0090 D4 / D11): every value `OWD_ALIAS_FIX` names — both the D4
+ * aliases a shipped schema once accepted and the wrong-layer spellings it
+ * never did, two histories declared as two maps below — and every other
  * non-canonical string, is refused by the schema with `invalid_value`. So on
  * any door that PARSES before the registry runs, this rule's alias branches
  * are unreachable by construction — the object never arrives. Measured on
@@ -108,8 +110,9 @@
  * Read the two alias branches below accordingly: they are NOT a second
  * opinion on the enum, and they are dead on the parsed doors on purpose. They
  * exist so the UNPARSED doors — `os lint` first, the docs gate second — name
- * the canonical replacement instead of letting a retired spelling ride to
- * `os build`, where the enum's generic `invalid_value` is the only message. A
+ * the canonical replacement instead of letting a retired or wrong-layer
+ * spelling ride to `os build`, where the enum's generic `invalid_value` is the
+ * only message. A
  * consumer crediting this rule id as live `error` coverage on a
  * `defineStack`-authored app is crediting the wrong gate: on that door the
  * credit belongs to the schema's closed enum.
@@ -152,13 +155,45 @@ export interface SecurityFinding {
 type AnyRec = Record<string, unknown>;
 
 const CANONICAL_OWD = ['private', 'public_read', 'public_read_write', 'controlled_by_parent'] as const;
-/** [ADR-0090 D4] Legacy alias → canonical fix-it mapping. */
-const OWD_ALIAS_FIX: Record<string, string> = {
+/**
+ * [ADR-0090 D4] The legacy `sharingModel` spellings a shipped schema once
+ * ACCEPTED, and the canonical value each becomes. D4 names exactly these
+ * THREE — "The legacy aliases `read`, `read_write`, `full` are **removed from
+ * the zod enum**" — and only these three have a retirement behind them: the
+ * `owd-legacy-read-aliases` ADR-0087 stored-row conversion for the two `read*`
+ * spellings, and the `13.owd-full-alias-removed` semantic entry for `full`.
+ */
+const OWD_RETIRED_ALIAS_FIX: Record<string, string> = {
   read: 'public_read',
   read_write: 'public_read_write',
   full: 'public_read_write',
+};
+
+/**
+ * Wrong-layer / misspelling fix-its: values NO shipped schema ever accepted
+ * *here*. They are NOT retired aliases, and nothing sits behind them to
+ * retire — no ADR-0087 conversion, no semantic-migration entry, and none is
+ * possible, because a conversion rewrites a spelling some shipped schema once
+ * took and the stored population for these is zero by construction (#16517
+ * read the enum's whole lifetime over complete history; `public` appears in no
+ * version of it).
+ *
+ * `public` is kept here rather than deleted because it catches a real
+ * authoring mistake. THREE neighbouring keys on the same `ObjectSchema` take
+ * `'public'` legally — `access.default` (`z.enum(['public', 'private'])`,
+ * ADR-0066) and `publicSharing.allowedAudiences`
+ * (`z.enum(['public', 'link_only', 'signed_in', 'email'])`) — and off-schema
+ * so does the sharing runtime's own internal vocabulary,
+ * `effectiveSharingModel(): 'private' | 'read' | 'public'`. `sharingModel` is
+ * the one neighbour that refuses it, and it fails CLOSED to `private` with no
+ * notice on the read path, so this fix-it is the author's only signal.
+ */
+const OWD_WRONG_LAYER_FIX: Record<string, string> = {
   public: 'public_read_write',
 };
+
+/** Every value this rule offers a fix-it for — both provenance groups. */
+const OWD_ALIAS_FIX: Record<string, string> = { ...OWD_RETIRED_ALIAS_FIX, ...OWD_WRONG_LAYER_FIX };
 /** D11 ordering for external ≤ internal (controlled_by_parent excluded). */
 const OWD_WIDTH: Record<string, number> = {
   private: 0,
@@ -182,6 +217,29 @@ function owdOf(obj: AnyRec): unknown {
   return obj.sharingModel;
 }
 
+/**
+ * The provenance half of an alias finding's message.
+ *
+ * The two halves of `OWD_ALIAS_FIX` do not share a history, so one sentence
+ * cannot serve both: calling `public` "a retired alias (ADR-0090 D4)" asserts
+ * an acceptance that never happened, and sends the reader looking for the
+ * conversion and the semantic entry that would exist if it had. The fix-it is
+ * identical either way; only this clause differs.
+ *
+ * The sibling keys are named undotted on purpose: the receiver-coverage
+ * meta-test in this rule's test file scans the module's CODE text for
+ * `receiver.key` reads and cannot tell one inside a message string from a real
+ * read, so a dotted spelling here would present as an undeclared read off a
+ * receiver that does not exist.
+ */
+function owdAliasProvenance(value: string): string {
+  return OWD_RETIRED_ALIAS_FIX[value]
+    ? `is a retired alias (ADR-0090 D4)`
+    : `is not an OWD value and never was — ADR-0090 D4 retired 'read', 'read_write' and 'full', ` +
+        `not this. '${value}' is legal on the neighbouring keys 'access' (its 'default') and ` +
+        `'publicSharing' (its 'allowedAudiences'), just not on this one`;
+}
+
 /**
  * A platform / system object: one the tenant did not author.
  *
@@ -394,7 +452,7 @@ export function validateSecurityPosture(stack: AnyRec, opts?: { nowMs?: number }
           where: `object "${objName}"`,
           path: `${objPath}.sharingModel`,
           message:
-            `sharingModel '${owd}' is a retired alias (ADR-0090 D4). The runtime fails CLOSED ` +
+            `sharingModel '${owd}' ${owdAliasProvenance(owd)}. The runtime fails CLOSED ` +
             `to 'private' on unknown values, so this object is NOT ${owd === 'read' ? 'readable' : 'writable'} org-wide.`,
           hint: `Replace with the canonical value: sharingModel: '${OWD_ALIAS_FIX[owd]}'.`,
         });
@@ -511,7 +569,7 @@ export function validateSecurityPosture(stack: AnyRec, opts?: { nowMs?: number }
           rule: SECURITY_OWD_ALIAS,
           where: `object "${objName}"`,
           path: `${objPath}.externalSharingModel`,
-          message: `externalSharingModel '${external}' is a retired alias (ADR-0090 D4).`,
+          message: `externalSharingModel '${external}' ${owdAliasProvenance(external)}.`,
           hint: `Replace with the canonical value: externalSharingModel: '${OWD_ALIAS_FIX[external]}'.`,
         });
       } else if (