@@ -0,0 +1,68 @@
+---
+"@objectstack/driver-memory": minor
+"@objectstack/driver-sql": patch
+"@objectstack/objectql": patch
+---
+
+fix(driver-memory,driver-sql): an explicit `tenancy.enabled: false` opt-out is sticky, so a partial `syncSchema` re-registration no longer flips a platform-global object's UNIQUE partition (#16729)
+
+## What was wrong
+
+`InMemoryDriver.syncSchema` recomputed its uniqueness constraints from whatever
+schema THAT call happened to carry. A second registration without a `tenancy`
+block — the `{ name, fields }` shape — fell through to the implicit
+`organization_id` heuristic, so a `unique` field moved from **one row per
+install** (`scopeField: null`, which is what `tenancy.enabled: false` declares)
+to **one row per organization**. A duplicate the declaration refuses then
+landed. Measured at the driver door on `origin/main` `d61139f1ba`:
+
+| sequence | second `key: 'K'`, different organization |
+|:--|:--|
+| register with `tenancy.enabled: false` | `REFUSED` — `UNIQUE_VIOLATION` / 409 |
+| …then re-register with `{ name, fields }` | **`LANDED`** |
+
+`SqlDriver` running the same sequence refuses in **both** cases: it has kept a
+sticky `tenantOptOutByTable` since #3249. `driver-memory` had mirrored the inner
+`computeTenantField` and not the wrapper that consults the record, so "mirrors
+`computeTenantField` arm for arm" stayed literally true while the pair diverged.
+
+It is silent in both directions — nothing logs the flip, and the refusal names
+the field, never the partition. That is the declared-vs-enforced shape Prime
+Directive #10 forbids, reached by a state change rather than by a missing check.
+
+## What it does now
+
+- **`@objectstack/driver-memory`** gains `computeAndRecordTenantField`, the
+  sticky resolver, and the `TenantOptOutRecord` type for the per-instance record
+  a driver owns. `InMemoryDriver` holds one and resolves through it, handing
+  BOTH declaration surfaces — field-level `unique` and declared `indexes[]` —
+  the same resolved column. `uniqueConstraintsFromFields` and
+  `uniqueConstraintsFromDeclaredIndexes` accept that column as an optional
+  second argument; called with one argument they answer exactly as before.
+  `tenantFieldOf` is unchanged and still a pure function of its argument.
+- **`@objectstack/driver-sql`**: the shard leaf resolved its tenant column with
+  the BARE `computeTenantField`, so a `rotateShards` sweep carrying no `tenancy`
+  block gave a shard an organization key part the base table's index does not
+  have — one object, two partitions, decided by which physical table a row
+  landed in. It now resolves through the record, keyed by the base table.
+- **`@objectstack/objectql`**: `LifecycleObjectLike` declares `tenancy`. The
+  Archiver hands that object straight to `cold.syncSchema`, and the published
+  type refused the key while the driver below read it — so an author writing a
+  fresh literal was pushed into producing exactly the partial re-registration
+  above. Same correction #16711 made where the shard leaf narrowed the key off
+  the object it was handed.
+
+The record is deliberately narrow. Only the explicit OPT-OUT is sticky: a
+declared `tenancy.tenantField` is not recorded, matching `SqlDriver`. An object
+that never declared the opt-out never enters the record, so a genuinely
+org-scoped object keeps its `organization_id` partition across a partial
+re-registration — an implementation answering `null` more often would not be
+stickier, it would be tenant isolation switched off. A carried `tenancy` block
+stays authoritative in both directions and CLEARS a recorded opt-out.
+
+`@objectstack/driver-memory` is `minor` for the two new public-entry exports.
+The behaviour repairs themselves are `patch`: each restores an implementation to
+the `tenancy.enabled: false` contract (`isTenancyDisabled`, ADR-0066) it was
+already declaring, rather than replacing one legal published answer with
+another. The `objectql` entry is a published type WIDENING — a key the interface
+refused is now accepted, and nothing that compiled before stops compiling.
@@ -31,10 +31,19 @@ export type { TenancyAwareSchema } from './memory-tenancy-guard.js';
 // identity and the scoping helpers, exported so a consumer can assert the
 // envelope (`code` AND `status`, never merely "it threw") without
 // string-matching the message.
+//
+// [#16729] `computeAndRecordTenantField` is published BESIDE `tenantFieldOf`,
+// not kept private, because publishing only the inner half is what let this
+// package diverge in the first place: `tenantFieldOf` mirrors
+// `SqlDriver.computeTenantField`, the stickiness lives in the wrapper AROUND
+// that function on the SQL side, and a reader who found only the inner half
+// exported mirrored only the inner half. The next driver reproducing this pair
+// sees both halves or repeats the same omission.
 export {
   UNIQUE_VIOLATION_CODE,
   UNIQUE_VIOLATION_STATUS,
   assertNoUniqueViolation,
+  computeAndRecordTenantField,
   declaredIndexViolationError,
   isDeclaredIndexConstraint,
   tenantFieldOf,
@@ -48,6 +57,7 @@ export type {
   MemoryDeclaredIndexConstraint,
   MemoryUniqueConstraint,
   MemoryUniqueEnforcement,
+  TenantOptOutRecord,
   UniqueAwareSchema,
 } from './memory-unique-constraint.js';
 
 
@@ -49,6 +49,7 @@ import {
 // module docblock.
 import {
   assertNoUniqueViolation,
+  computeAndRecordTenantField,
   uniqueConstraintsFromDeclaredIndexes,
   uniqueConstraintsFromFields,
   type MemoryUniqueEnforcement,
@@ -404,6 +405,27 @@ export class InMemoryDriver implements IDataDriver {
    * the data it happens to hold.
    */
   private uniqueConstraints: Map<string, MemoryUniqueEnforcement[]> = new Map();
+
+  /**
+   * [#16729] Objects whose schema EXPLICITLY declared `tenancy.enabled: false`,
+   * this driver's counterpart of `SqlDriver.tenantOptOutByTable` and the record
+   * {@link computeAndRecordTenantField} maintains.
+   *
+   * Sticky across re-registrations on purpose: a later `syncSchema` that omits
+   * the `tenancy` block must NOT resurrect org-scoping of the uniqueness key
+   * via the implicit `organization_id` heuristic. Without it a platform-global
+   * object's UNIQUE partition silently moved from one row per install to one
+   * row per organization, and the duplicate its declaration refuses LANDED.
+   *
+   * Unlike {@link uniqueConstraints} it is deliberately NOT cleared by
+   * `dropTable`. That map is cleared because a constraint outliving its table
+   * would be ENFORCED over a table nobody declared; this record enforces
+   * nothing on its own — it only decides which partition the NEXT declaration
+   * resolves to, and the last authoritative word on this object was still
+   * "platform-global". Dropping a table is not a schema declaring itself
+   * tenant-scoped, and only such a declaration clears the record.
+   */
+  private tenantOptOutByObject: Set<string> = new Set();
   private transactions: Map<string, MemoryTransaction> = new Map();
   private persistenceAdapter: PersistenceAdapterInterface | null = null;
 
@@ -1978,9 +2000,18 @@ export class InMemoryDriver implements IDataDriver {
     // an already-duplicated pair is reported by the first write that touches
     // it — the same posture `driver-sql` takes when a unique index cannot be
     // built over dirty data (it announces, it does not delete rows).
+    // [#16729] Resolve the tenant column through the STICKY record rather than
+    // from this call's schema alone. `syncSchema` is idempotent and is called
+    // again with whatever schema the caller happens to hold; a call carrying no
+    // `tenancy` block would otherwise fall through to the implicit
+    // `organization_id` heuristic and re-scope an object that declared itself
+    // platform-global. Both surfaces are handed the SAME resolved column, so
+    // the field-level and declared-index keys of one object cannot disagree
+    // about which partition it lives in.
+    const tenantField = computeAndRecordTenantField(this.tenantOptOutByObject, object, schema);
     this.uniqueConstraints.set(object, [
-      ...uniqueConstraintsFromFields(schema),
-      ...uniqueConstraintsFromDeclaredIndexes(schema),
+      ...uniqueConstraintsFromFields(schema, tenantField),
+      ...uniqueConstraintsFromDeclaredIndexes(schema, tenantField),
     ]);
     if (kinds.size > 0) {
       const table = this.db[object];
 
@@ -300,20 +300,105 @@ export function tenantFieldOf(schema: UniqueAwareSchema | null | undefined): str
   return null;
 }
 
+/**
+ * [#16729] One driver's record of the objects whose schema EXPLICITLY declared
+ * `tenancy.enabled === false` — this package's counterpart of `SqlDriver`'s
+ * `tenantOptOutByTable`.
+ *
+ * Owned by the DRIVER INSTANCE, never by this module. Two `InMemoryDriver`s in
+ * one process are two independent stores (this driver's whole shape is
+ * per-instance state), so a module-level record would let one store's
+ * declaration decide another store's uniqueness partition — a fresh
+ * cross-instance channel introduced by the fix for a cross-registration one.
+ * `SqlDriver` holds its own record per instance for the same reason.
+ */
+export type TenantOptOutRecord = Set<string>;
+
+/**
+ * [#16729] {@link tenantFieldOf} + maintenance of the sticky explicit-opt-out
+ * record. Mirrors `SqlDriver.computeAndRecordTenantField` arm for arm, and it
+ * is the arm this package was missing.
+ *
+ * ## Why the mirror needed a SECOND function, not a change to the first
+ *
+ * `driver-memory` already reproduced `SqlDriver.computeTenantField` faithfully
+ * as {@link tenantFieldOf}. The stickiness, though, does not live in that
+ * function on the SQL side either: it lives in the WRAPPER around it. So the
+ * inner half was mirrored and the outer half was not, and "this mirrors
+ * `computeTenantField` arm for arm" stayed literally true while the pair as a
+ * whole diverged. {@link tenantFieldOf} is therefore UNCHANGED and still
+ * answers from the passed schema alone — a pure function of its argument is
+ * what its own pins assert, and they remain correct.
+ *
+ * ## What the record buys
+ *
+ * A schema that carries a `tenancy` declaration is authoritative: it sets or
+ * clears the record and is computed normally. A schema WITHOUT one — a partial
+ * re-registration — preserves a previously declared opt-out instead of letting
+ * the implicit `organization_id` heuristic re-scope a platform-global object.
+ * Without it, a second `syncSchema` carrying only `{ name, fields }` silently
+ * moves a `unique` field from ONE row per install (`scopeField: null`, which is
+ * what `tenancy.enabled: false` declares) to one row per organization: a
+ * duplicate the declaration refuses then LANDS, and nothing announces the
+ * change — the declared-vs-enforced divergence Prime Directive #10 forbids,
+ * reached by a state change rather than by a missing check.
+ *
+ * ## Only the OPT-OUT is sticky, deliberately
+ *
+ * A declared `tenancy.tenantField` is NOT recorded, so a partial
+ * re-registration of a custom-tenant-column object still falls back to
+ * `organization_id`. That is not an oversight: it is what `SqlDriver` does, and
+ * this module's contract is to answer as `driver-sql` answers. Recording more
+ * here would be a second, easier answer to "what does `unique` mean" — the
+ * one-contract-two-numbers defect this module exists to close.
+ *
+ * A genuinely tenant-scoped object (no `tenancy` block, an `organization_id`
+ * column) never enters the record, so it keeps its `organization_id` partition
+ * across a partial re-registration exactly as before. An implementation that
+ * answered `null` more often than this one would not be stickier, it would be
+ * tenant isolation switched off.
+ */
+export function computeAndRecordTenantField(
+  record: TenantOptOutRecord,
+  key: string,
+  schema: UniqueAwareSchema | null | undefined,
+): string | null {
+  // A carried `tenancy` block is AUTHORITATIVE in both directions: it records a
+  // fresh opt-out, and it CLEARS a stale one. `!= null` is the SQL side's test
+  // — the declaration's PRESENCE is what makes it authoritative, so a
+  // `tenancy: {}` that declares no opt-out clears the record too.
+  if (schema?.tenancy != null) {
+    if (isTenancyDisabled(schema)) record.add(key);
+    else record.delete(key);
+    return tenantFieldOf(schema);
+  }
+  if (record.has(key)) return null;
+  return tenantFieldOf(schema);
+}
+
 /**
  * The constraints an object's field-level `unique` declarations ask for.
  *
  * The single place a `unique` declaration becomes a constraint in this package,
  * so the create, update and update-many paths cannot disagree about what one
  * means — the same reason `uniqueIndexesFromFields` is the single place on the
  * SQL side.
+ *
+ * [#16729] `tenantField` is the RESOLVED tenant column. It defaults to
+ * {@link tenantFieldOf} of this very schema, so the published one-argument call
+ * answers exactly as before; a caller holding a {@link TenantOptOutRecord}
+ * passes {@link computeAndRecordTenantField}'s answer instead, and a partial
+ * re-registration then cannot re-scope an object that declared itself
+ * platform-global. `driver-sql` threads the resolved column into
+ * `syncDeclaredIndexes` rather than letting that leaf recompute it, for this
+ * same reason.
  */
 export function uniqueConstraintsFromFields(
   schema: UniqueAwareSchema | null | undefined,
+  tenantField: string | null = tenantFieldOf(schema),
 ): MemoryUniqueConstraint[] {
   const fields = schema?.fields;
   if (!fields) return [];
-  const tenantField = tenantFieldOf(schema);
   const out: MemoryUniqueConstraint[] = [];
   for (const [name, field] of Object.entries(fields)) {
     const unique = (field as { unique?: unknown } | null | undefined)?.unique;
@@ -344,13 +429,22 @@ export function uniqueConstraintsFromFields(
  * `driver-memory` must not depend on `driver-sql`, so the arms are reproduced
  * and pinned here (`memory-declared-index-unique.test.ts`), the way
  * {@link tenantFieldOf} reproduces `SqlDriver.computeTenantField`.
+ *
+ * [#16729] `tenantField` is the RESOLVED tenant column. It defaults to
+ * {@link tenantFieldOf} of this very schema, so the published one-argument call
+ * answers exactly as before; a caller holding a {@link TenantOptOutRecord}
+ * passes {@link computeAndRecordTenantField}'s answer instead, and a partial
+ * re-registration then cannot re-scope an object that declared itself
+ * platform-global. `driver-sql` threads the resolved column into
+ * `syncDeclaredIndexes` rather than letting that leaf recompute it, for this
+ * same reason.
  */
 export function uniqueConstraintsFromDeclaredIndexes(
   schema: UniqueAwareSchema | null | undefined,
+  tenantField: string | null = tenantFieldOf(schema),
 ): MemoryDeclaredIndexConstraint[] {
   const declared = schema?.indexes;
   if (!Array.isArray(declared)) return [];
-  const tenantField = tenantFieldOf(schema);
   const out: MemoryDeclaredIndexConstraint[] = [];
   for (const idx of declared) {
     // The same filter the SQL side applies, and nothing more: a non-string or