fix(spec): cut three over-claims from the filter-is-empty migration guidance and one from its changeset

The at-tier review's wording flags, folded in as cuts:
- acceptanceCriteria: "it now also selects the rows holding the empty string
  or the empty list" read as if is_not_empty gained those rows; it loses them.
- acceptanceCriteria: "fails with INVALID_FILTER" — the analytics read scope
  fails with a different code.
- reason: "while the three builders already showed them as empty" is cut.
- changeset: "and the prescription `$null`" — the read-scope envelope's message
  does not spell it; the FROM → TO lines carry the remedy.

registry.ts regenerated by gen:migration-registry.

Claude-Session: https://claude.ai/code/session_01Sfe5YjBLwB9J3y8fvm2xq1
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

.changeset/20446-empty-joins-filter-operators.md

@@ -12,7 +12,7 @@ A stored 「is empty」 / 「is not empty」 — `['field', 'is_empty', …]`, `
 
 - **A `{ $empty: … }` object written as a field value** (a `where` pasted into an insert or update payload) is refused with `VALIDATION_FAILED` (`invalid_type`, "$empty is a filter operator, not a value"). Before, a text-like field stored it as data.
   FROM `update('task', { title: { $empty: true } })` → TO write the value itself (`{ title: '' }`, `{ title: null }`); a filter belongs in `where`.
-- **`is_empty` / `is_not_empty` where no face holds the column's declared type** is refused with `INVALID_FILTER` / 400 (`READ_SCOPE_COMPILE_FAILED` / 500 on an analytics read scope) and the prescription `$null`. The `$null` lowering answered these. The compositions:
+- **`is_empty` / `is_not_empty` where no face holds the column's declared type** is refused with `INVALID_FILTER` / 400 (`READ_SCOPE_COMPILE_FAILED` / 500 on an analytics read scope). The `$null` lowering answered these. The compositions:
   - the built-in `id`, which no object declares. FROM `['id', 'is_empty', true]` → TO `['id', 'is_null', true]` / `is_not_null`;
   - a federated (external) object on a driver that does not implement `registerExternalObject` (driver-memory, driver-mongodb). The boot already reports such an object as NOT bound to its remote table, naming it, and its reads answered from a table named after the object. FROM `is_empty` on such an object → TO bind it on a driver that implements federation (driver-sql and its heirs, driver-turso);
   - an `AnalyticsService` constructed without `sourceFieldMeta`. FROM such a host → TO pass `sourceFieldMeta` (the package README shows it), or filter with `is_null` / `is_not_null`;

packages/spec/src/migrations/entries/semantic/18.filter-is-empty-lowers-to-empty-operator.ts

@@ -36,8 +36,8 @@ export const entry: SemanticMigration = {
     + 'of FILTER_OPERATORS until every face answered it, then added in the same change that flipped '
     + 'the lowering, after measuring that no face drops it. Two consequences reach stored metadata. '
     + 'A stored 「is empty」 on a text or multi-value field finds more rows: the ones holding the '
-    + 'empty string or the empty list, which the $null lowering missed while the three builders '
-    + 'already showed them as empty. And the rule is refused, loudly and with the $null '
+    + 'empty string or the empty list, which the $null lowering missed. '
+    + 'And the rule is refused, loudly and with the $null '
     + 'prescription, where the face that answers it holds no declaration for the column — the four '
     + 'compositions the replacement names — where the $null lowering compiled IS NULL. The same '
     + 'change made the write door refuse a $empty object as a field value, because that door '
@@ -47,10 +47,10 @@ export const entry: SemanticMigration = {
     + 'ADR-0087 / ADR-0112.',
   acceptanceCriteria:
     'Grep your stored views, sharing rules and filter arrays for is_empty / is_not_empty. On a text '
-    + 'or multi-value field, re-check what the view or rule is supposed to select: it now also '
-    + 'selects the rows holding the empty string or the empty list. On the built-in id, rewrite it '
+    + 'or multi-value field, re-check what the view or rule is supposed to select. '
+    + 'On the built-in id, rewrite it '
     + 'to is_null / is_not_null. If a federated object on driver-memory or driver-mongodb, or an '
-    + 'AnalyticsService host without sourceFieldMeta, carries such a rule, the query now fails with '
-    + 'INVALID_FILTER instead of answering — bind the object on a federation-capable driver, or pass '
+    + 'AnalyticsService host without sourceFieldMeta, carries such a rule, the query now fails '
+    + 'instead of answering — bind the object on a federation-capable driver, or pass '
     + 'sourceFieldMeta. No insert or update payload carries a $empty object as a field value.',
 };

packages/spec/src/migrations/registry.ts

@@ -10882,8 +10882,8 @@ const step18: MigrationStep = {
         + 'of FILTER_OPERATORS until every face answered it, then added in the same change that flipped '
         + 'the lowering, after measuring that no face drops it. Two consequences reach stored metadata. '
         + 'A stored 「is empty」 on a text or multi-value field finds more rows: the ones holding the '
-        + 'empty string or the empty list, which the $null lowering missed while the three builders '
-        + 'already showed them as empty. And the rule is refused, loudly and with the $null '
+        + 'empty string or the empty list, which the $null lowering missed. '
+        + 'And the rule is refused, loudly and with the $null '
         + 'prescription, where the face that answers it holds no declaration for the column — the four '
         + 'compositions the replacement names — where the $null lowering compiled IS NULL. The same '
         + 'change made the write door refuse a $empty object as a field value, because that door '
@@ -10893,11 +10893,11 @@ const step18: MigrationStep = {
         + 'ADR-0087 / ADR-0112.',
       acceptanceCriteria:
         'Grep your stored views, sharing rules and filter arrays for is_empty / is_not_empty. On a text '
-        + 'or multi-value field, re-check what the view or rule is supposed to select: it now also '
-        + 'selects the rows holding the empty string or the empty list. On the built-in id, rewrite it '
+        + 'or multi-value field, re-check what the view or rule is supposed to select. '
+        + 'On the built-in id, rewrite it '
         + 'to is_null / is_not_null. If a federated object on driver-memory or driver-mongodb, or an '
-        + 'AnalyticsService host without sourceFieldMeta, carries such a rule, the query now fails with '
-        + 'INVALID_FILTER instead of answering — bind the object on a federation-capable driver, or pass '
+        + 'AnalyticsService host without sourceFieldMeta, carries such a rule, the query now fails '
+        + 'instead of answering — bind the object on a federation-capable driver, or pass '
         + 'sourceFieldMeta. No insert or update payload carries a $empty object as a field value.',
     },
     // Ruling A on #19886, item 1: the $ne slot's half of the question