diff --git a/.changeset/30494-fail-open-date-sentences.md b/.changeset/30494-fail-open-date-sentences.md
new file mode 100644
index 00000000000..58a1509df5e
--- /dev/null
+++ b/.changeset/30494-fail-open-date-sentences.md
@@ -0,0 +1,14 @@
+---
+'@objectstack/formula': patch
+---
+
+fix(formula): an advisory validation rule's date verdict says the rule is skipped and the write proceeds
+
+Clause-②: yes (widening)
+Metadata-protocol: none
+
+- **`@objectstack/formula`: two codes join `ExpressionRefusalCode`** (`EXPRESSION_REFUSAL_CODES`), with the params of the code each splits from: `date-arithmetic-fail-open` and `date-text-arithmetic-fail-open`.
+- On an advisory (`severity: 'warning'` / `'info'`) validation rule (`faultOutcome: 'fail-open'`), date arithmetic used to be told "this faults at runtime, so the field silently evaluates to null". There is no field there, and nothing reads null: the rule is skipped and logged, and the write proceeds. The verdict now closes on the sentence `type-mismatch-fail-open` already uses for that outcome. This replaces the earlier note that an advisory rule keeps `date-arithmetic` / `date-text-arithmetic`.
+- A formula field keeps `date-arithmetic` / `date-text-arithmetic` and the null sentence. A consumer keyed to the old codes on an advisory rule re-keys to the new ones.
+- The grade is unchanged: the verdict is an error, as before. What is refused, warned or passed is unchanged.
+- `@objectstack/lint` and `@objectstack/mcp` `validate_expression` already pass `faultOutcome: 'fail-open'` for an advisory rule, so both serve the new sentence with no change of their own.
diff --git a/packages/formula/src/expression-refusal-codes.test.ts b/packages/formula/src/expression-refusal-codes.test.ts
index 62e15c1b98c..f8aae2e37a4 100644
--- a/packages/formula/src/expression-refusal-codes.test.ts
+++ b/packages/formula/src/expression-refusal-codes.test.ts
@@ -313,6 +313,26 @@ const PINS: { readonly [C in ExpressionRefusalCode]: readonly [Pin<C>, ...Pin<C>
         'Use `daysBetween(a, b)` for the span in whole days, and `daysFromNow(n)` / `addDays(d, n)` / `addMonths(d, n)` to shift a date.',
     },
   ],
+  // [#30494] An advisory (fail-open) rule: the fault skips the rule and the
+  // write proceeds, nothing reads null.
+  'date-arithmetic-fail-open': [
+    {
+      produce: () =>
+        onlyError('predicate', 'record.close_date + 1 > 3', {
+          scope: 'record',
+          fieldTypes: { close_date: 'date' },
+          faultOutcome: 'fail-open',
+        }),
+      params: { operands: 'google.protobuf.Timestamp + int', reference: 'record.close_date' },
+      message:
+        'date arithmetic `google.protobuf.Timestamp + int` — `record.close_date` is a date, and CEL can\'t do arithmetic ' +
+        'on dates: ' +
+        'this faults at runtime, and here the rule is advisory, so a rule that cannot be evaluated is skipped, not refused: ' +
+        'the write proceeds, the rule is never applied (its advisory never fires), and the only trace is a log line saying ' +
+        'it could not be evaluated. ' +
+        'Use `daysBetween(a, b)` for the span in whole days, and `daysFromNow(n)` / `addDays(d, n)` / `addMonths(d, n)` to shift a date.',
+    },
+  ],
   // [#30016] A flattened (flow) condition: the fault fails the run, it never
   // reads null — `run-fails` where the run is proven to hold the field.
   'date-arithmetic-run-fails': [
@@ -377,6 +397,24 @@ const PINS: { readonly [C in ExpressionRefusalCode]: readonly [Pin<C>, ...Pin<C>
         'Use `daysBetween(a, b)` for the span in whole days, and `daysFromNow(n)` / `addDays(d, n)` / `addMonths(d, n)` to shift a date.',
     },
   ],
+  'date-text-arithmetic-fail-open': [
+    {
+      produce: () =>
+        onlyError('predicate', 'record.end_date - record.start_date > duration("24h")', {
+          scope: 'record',
+          fieldTypes: { start_date: 'date', end_date: 'date' },
+          faultOutcome: 'fail-open',
+        }),
+      params: { operands: 'DateText - DateText', reference: 'record.start_date' },
+      message:
+        'date arithmetic `DateText - DateText` — `record.start_date` is a date field, and the runtime holds a date field ' +
+        'as its text (`YYYY-MM-DD`, or an ISO-8601 instant for a date-time), which CEL can\'t do arithmetic on: ' +
+        'this faults at runtime, and here the rule is advisory, so a rule that cannot be evaluated is skipped, not refused: ' +
+        'the write proceeds, the rule is never applied (its advisory never fires), and the only trace is a log line saying ' +
+        'it could not be evaluated. ' +
+        'Use `daysBetween(a, b)` for the span in whole days, and `daysFromNow(n)` / `addDays(d, n)` / `addMonths(d, n)` to shift a date.',
+    },
+  ],
   'date-text-arithmetic-run-fails': [
     {
       produce: () =>
@@ -752,6 +790,15 @@ const SWEEP_SCHEMAS: readonly (ExprSchemaHint | undefined)[] = [
     fieldTypes: { close_date: 'date' },
     faultOutcome: 'fail-closed',
   },
+  // [#30494] The same date schema on an advisory rule reaches the date
+  // verdicts' `-fail-open` codes.
+  {
+    scope: 'record',
+    objectName: 'deal',
+    fields: ['close_date'],
+    fieldTypes: { close_date: 'date' },
+    faultOutcome: 'fail-open',
+  },
   {
     scope: 'flattened',
     objectName: 'deal',
diff --git a/packages/formula/src/expression-refusal.ts b/packages/formula/src/expression-refusal.ts
index 243a4132b94..f69d8c0cc3b 100644
--- a/packages/formula/src/expression-refusal.ts
+++ b/packages/formula/src/expression-refusal.ts
@@ -167,7 +167,8 @@ export interface ExpressionRefusalParams {
    * operand types; `reference` is the field as written, when it is known. A
    * flattened (flow) condition is `date-arithmetic-run-fails` /
    * `date-arithmetic-run-may-fail`; a fail-closed site is
-   * `date-arithmetic-fail-closed`. An advisory rule's stays this code.
+   * `date-arithmetic-fail-closed`, and an advisory rule's is
+   * `date-arithmetic-fail-open`.
    */
   'date-arithmetic': { readonly operands: string; readonly reference?: string };
   /**
@@ -176,7 +177,8 @@ export interface ExpressionRefusalParams {
    * that text. `operands` are the CEL operand types (the text is `DateText`);
    * `reference` is the field as written, when it is known. A flattened (flow)
    * condition is `date-text-arithmetic-run-fails` / `-run-may-fail`; a
-   * fail-closed site is `date-text-arithmetic-fail-closed`.
+   * fail-closed site is `date-text-arithmetic-fail-closed`, an advisory rule's
+   * `date-text-arithmetic-fail-open`.
    */
   'date-text-arithmetic': { readonly operands: string; readonly reference?: string };
   /**
@@ -204,6 +206,14 @@ export interface ExpressionRefusalParams {
   'date-arithmetic-fail-closed': { readonly operands: string; readonly reference?: string };
   /** [#30250] ERROR: `date-text-arithmetic`, at a `date-arithmetic-fail-closed` site. */
   'date-text-arithmetic-fail-closed': { readonly operands: string; readonly reference?: string };
+  /**
+   * [#30494] ERROR: `date-arithmetic` in an advisory (`warning` / `info`)
+   * validation rule, a site that FAILS OPEN — the fault skips the rule and the
+   * write proceeds (the `type-mismatch-fail-open` outcome). It never reads null.
+   */
+  'date-arithmetic-fail-open': { readonly operands: string; readonly reference?: string };
+  /** [#30494] ERROR: `date-text-arithmetic`, at a `date-arithmetic-fail-open` site. */
+  'date-text-arithmetic-fail-open': { readonly operands: string; readonly reference?: string };
   /**
    * A formula that computes a `google.protobuf.Duration`
    * (`today() - record.start_date`), which a field reads as `{}`. `reference`
@@ -317,6 +327,8 @@ const CODE_TABLE = {
   'date-text-arithmetic-run-may-fail': true,
   'date-arithmetic-fail-closed': true,
   'date-text-arithmetic-fail-closed': true,
+  'date-arithmetic-fail-open': true,
+  'date-text-arithmetic-fail-open': true,
   'date-duration-value': true,
   'type-mismatch': true,
   'type-mismatch-fail-closed': true,
diff --git a/packages/formula/src/validate.test.ts b/packages/formula/src/validate.test.ts
index 1f263290581..114780cbefe 100644
--- a/packages/formula/src/validate.test.ts
+++ b/packages/formula/src/validate.test.ts
@@ -1139,14 +1139,45 @@ describe('validateExpression (ADR-0032)', () => {
         );
         expect(r.errors[0].message, source).not.toMatch(/evaluates to null/);
       }
-      // Controls: a formula field (no outcome) keeps the null sentence; so does
-      // an advisory rule (`fail-open`), which #30250 does not cover.
-      for (const [role, source, hint, code] of [
-        ['value', 'record.start_date + 1', schema, 'date-arithmetic'],
-        ['value', 'record.end_date - record.start_date', schema, 'date-text-arithmetic'],
-        ['predicate', 'record.start_date + 1 > 3', { ...schema, faultOutcome: 'fail-open' }, 'date-arithmetic'],
+      // Controls: a formula field (no outcome) keeps the null sentence. An
+      // advisory rule (`fail-open`) is #30494's, below.
+      for (const [role, source, code] of [
+        ['value', 'record.start_date + 1', 'date-arithmetic'],
+        ['value', 'record.end_date - record.start_date', 'date-text-arithmetic'],
       ] as const) {
-        const r = validateExpression(role, source, hint);
+        const r = validateExpression(role, source, schema);
+        expect(r.errors.map((e) => e.code), source).toEqual([code]);
+        expect(r.errors[0].message, source).toContain('this faults at runtime, so the field silently evaluates to null');
+      }
+    });
+
+    // [#30494] On an advisory (`warning` / `info`) validation rule a fault
+    // skips the rule and the write proceeds: nothing reads null. The date
+    // verdicts there close on the `type-mismatch-fail-open` clause, under their
+    // own codes. The grade stays an error.
+    it('on an advisory rule says the rule is skipped and the write proceeds, not that the field reads null (#30494)', () => {
+      const open = { ...schema, faultOutcome: 'fail-open' } as const;
+      for (const [source, code] of [
+        ['record.start_date + 1 > 3', 'date-arithmetic-fail-open'],
+        ['record.end_date - record.start_date > duration("24h")', 'date-text-arithmetic-fail-open'],
+      ] as const) {
+        const r = validateExpression('predicate', source, open);
+        expect(r.warnings, source).toHaveLength(0);
+        expect(r.errors.map((e) => e.code), source).toEqual([code]);
+        expect(r.errors[0].message, source).toContain(
+          'this faults at runtime, and here the rule is advisory, so a rule that cannot be evaluated is skipped, not ' +
+            'refused: the write proceeds, the rule is never applied (its advisory never fires), and the only trace is a ' +
+            'log line saying it could not be evaluated.',
+        );
+        expect(r.errors[0].message, source).not.toMatch(/evaluates to null/);
+      }
+      // Control: the same predicates on a formula-field site (no outcome) keep
+      // their codes and the null sentence.
+      for (const [source, code] of [
+        ['record.start_date + 1 > 3', 'date-arithmetic'],
+        ['record.end_date - record.start_date > duration("24h")', 'date-text-arithmetic'],
+      ] as const) {
+        const r = validateExpression('predicate', source, schema);
         expect(r.errors.map((e) => e.code), source).toEqual([code]);
         expect(r.errors[0].message, source).toContain('this faults at runtime, so the field silently evaluates to null');
       }
diff --git a/packages/formula/src/validate.ts b/packages/formula/src/validate.ts
index 4e642385fe4..8931039644a 100644
--- a/packages/formula/src/validate.ts
+++ b/packages/formula/src/validate.ts
@@ -440,9 +440,10 @@ const DATE_FAIL_CLOSED_CLAUSE =
  *    (`date − date + 1`, `today() + 30`) — always faults at runtime and never
  *    recovers, so it blocks the build. A formula reads that fault as null; a
  *    flattened (flow) condition's fault fails the run, under the
- *    `date-arithmetic-run-fails` / `-run-may-fail` codes (#30016), and a
+ *    `date-arithmetic-run-fails` / `-run-may-fail` codes (#30016), a
  *    fail-closed site's refuses the write, under `date-arithmetic-fail-closed`
- *    (#30250, {@link dateArm}).
+ *    (#30250), and an advisory rule's skips the rule, under
+ *    `date-arithmetic-fail-open` (#30494, {@link dateArm}).
  *  - `type-mismatch` (**warning**): a text/boolean field used with an
  *    arithmetic/ordering operator against a number — nulls unless the text value
  *    happens to be numeric, so it stays advisory. An **error** where the caller
@@ -611,25 +612,32 @@ function typeSoundnessIssue(
  * where it holds the date: `run-may-fail`. A `record`-scoped site that fails
  * closed (`faultOutcome: 'fail-closed'`: an `error` validation rule, a field
  * write rule, an option `visibleWhen`, a hook `condition`) refuses the write
- * on the fault: `fail-closed` (#30250). An advisory rule (`fail-open`) keeps
- * the null sentence. The grade stays an error everywhere.
+ * on the fault: `fail-closed` (#30250). An advisory rule (`faultOutcome:
+ * 'fail-open'`) is skipped on the fault and the write proceeds: `fail-open`,
+ * the `type-mismatch-fail-open` clause (#30494). The grade stays an error
+ * everywhere.
  */
-type DateArm = 'run-fails' | 'run-may-fail' | 'fail-closed';
+type DateArm = 'run-fails' | 'run-may-fail' | 'fail-closed' | 'fail-open';
 function dateArm(
   scope: 'record' | 'flattened',
   faultOutcome: ExprSchemaHint['faultOutcome'],
   bareNamesUnproven: boolean | undefined,
 ): DateArm | null {
-  if (scope !== 'flattened') return faultOutcome === 'fail-closed' ? 'fail-closed' : null;
+  if (scope !== 'flattened') {
+    return faultOutcome === 'fail-closed' || faultOutcome === 'fail-open' ? faultOutcome : null;
+  }
   return faultOutcome === 'run-fails' && !bareNamesUnproven ? 'run-fails' : 'run-may-fail';
 }
 
 /**
- * [#30016, #30250] The fault clause of a date verdict whose fault does not read
- * null; `held` names what a flow condition's field holds at run time.
+ * [#30016, #30250, #30494] The fault clause of a date verdict whose fault does
+ * not read null; `held` names what a flow condition's field holds at run time.
+ * An advisory rule's is the type mismatch's own `fail-open` clause, word for
+ * word: one outcome, one sentence.
  */
 function dateArmFault(arm: DateArm, ref: string | null, held: 'date' | 'text'): string {
   if (arm === 'fail-closed') return `this faults at runtime, and here ${DATE_FAIL_CLOSED_CLAUSE}`;
+  if (arm === 'fail-open') return `this faults at runtime, and here ${TYPE_MISMATCH_FAULT_ARMS['fail-open'].clause}`;
   const fails =
     'a flow condition that cannot be evaluated fails the run: the flow stops at this condition and the ' +
     'work the flow exists to do is not done (it does not read null).';
@@ -645,8 +653,9 @@ function dateArmFault(arm: DateArm, ref: string | null, held: 'date' | 'text'):
  *  - `date-text-arithmetic`: arithmetic on that text the evaluator faults on —
  *    `record.end_date - record.start_date` (either field kind), `record.d -
  *    duration('24h')` — so the expression reads null (in a flow condition the
- *    run fails instead, and on a fail-closed site the write is refused:
- *    `flowArm`, #30016, #30250). Any role.
+ *    run fails instead, on a fail-closed site the write is refused, and on an
+ *    advisory rule the rule is skipped: `flowArm`, #30016, #30250, #30494).
+ *    Any role.
  *  - `date-duration-value`: a formula (`value` role) that computes a
  *    `google.protobuf.Duration` — `today() - record.start_date` — which a field
  *    serialises as `{}`. A predicate that COMPARES a duration
diff --git a/packages/lint/src/validate-expressions.test.ts b/packages/lint/src/validate-expressions.test.ts
index 1c7255f3108..bc84cfa2feb 100644
--- a/packages/lint/src/validate-expressions.test.ts
+++ b/packages/lint/src/validate-expressions.test.ts
@@ -1382,6 +1382,39 @@ describe('validateStackExpressions (ADR-0032 build-time)', () => {
       expect(formula[0]!.message).toContain('this faults at runtime, so the field silently evaluates to null');
     });
 
+    // [#30494] An advisory (`warning` / `info`) validation rule fails open: a
+    // fault skips the rule and the write proceeds, so its date arithmetic says
+    // so, still an error. Control: a formula field keeps the null sentence.
+    it('says an advisory validation rule\'s date arithmetic skips the rule; a formula keeps the null sentence (#30494)', () => {
+      const issues = validateStackExpressions({
+        objects: [{
+          name: 'crm_opportunity',
+          fields: {
+            close_date: { type: 'date' },
+            end_date: { type: 'date' },
+            next_day: { type: 'formula', expression: 'record.close_date + 1' },
+          },
+          validations: [
+            { name: 'late', condition: 'record.close_date + 1 > 3', severity: 'warning' },
+            { name: 'long', condition: 'record.end_date - record.close_date > duration("24h")', severity: 'info' },
+          ],
+        }],
+      });
+      const found = issues.filter(i => /^date arithmetic/.test(i.message));
+      expect(found.map(i => i.severity)).toEqual(['error', 'error', 'error']);
+      const rules = found.filter(i => /validation/.test(i.where));
+      expect(rules).toHaveLength(2);
+      for (const i of rules) {
+        expect(i.message, i.where).toContain(
+          'the rule is advisory, so a rule that cannot be evaluated is skipped, not refused: the write proceeds',
+        );
+        expect(i.message, i.where).not.toMatch(/evaluates to null|is refused, not skipped/);
+      }
+      const formula = found.filter(i => !/validation/.test(i.where));
+      expect(formula).toHaveLength(1);
+      expect(formula[0]!.message).toContain('this faults at runtime, so the field silently evaluates to null');
+    });
+
     // [#29959] `seedRunVariables` seeds the flow's declared variables before it
     // flattens the record, and the flattening skips a name already bound: a
     // bare `title` here reads the NUMBER variable and `title > 5` runs. Only