diff --git a/packages/drivers/driver-sql/src/sql-driver.ts b/packages/drivers/driver-sql/src/sql-driver.ts
index 543f3cc91a..409928480f 100644
--- a/packages/drivers/driver-sql/src/sql-driver.ts
+++ b/packages/drivers/driver-sql/src/sql-driver.ts
@@ -3629,6 +3629,28 @@ export class SqlDriver implements IDataDriver {
    *     the last digit run), so there is nothing shared to hoist — spec answers
    *     `undefined` for an unanchored slot rather than pick one of the two.
    *
+   * ## The unanchored arm is IMPLEMENTATION DETAIL, outside the declared contract (#7287)
+   *
+   * That refusal is now a DECLARED boundary, not merely an absent agreement: the
+   * #7287 ruling (2026-08-10, 「宣告边界」) states that a stored value carrying
+   * non-digit content on an unanchored format is out of contract for counter
+   * readback, and that `readAutonumberCounter`'s `undefined` for that slot is the
+   * contract rather than a gap. The boundary and its rationale live in that
+   * function's TSDoc in `packages/spec/src/data/autonumber-format.ts`; the pins
+   * are `packages/spec/src/data/autonumber-unanchored-boundary.test.ts`.
+   *
+   * So the concatenate-every-digit reading below is THIS DRIVER'S behavior, not a
+   * promise the platform makes. On the inputs the contract admits — pure-digit
+   * values, which is what `renderAutonumber` emits for an unanchored format — it
+   * answers the same number the engine does. On mixed-content values it may
+   * answer differently (`'SO-2024-0007'` → `20240007` here, `7` in the engine's
+   * `readStoredAutonumberCounter`), and that difference is out of contract on
+   * both sides, not a defect on either.
+   *
+   * Consequently the ruling moves nothing here: neither this reading nor the
+   * engine's was hoisted into the shared helper, precisely because doing so would
+   * move live behavior on the other side over record numbers already issued.
+   *
    * ## Why the suffix is NOT pushed into the LIKE
    *
    * `like 'prefix%suffix'` looks tempting and is wrong: the counter scope is the
diff --git a/packages/objectql/src/engine.ts b/packages/objectql/src/engine.ts
index f43be49db7..47af03335e 100644
--- a/packages/objectql/src/engine.ts
+++ b/packages/objectql/src/engine.ts
@@ -372,6 +372,27 @@ interface IssuedAutonumber {
  *     concatenates every digit), which is exactly why spec refuses to answer for
  *     an unanchored slot instead of picking one of the two.
  *
+ * # The unanchored arm is IMPLEMENTATION DETAIL, outside the declared contract (#7287)
+ *
+ * Spec's refusal above is no longer just an absence of agreement: the #7287
+ * ruling (2026-08-10, 「宣告边界」) DECLARES that a stored value carrying
+ * non-digit content on an unanchored format is out of contract for counter
+ * readback, and that `readAutonumberCounter`'s `undefined` for that slot is the
+ * contract rather than a gap. The boundary and its rationale live in that
+ * function's TSDoc in `packages/spec/src/data/autonumber-format.ts`; the pins
+ * are `packages/spec/src/data/autonumber-unanchored-boundary.test.ts`.
+ *
+ * So the last-digit-run reading below is THIS ENGINE'S behavior, not a promise
+ * the platform makes. On the inputs the contract admits — pure-digit values,
+ * which is what `renderAutonumber` emits for an unanchored format — it answers
+ * the same number the SQL driver does. On mixed-content values it may answer
+ * differently (`'SO-2024-0007'` → `7` here, `20240007` there), and that
+ * difference is out of contract on both sides, not a defect on either.
+ *
+ * Consequently the ruling moves nothing here: neither this reading nor the
+ * driver's was hoisted into the shared helper, precisely because doing so would
+ * move live behavior on the other side over record numbers already issued.
+ *
  * The unanchored branch uses the linear `/\d+/g` — a backtracking lookahead here
  * is a polynomial-ReDoS sink on stored values full of zeros (CodeQL
  * js/polynomial-redos).
diff --git a/packages/spec/src/data/autonumber-format.ts b/packages/spec/src/data/autonumber-format.ts
index 9bdb37be28..aeae0b85a7 100644
--- a/packages/spec/src/data/autonumber-format.ts
+++ b/packages/spec/src/data/autonumber-format.ts
@@ -336,6 +336,57 @@ export function renderAutonumber(input: RenderAutonumberInput): RenderedAutonumb
  * Hoisting either one here would make this contract claim an agreement that does
  * not exist. Each side documents its own fallback at its own call site.
  *
+ * # The declared boundary: mixed-content unanchored values are OUT OF CONTRACT (#7287)
+ *
+ * That refusal is not a gap waiting to be filled — as of the maintainer's ruling
+ * on #7287 (2026-08-10, 「宣告边界」, treatment (2)) it IS the contract:
+ *
+ * > **On an UNANCHORED format (`prefix === '' && suffix === ''`), a stored value
+ * > carrying any non-digit content is out of contract for counter readback.**
+ * > `undefined` is this function's answer for that slot, permanently.
+ *
+ * Why declare it rather than pick a reading. The two consumers have read such a
+ * value differently since before this helper existed, and both readings are
+ * pinned by their own tests:
+ *
+ *   - the engine's `readStoredAutonumberCounter`
+ *     (`packages/objectql/src/engine.ts`) takes the **last digit run** —
+ *     `'SO-2024-0007'` → `7`;
+ *   - the SQL driver's `scanMaxNumericTail`
+ *     (`packages/drivers/driver-sql/src/sql-driver.ts`) **concatenates every
+ *     digit** — the same value → `20240007`.
+ *
+ * Ruling either one to be the contract would move live behavior on the other
+ * side, over stored business identifiers that are not reclaimable once issued —
+ * which is why #7247 refused the hoist as a rider, and why #7287 rejects it
+ * outright rather than picking a side. Declaring the input out of contract costs
+ * nothing that was ever promised: no reading was ever specified for it.
+ *
+ * The boundary is drawn by CONTENT, and deliberately wider than the observed
+ * divergence. A **pure-digit** value — which is exactly what `renderAutonumber`
+ * emits for an unanchored format — is inside the contract, and both sides answer
+ * the same number for it: `'0007'` reads as `7` either way. Everything else is
+ * outside, including mixed-content values the two readings happen to agree on
+ * (`'CASE-12'` is `12` both ways: divergence needs TWO digit runs, and that one
+ * has one). Narrowing the boundary to "values the sides actually disagree on"
+ * would make it undecidable from the value alone — a caller would have to know
+ * which consumer is running to know whether its input is in contract, which is
+ * the very "same metadata, different driver, different number" property this
+ * boundary exists to bound. So the out-of-contract face is simply
+ * legacy/migrated data: a dash-separated string in a column later declared
+ * autonumber.
+ *
+ * Reachability, and why the boundary is worth stating now: #6555's Route-3
+ * ruling (PR #7265) made `{0000}` the declared default for format-less
+ * autonumber fields, and `{0000}` renders neither prefix nor suffix — so the
+ * DEFAULT authoring shape resolves to this unanchored slot on both sides.
+ *
+ * Consequence for the consumers, also recorded by the ruling: neither moves.
+ * Each keeps its current unanchored reading as **implementation detail outside
+ * this boundary**, not as a contract this file underwrites. See the pins in
+ * `autonumber-unanchored-boundary.test.ts`, and the ruling itself at
+ * https://github.com/objectstack-ai/objectstack/issues/7287#issuecomment-5238560707.
+ *
  * The digit match is the linear `/^\d+/` — a backtracking lookahead here is a
  * polynomial-ReDoS sink on stored values full of zeros (CodeQL
  * js/polynomial-redos).
diff --git a/packages/spec/src/data/autonumber-unanchored-boundary.test.ts b/packages/spec/src/data/autonumber-unanchored-boundary.test.ts
new file mode 100644
index 0000000000..bc64f1b6e2
--- /dev/null
+++ b/packages/spec/src/data/autonumber-unanchored-boundary.test.ts
@@ -0,0 +1,147 @@
+// Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * Pins for the contract boundary declared on #7287 (maintainer ruling
+ * 2026-08-10, 「宣告边界」, treatment (2)):
+ *
+ *   On an UNANCHORED format (`prefix === '' && suffix === ''`), a stored value
+ *   carrying non-digit content is OUT OF CONTRACT for counter readback.
+ *   `readAutonumberCounter`'s `undefined` for that slot is the contract, not a
+ *   gap — permanently.
+ *
+ * These cases exist to make that boundary fail loudly if a later change tries to
+ * fill the slot in: hoisting the engine's reading (last digit run) or the SQL
+ * driver's (concatenate every digit) into the shared helper would move live
+ * behavior on the other side, over record numbers that are not reclaimable once
+ * issued. #7247 refused that hoist as a rider; #7287 rejects it outright.
+ *
+ * The tests below assert only `readAutonumberCounter` — spec's declared surface.
+ * The two consumers' readings are modelled here ONLY to show WHY the slot is out
+ * of contract (they disagree on exactly the inputs the boundary excludes, and
+ * agree on the ones it admits); neither model is a contract, and the real
+ * implementations live at their own call sites.
+ */
+
+import { describe, it, expect } from 'vitest';
+import { parseAutonumberFormat, renderAutonumber, readAutonumberCounter } from './autonumber-format';
+
+const NOW = new Date('2026-06-17T21:30:00.000Z');
+
+/**
+ * The engine's unanchored reading, mirrored from `readStoredAutonumberCounter`
+ * in `packages/objectql/src/engine.ts` — the LAST digit run of the value.
+ * Illustration only: this file pins nothing about the engine.
+ */
+function engineUnanchoredReading(value: string): number | undefined {
+  const runs = value.match(/\d+/g);
+  const digits = runs ? runs[runs.length - 1] : undefined;
+  return digits ? parseInt(digits, 10) : undefined;
+}
+
+/**
+ * The SQL driver's unanchored reading, mirrored from `scanMaxNumericTail` in
+ * `packages/drivers/driver-sql/src/sql-driver.ts` — EVERY digit, concatenated.
+ * Illustration only: this file pins nothing about the driver.
+ */
+function driverSqlUnanchoredReading(value: string): number | undefined {
+  const n = parseInt(value.replace(/[^0-9]/g, ''), 10);
+  return Number.isFinite(n) ? n : undefined;
+}
+
+describe('the unanchored readback boundary (#7287 ruling: mixed content is out of contract)', () => {
+  it('the declared default format {0000} (#6555, PR #7265) really does render an UNANCHORED pair', () => {
+    // The premise the boundary hangs on: the default authoring shape is the one
+    // that lands in this slot, which is why the boundary is worth declaring.
+    const r = renderAutonumber({ tokens: parseAutonumberFormat('{0000}'), seq: 7, now: NOW });
+    expect(r.prefix).toBe('');
+    expect(r.suffix).toBe('');
+    expect(r.value).toBe('0007');
+  });
+
+  describe('OUT OF CONTRACT — non-digit content on an unanchored format reads as undefined', () => {
+    it.each([
+      ['A1B2', 'digits split by letters — the shape the two readings disagree on most sharply'],
+      ['CASE-12', 'a dash-separated legacy value against a bare {0000}'],
+      ['SO-2024-0007', 'the issue-body example: engine reads 7, driver-sql reads 20240007'],
+      ['2026-06-17', 'a date-looking value in a column later declared autonumber'],
+      ['INV/0042', 'a separator other than a dash — the boundary is content, not punctuation'],
+      ['0007 (void)', 'digits first, non-digit content trailing'],
+      ['v2.1', 'digits inside an unrelated version-shaped identifier'],
+      ['DRAFT', 'no digits at all — still out of contract, and still undefined'],
+    ])(
+      'out of contract: %s reads as undefined — the declared boundary, not a gap (#7287)',
+      (value) => {
+        expect(readAutonumberCounter(value, '', '')).toBeUndefined();
+      },
+    );
+
+    it.each([
+      ['A1B2'],
+      ['SO-2024-0007'],
+      ['2026-06-17'],
+      ['v2.1'],
+    ])(
+      'why %s is out of contract: the two consumers read it as DIFFERENT numbers',
+      (value) => {
+        expect(engineUnanchoredReading(value)).not.toBe(driverSqlUnanchoredReading(value));
+        // And spec declines to break the tie — that refusal IS the contract.
+        expect(readAutonumberCounter(value, '', '')).toBeUndefined();
+      },
+    );
+
+    it.each([['CASE-12', 12], ['INV/0042', 42], ['DRAFT-7', 7]])(
+      'out of contract even though the two consumers happen to agree on %s (%i)',
+      (value, agreed) => {
+        // The boundary is drawn by CONTENT, deliberately wider than the observed
+        // divergence: divergence needs TWO digit runs, so a mixed-content value
+        // carrying only one reads the same number either way. Narrowing the
+        // boundary to "values the two sides actually disagree on" would make it
+        // undecidable from the value alone — a caller would have to know which
+        // consumer is running to know whether it is in contract, which is the
+        // very "same metadata, different driver, different number" property
+        // #7287 exists to bound. So: still out of contract, still undefined.
+        expect(engineUnanchoredReading(value)).toBe(agreed);
+        expect(driverSqlUnanchoredReading(value)).toBe(agreed);
+        expect(readAutonumberCounter(value, '', '')).toBeUndefined();
+      },
+    );
+  });
+
+  describe('INSIDE the contract — pure-digit unanchored values, where both sides agree', () => {
+    it.each([['0007', 7], ['10', 10], ['0000', 0], ['123456', 123456]])(
+      'in contract: %s carries no non-digit content, so both consumers read %i',
+      (value, expected) => {
+        expect(engineUnanchoredReading(value)).toBe(expected);
+        expect(driverSqlUnanchoredReading(value)).toBe(expected);
+      },
+    );
+
+    it('what renderAutonumber itself emits for {0000} stays inside the boundary', () => {
+      // The in-contract face is the one the platform generates: an unanchored
+      // format renders pure digits, so a store the platform filled reads the
+      // same number on either side. The out-of-contract face is legacy/migrated
+      // data that arrived by some other path.
+      const tokens = parseAutonumberFormat('{0000}');
+      for (const seq of [0, 7, 42, 9999, 123456]) {
+        const { value } = renderAutonumber({ tokens, seq, now: NOW });
+        expect(engineUnanchoredReading(value)).toBe(seq);
+        expect(driverSqlUnanchoredReading(value)).toBe(seq);
+      }
+    });
+
+    it('agreement on the digits does NOT make the shared helper answer for the slot', () => {
+      // The boundary is about which INPUTS are in contract; the shared helper's
+      // declared job stays the ANCHORED inverse of renderAutonumber. Even where
+      // the two consumers agree, spec does not underwrite an unanchored reading
+      // — each side answers from its own implementation detail.
+      expect(readAutonumberCounter('0007', '', '')).toBeUndefined();
+    });
+  });
+
+  it('an anchored format is untouched by this boundary — non-digit content still reads normally there', () => {
+    // Guard against the boundary being read too widely: it is scoped to the
+    // unanchored slot. `CASE-0007` against the pair `{prefix: 'CASE-'}` is in
+    // contract and answers 7, mixed content and all.
+    expect(readAutonumberCounter('CASE-0007', 'CASE-', '')).toBe(7);
+  });
+});