diff --git a/.changeset/analytics-coded-400-rejected.md b/.changeset/analytics-coded-400-rejected.md
new file mode 100644
index 0000000000..1b0272bfff
--- /dev/null
+++ b/.changeset/analytics-coded-400-rejected.md
@@ -0,0 +1,26 @@
+---
+'@object-ui/data-objectstack': minor
+---
+
+`classifyAnalyticsFailure` now reads a 400 as a refusal of the query body we
+sent regardless of which ADR-0112 `code` it carries, so `aggregate()` no
+longer answers a rejected filter with client-side numbers from a different
+door (objectui#7755).
+
+Before this fix, only 400 `VALIDATION_FAILED` (and a code-less 400) threw
+`AnalyticsQueryRejectedError`. Any OTHER coded 400 — `service-analytics` ships
+its own 400 `INVALID_FILTER` on a filter shape it refuses — matched none of
+`classifyAnalyticsFailure`'s branches and fell through to `unknown`, which
+`aggregate()`'s catch has no arm for, so it silently degraded to
+`aggregateViaFind`: a re-read through `find()`'s `$filter` query-string
+contract, which accepts array shapes the analytics request body does not. A
+filter the analytics route refused could still be answered — with a
+plausible, wrong number, and no sign the request had a defect.
+
+The fix is a floor UNDER the existing code branches, not a replacement for
+them: `NOT_IMPLEMENTED` / `ROUTE_NOT_FOUND` still win `not-installed`,
+`VALIDATION_FAILED` / `UNAUTHENTICATED` / `CUBE_NOT_FOUND` still win their own
+outcomes first (objectui#5721). Only a 400 that none of those four already
+claimed now falls to the new floor instead of past it. An unmatched NON-400
+coded error (e.g. a coded 5xx) is unaffected and keeps degrading exactly as
+before — this fix is scoped to the 400 case only.
diff --git a/packages/data-objectstack/src/aggregate-capability.test.ts b/packages/data-objectstack/src/aggregate-capability.test.ts
index 2fbf9fb527..93386dbbaf 100644
--- a/packages/data-objectstack/src/aggregate-capability.test.ts
+++ b/packages/data-objectstack/src/aggregate-capability.test.ts
@@ -37,6 +37,7 @@
  *   | 404 `ROUTE_NOT_FOUND`          | degrade LOUDLY     |
  *   | 404/501, no `code` at all      | degrade LOUDLY     |
  *   | 400 `VALIDATION_FAILED`        | THROW              |
+ *   | 400, any OTHER code (or none)  | THROW              |
  *   | 401 `UNAUTHENTICATED`          | THROW              |
  *   | 404 `CUBE_NOT_FOUND`           | THROW              |
  *   | 5xx, network, unknown code     | degrade SILENTLY   |
@@ -45,6 +46,14 @@
  * The rows that matter most are the two 404s with DIFFERENT outcomes
  * (objectui#5721): they are the same transport status, so only the ADR-0112
  * `code` can tell them apart, and a status-first classifier fails them both.
+ *
+ * The "400, any OTHER code" row (objectui#7755) is the opposite lesson on the
+ * SAME classifier: a `VALIDATION_FAILED`-only check let a coded 400 the
+ * classifier does not enumerate — `service-analytics` ships its own 400
+ * `INVALID_FILTER` on a filter shape it refuses — fall through every branch to
+ * `unknown`, which `aggregate()`'s catch has no arm for, so it silently
+ * answered the refusal with `aggregateViaFind`'s client-side numbers. Here the
+ * transport status alone is decisive once it is 400, regardless of code.
  */
 
 import { describe, it, expect, beforeEach, vi } from 'vitest';
@@ -174,6 +183,39 @@ describe('aggregate() when the server REJECTS our query body', () => {
     // No silent second answer from a different code path.
     expect(calls.some((c) => c.includes('/api/v1/data'))).toBe(false);
   });
+
+  /*
+   * objectui#7755 — the pin for the coded-400 gap. `INVALID_FILTER` is the
+   * real code `service-analytics` ships on a 400 for a filter shape it
+   * refuses (spec/src/api/errors.zod.ts standard catalog), chosen deliberately
+   * over a made-up code so this pin cannot pass by accident. Pre-fix,
+   * `classifyAnalyticsFailure` only recognised `VALIDATION_FAILED` on a 400;
+   * any OTHER code fell through every branch to `unknown`, which
+   * `aggregate()`'s catch has no arm for, so it silently re-answered the
+   * refusal through `aggregateViaFind` — a different door with a different
+   * filter contract ($filter query-string parsing accepts array shapes the
+   * analytics body does not) — producing a plausible number for a query the
+   * server had just refused.
+   */
+  it('400 INVALID_FILTER (a coded 400 the classifier does not name) also throws — it must NOT be answered by the fallback', async () => {
+    const { fetchImpl, calls } = makeFetch(400, {
+      success: false,
+      error: {
+        code: 'INVALID_FILTER',
+        httpStatus: 400,
+        message: 'Invalid filter: unsupported operator "regex" for field "stage"',
+      },
+    });
+
+    const err = await makeAdapter(fetchImpl).aggregate('opportunity', SUM_BY_STAGE).catch((e) => e);
+
+    expect(err).toBeInstanceOf(Error);
+    expect((err as { code?: string }).code).toBe('ANALYTICS_QUERY_REJECTED');
+    expect((err as { serverCode?: string }).serverCode).toBe('INVALID_FILTER');
+    expect(String(err.message)).toContain('unsupported operator');
+    // The point of this card: no silent second answer from a different door.
+    expect(calls.some((c) => c.includes('/api/v1/data'))).toBe(false);
+  });
 });
 
 describe('aggregate() on a healthy analytics endpoint', () => {
diff --git a/packages/data-objectstack/src/index.ts b/packages/data-objectstack/src/index.ts
index 78acecd040..99f408b1c5 100644
--- a/packages/data-objectstack/src/index.ts
+++ b/packages/data-objectstack/src/index.ts
@@ -1126,11 +1126,18 @@ export class AnalyticsQueryRejectedError extends Error {
  *     `ROUTE_NOT_FOUND` (framework#4019 stops mounting the routes at all).
  *     A client-side aggregate over a scoped `find()` answers the chart
  *     correctly, and the operator is told once that the semantic layer is off.
- *   - **`rejected`** — *THROW*. The server refused OUR body (400
- *     `VALIDATION_FAILED`; framework#4010 validates `/analytics/query` at the
- *     entry). Degrading would answer our own contract violation with plausible
- *     numbers from a different code path and bury it — the misdirection
- *     framework#3878 documented.
+ *   - **`rejected`** — *THROW*. The server refused OUR body: 400
+ *     `VALIDATION_FAILED` (framework#4010 validates `/analytics/query` at the
+ *     entry) OR any other coded 400 (objectui#7755 — e.g. `service-analytics`
+ *     ships its own 400 `INVALID_FILTER` on a filter shape it refuses). The
+ *     status alone is decisive once it is 400: a producer that refuses the
+ *     body and ships a code this consumer does not enumerate is refusing it
+ *     exactly as hard as one that ships `VALIDATION_FAILED` — the refusal is
+ *     in the transport fact, not in which code spells it. Degrading would
+ *     answer our own contract violation with plausible numbers from a
+ *     different code path (`find()`'s `$filter` accepts array shapes the
+ *     analytics body does not) and bury it — the misdirection framework#3878
+ *     documented.
  *   - **`unauthenticated`** — *THROW*. 401 `UNAUTHENTICATED`: the request was
  *     refused before it ran, so it is evidence about the SESSION and none at
  *     all about the capability. Degrading is not merely misleading here, it is
@@ -1182,16 +1189,30 @@ export function classifyAnalyticsFailure(
   // ④ Analytics answered; the cube this query named is the thing that is missing.
   if (errorCodeIs({ code }, 'CUBE_NOT_FOUND')) return { kind: 'cube-not-found', code, message };
 
-  // ⑤ Residual — the answer declared NO ADR-0112 code, so no ObjectStack route
+  // ⑤ A FLOOR beneath the four code branches above, not a fifth alongside them:
+  //   any 400 is a refusal of the body WE sent, whether or not its code is one
+  //   of the ones this function happens to enumerate (objectui#7755). Reading
+  //   the status only in the code-less residual below let a coded-but-
+  //   unrecognized 400 — `service-analytics` ships 400 `INVALID_FILTER` on a
+  //   filter shape it refuses — fall through this whole ladder to `unknown`,
+  //   and `aggregate()`'s catch has no `unknown` arm, so it silently answered
+  //   the refusal with `aggregateViaFind`'s client-side numbers instead of
+  //   throwing `AnalyticsQueryRejectedError`. This branch never fires for a
+  //   400 the branches above already claimed more specifically — none of ①-④
+  //   test the status, so none of them can be shadowed by moving this earlier.
+  if (status === 400) return { kind: 'rejected', code, message };
+
+  // ⑥ Residual — the answer declared NO ADR-0112 code, so no ObjectStack route
   //   wrote it (a proxy, a gateway, a host with no API mounted). Only here is
   //   the bare status the best signal available, and only because every code
   //   branch has already declined: this face's own 404s all ship a `code`, so a
-  //   code-less 404 cannot be the unknown-cube case.
+  //   code-less 404 cannot be the unknown-cube case. (The 400 case that used to
+  //   live here moved up to ⑤ so it applies whether or not a code is present;
+  //   this residual would never have reached it anyway once ⑤ runs first.)
   if (code === undefined) {
     if (status !== undefined && ANALYTICS_ABSENT_STATUSES.includes(status)) {
       return { kind: 'not-installed', code, message };
     }
-    if (status === 400) return { kind: 'rejected', code, message };
     if (status === 401) return { kind: 'unauthenticated', code, message };
   }