fix(rest): the export door truncates its page chunk where it reads it, so no fractional limit reaches the normalizer

Claude-Session: https://claude.ai/code/session_01A3FoRXqj2EgAzPQbXU3Kzh
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

packages/rest/src/data-action-routes.ts

@@ -1020,7 +1020,13 @@ export function registerDataActionEndpoints(this: DataActionRouteHost, basePath:
                 // the same rows in the same order, so no value of it can widen or
                 // substitute the answer, and refusing one would turn a correct
                 // export into a `400`.
-                const chunkSize = Math.min(MAX_CHUNK, Math.max(50, q.page != null ? Number(q.page) || 500 : 500));
+                //
+                // [#25229] …which is why it is TRUNCATED where it is read: the
+                // chunk becomes each `findData`'s `limit`, and the normalizer
+                // refuses a fractional window (`?page=100.5` was a `take` of
+                // 100.5, answered 400 naming `limit`, a parameter the caller
+                // never wrote).
+                const chunkSize = Math.min(MAX_CHUNK, Math.max(50, q.page != null ? Math.trunc(Number(q.page)) || 500 : 500));
                 // Colour cells only for xlsx within the style cap; decided up
                 // front (before streaming) since we can't know the true row
                 // count until the stream drains.

packages/rest/src/rest-server-query-number-census.test.ts

@@ -457,13 +457,27 @@ describe('#20139 census — exemption: export `?page=` changes chunking, never t
         const absent = await exportWith({});
         expect(absent.status).toBe(200);
         expect(JSON.parse(absent.streamed)).toHaveLength(ROWS.length);
-        for (const page of ['abc', '', ' ', '1.5', 'Infinity', '-5', '50', '5000']) {
+        for (const page of ['abc', '', ' ', '1.5', '100.5', 'Infinity', '-5', '50', '5000']) {
             const answer = await exportWith({ page });
             expect(answer.status, `?page=${JSON.stringify(page)}`).toBe(200);
             expect(answer.streamed, `?page=${JSON.stringify(page)} changed the exported rows`).toBe(absent.streamed);
         }
     });
 
+    it('[#25229] every chunk handed to `findData` is a whole count, whatever `page` holds', async () => {
+        // The normalizer refuses a fractional or negative window with a 400
+        // naming `limit` — a parameter an export caller never wrote. `100.5`
+        // survives the 50..5000 clamp, so only truncation at the read keeps it
+        // out; this stub `findData` records the window it was handed.
+        for (const page of ['abc', '', '1.5', '100.5', 'Infinity', '-5', '50', '5000']) {
+            const { takes } = await exportWith({ page });
+            expect(takes.length, `?page=${JSON.stringify(page)}`).toBeGreaterThan(0);
+            for (const take of takes) {
+                expect(Number.isSafeInteger(take) && take >= 0, `?page=${JSON.stringify(page)} handed findData limit ${take}`).toBe(true);
+            }
+        }
+    });
+
     it('an unreadable `page` is answered exactly as an absent one: the default 500-row chunk', async () => {
         const absent = await exportWith({});
         expect(absent.takes).toEqual([500, 500, 200]);