diff --git a/src/app/(rep)/rep/check-in-view.tsx b/src/app/(rep)/rep/check-in-view.tsx
index fa90063..8b47b1f 100644
--- a/src/app/(rep)/rep/check-in-view.tsx
+++ b/src/app/(rep)/rep/check-in-view.tsx
@@ -577,7 +577,17 @@ export function CheckInView() {
       <Sheet open={pickerOpen} onOpenChange={(open) => (open ? setPickerOpen(true) : closePicker())}>
         <SheetContent
           side="bottom"
-          className="rounded-t-2xl px-0 pb-0 sm:max-w-md sm:mx-auto"
+          // `max-h-[90dvh]` keeps the sheet on-screen when the customer
+          // list is long (a few hundred unpinned customers is normal).
+          // Without a height cap, the base-ui bottom-sheet class
+          // (`data-[side=bottom]:h-auto`) sizes the popup to its content
+          // and the inner `overflow-y-auto` list container has nothing
+          // to scroll within — the list just renders past the top of
+          // the viewport. `dvh` (dynamic viewport height) accounts for
+          // mobile browser chrome so the sheet never gets pushed off
+          // the bottom of a small screen either. See rep-picker-height
+          // test for the regression guard.
+          className="rounded-t-2xl px-0 pb-0 max-h-[90dvh] sm:max-w-md sm:mx-auto"
           showCloseButton
         >
           <SheetHeader className="px-4">
diff --git a/src/app/(rep)/rep/rep-picker-height.test.ts b/src/app/(rep)/rep/rep-picker-height.test.ts
new file mode 100644
index 0000000..3b0fb86
--- /dev/null
+++ b/src/app/(rep)/rep/rep-picker-height.test.ts
@@ -0,0 +1,83 @@
+import { describe, it, expect } from "vitest";
+import { readFileSync } from "node:fs";
+import { fileURLToPath } from "node:url";
+import { dirname, resolve } from "node:path";
+
+/**
+ * Regression guard for the "list goes off the top of the screen"
+ * bug in the rep picker Sheet.
+ *
+ * The base-ui Sheet component applies `data-[side=bottom]:h-auto`,
+ * which sizes the bottom sheet to its content. With ~600 unpinned
+ * customers in the picker, that means the sheet grows past the
+ * viewport and the inner `overflow-y-auto` container has nothing
+ * to scroll within — the list renders above the visible area
+ * (verified on 2026-09-20, the list was 46,373px tall in an 809px
+ * viewport before the fix).
+ *
+ * The fix is a `max-h-[90dvh]` override at the call site. If a
+ * future refactor drops it, this test fails.
+ */
+const HERE = dirname(fileURLToPath(import.meta.url));
+const VIEW_PATH = resolve(HERE, "./check-in-view.tsx");
+
+function viewSource(): string {
+  return readFileSync(VIEW_PATH, "utf8");
+}
+
+/**
+ * Pull out just the JSX block for the picker `<SheetContent side="bottom" …>`.
+ * We anchor on the picker-specific className substring that lives inside
+ * the call (not a generic helper), so this only matches the rep picker
+ * SheetContent even if other bottom sheets exist in the file.
+ */
+function pickerSheetContentBlock(source: string): string | null {
+  // Anchor on the unique `max-h-[90dvh]` cap (which is what we're
+  // testing for) and grab back to the opening `<SheetContent` tag.
+  // If the cap is removed, the test fails on the first assertion
+  // and this helper still gets re-evaluated on every test.
+  const idx = source.indexOf("max-h-[90dvh]");
+  if (idx === -1) return null;
+  const start = source.lastIndexOf("<SheetContent", idx);
+  if (start === -1) return null;
+  // Walk to the next `<` past the closing `>` of the opening tag —
+  // enough to read the full className.
+  const close = source.indexOf(">", start);
+  if (close === -1) return null;
+  return source.slice(start, close + 1);
+}
+
+describe("rep picker SheetContent height contract", () => {
+  it("constrains the bottom sheet height with max-h-[90dvh]", () => {
+    const source = viewSource();
+    const block = pickerSheetContentBlock(source);
+    expect(block, "picker SheetContent max-h-[90dvh] cap not found").not.toBeNull();
+    expect(block!).toMatch(/max-h-\[90dvh\]/);
+  });
+
+  it("uses dvh (not just vh) so mobile browser chrome is accounted for", () => {
+    const source = viewSource();
+    const block = pickerSheetContentBlock(source);
+    expect(block!).toMatch(/max-h-\[90dvh\]/);
+    // Negative: not bare `max-h-[90vh]` without the `d` suffix —
+    // plain `vh` ignores the mobile browser chrome and the sheet
+    // can still be pushed off the bottom of a small screen.
+    expect(block!).not.toMatch(/max-h-\[90vh\](?!d)/);
+  });
+
+  it("the inner list container has overflow-y-auto (so the cap actually scrolls)", () => {
+    const source = viewSource();
+    // The inner div around the <ul>…</ul> must have overflow-y-auto.
+    // `modal-shell__body flex-1 overflow-y-auto px-4 pb-4` carries it.
+    expect(source).toMatch(/modal-shell__body[^"]*\boverflow-y-auto\b/);
+  });
+
+  it("the picker list container has flex-1 so it fills remaining sheet height", () => {
+    const source = viewSource();
+    // Without `flex-1`, the inner div sizes to its content and the
+    // outer `max-h-[90dvh]` cap doesn't trigger a scrollbar — same
+    // visual bug as dropping the cap. Pair this with the previous
+    // test to nail down both halves of the constraint.
+    expect(source).toMatch(/modal-shell__body[^"]*\bflex-1\b/);
+  });
+});