diff --git a/supabase/functions/edifice-map-generator/index.ts b/supabase/functions/edifice-map-generator/index.ts
index 95ced7f..e2c4866 100644
--- a/supabase/functions/edifice-map-generator/index.ts
+++ b/supabase/functions/edifice-map-generator/index.ts
@@ -304,18 +304,30 @@ function crc32(data: Uint8Array): number {
   return (c ^ 0xFFFFFFFF) >>> 0;
 }
 
-async function zlibDecompress(data: Uint8Array): Promise<Uint8Array> {
+async function zlibDecompress(data: Uint8Array<ArrayBuffer>): Promise<Uint8Array<ArrayBuffer>> {
   return streamTransform(new DecompressionStream("deflate"), data);
 }
 
-async function zlibCompress(data: Uint8Array): Promise<Uint8Array> {
+async function zlibCompress(data: Uint8Array<ArrayBuffer>): Promise<Uint8Array<ArrayBuffer>> {
   return streamTransform(new CompressionStream("deflate"), data);
 }
 
+// Two type facts drive these signatures under Deno 2.x / TypeScript 5.7, and neither is
+// cosmetic:
+//   1. CompressionStream and DecompressionStream declare `writable: WritableStream<BufferSource>`,
+//      which is wider than Uint8Array — so a `TransformStream<Uint8Array, Uint8Array>`
+//      parameter asked for something narrower than either class provides.
+//   2. Since TS 5.7 typed arrays are generic over their backing buffer: bare `Uint8Array`
+//      means `Uint8Array<ArrayBufferLike>`, which admits SharedArrayBuffer, while
+//      `BufferSource` requires `ArrayBufferView<ArrayBuffer>`. So a bare Uint8Array is not
+//      writable to these streams.
+// Hence `Uint8Array<ArrayBuffer>` throughout the PNG codec path: it states that these buffers
+// are never shared, which is already true — every one of them comes from `new Uint8Array(n)`
+// or a `Response.arrayBuffer()`. A cast would have silenced the checker without saying so.
 async function streamTransform(
-  xform: TransformStream<Uint8Array, Uint8Array>,
-  data: Uint8Array,
-): Promise<Uint8Array> {
+  xform: TransformStream<BufferSource, Uint8Array>,
+  data: Uint8Array<ArrayBuffer>,
+): Promise<Uint8Array<ArrayBuffer>> {
   const writer = xform.writable.getWriter();
   const reader = xform.readable.getReader();
   const chunks: Uint8Array[] = [];