fix(liveshare-protocol): release a stream whose unreadable open reached the owner

A 200 open whose body was not a JSON object threw from readable() before the
abort listener was armed, so the page never sent stream-cancel and the owner
held the id until its own budget expired. The unreadable-open path now
cancels the id before rethrowing; the spec pins the cancel.

packages/experimental/liveshare-protocol/src/viewer-carrier.ts

@@ -14,7 +14,7 @@
  * {@link installViewerCarrier} runs in the browser from its own source text, so it must reference no
  * module binding: every constant and helper it needs is declared inside its body.
  *
- * @module @deepseek-ai/dsh-experimental-liveshare-protocol/src/viewer-carrier
+ * @module @deepseek-ai/dsh-experimental-liveshare-protocol
  */
 
 /** Page global naming the share one viewer page presents; the Liveshare client plugin reads it. */
@@ -227,7 +227,7 @@ export function installViewerCarrier(options: ViewerCarrierOptions): void {
       const id = nextStreamId++
       signal.throwIfAborted()
       // Each path below sends this at most once: the abort listener only runs on abort, the final
-      // block only without one, and the open paths return before either is armed.
+      // block only without one, and an open that ends the stream cancels here before either is armed.
       const cancel = (): void => {
         void post({ op: 'stream-cancel', id }, endpoint).catch(() => undefined)
       }
@@ -247,7 +247,15 @@ export function installViewerCarrier(options: ViewerCarrierOptions): void {
       // no stream for it: polling that id would only read `stream-not-found`, which looks like a lost
       // logical stream and would be re-opened forever. The frame's own code decides instead — an owner
       // refusal such as `remote-access/denied` is terminal, while a lost stream stays re-openable.
-      const refusedOpen = failure(readable(opened, endpoint), endpoint)
+      let openedBody: Record<string, unknown>
+      try {
+        openedBody = readable(opened, endpoint)
+      } catch (error) {
+        // A 200 answer the page cannot read reached the owner, which may already hold this stream id.
+        if (opened.status === 200) cancel()
+        throw error
+      }
+      const refusedOpen = failure(openedBody, endpoint)
       if (refusedOpen !== undefined) throw refusedOpen
       signal.addEventListener('abort', cancel, { once: true })
       try {

packages/experimental/liveshare-protocol/tests/viewer-carrier.client.spec.ts

@@ -230,7 +230,8 @@ describe('viewer carrier streams', () => {
     expect(posted.map(request => request.op)).toEqual(['stream-open', 'stream-next', 'stream-cancel'])
     const empty = await readStream([{ status: 200, body: [] }])
     expect(markerOf(empty.error)).toEqual({ kind: 'carrier' })
-    expect(empty.posted.map(request => request.op)).toEqual(['stream-open'])
+    // The 200 open reached the owner, so a body the page cannot read still releases the stream id.
+    expect(empty.posted.map(request => request.op)).toEqual(['stream-open', 'stream-cancel'])
   })
 
   it('keeps an authentication refusal terminal whatever code its body carries', async () => {