Let plugins stream live events and binary data to the app (#8527)

* feat(plugins): stream events and bytes between plugins and the app

Plugins can declare a subscription with defineSubscription, handle it with
server.handle(contract, (input, { push, signal })), and listen from a surface
with useSubscription or client.subscribe. A top-level Uint8Array in an event,
an RPC output, or an RPC input crosses the wire as a binary frame (opcodes
0x20-0x2f) without JSON or base64; a nested one fails validation on the sender.

Each subscriber runs its own handler, owned by the session that subscribed,
so release, disconnect, plugin stop and reload need no plugin code. The
runtime buffers pushes until the subscribe response has gone out, so a client
never sees an event for a subscription it does not know yet.

Gated on server_info.features.pluginSubscriptions; binary outputs reach only
clients that advertise plugin_binary_payloads.

* fix(plugins): close subscription gaps found in review

- Losing daemon.manage now releases the session's plugin subscriptions;
  binary events bypass the outbound permission check, so streams would
  otherwise outlive the revocation.
- A subscribe that times out sends unsubscribe, since the plugin may
  still start the handler after the daemon gave up.
- The byte limit leaves room for the largest frame header and routing,
  and lives in assertPluginWireValue so events, outputs and inputs share it.
- A release right after the host accepted keeps `ready` resolved, so a
  handler that returns at once reports closed rather than an error.
- Session trace logging tolerates loggers without isLevelEnabled.

* fix(plugins): withhold binary plugin results after plugin access is revoked

A binary RPC output or event skipped the outbound permission check its
JSON form passes, so an RPC in flight when daemon.manage was revoked still
delivered its bytes. Each frame now checks the permission of the JSON
message it stands in for.

* test(plugins): cover subscriptions in a real browser instead of JSDOM

The app subscription tests mounted hooks in JSDOM, which docs/testing.md
rules out. The adapter and contract behavior is now a plain unit test,
and a Playwright spec drives the diff-watch and media-stream examples:
JSON events following file changes, streamed bytes, and an upload.

* test(plugins): add the plain subscription unit test and the browser spec

* fix(plugins): apply subscription schema transforms once

Both ends parsed each subscription value, and the sender sent its parse
output, so the receiver parsed a schema's output as fresh input. An event
schema like z.string().transform((s) => s.length) closed the stream as
invalid. The sender now validates and sends the value as given; the
receiver's parse produces what the handler or callback sees.

* fix(plugins): parse a subscription's input once in the plugin process

server.handle wrapped subscription handlers in a second input parse, so a
transforming input schema rejected its own parsed output before the
handler ran.

packages/plugin/src/rpc.ts

@@ -9,6 +9,12 @@ export interface PluginRpcContract<
   output: OutputSchema;
 }
 
+/**
+ * `z.instanceof(Uint8Array)` infers `Uint8Array<ArrayBuffer>`; values crossing the wire accept any
+ * `Uint8Array`, including a `Buffer` or a view of a shared buffer.
+ */
+export type PluginWireInput<Value> = Value extends Uint8Array ? Uint8Array : Value;
+
 export type RpcInput<Contract extends PluginRpcContract> = ZodOutput<Contract["input"]>;
 export type RpcOutput<Contract extends PluginRpcContract> = ZodInput<Contract["output"]>;
 
@@ -31,9 +37,99 @@ export function defineRpc<InputSchema extends ZodType, OutputSchema extends ZodT
 export async function callPluginRpc<InputSchema extends ZodType, OutputSchema extends ZodType>(
   contract: PluginRpcContract<InputSchema, OutputSchema>,
   invoke: (method: string, input: unknown) => Promise<unknown>,
-  input: ZodInput<InputSchema>,
+  input: PluginWireInput<ZodInput<InputSchema>>,
 ): Promise<ZodOutput<OutputSchema>> {
   const parsedInput = await contract.input.parseAsync(input);
   const output = await invoke(contract.name, parsedInput);
   return contract.output.parseAsync(output);
 }
+
+export interface PluginSubscriptionContract<
+  InputSchema extends ZodType = ZodType,
+  EventSchema extends ZodType = ZodType,
+> {
+  name: string;
+  input: InputSchema;
+  event: EventSchema;
+}
+
+export type SubscriptionInput<Contract extends PluginSubscriptionContract> = ZodOutput<
+  Contract["input"]
+>;
+export type SubscriptionEvent<Contract extends PluginSubscriptionContract> = ZodOutput<
+  Contract["event"]
+>;
+
+interface SubscriptionDefinition<InputSchema extends ZodType, EventSchema extends ZodType> {
+  name: string;
+  input: InputSchema;
+  event: EventSchema;
+}
+
+export function defineSubscription<InputSchema extends ZodType, EventSchema extends ZodType>(
+  definition: SubscriptionDefinition<InputSchema, EventSchema>,
+): PluginSubscriptionContract<InputSchema, EventSchema> {
+  const name = definition.name.trim();
+  if (!RPC_NAME.test(name)) throw new Error(`Invalid plugin subscription: ${definition.name}`);
+  return { ...definition, name };
+}
+
+/** One subscription from a client surface. Calling it or `release()` ends it. */
+export type PluginSubscriptionHandle = (() => void) & {
+  /** Resolves once the plugin acknowledged the subscription; rejects if it refused. */
+  readonly ready: Promise<void>;
+  release(): Promise<void>;
+};
+
+export interface PluginSubscriptionObserver {
+  event(event: unknown): void;
+  closed(error?: Error): void;
+}
+
+export interface PluginSubscriptionClosed {
+  /** Set when the plugin's handler failed, the plugin stopped, or an event failed validation. */
+  error?: Error;
+}
+
+export interface PluginSubscribeOptions {
+  /** Aborting releases the subscription. */
+  signal?: AbortSignal;
+  /** Runs once when the daemon closes the subscription. Not called after a release. */
+  onClosed?: (closed: PluginSubscriptionClosed) => void;
+}
+
+export function subscribePluginRpc<InputSchema extends ZodType, EventSchema extends ZodType>(
+  contract: PluginSubscriptionContract<InputSchema, EventSchema>,
+  subscribe: (
+    method: string,
+    input: unknown,
+    observer: PluginSubscriptionObserver,
+  ) => PluginSubscriptionHandle,
+  input: PluginWireInput<ZodInput<InputSchema>>,
+  onEvent: (event: ZodOutput<EventSchema>) => void,
+  options: PluginSubscribeOptions = {},
+): PluginSubscriptionHandle {
+  // The plugin parses the input into the schema's output, so it receives the input as given.
+  contract.input.parse(input);
+  let closed = false;
+  function close(error?: Error) {
+    if (closed) return;
+    closed = true;
+    options.onClosed?.(error ? { error } : {});
+  }
+  const handle = subscribe(contract.name, input, {
+    event(event) {
+      if (closed) return;
+      const parsed = contract.event.safeParse(event);
+      if (parsed.success) return onEvent(parsed.data);
+      handle();
+      close(new Error(`Plugin subscription ${contract.name} sent an invalid event`));
+    },
+    closed: close,
+  });
+  if (options.signal) {
+    if (options.signal.aborted) handle();
+    else options.signal.addEventListener("abort", () => handle(), { once: true });
+  }
+  return handle;
+}