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JSON form passes, so an RPC in flight when daemon.manage was revoked still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.

docs/plugins.md

@@ -357,9 +357,27 @@ keys are stored under a `param.` prefix; plugins never see it and may use any ke
 `openScreen` validates its input once (`parsePluginOpenScreenInput`); code past it trusts the
 params.
 
-RPC contracts validate inputs and outputs in both the app and plugin subprocess. `useRpc` returns a
-typed async function. Use the host-provided `@tanstack/react-query` for request state and caching;
-Paseo gives each plugin installation its own query client.
+RPC and subscription contracts validate inputs, outputs, and events in both the app and plugin
+subprocess. `useRpc` returns a typed async function. Use the host-provided `@tanstack/react-query`
+for request state and caching; Paseo gives each plugin installation its own query client.
+
+A subscription is a session-owned observation (`plugin-rpc` delivery family): the session that
+subscribed owns its lifetime, so release, disconnect, plugin stop, and reload need no plugin code.
+Each subscriber gets its own handler call in the subprocess; there is no fan-out or replay. The
+runtime buffers pushes until the session has sent `plugin.rpc.subscribe.response`, so a client
+never sees an event for an unknown subscription. The app installation's lifetime aborts every
+subscription its surfaces left open, and a reload replaces the installation, which resubscribes
+mounted hooks.
+
+The byte rule (a top-level `Uint8Array` is binary, a nested one is a validation error) is checked
+once per hop by `assertPluginWireValue`. Bytes ride plugin binary frames, opcodes `0x20`-`0x2f`
+(`packages/protocol/src/binary-frames/plugin.ts`); nothing on the path copies or re-encodes them,
+and `plugin-subscriptions.perf.e2e.test.ts` locks that. Keep it that way: never stringify a plugin
+payload for a log, and the client's bootstrap buffer holds bytes only until the first observer
+attaches. Binary outputs reach only clients that send `pluginBinaryPayloads`. A binary input
+frame (`0x22`) becomes a synthetic `plugin.rpc.invoke.request` and runs through the normal message
+path, so it is authorized like any other invoke. The author contract, including the native upload
+limit, is in [stream events from the daemon](../public-docs/plugins/reference.md#subscriptions).
 
 `usePaseo()` and the handler's `{ paseo }` context expose the same `PaseoApi`: projects,
 workspaces, agents, terminals, providers, and daemon config. They do not expose connection lifecycle.