fix(acp): follow server defaults and refresh the session catalog - #52286

Closes #50236 | Closes #51819 | Closes #50378 | Closes #49630 | Refs #52284, #52259, #51478 | Supersedes #50619

Why the change

Since 8905af5074 removed the plugin activation wait (first shipped in v2.0.4), opencode acp reads its model/agent/command catalog before config and plugins have loaded, caches that snapshot for the life of the process, and locks new sessions to its stale defaults, so config-defined agents, default_agent, providers, the configured model, and agent permission rules silently don't apply; after this change ACP sessions use the server's real defaults and the client catalog catches up as soon as those plugins finish loading.

Special things to note

• No protocol change, and the activation wait stays removed. ACP now refreshes on catalog events, the same way the mini TUI and the app already do. The ACP layer stays Promise-based to match the rest of packages/cli/src/acp; moving it to Effect is a separate follow-up.
• session/new no longer sends agent/model. The server picks them at prompt time, after plugins have loaded, so permissions are correct even when the first session/new response still shows build. Clients that ignore config_option_update can show a stale mode/model until they re-read options. A side effect: sessions whose mode/model the client never set now follow later default_agent/model config changes.
• Reproduced on macOS against real opencode acp processes with the ACP: agents/permissions/default_agent from OPENCODE_CONFIG_CONTENT silently ignored across v2 (2.0.3-2.2.0); file-based agent registration regressed after 2.0.3 #52284 config (env content and global config file): before, the first session/new got build about half the time and the cached cwd never recovered; after, every stale response is followed by a config_option_update to copilot-build, and later sessions in the same cwd start correct. The part of ACP: agents/permissions/default_agent from OPENCODE_CONFIG_CONTENT silently ignored across v2 (2.0.3-2.2.0); file-based agent registration regressed after 2.0.3 #52284 that says env content was already inert on 2.0.3 did not reproduce on macOS (16/16 correct on 2.0.3) and still needs a Windows repro, so that issue is only referenced.

Change outline

Catalog loading moves out of the service into its own module. Each cwd gets one live catalog object that sessions point at, instead of each session holding its own copy.

 packages/cli/src/acp/
+├── catalog.ts    # Catalog type, load() (moved), one event subscription, per-cwd reload
 └── service.ts    # sessions point at a live catalog, follow server defaults, retry on unknown ids

 type Attached = {
-  catalog: Catalog
-  model: ModelRef
-  modeID: string
+  readonly catalog: ACPCatalog.Live   // { cwd, current: Catalog }, shared per cwd
+  model?: ModelRef                    // unset = follow server default
+  modeID?: string                     // unset = follow server default
 }

Session creation stops locking in the snapshot defaults.

 newSession(cwd)
   await catalogs.get(cwd)
-  session.create({ location, agent: catalog.defaultModeID, model: catalog.defaultModel })
+  session.create({ location })
   attach(...)

The catalog stays live instead of being a one-time snapshot.

catalogs.get(cwd)                          first use of a cwd
  subscribe()                              one /api/event subscription per ACP connection, before the first read
  load(cwd)                                unchanged polling read

on model.updated | agent.updated | command.updated  (for that location, or all when unscoped)
  reload(live)                             one reload in flight + one queued per cwd
    live.current = load(cwd)
    changed(live, previous)                per attached session:
      config_option_update                   if its options changed
      available_commands_update              if commands changed

set_config_option / set_mode fails with InvalidModel | InvalidMode | InvalidEffort
  reload(live) once, then try again         fixes "model not found" for config models