feat(acp): run harnesses without hooks and share one server pool

src/bundled/goose/goose.ts

@@ -53,6 +53,8 @@ export const GOOSE: AcpHooks = {
   program: "goose",
   missing: "goose-acp is missing from this Buzz build.",
   env: ENV,
+  // goose is asked to close every session, advertised or not.
+  closeSession: "always",
   newSessionMeta: (buzz, { title, provider }) => ({
     // The session's whole tool set: goose's developer tools and the Buzz
     // tools, so extensions in the owner's goose config and plugins never load

src/bundled/goose/runtime.ts

@@ -37,7 +37,7 @@ import {
   turnPrompt,
 } from "../claude-code/prompt";
 import type { ServeMcp, Spawn, ToolServer } from "./goose";
-import { AgentSessions, ServerPool, SharedProcess } from "./sessions";
+import { AgentSessions, SharedProcess } from "./sessions";
 
 export type Config = Readonly<{
   /** A model the provider offers; empty uses the provider's default, or the
@@ -108,8 +108,6 @@ type Entry = {
 
 export class GooseRuntime {
   private readonly agents = new Map<string, Entry>();
-  /** The MCP servers every agent's sessions share. */
-  private readonly pool = new ServerPool();
   /** The goose every agent's sessions open in. */
   private readonly goose = new SharedProcess(
     (id, options) => this.spawn(id, options),
@@ -502,7 +500,6 @@ export class GooseRuntime {
       spawn: (id, options) => this.spawn(id, options),
       tools,
       process: this.goose,
-      pool: this.pool,
       onChange: () => this.notify(),
       // Read as each turn starts, so a change needs no restart.
       choice: () => ({

src/features/agent-harness/acp/agent-sessions.ts

@@ -3,8 +3,8 @@
 // conversation's session is closed; its next message opens a new one, shown
 // the conversation again. A one-off turn (a watch or timer wake) gets a
 // session of its own, closed when it ends. Every session holds one of the
-// host's MCP servers, in a pool the plugin's agents share, and the least
-// recently used idle session closes to make room. Nothing is saved: sessions
+// host's MCP servers, in one pool every ACP plugin's agents share, and the
+// least recently used idle session closes to make room, whichever plugin's. Nothing is saved: sessions
 // live as long as the app does.
 import type { AcpProcess } from "./process";
 import type { AcpSession } from "./session";
@@ -18,8 +18,8 @@ import type {
 
 /** A conversation's session closes after this long without a message. */
 export const IDLE_MS = 15 * 60_000;
-/** The most MCP servers a pool's sessions hold at once, below the host's 64 for
- * every plugin, so other plugins keep room. */
+/** The most MCP servers the pool's sessions hold at once, below the host's 64
+ * for every plugin, so plugins not on this client keep room. */
 export const POOL_LIMIT = 48;
 
 /** A session's hold on one MCP server in the pool. */
@@ -30,8 +30,7 @@ export type Slot = {
   evict(): Promise<unknown>;
 };
 
-/** The MCP servers a plugin's agents' sessions hold, least recently used
- * first. One runtime shares one. */
+/** The MCP servers agents' sessions hold, least recently used first. */
 export class ServerPool {
   private readonly slots = new Set<Slot>();
   constructor(private readonly limit = POOL_LIMIT) {}
@@ -71,6 +70,9 @@ export class ServerPool {
   }
 }
 
+/** The pool every ACP plugin's sessions share. */
+export const SHARED_POOL = new ServerPool();
+
 /** What a session is opened with. */
 export type Launch = Readonly<{
   /** The agent's working directory, absolute or `~/…`. */
@@ -86,8 +88,8 @@ export type SessionsOptions = Readonly<{
   tools: ToolServer;
   /** The process its sessions open in, started when needed. */
   process: Readonly<{ get(): Promise<AcpProcess> }>;
-  /** The servers its plugin's sessions hold. */
-  pool: ServerPool;
+  /** The servers its sessions hold: the shared pool unless given. */
+  pool?: ServerPool;
   /** The agent's current settings, for a new session. */
   launch(): Promise<Launch>;
   /** The agent's provider and model now, which each new turn runs on. */
@@ -309,6 +311,9 @@ export class AgentSessions {
     for (const live of this.once.values()) if (live) void this.close(live);
   }
 
+  private get pool() {
+    return this.options.pool ?? SHARED_POOL;
+  }
   private stale(live: Live) {
     return live.fingerprint !== this.options.fingerprint();
   }
@@ -320,7 +325,8 @@ export class AgentSessions {
     title: string | undefined,
     use: (live: Live) => unknown,
   ): Promise<Live> {
-    const { pool, spawn } = this.options;
+    const { spawn } = this.options;
+    const { pool } = this;
     // Read before `launch` reads the settings, so it never describes newer ones.
     const fingerprint = this.options.fingerprint();
     const launch = await this.options.launch();
@@ -408,7 +414,7 @@ export class AgentSessions {
   }
   /** Notes what the session has been shown and restarts its idle countdown. */
   private touch(key: string, live: Live, seen?: number) {
-    this.options.pool.touch(live.slot);
+    this.pool.touch(live.slot);
     clearTimeout(live.timer);
     live.timer = setTimeout(() => {
       if (live.session.busy) this.touch(key, live);