fix: Gate unsupported-slash-command on SDK command list

packages/agent/src/adapters/claude/UPSTREAM.md

@@ -53,6 +53,7 @@ Fork of `@anthropic-ai/claude-agent-acp`. Upstream repo: https://github.com/anth
 | Auth methods | `claude-ai-login` + `console-login` | Returns empty `authMethods` | Auth handled externally |
 | Session fingerprinting | Implicit teardown on cwd/mcp change | Explicit `refreshSession()` | Caller-initiated is more predictable |
 | Shutdown on ACP close | Process exits | No standalone process | Agent is embedded in server |
+| Unsupported slash commands | Loops silently on early idle | Emits "Unsupported slash command" chunk, gated on `initializationResult().commands` so plugin/skill commands (e.g. `/skills-store`) whose echoes use a fresh uuid are not false-flagged | The SDK consumes some slash commands without producing output (e.g. `/plugin` in non-interactive mode); without this we hang. The known-commands gate avoids racing plugin/skill loads where idle can arrive before the transformed user-message echo. |
 
 ## Changes Ported in v0.30.0 Sync
 

packages/agent/src/adapters/claude/claude-agent.slash-command.test.ts

@@ -34,7 +34,11 @@ function makeAgent(): { agent: Agent; client: ClientMocks } {
   return { agent, client };
 }
 
-function installFakeSession(agent: Agent, sessionId: string): MockQuery {
+function installFakeSession(
+  agent: Agent,
+  sessionId: string,
+  knownSlashCommands?: Set<string>,
+): MockQuery {
   const query = createMockQuery();
   const input = new Pushable();
   const abortController = new AbortController();
@@ -63,6 +67,7 @@ function installFakeSession(agent: Agent, sessionId: string): MockQuery {
     taskRunId: "run-1",
     lastContextWindowSize: 200_000,
     modelId: "claude-sonnet-4-6",
+    knownSlashCommands,
   };
 
   (agent as unknown as { session: typeof session }).session = session;
@@ -99,21 +104,36 @@ describe("ClaudeAcpAgent.prompt — early idle handling", () => {
       label: "unsupported slash command surfaces error and ends turn",
       sessionId: "s-slash",
       prompt: "/plugin install slack",
+      knownCommands: undefined,
       expectsUnsupportedChunk: true,
       commandInMessage: "/plugin",
     },
     {
       label: "non-slash prompt with early idle is silently skipped",
       sessionId: "s-regular",
       prompt: "hello",
+      knownCommands: undefined,
+      expectsUnsupportedChunk: false,
+      commandInMessage: null,
+    },
+    {
+      label:
+        "known plugin/skill command with early idle is not flagged as unsupported",
+      sessionId: "s-skill",
+      prompt: "/skills-store use my address pr review skill",
+      knownCommands: new Set(["skills-store"]),
       expectsUnsupportedChunk: false,
       commandInMessage: null,
     },
   ] as const;
 
   it.each(cases)("$label", async (tc) => {
     const { agent, client } = makeAgent();
-    const query = installFakeSession(agent, tc.sessionId);
+    const query = installFakeSession(
+      agent,
+      tc.sessionId,
+      tc.knownCommands as Set<string> | undefined,
+    );
 
     const promptPromise = agent.prompt({
       sessionId: tc.sessionId,

packages/agent/src/adapters/claude/claude-agent.ts

@@ -43,6 +43,7 @@ import {
   type Query,
   query,
   type SDKUserMessage,
+  type SlashCommand,
 } from "@anthropic-ai/claude-agent-sdk";
 import { v7 as uuidv7 } from "uuid";
 import packageJson from "../../../package.json" with { type: "json" };
@@ -143,6 +144,17 @@ function readClaudeMdQuietly(cwd: string, logger: Logger): string | undefined {
   }
 }
 
+function collectKnownSlashCommands(
+  commands: SlashCommand[] | undefined,
+): Set<string> {
+  const names = new Set<string>();
+  if (!commands) return names;
+  for (const cmd of commands) {
+    if (cmd.name) names.add(cmd.name);
+  }
+  return names;
+}
+
 function sanitizeTitle(text: string): string {
   const sanitized = text
     .replace(/[\r\n]+/g, " ")
@@ -500,7 +512,17 @@ export class ClaudeAcpAgent extends BaseAcpAgent {
                 // and produced no output (e.g. /plugin in a non-interactive
                 // context). Without this branch we would loop forever waiting
                 // for an echo that never comes; surface a clear error instead.
-                if (commandMatch) {
+                //
+                // Only fire for commands the SDK does NOT recognize. Plugin
+                // and skill commands (e.g. /skills-store) produce a fresh
+                // user-message echo with a new uuid that our replay check
+                // can't match, so an early idle here is a race, not a real
+                // "unsupported" — fall through and let the loop continue.
+                const cmdName = commandMatch?.[1].slice(1);
+                const known =
+                  cmdName !== undefined &&
+                  this.session.knownSlashCommands?.has(cmdName) === true;
+                if (commandMatch && !known) {
                   const cmd = commandMatch[1];
                   this.logger.warn(
                     "Slash command produced no output; treating as unsupported",
@@ -520,6 +542,8 @@ export class ClaudeAcpAgent extends BaseAcpAgent {
                 }
                 this.logger.debug("Skipping idle state before prompt replay", {
                   sessionId: params.sessionId,
+                  command: commandMatch?.[1],
+                  known,
                 });
                 break;
               }
@@ -1305,6 +1329,9 @@ export class ClaudeAcpAgent extends BaseAcpAgent {
             `Session ${forkSession ? "fork" : "resumption"} timed out for sessionId=${sessionId}`,
           );
         }
+        session.knownSlashCommands = collectKnownSlashCommands(
+          result.value.commands,
+        );
       } catch (err) {
         settingsManager.dispose();
         if (
@@ -1356,6 +1383,9 @@ export class ClaudeAcpAgent extends BaseAcpAgent {
             `Session initialization timed out for sessionId=${sessionId}`,
           );
         }
+        session.knownSlashCommands = collectKnownSlashCommands(
+          initResult.value.commands,
+        );
       } catch (err) {
         settingsManager.dispose();
         this.logger.error("Session initialization failed", {

packages/agent/src/adapters/claude/types.ts

@@ -68,6 +68,13 @@ export type Session = BaseSession & {
   emitRawSDKMessages: boolean | SDKMessageFilter[];
   /** Refreshed at session init and on MCP/skill changes. */
   contextBreakdownBaseline?: ContextBreakdownBaseline;
+  /**
+   * Slash command names (without leading slash) the SDK recognizes for this
+   * session — built-ins plus plugin/skill commands. Captured from the SDK's
+   * init response. Used to distinguish "command produced no output" from
+   * "command is genuinely unknown" when the session goes idle without an echo.
+   */
+  knownSlashCommands?: Set<string>;
 };
 
 export type ToolUseCache = {