fix: run built-in slash commands when the client attaches context

src/acp-agent.ts

@@ -2190,6 +2190,31 @@ const SESSION_ENDED_MESSAGE = "The Claude Agent session has ended. Please start
 // message and without invoking the model.
 const LOCAL_ONLY_COMMANDS = new Set(["/context", "/heapdump", "/extra-usage"]);
 
+// Built-in commands that never use attached context. Clients like Air attach
+// editor context (resources, extra text chunks) to every prompt, but Claude
+// Code runs a slash command only when the user message is a single text block.
+const CONTEXT_FREE_COMMANDS = new Set([
+  ...LOCAL_ONLY_COMMANDS,
+  "/compact",
+  "/usage",
+  "/cost",
+  "/stats",
+  "/status",
+  "/model",
+  "/mcp",
+  "/remote-control",
+]);
+
+/** Drops the chunks after a context-free built-in command (see
+ *  `CONTEXT_FREE_COMMANDS`), keeping the command and its arguments. Returns
+ *  `prompt` itself when it isn't such a command. */
+export function withoutCommandContext(prompt: PromptRequest["prompt"]): PromptRequest["prompt"] {
+  const first = prompt[0];
+  if (prompt.length < 2 || first?.type !== "text") return prompt;
+  const command = first.text.trimStart().split(/\s/, 1)[0];
+  return CONTEXT_FREE_COMMANDS.has(command) ? [first] : prompt;
+}
+
 // Commands whose marker-only transcript records are ACP/client-local UI noise,
 // not model-visible user prompts. Marker-only custom slash skills are not in
 // this list, so replay can reconstruct them from `<command-name>`/`<command-args>`.
@@ -3901,6 +3926,9 @@ export class ClaudeAcpAgent {
       throw RequestError.internalError(undefined, SESSION_ENDED_MESSAGE);
     }
 
+    const prompt = withoutCommandContext(params.prompt);
+    if (prompt !== params.prompt) params = { ...params, prompt };
+
     const remoteControlCommand = parseRemoteControlCommand(params.prompt);
     if (
       remoteControlCommand &&

src/tests/acp-agent.test.ts

@@ -36,6 +36,7 @@ import { ToolCallFieldTracker } from "../tool-calls/field-tracker.js";
 import {
   toAcpNotifications,
   promptToClaude,
+  withoutCommandContext,
   isLocalCommandMetadata,
   isReplayHiddenMetaMessage,
   isSyntheticLoginMessage,
@@ -4716,6 +4717,50 @@ describe("escape markdown", () => {
   });
 });
 
+describe("withoutCommandContext", () => {
+  const link = { type: "resource_link", uri: "file:///a.ts", name: "a.ts" } as const;
+  const resource = {
+    type: "resource",
+    resource: { uri: "file:///a.ts", text: "const a = 1;" },
+  } as const;
+
+  /** `/compact` with attached editor context keeps only the text chunk. */
+  it("drops context after /compact", () => {
+    const text = { type: "text", text: "/compact" } as const;
+    expect(withoutCommandContext([text, link, resource])).toEqual([text]);
+  });
+
+  /** Arguments in the command chunk survive; the attached resource goes. */
+  it("keeps command arguments and drops context", () => {
+    const text = { type: "text", text: "/compact focus on tests" } as const;
+    expect(withoutCommandContext([text, resource])).toEqual([text]);
+  });
+
+  /** An extra text chunk after `/usage` is dropped too. */
+  it("drops trailing text chunks after /usage", () => {
+    const text = { type: "text", text: "/usage" } as const;
+    expect(withoutCommandContext([text, { type: "text", text: "editor context" }])).toEqual([text]);
+  });
+
+  /** Skills and custom commands use attached context, so the prompt is untouched. */
+  it("leaves custom commands unchanged", () => {
+    const prompt = [{ type: "text", text: "/code-review" } as const, resource];
+    expect(withoutCommandContext(prompt)).toBe(prompt);
+  });
+
+  /** A plain text prompt with a resource is untouched. */
+  it("leaves plain prompts unchanged", () => {
+    const prompt = [{ type: "text", text: "explain this" } as const, resource];
+    expect(withoutCommandContext(prompt)).toBe(prompt);
+  });
+
+  /** `/mcp:server:cmd` is an MCP prompt, not the `/mcp` built-in. */
+  it("leaves MCP prompt commands unchanged", () => {
+    const prompt = [{ type: "text", text: "/mcp:server:cmd" } as const, resource];
+    expect(withoutCommandContext(prompt)).toBe(prompt);
+  });
+});
+
 describe("prompt conversion", () => {
   it("should not change built-in slash commands", () => {
     const message = promptToClaude({

src/tests/mcp-command.test.ts

@@ -635,25 +635,33 @@ describe("/mcp", () => {
     expect(text()).toBe(formatMcpStatus(SERVERS));
   });
 
-  it("leaves the text of other /mcp prompts unchanged", async () => {
-    const { agent, sdkQuery, forwarded, text, prompt } = setup();
+  /** A client like Air attaches editor context to `/mcp`; the adapter drops it and still shows the status. */
+  it("shows the status for /mcp with attached context", async () => {
+    const { agent, sdkQuery, forwarded, text } = setup();
 
-    await prompt("/mcp:github:prompt");
-    await prompt("/mcp help");
     await agent.prompt({
       sessionId: "test-session",
       prompt: [
         { type: "text", text: "/mcp" },
-        { type: "text", text: "more" },
+        { type: "resource", resource: { uri: "file:///a.ts", text: "const a = 1;" } },
       ],
     });
 
+    expect(forwarded).toEqual(["/mcp"]);
+    expect(text()).toBe(formatMcpStatus(SERVERS));
+    expect(sdkQuery.mcpServerStatus).toHaveBeenCalled();
+  });
+
+  it("leaves the text of other /mcp prompts unchanged", async () => {
+    const { sdkQuery, forwarded, text, prompt } = setup();
+
+    await prompt("/mcp:github:prompt");
+    await prompt("/mcp help");
+
     // The adapter rewrites an MCP prompt command into the Claude Code form.
-    expect(forwarded).toEqual(["/github:prompt (MCP)", "/mcp help", "/mcp more"]);
+    expect(forwarded).toEqual(["/github:prompt (MCP)", "/mcp help"]);
     expect(text()).toBe(
-      ["/github:prompt (MCP)", "/mcp help", "/mcp more"]
-        .map((command) => cliText(command, SERVERS))
-        .join(""),
+      ["/github:prompt (MCP)", "/mcp help"].map((command) => cliText(command, SERVERS)).join(""),
     );
     expect(sdkQuery.mcpServerStatus).not.toHaveBeenCalled();
   });