Support /compact (#51)

It would be nice to also support sending status via hooks when the
compact action is happening (and maybe show something in the UI to show
where compacting happened in the thread) but for now this at least
allows it.

---------

Signed-off-by: Ben Brandt <benjamin.j.brandt@gmail.com>

Author: benbrandt

src/acp-agent.ts

@@ -284,6 +284,24 @@ export class ClaudeAcpAgent implements Agent {
             continue;
           }
 
+          // Slash commands like /compact can generate invalid output... doesn't match
+          // their own docs: https://docs.anthropic.com/en/docs/claude-code/sdk/sdk-slash-commands#%2Fcompact-compact-conversation-history
+          if (
+            typeof message.message.content === "string" &&
+            message.message.content.includes("<local-command-stdout>")
+          ) {
+            console.log(message.message.content);
+            break;
+          }
+
+          if (
+            typeof message.message.content === "string" &&
+            message.message.content.includes("<local-command-stderr>")
+          ) {
+            console.error(message.message.content);
+            break;
+          }
+
           if (
             message.message.model === "<synthetic>" &&
             message.message.content.length === 1 &&
@@ -361,7 +379,6 @@ async function getAvailableSlashCommands(query: Query): Promise<AvailableCommand
     "bashes", // Modal
     "bug", // Modal
     "clear", // Escape Codes
-    "compact", // Not supported via SDK?
     "config", // Modal
     "context", // Escape Codes
     "cost", // Escape Codes
@@ -390,14 +407,14 @@ async function getAvailableSlashCommands(query: Query): Promise<AvailableCommand
     "todos", // Escape Codes
     "vim", // Not needed
   ];
-  //todo: Do not use `as any` once `supportedCommands` is exposed via the typescript interface
-  const commands = await (query as any).supportedCommands();
+  const commands = await query.supportedCommands();
 
   return commands
-    .map((command: { name: string; description: string; argumentHint: string }) => {
+    .map((command) => {
       const input = command.argumentHint ? { hint: command.argumentHint } : null;
       return {
         name: command.name,
+        // @ts-expect-error type in the ts interface
         description: command.description || "",
         input,
       };

src/tests/acp-agent.test.ts

@@ -191,6 +191,50 @@ describe.skipIf(!process.env.RUN_INTEGRATION_TESTS)("ACP subprocess integration"
 
     expect(client.takeReceivedText()).toContain("Hello GPT-5");
   }, 30000);
+
+  it("/compact works", async () => {
+    const { client, connection, newSessionResponse } = await setupTestSession(__dirname);
+
+    const commands = await client.availableCommandsPromise;
+
+    expect(commands).toContainEqual({
+      description:
+        "Clear conversation history but keep a summary in context. Optional: /compact [instructions for summarization]",
+      input: {
+        hint: "<optional custom summarization instructions>",
+      },
+      name: "compact",
+    });
+
+    // Error case (no previous message)
+    await connection.prompt({
+      prompt: [{ type: "text", text: "/compact" }],
+      sessionId: newSessionResponse.sessionId,
+    });
+
+    expect(client.takeReceivedText()).toBe("");
+
+    // Send something
+    await connection.prompt({
+      prompt: [{ type: "text", text: "Hi" }],
+      sessionId: newSessionResponse.sessionId,
+    });
+    // Clear response
+    client.takeReceivedText();
+
+    // Test with instruction
+    await connection.prompt({
+      prompt: [
+        {
+          type: "text",
+          text: "/compact greeting",
+        },
+      ],
+      sessionId: newSessionResponse.sessionId,
+    });
+
+    expect(client.takeReceivedText()).toContain("");
+  }, 30000);
 });
 
 describe("tool conversions", () => {