feat: send user request as separate content block for slash command support (#785)

* feat: send user request as separate content block for slash command support

When in tag mode with the SDK path, extracts the user's request from the
trigger comment (text after @claude) and sends it as a separate content
block. This enables the CLI to process slash commands like "/review-pr".

- Add extract-user-request utility to parse trigger comments
- Write user request to separate file during prompt generation
- Send multi-block SDKUserMessage when user request file exists
- Add tests for the extraction utility

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* fix: address PR feedback

- Fix potential ReDoS vulnerability by using string operations instead of regex
- Remove unused extractUserRequestFromEvent function and tests
- Extract USER_REQUEST_FILENAME to shared constants
- Conditionally log user request based on showFullOutput setting
- Add JSDoc documentation to extractUserRequestFromContext

---------

Co-authored-by: Claude <noreply@anthropic.com>

base-action/src/run-claude-sdk.ts

@@ -1,14 +1,81 @@
 import * as core from "@actions/core";
-import { readFile, writeFile } from "fs/promises";
+import { readFile, writeFile, access } from "fs/promises";
+import { dirname, join } from "path";
 import { query } from "@anthropic-ai/claude-agent-sdk";
 import type {
   SDKMessage,
   SDKResultMessage,
+  SDKUserMessage,
 } from "@anthropic-ai/claude-agent-sdk";
 import type { ParsedSdkOptions } from "./parse-sdk-options";
 
 const EXECUTION_FILE = `${process.env.RUNNER_TEMP}/claude-execution-output.json`;
 
+/** Filename for the user request file, written by prompt generation */
+const USER_REQUEST_FILENAME = "claude-user-request.txt";
+
+/**
+ * Check if a file exists
+ */
+async function fileExists(path: string): Promise<boolean> {
+  try {
+    await access(path);
+    return true;
+  } catch {
+    return false;
+  }
+}
+
+/**
+ * Creates a prompt configuration for the SDK.
+ * If a user request file exists alongside the prompt file, returns a multi-block
+ * SDKUserMessage that enables slash command processing in the CLI.
+ * Otherwise, returns the prompt as a simple string.
+ */
+async function createPromptConfig(
+  promptPath: string,
+  showFullOutput: boolean,
+): Promise<string | AsyncIterable<SDKUserMessage>> {
+  const promptContent = await readFile(promptPath, "utf-8");
+
+  // Check for user request file in the same directory
+  const userRequestPath = join(dirname(promptPath), USER_REQUEST_FILENAME);
+  const hasUserRequest = await fileExists(userRequestPath);
+
+  if (!hasUserRequest) {
+    // No user request file - use simple string prompt
+    return promptContent;
+  }
+
+  // User request file exists - create multi-block message
+  const userRequest = await readFile(userRequestPath, "utf-8");
+  if (showFullOutput) {
+    console.log("Using multi-block message with user request:", userRequest);
+  } else {
+    console.log("Using multi-block message with user request (content hidden)");
+  }
+
+  // Create an async generator that yields a single multi-block message
+  // The context/instructions go first, then the user's actual request last
+  // This allows the CLI to detect and process slash commands in the user request
+  async function* createMultiBlockMessage(): AsyncGenerator<SDKUserMessage> {
+    yield {
+      type: "user",
+      session_id: "",
+      message: {
+        role: "user",
+        content: [
+          { type: "text", text: promptContent }, // Instructions + GitHub context
+          { type: "text", text: userRequest }, // User's request (may be a slash command)
+        ],
+      },
+      parent_tool_use_id: null,
+    };
+  }
+
+  return createMultiBlockMessage();
+}
+
 /**
  * Sanitizes SDK output to match CLI sanitization behavior
  */
@@ -63,7 +130,8 @@ export async function runClaudeWithSdk(
   promptPath: string,
   { sdkOptions, showFullOutput, hasJsonSchema }: ParsedSdkOptions,
 ): Promise<void> {
-  const prompt = await readFile(promptPath, "utf-8");
+  // Create prompt configuration - may be a string or multi-block message
+  const prompt = await createPromptConfig(promptPath, showFullOutput);
 
   if (!showFullOutput) {
     console.log(

src/create-prompt/index.ts

@@ -21,8 +21,12 @@ import type { ParsedGitHubContext } from "../github/context";
 import type { CommonFields, PreparedContext, EventData } from "./types";
 import { GITHUB_SERVER_URL } from "../github/api/config";
 import type { Mode, ModeContext } from "../modes/types";
+import { extractUserRequest } from "../utils/extract-user-request";
 export type { CommonFields, PreparedContext } from "./types";
 
+/** Filename for the user request file, read by the SDK runner */
+const USER_REQUEST_FILENAME = "claude-user-request.txt";
+
 // Tag mode defaults - these tools are needed for tag mode to function
 const BASE_ALLOWED_TOOLS = [
   "Edit",
@@ -847,6 +851,55 @@ f. If you are unable to complete certain steps, such as running a linter or test
   return promptContent;
 }
 
+/**
+ * Extracts the user's request from the prepared context and GitHub data.
+ *
+ * This is used to send the user's actual command/request as a separate
+ * content block, enabling slash command processing in the CLI.
+ *
+ * @param context - The prepared context containing event data and trigger phrase
+ * @param githubData - The fetched GitHub data containing issue/PR body content
+ * @returns The extracted user request text (e.g., "/review-pr" or "fix this bug"),
+ *          or null for assigned/labeled events without an explicit trigger in the body
+ *
+ * @example
+ * // Comment event: "@claude /review-pr" -> returns "/review-pr"
+ * // Issue body with "@claude fix this" -> returns "fix this"
+ * // Issue assigned without @claude in body -> returns null
+ */
+function extractUserRequestFromContext(
+  context: PreparedContext,
+  githubData: FetchDataResult,
+): string | null {
+  const { eventData, triggerPhrase } = context;
+
+  // For comment events, extract from comment body
+  if (
+    "commentBody" in eventData &&
+    eventData.commentBody &&
+    (eventData.eventName === "issue_comment" ||
+      eventData.eventName === "pull_request_review_comment" ||
+      eventData.eventName === "pull_request_review")
+  ) {
+    return extractUserRequest(eventData.commentBody, triggerPhrase);
+  }
+
+  // For issue/PR events triggered by body content, extract from the body
+  if (githubData.contextData?.body) {
+    const request = extractUserRequest(
+      githubData.contextData.body,
+      triggerPhrase,
+    );
+    if (request) {
+      return request;
+    }
+  }
+
+  // For assigned/labeled events without explicit trigger in body,
+  // return null to indicate the full context should be used
+  return null;
+}
+
 export async function createPrompt(
   mode: Mode,
   modeContext: ModeContext,
@@ -895,6 +948,22 @@ export async function createPrompt(
       promptContent,
     );
 
+    // Extract and write the user request separately for SDK multi-block messaging
+    // This allows the CLI to process slash commands (e.g., "@claude /review-pr")
+    const userRequest = extractUserRequestFromContext(
+      preparedContext,
+      githubData,
+    );
+    if (userRequest) {
+      await writeFile(
+        `${process.env.RUNNER_TEMP || "/tmp"}/claude-prompts/${USER_REQUEST_FILENAME}`,
+        userRequest,
+      );
+      console.log("===== USER REQUEST =====");
+      console.log(userRequest);
+      console.log("========================");
+    }
+
     // Set allowed tools
     const hasActionsReadPermission = false;
 

src/utils/extract-user-request.ts

@@ -0,0 +1,32 @@
+/**
+ * Extracts the user's request from a trigger comment.
+ *
+ * Given a comment like "@claude /review-pr please check the auth module",
+ * this extracts "/review-pr please check the auth module".
+ *
+ * @param commentBody - The full comment body containing the trigger phrase
+ * @param triggerPhrase - The trigger phrase (e.g., "@claude")
+ * @returns The user's request (text after the trigger phrase), or null if not found
+ */
+export function extractUserRequest(
+  commentBody: string | undefined,
+  triggerPhrase: string,
+): string | null {
+  if (!commentBody) {
+    return null;
+  }
+
+  // Use string operations instead of regex for better performance and security
+  // (avoids potential ReDoS with large comment bodies)
+  const triggerIndex = commentBody
+    .toLowerCase()
+    .indexOf(triggerPhrase.toLowerCase());
+  if (triggerIndex === -1) {
+    return null;
+  }
+
+  const afterTrigger = commentBody
+    .substring(triggerIndex + triggerPhrase.length)
+    .trim();
+  return afterTrigger || null;
+}

test/extract-user-request.test.ts

@@ -0,0 +1,77 @@
+import { describe, test, expect } from "bun:test";
+import { extractUserRequest } from "../src/utils/extract-user-request";
+
+describe("extractUserRequest", () => {
+  test("extracts text after @claude trigger", () => {
+    expect(extractUserRequest("@claude /review-pr", "@claude")).toBe(
+      "/review-pr",
+    );
+  });
+
+  test("extracts slash command with arguments", () => {
+    expect(
+      extractUserRequest(
+        "@claude /review-pr please check the auth module",
+        "@claude",
+      ),
+    ).toBe("/review-pr please check the auth module");
+  });
+
+  test("handles trigger phrase with extra whitespace", () => {
+    expect(extractUserRequest("@claude    /review-pr", "@claude")).toBe(
+      "/review-pr",
+    );
+  });
+
+  test("handles trigger phrase at start of multiline comment", () => {
+    const comment = `@claude /review-pr
+Please review this PR carefully.
+Focus on security issues.`;
+    expect(extractUserRequest(comment, "@claude")).toBe(
+      `/review-pr
+Please review this PR carefully.
+Focus on security issues.`,
+    );
+  });
+
+  test("handles trigger phrase in middle of text", () => {
+    expect(
+      extractUserRequest("Hey team, @claude can you review this?", "@claude"),
+    ).toBe("can you review this?");
+  });
+
+  test("returns null for empty comment body", () => {
+    expect(extractUserRequest("", "@claude")).toBeNull();
+  });
+
+  test("returns null for undefined comment body", () => {
+    expect(extractUserRequest(undefined, "@claude")).toBeNull();
+  });
+
+  test("returns null when trigger phrase not found", () => {
+    expect(extractUserRequest("Please review this PR", "@claude")).toBeNull();
+  });
+
+  test("returns null when only trigger phrase with no request", () => {
+    expect(extractUserRequest("@claude", "@claude")).toBeNull();
+  });
+
+  test("handles custom trigger phrase", () => {
+    expect(extractUserRequest("/claude help me", "/claude")).toBe("help me");
+  });
+
+  test("handles trigger phrase with special regex characters", () => {
+    expect(
+      extractUserRequest("@claude[bot] do something", "@claude[bot]"),
+    ).toBe("do something");
+  });
+
+  test("is case insensitive", () => {
+    expect(extractUserRequest("@CLAUDE /review-pr", "@claude")).toBe(
+      "/review-pr",
+    );
+    expect(extractUserRequest("@Claude /review-pr", "@claude")).toBe(
+      "/review-pr",
+    );
+  });
+});