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>

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",
+    );
+  });
+});