From 0ce1d9fd7b38fe1a47d0d4d7eba548704101fd62 Mon Sep 17 00:00:00 2001
From: Colin McDonnell <colinmcd94@gmail.com>
Date: Thu, 20 Nov 2025 16:31:00 -0800
Subject: [PATCH] deterministically set up working branch

---
 agents/instructions.ts |  1 +
 external.ts            |  6 ++++++
 main.ts                |  3 ++-
 utils/setup.ts         | 40 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/agents/instructions.ts b/agents/instructions.ts
index cec07ce..785fa71 100644
--- a/agents/instructions.ts
+++ b/agents/instructions.ts
@@ -16,6 +16,7 @@ You do not add unecessary comments, tests, or documentation unless explicitly pr
 You adapt your writing style to the style of your coworkers, while never being unprofessional.
 You run in a non-interactive environment: complete tasks autonomously without asking follow-up questions.
 You make reasonable assumptions when details are missing, but fail with an explicit error if critical information is missing (e.g. user asks to review a PR but does not provide a link or ID).
+Never push commits directly to protected branches: main, master, production. Always create a feature branch.
 
 ## SECURITY
 
diff --git a/external.ts b/external.ts
index 29cf583..efda803 100644
--- a/external.ts
+++ b/external.ts
@@ -46,6 +46,7 @@ export type PayloadEvent =
       pr_number: number;
       pr_title: string;
       pr_body: string | null;
+      branch: string;
       [key: string]: any;
     }
   | {
@@ -53,6 +54,7 @@ export type PayloadEvent =
       pr_number: number;
       pr_title: string;
       pr_body: string | null;
+      branch: string;
       [key: string]: any;
     }
   | {
@@ -63,6 +65,7 @@ export type PayloadEvent =
       review_state: string;
       review_comments: any[];
       context: any;
+      branch: string;
       [key: string]: any;
     }
   | {
@@ -72,6 +75,7 @@ export type PayloadEvent =
       comment_id: number;
       comment_body: string;
       thread?: any;
+      branch: string;
       [key: string]: any;
     }
   | {
@@ -100,6 +104,7 @@ export type PayloadEvent =
       comment_id: number;
       comment_body: string;
       issue_number: number;
+      branch?: string;
       [key: string]: any;
     }
   | {
@@ -108,6 +113,7 @@ export type PayloadEvent =
       pr_title: string;
       pr_body: string | null;
       pull_request: any;
+      branch: string;
       check_suite: {
         id: number;
         head_sha: string;
diff --git a/main.ts b/main.ts
index cd79f3c..72ef58c 100644
--- a/main.ts
+++ b/main.ts
@@ -17,7 +17,7 @@ import {
   revokeInstallationToken,
   setupGitHubInstallationToken,
 } from "./utils/github.ts";
-import { setupGitAuth, setupGitConfig } from "./utils/setup.ts";
+import { setupGitAuth, setupGitBranch, setupGitConfig } from "./utils/setup.ts";
 
 // runtime validation using agents (needed for ArkType)
 // Note: The AgentName type is defined in external.ts, this is the runtime validator
@@ -57,6 +57,7 @@ export async function main(inputs: Inputs): Promise<MainResult> {
     setupMcpLogPolling(ctx);
 
     ctx.payload = parsePayload(inputs);
+    setupGitBranch(ctx.payload);
     setupMcpServers(ctx);
     await installAgentCli(ctx);
     validateApiKey(ctx);
diff --git a/utils/setup.ts b/utils/setup.ts
index e204569..985d38a 100644
--- a/utils/setup.ts
+++ b/utils/setup.ts
@@ -1,5 +1,6 @@
 import { execSync } from "node:child_process";
 import { existsSync, rmSync } from "node:fs";
+import type { Payload } from "../external.ts";
 import { log } from "./cli.ts";
 import type { RepoContext } from "./github.ts";
 import { $ } from "./shell.ts";
@@ -91,3 +92,42 @@ export function setupGitAuth(githubToken: string, repoContext: RepoContext): voi
   $("git", ["remote", "set-url", "origin", remoteUrl]);
   log.info("✓ Updated remote URL with authentication token");
 }
+
+/**
+ * Setup git branch based on payload event context
+ * Automatically checks out the appropriate branch before agent execution
+ */
+export function setupGitBranch(payload: Payload): void {
+  // Only set up git branch in GitHub Actions environment
+  // In local testing, this might interfere with local git state
+  if (!process.env.GITHUB_ACTIONS) {
+    return;
+  }
+
+  const branch = payload.event.branch;
+
+  if (!branch) {
+    log.debug("No branch specified in payload, using default branch");
+    return;
+  }
+
+  log.info(`🌿 Setting up git branch: ${branch}`);
+
+  try {
+    // Fetch the branch from origin
+    log.debug(`Fetching branch from origin: ${branch}`);
+    execSync(`git fetch origin ${branch}`, { stdio: "pipe" });
+
+    // Checkout the branch, creating local tracking branch
+    log.debug(`Checking out branch: ${branch}`);
+    execSync(`git checkout -B ${branch} origin/${branch}`, { stdio: "pipe" });
+
+    log.info(`✓ Successfully checked out branch: ${branch}`);
+  } catch (error) {
+    // If git operations fail, log warning but don't fail the action
+    // The agent might still be able to work with the default branch
+    log.warning(
+      `Failed to checkout branch ${branch}: ${error instanceof Error ? error.message : String(error)}`
+    );
+  }
+}