From e60c96823d45e89c2d8dea6e0ab7cb280dccd57a Mon Sep 17 00:00:00 2001
From: Daniel Imms <2193314+Tyriar@users.noreply.github.com>
Date: Fri, 13 Feb 2026 08:10:16 -0800
Subject: [PATCH] Add hook to setup repo when agent starts

Fixes #5605
---
 .github/hooks/setupRepo.json |  10 +++
 bin/agent/setup-repo.mjs     | 138 +++++++++++++++++++++++++++++++++++
 package.json                 |   3 +-
 3 files changed, 150 insertions(+), 1 deletion(-)
 create mode 100644 .github/hooks/setupRepo.json
 create mode 100644 bin/agent/setup-repo.mjs

diff --git a/.github/hooks/setupRepo.json b/.github/hooks/setupRepo.json
new file mode 100644
index 00000000..5dd0c656
--- /dev/null
+++ b/.github/hooks/setupRepo.json
@@ -0,0 +1,10 @@
+{
+	"hooks": {
+		"SessionStart": [
+			{
+				"type": "command",
+				"command": "npm run agent:setup-repo"
+			}
+		]
+	}
+}
\ No newline at end of file
diff --git a/bin/agent/setup-repo.mjs b/bin/agent/setup-repo.mjs
new file mode 100644
index 00000000..2db85d87
--- /dev/null
+++ b/bin/agent/setup-repo.mjs
@@ -0,0 +1,138 @@
+// @ts-check
+
+import { cpSync, existsSync, lstatSync, readFileSync } from 'node:fs';
+import { spawnSync } from 'node:child_process';
+import { basename, dirname, resolve, sep } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const repoRoot = resolve(dirname(fileURLToPath(import.meta.url)), '../..');
+const nodeModulesPath = resolve(repoRoot, 'node_modules');
+const npmExecutable = process.platform === 'win32' ? 'npm.cmd' : 'npm';
+
+/** @typedef {{ folder: string; reason: string }} Candidate */
+
+/** @param {string} message */
+function log(message) {
+  console.info(`[setup-fast] ${message}`);
+}
+
+/** @param {string[]} args */
+function runNpm(args) {
+  log(`Running: npm ${args.join(' ')}`);
+  const result = spawnSync(npmExecutable, args, {
+    cwd: repoRoot,
+    stdio: 'inherit'
+  });
+  if (result.error) {
+    throw result.error;
+  }
+  if ((result.status ?? 1) !== 0) {
+    process.exit(result.status ?? 1);
+  }
+}
+
+/**
+ * @param {Candidate[]} candidates
+ * @param {string | undefined} folder
+ * @param {string} reason
+ */
+function addCandidate(candidates, folder, reason) {
+  if (!folder) {
+    return;
+  }
+  if (candidates.some(candidate => candidate.folder === folder)) {
+    return;
+  }
+  candidates.push({ folder, reason });
+  log(`Candidate found (${reason}): ${folder}`);
+}
+
+function detectMainSiblingFolder() {
+  const currentFolderName = basename(repoRoot);
+  if (!currentFolderName.startsWith('xterm.js') || currentFolderName === 'xterm.js') {
+    log(`Current folder is "${currentFolderName}", skipping xterm.js sibling lookup.`);
+    return undefined;
+  }
+  const siblingFolder = resolve(dirname(repoRoot), 'xterm.js');
+  log(`Current folder is "${currentFolderName}", sibling main folder candidate: ${siblingFolder}`);
+  return siblingFolder;
+}
+
+function detectWorktreeMainFolder() {
+  const gitPath = resolve(repoRoot, '.git');
+  if (!existsSync(gitPath)) {
+    log('No .git entry found at repo root.');
+    return undefined;
+  }
+  const gitStat = lstatSync(gitPath);
+  if (!gitStat.isFile()) {
+    log('.git is not a file, this repo does not appear to be a worktree checkout.');
+    return undefined;
+  }
+  const gitFileContent = readFileSync(gitPath, 'utf8').trim();
+  const gitDirMatch = /^gitdir:\s*(.+)$/m.exec(gitFileContent);
+  if (!gitDirMatch) {
+    log('Could not parse gitdir from .git file.');
+    return undefined;
+  }
+
+  const gitDirPath = resolve(repoRoot, gitDirMatch[1].trim());
+  log(`Parsed gitdir from .git file: ${gitDirPath}`);
+
+  const normalizedGitDirPath = gitDirPath.replace(/\\/g, '/');
+  const worktreeMarker = '/.git/worktrees/';
+  const markerIndex = normalizedGitDirPath.indexOf(worktreeMarker);
+  if (markerIndex === -1) {
+    log('gitdir path does not contain /.git/worktrees/, skipping worktree main folder lookup.');
+    return undefined;
+  }
+
+  const normalizedMainFolder = normalizedGitDirPath.slice(0, markerIndex);
+  const mainFolder = sep === '/' ? normalizedMainFolder : normalizedMainFolder.split('/').join(sep);
+  log(`Worktree main folder candidate: ${mainFolder}`);
+  return mainFolder;
+}
+
+function resolveSourceFolder() {
+  /** @type {Candidate[]} */
+  const candidates = [];
+  addCandidate(candidates, detectMainSiblingFolder(), 'xterm.js sibling');
+  addCandidate(candidates, detectWorktreeMainFolder(), 'worktree main repo');
+
+  for (const candidate of candidates) {
+    const candidateNodeModulesPath = resolve(candidate.folder, 'node_modules');
+    if (existsSync(candidateNodeModulesPath)) {
+      log(`Using candidate (${candidate.reason}) with node_modules: ${candidate.folder}`);
+      return candidate.folder;
+    }
+    log(`Candidate skipped (${candidate.reason}), node_modules missing: ${candidateNodeModulesPath}`);
+  }
+
+  log('No candidate folder with node_modules was found.');
+  return undefined;
+}
+
+if (!existsSync(nodeModulesPath)) {
+  log(`node_modules missing: ${nodeModulesPath}`);
+  const sourceFolder = resolveSourceFolder();
+  if (sourceFolder) {
+    const sourceNodeModulesPath = resolve(sourceFolder, 'node_modules');
+    log(`Copying node_modules from ${sourceNodeModulesPath} to ${nodeModulesPath}`);
+    try {
+      cpSync(sourceNodeModulesPath, nodeModulesPath, { recursive: true });
+      log('node_modules copy completed.');
+    } catch (error) {
+      const message = error instanceof Error ? error.message : String(error);
+      log(`node_modules copy failed: ${message}`);
+      log('Falling back to npm ci.');
+      runNpm(['ci']);
+    }
+  } else {
+    log('No source folder available, running npm ci.');
+    runNpm(['ci']);
+  }
+} else {
+  log(`node_modules already exists: ${nodeModulesPath}`);
+}
+
+runNpm(['run', 'setup']);
diff --git a/package.json b/package.json
index 8c0f4462..267477a1 100644
--- a/package.json
+++ b/package.json
@@ -72,7 +72,8 @@
     "prepackage-headless": "npm run esbuild-package-headless-only",
     "package-headless": "webpack --config ./webpack.config.headless.js",
     "postpackage-headless": "node ./bin/package_headless.js",
-    "prepublishOnly": "npm run package"
+    "prepublishOnly": "npm run package",
+    "agent:session-start": "node bin/agent/setup-repo.mjs"
   },
   "devDependencies": {
     "@lunapaint/png-codec": "^0.2.0",