fix(security): harden skill apply and activation flows

Restrict auto-apply to trusted review comments so spoofed issue comments
cannot write optimized SKILL.md content into pull request branches.

Reject activation symlinks that escape the source root and add
regression coverage for both security checks.

tools/scripts/apply_skill_optimization.cjs

@@ -5,6 +5,8 @@ const path = require('node:path');
 const { execFileSync } = require('node:child_process');
 
 const REVIEW_HEADING = '## Tessl Skill Review';
+const TRUSTED_AUTHOR_ASSOCIATIONS = new Set(['OWNER', 'MEMBER', 'COLLABORATOR']);
+const DEFAULT_ALLOWED_REVIEW_BOT_LOGINS = ['github-actions[bot]'];
 
 function getRequiredEnv(name) {
   const value = process.env[name];
@@ -88,7 +90,46 @@ function ensureRepoRelative(filePath) {
   return resolved;
 }
 
-async function findLatestReviewComment(owner, repo, prNumber) {
+function parseAllowedReviewBotLogins(envValue = process.env.APPLY_OPTIMIZE_ALLOWED_REVIEW_BOT_LOGINS) {
+  if (!envValue) {
+    return DEFAULT_ALLOWED_REVIEW_BOT_LOGINS;
+  }
+
+  const logins = envValue
+    .split(',')
+    .map((item) => item.trim())
+    .filter(Boolean);
+
+  return logins.length > 0 ? logins : DEFAULT_ALLOWED_REVIEW_BOT_LOGINS;
+}
+
+function isTrustedReviewComment(comment, allowedBotLogins = DEFAULT_ALLOWED_REVIEW_BOT_LOGINS) {
+  if (!comment?.body || !comment.body.includes(REVIEW_HEADING)) {
+    return false;
+  }
+
+  if (TRUSTED_AUTHOR_ASSOCIATIONS.has(comment.author_association)) {
+    return true;
+  }
+
+  const login = comment.user?.login;
+  const userType = comment.user?.type;
+  return Boolean(login && userType === 'Bot' && allowedBotLogins.includes(login));
+}
+
+function selectLatestTrustedReviewComment(comments, allowedBotLogins = DEFAULT_ALLOWED_REVIEW_BOT_LOGINS) {
+  let latest = null;
+
+  for (const comment of comments) {
+    if (isTrustedReviewComment(comment, allowedBotLogins)) {
+      latest = comment;
+    }
+  }
+
+  return latest;
+}
+
+async function findLatestTrustedReviewComment(owner, repo, prNumber, allowedBotLogins) {
   let page = 1;
   let latest = null;
 
@@ -97,11 +138,7 @@ async function findLatestReviewComment(owner, repo, prNumber) {
       `/repos/${owner}/${repo}/issues/${prNumber}/comments?per_page=100&page=${page}`,
     );
 
-    for (const comment of comments) {
-      if (comment.body && comment.body.includes(REVIEW_HEADING)) {
-        latest = comment;
-      }
-    }
+    latest = selectLatestTrustedReviewComment(comments, allowedBotLogins) ?? latest;
 
     if (comments.length < 100) {
       return latest;
@@ -133,6 +170,7 @@ async function main() {
   }
 
   const pr = await githubRequest(`/repos/${owner}/${repo}/pulls/${prNumber}`);
+  const allowedReviewBotLogins = parseAllowedReviewBotLogins();
 
   if (pr.head.repo.full_name !== repoSlug) {
     throw new Error(
@@ -140,9 +178,16 @@ async function main() {
     );
   }
 
-  const reviewComment = await findLatestReviewComment(owner, repo, prNumber);
+  const reviewComment = await findLatestTrustedReviewComment(
+    owner,
+    repo,
+    prNumber,
+    allowedReviewBotLogins,
+  );
   if (!reviewComment || !reviewComment.body) {
-    throw new Error('No Tessl skill review comment found on this PR. Run the review first.');
+    throw new Error(
+      'No trusted Tessl skill review comment found on this PR. Run the review first.',
+    );
   }
 
   const optimizedFiles = extractOptimizedContent(reviewComment.body);
@@ -205,7 +250,18 @@ async function main() {
   await postComment(owner, repo, prNumber, body);
 }
 
-main().catch((error) => {
-  console.error(error instanceof Error ? error.stack : String(error));
-  process.exitCode = 1;
-});
+if (require.main === module) {
+  main().catch((error) => {
+    console.error(error instanceof Error ? error.stack : String(error));
+    process.exitCode = 1;
+  });
+}
+
+module.exports = {
+  DEFAULT_ALLOWED_REVIEW_BOT_LOGINS,
+  REVIEW_HEADING,
+  findLatestTrustedReviewComment,
+  isTrustedReviewComment,
+  parseAllowedReviewBotLogins,
+  selectLatestTrustedReviewComment,
+};