fix: handle missing comment payload in Forgejo review comment events

Forgejo's pull_request_review_comment event does not include a
top-level `comment` object in the payload (it's undefined), causing
a crash: "undefined is not an object (evaluating 'context.payload.comment.body')".

- trigger.ts: On Forgejo, always trigger for pull_request_review_comment
  events since the workflow already gates on event name alone
- create-prompt/index.ts: Use optional chaining for comment fields,
  fall back to actor/empty values (data fetcher provides full data)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/create-prompt/index.ts

@@ -142,9 +142,13 @@ export function prepareContext(
     commentBody = context.payload.review.body ?? "";
     triggerUsername = context.payload.review.user.login;
   } else if (isPullRequestReviewCommentEvent(context)) {
-    commentId = context.payload.comment.id.toString();
+    // Forgejo's pull_request_review_comment payload may not include a
-    commentBody = context.payload.comment.body;
+    // top-level `comment` object.  Use optional chaining and fall back
-    triggerUsername = context.payload.comment.user.login;
+    // to actor/empty values — the data fetcher provides the full data.
+    commentId = (context.payload as any).comment?.id?.toString();
+    commentBody = (context.payload as any).comment?.body ?? "";
+    triggerUsername =
+      (context.payload as any).comment?.user?.login ?? context.actor;
   } else if (isIssuesEvent(context)) {
     triggerUsername = context.payload.issue.user.login;
   }

src/github/validation/trigger.ts

@@ -10,6 +10,7 @@ import {
   isPullRequestReviewCommentEvent,
 } from "../context";
 import type { ParsedGitHubContext } from "../context";
+import { detectPlatform } from "../../platform/detector";
 
 export function checkContainsTrigger(context: ParsedGitHubContext): boolean {
   const {
@@ -119,6 +120,21 @@ export function checkContainsTrigger(context: ParsedGitHubContext): boolean {
     isIssueCommentEvent(context) ||
     isPullRequestReviewCommentEvent(context)
   ) {
+    // Forgejo's pull_request_review_comment payload does NOT include a
+    // top-level `comment` object (it's undefined).  On Forgejo, the
+    // workflow `if:` already gates on event name alone, so always trigger
+    // here — the actual comment data is fetched via REST in the data
+    // fetcher, and non-matching comments won't produce useful output.
+    if (
+      isPullRequestReviewCommentEvent(context) &&
+      detectPlatform() === "forgejo"
+    ) {
+      console.log(
+        "Forgejo pull_request_review_comment: triggering (payload lacks comment body)",
+      );
+      return true;
+    }
+
     const commentBody = isIssueCommentEvent(context)
       ? context.payload.comment.body
       : context.payload.comment.body;