fix(github): prevent duplicate review score headings (#18321)

Clarify the shared GitHub review submission contract for new and existing bots.
Remove copied score headings while preserving the structured score and saved assessment.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

packages/shared/src/validators/chat-github.ts

@@ -113,8 +113,12 @@ export const githubReviewAssessmentSchema = z
       z.literal(5),
     ]),
     complete: z.boolean(),
-    summary: z.string().trim().min(1).max(24000),
-    rationale: z.string().trim().min(1).max(12000),
+    summary: z.string().trim().min(1).max(24000).describe(
+      "Review body only: describe the change, findings, and verdict. Paperclip adds the bot-name/score heading and reviewed-commit, coverage, and task/run footer; do not include them here or copy a previously published comment.",
+    ),
+    rationale: z.string().trim().min(1).max(12000).describe(
+      "Explain the score, supporting evidence, and remaining risk. Published after summary. Do not repeat the summary, score heading, or generated footer; put reviewed paths and limitations in coverage.",
+    ),
     coverage: z
       .object({
         reviewedPaths: z.array(z.string().min(1).max(1024)).max(5000),