fix: add chapter_ref/chapter_number to package schema; drop requires block

- Package step schema now includes chapter_ref and chapter_number so the LLM
  extracts them from the task name even when context vars are missing.
- Previously removed requires: block was the only guard; now the package step
  itself self-heals by asking the LLM to derive these values.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

templates/book_chapter.yml

@@ -429,10 +429,16 @@ steps:
       The draft chapter has been written, self-checked, and committed.
       The character-state from PASS 3 is provided above.
 
-      Summarize the character state changes for {chapter_ref} in the `chapter_state` field
+      Summarize the character state changes in the `chapter_state` field
       (2-3 sentences max). This is used for bookkeeping -- the chapter text itself is passed
       to reviewers directly.
 
+      CHAPTER IDENTIFICATION (required fields):
+      Extract the chapter reference from the task name or task context:
+      - chapter_number: the plain chapter number as a string (e.g. "8" from "Write Chapter 8: ...")
+      - chapter_ref: zero-padded two-digit reference (e.g. "ch-08" for chapter 8)
+      If not available in context, derive it from the chapter number in the task name.
+
       NEW CHARACTER DETECTION:
       For each NEW character introduced this chapter (not previously known), emit one
       create_task action using task_type: character_sheet.
@@ -444,6 +450,8 @@ steps:
       Now confirm the chapter is ready for review.
     schema:
       chapter_state: string
+      chapter_ref: string
+      chapter_number: string
     spawn:
       - task_type: chapter_review
         task_name: "Review (Devon): {chapter_ref}"