Wire the caption merge, and write the target architecture down

merge_faceless_captions had been written and never called; both crop
endpoints called the non-destructive context_fragment_links instead, with no
decision recording that choice. Wiring it changes panel count and every panel
index, so the chapter needs a re-crop with the panels prefix cleared first --
crop_webtoon skips an upload when the key already exists, which is right for a
resume and silently wrong after a slicing change. Noted at the line.

It does not cover the head-in-one-shot body-in-the-next split that prompted
the question. _merge_plan only folds a fragment that has text and no face.

ARCHITECTURE.md is the target shape from the user's design, with what exists
against each section today. Nothing in it is built.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CLAUDE.md

@@ -11,6 +11,7 @@ Goal, invariants, and working rules. Read this first.
 | `caveats/` | every known limit and its revisit trigger, indexed in `caveats/CLAUDE.md` |
 | `AGENTS.md` | commands, with the traps beside them |
 | `AUDIT.md` | the 2026-08-11 pipeline audit, the source of the roadmap |
+| `ARCHITECTURE.md` | the target shape of the pipeline, and what exists against it today |
 | `spec-v3.md` | current quality and look work, marked DONE/TODO per item |
 
 Do not restate a finding here. Point at the decision.