test: pin skill appendix sync and SKILL.md-only seeding (C-line, no behaviour change)

- test_skill_appendix_sync: all 9 appendix chapters 00..08 in order,
  body role-matrix set == appendix role-title set, authority
  statement on both sides, GitHub guarantee in body + named
  appendix chapters 00/04/07, seeded copy byte-identical with
  full appendix. Previously only 00/08 existence was asserted.
- test_skill_seed_pinning: only SKILL.md copied (pack extras never
  land, never resurrected), tenant extras left alone, tenant-modified
  SKILL.md never overwritten across repeats, identical = noop,
  deleted SKILL.md re-seeded (documented boundary, not deletion
  preservation).
- skill_seed.py: evaluation note only (why whole-dir copy is not
  done); no code change.

cloud/skill_seed.py

@@ -55,6 +55,27 @@ copying is not adopted unless a future evaluation proves both
 content-preservation AND deletion-preservation. Until then, only
 SKILL.md is seeded; extra files in a pack directory are ignored
 (pinned by test_merge_gate_protectskill.py).
+
+Evaluation note (2026-10-31, skill-engineering convergence line;
+comment only, behaviour unchanged -- see
+cloud/tests/test_skill_seed_pinning.py, which pins it):
+whole-directory copy is explicitly NOT done, for three reasons.
+(1) The pack today ships exactly one file per skill (SKILL.md;
+verified: cloud/skills/*/ contains nothing else), so copying a
+whole directory has zero benefit today and would silently start
+copying future extras (templates/, README) without review.
+(2) Per-file skip-if-differ cannot preserve a tenant deletion:
+a missing destination is copied by design, so whole-dir copy
+would resurrect tenant-deleted auxiliary files on the next run.
+SKILL.md-only copy bounds that resurrection surface to the single
+SKILL.md file itself (auxiliary deletions are preserved trivially
+because those files never landed in the tenant home).
+(3) Seeding never prunes the tenant directory, so tenant-added
+files in a skill directory are left alone by the same rule.
+Boundary, stated plainly so it is not misread: a tenant-deleted
+SKILL.md IS re-seeded (missing = copied); only the differ-guard
+preserves edits. Preserving a SKILL.md deletion would need a
+tombstone, which is new behaviour, not a convergence fix.
 """
 
 import shutil