feat(ysync): lib_symbols travel + layout save-sync (miss 08), TS hot-path opts (12), diff-on-rebind adopt (13) — doc 18

Miss 08A: the binding stores wire-carried (lib_symbols …) definitions in
kdoc_libsymbols and prefixes them on apply wires — a joiner that never saw a
symbol adopts it WITH its definition (new e2e ysync-libsymbols.spec.ts).
Miss 08B: registerSaveHook gains onSavedText; WasmTool routes saved-file text
to syncLayoutToY (per sheet room via the manager's syncLayoutFromSave, or the
single-room doc) so title block / paper / setup edits converge instead of
drifting. Opt 12 (TS half): zod off the observer hot path (yToItemUnchecked),
children index built once per conversion. Opt 13: seed()'s adopt diffs the
editor snapshot against the doc view and applies only the doc-authoritative
difference — clean rebinds apply nothing, the adopt undo entry shrinks to the
real changed set. Opt 14 deliberately deferred (doc 18). All TS-side; no wasm
rebuild (the C++ blob/findLib sides already carried definitions).

Verified: shared 107, standalone 79 (+2 known pre-existing wasm-assets),
ysync e2e 21/21 chromium, collab regression 21/3-skip firefox.

Bumps: web/pcbjam-shared (lib_symbols channel + syncLayoutToY + opts).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JgThWXtdvrYLK47EDFoGdq

docs/features/ysync-review/14-opt-item-granularity-bandwidth.md

@@ -1,7 +1,7 @@
 # Optimization 14 — Item-level body granularity: whole-item payloads per nudge, LWW drops concurrent property edits
 
 **Severity:** known/documented v1 tradeoff — recorded here so its costs are visible when prioritizing
-**Status:** open (deliberate design decision; revisit trigger below)
+**Status:** open (deliberate design decision; revisit trigger below — reaffirmed 2026-07-03, see [18](18-miss08-opts-12-13.md))
 
 ## Where