Chart builder: data-aware defaults, one-click hint fixes, canvas preview, fullscreen modal

docs/IMPLEMENTATION-PLAN.md

@@ -289,10 +289,14 @@ the reference.
 
 **Goal:** no-JSON chart composition from a dataset → a new snippet.
 
-> **Enhancement backlog** beyond the Tier-B floor (aggregation, binning, stacking,
-> temporal granularity, sort/orientation, cardinality-based warnings, Tier C
-> intent-first) lives in [`docs/chart-builder-research.md`](chart-builder-research.md) §8
-> — its single home, so these stop living in chat.
+> **Enhancement push (post-M4).** The forward plan now lives in
+> [`docs/chart-builder-enhancement-scope.md`](chart-builder-enhancement-scope.md) — it merges
+> the Tier-B backlog ([`chart-builder-research.md`](chart-builder-research.md) §8) with the
+> Lyra interaction review ([`lyra-review.md`](lyra-review.md)) and sets a **Tier-C** target.
+> Shipped beyond the Tier-B floor so far: per-channel aggregate/bin/`timeUnit`, sort/stack;
+> **actionable hints** (one-click warning fixes); and a builder UX/perf batch (near-fullscreen
+> modal, canvas preview + canvas max-dimension guard, data-aware default pre-population). See
+> the scope doc §4 for the sequenced plan and current status.
 
 **Core**