perf(ui): memo reactive scope by editor version + eval guard (SBX-0)

[eliotlim]

Problem

Every reactive block calls computeScope in its own unmemoized render body, so a doc with B reactive blocks and F formulas does O(B×F) new Function compiles per keystroke. Nothing prevents a new evaluator from landing. Precondition for the OB-146 sandbox (a per-eval QuickJS VM is only viable once this collapses). Board: SBX-0.

Solution

(a) Memoize computeScope keyed on the editor version counter, shared across all reactive call sites — one scope computation per (doc version, render pass). (b) Add no-new-func/no-eval to eslint with explicit per-line disables at the known evaluator sites, so a 6th cannot land silently. New deps: none. No behavior change.

Before / After

Behavior	Before	After
Scope compute (3 blocks × 3 formulas)	9 compiles on initial render	3 (1 computeScope call/version)
New new Function/eval	Lints clean	Lint error unless explicitly disabled
Reactive correctness (chained formulas, slider→chart, grouped inputs)	—	Unchanged (verified: 3→6→7, KPI 2→7)

No visual change.

Test procedure

1. pnpm --filter @book.dev/ui test (kit/reactive: 16 files, 152 tests) — incl. a call-count spy asserting computeScope runs once/version.
2. Add a new Function('') anywhere → pnpm --filter @book.dev/ui lint errors.

Operational notes

• SBX-1 (async eval contract) stacks on this branch — merge SBX-0 first.
• The exported-HTML evaluator (toHtml.ts:1352) is template-string content ESLint can't inspect — covered by SBX-3, not this guard.

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Verify: ui lint + typecheck + tests + build green. Gate: code (Quinn).

🤖 Generated with Claude Code

https://claude.ai/code/session_018RUicirLRuuZvjJN13N6yN

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Project	Deployment	Actions	Updated (UTC)
app.book.pub	Ready	Preview	Aug 10, 2026 1:04pm