Apply structure guidance to a 20-file sample

Status summary#

Complete in draft PR #2306, stacked on PR #2305. Exactly 20 non-test JS/TS source files changed: exceptional branches use early returns, value-selection ternaries remain shared, one untyped boundary uses a strict schema, one single-use helper was inlined, and unnecessary falsy distinctions were collapsed. Full typecheck, lint, formatting, and tests pass.

Spec#

Select 20 production source files with clear violations of the structure rules. Used small handwritten files across apps and packages; generated, vendored, test, and spec files were excluded.
Apply the rules with file-by-file judgment. Kept valid numeric and nullable distinctions; empty optional search/config strings now follow their existing fallback meaning.
Preserve valid behavior and add no compatibility fallbacks. Full monorepo typecheck, lint, and tests pass.
Keep the source diff to exactly 20 files. The task record is the only non-source addition.
Open a draft PR with rules/structure-guidance as its base. Opened disposable sample PR #2306.

Decisions and assumptions#

“Arbitrary” means the slice need not follow a product boundary; files are selected for small, legible examples rather than maximum impact.
The new rules are advisory and semantic. Every edit must make the local code clearer.
Tests and specs are excluded by the rule frontmatter and remain unchanged.

Implementation log#

Started from PR #2305 and merged its follow-up filename correction without rewriting history.
Review of the first sample sharpened the conditional guidance: ternaries still choose handlers, argument bundles, and positive JSX alternatives when expanding them would duplicate work, add mutation, or obscure the predicate.
The browser-feed state boundary now recognizes the legacy empty state with z.strictObject({}) instead of an anonymous chain of runtime checks.
The source diff is 60 additions and 75 removals.
pnpm typecheck, pnpm lint, targeted formatting checks, the focused 39-case repo-file suite, and the full monorepo pnpm test pass (including 2,333 passing OS tests).