ui-react: helpers that only tests call are shipped in src #2525

Context

ui-react ships logic in src that only tests call. Each item below was checked with git grep -nw <name> -- packages ':!*CHANGELOG*': the hits are the definition plus test files only.

inlineRenderedFences is a retired path. The share pipeline now pre-renders fences in preRenderBrowserFences with its own byte budget (INLINE_BUDGET_BYTES, packages/ui-react/src/lib/content-renderer-share.ts:7), so tests/mermaid-fences.test.ts tests a budget rule production no longer applies. A JSDoc block written for the removed inliner sits orphaned above the budget constant (packages/ui-react/src/lib/mermaid.ts:205-212).

Dead logic with green tests reads as covered behaviour, and it gets maintained in every refactor of these files.

Scope

• Delete trackerWords and its private helpers, inlineRenderedFences, INLINE_BUDGET_CHARS and the orphaned JSDoc, nodeSize, SwitchRow and the clearGraphSceneCache wrapper, together with the tests that only exercise them.
• Move createTabHub from src to a test fixture under packages/ui-react/tests/.

Out of scope

• ToolCallTimeline (the sibling issue in this epic).
• Any symbol exported from a package entry (packages/ui-react/src/index.ts, content-figures). Removing one of those is an API change and needs its own issue.
• Rewriting the tracker, mermaid or graph production paths.

Acceptance criteria

• git grep -nw -e trackerWords -e inlineRenderedFences -e INLINE_BUDGET_CHARS -e nodeSize -e SwitchRow -- packages/ui-react returns nothing.
• git grep -n createTabHub -- packages/ui-react/src returns nothing, and tests/answer-delivery.test.ts passes using the fixture.
• Production tracker wording and share fence pre-rendering stay covered by tests that call the production functions. Name them in the PR.
• bun run test packages/ui-react and bun run typecheck pass, and the api-report for ui-react is unchanged.

Verification

bun run test packages/ui-react
bun run typecheck
bun run lint

Contract impact

None. No public export changes.

Found by a repository review on 2026-10-22.