fix: de-optimize route chunks with shared exported declarations

[comp615]

Fixes #15335.

Problem

Route chunk dependency analysis follows references into exported function and class declarations, but previously excluded those declarations from shared-statement detection. Chunk generation then removed a sibling exported declaration whose name did not match the target export, leaving a dangling runtime reference in the emitted chunk.

This affects current main and the v8.2.0 release.

Fix

Treat exported function and class declarations as atomic top-level dependencies. When they are shared by route exports:

• default route splitting de-optimizes the affected export and keeps the route module intact;
• splitRouteModules: "enforce" fails the build with the existing guidance to extract shared code into another module.

The generation path remains unchanged, avoiding duplicated class identity, static state, and module-local state across chunks. Independent exported declarations remain chunkable.

The first commit contains the failing runtime reproduction. The second moves that coverage into the split-route-module integration suite and applies the fix.

Tests

• pnpm test route-chunks-test --runInBand
• pnpm build
• pnpm test:integration:run split-route-modules --project chromium
• pnpm typecheck
• pnpm changes:validate
• pnpm lint (passes with six existing warnings)

🤖 This pull request and its implementation were prepared with AI assistance.