Isolate content script build to prevent silent chunk-import breakage

[Copilot]

Chrome content scripts injected via chrome.scripting.executeScript must be self-contained — they cannot resolve Rollup-emitted chunk imports at runtime. Including selection-overlay.ts in the multi-entry build was a latent trap: any future shared import would silently break the content script with no build-time warning.

Changes

• vite.content.config.ts (new) — Dedicated single-entry Vite build for the content script. A single-entry Rollup build inlines all static imports unconditionally; no chunks are ever emitted regardless of future refactors. emptyOutDir: false appends to dist/ without clobbering the main build.

• vite.config.ts — Removes content/selection-overlay from the multi-entry input.

• package.json — Runs both builds sequentially:

  "build": "tsc && vite build && vite build --config vite.content.config.ts"

The result: dist/content/selection-overlay.js is a fully self-contained bundle. Future imports added to the content script will always be inlined, making the isolation structural rather than incidental.

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Feature][High] Vite chunk output risks breaking content script isolation in future refactors</issue_title>
<issue_description>## Summary

The Vite/Rollup build configuration allows shared chunk extraction across all entry points, including the content script. This creates a latent build fragility: any future import added to selection-overlay.ts from a shared module will silently break the content script at runtime.

Details

File: vite.config.ts, lines 47-50

The configuration specifies chunkFileNames: 'chunks/[name].js', and multiple entry points (popup, options, background, offscreen, share, content/selection-overlay) share dependencies. Rollup extracts shared code into common chunks.

Problem: Chrome extension content scripts cannot load ES module chunks — they must be self-contained. chrome.scripting.executeScript with a single file path cannot resolve chunk imports. The content script (selection-overlay.ts) currently works because it has no shared imports, but this is fragile.

Impact:

• Any future refactoring that adds a shared import to selection-overlay.ts will break the content script at runtime
• No build-time error will warn the developer — the breakage is silent
• This is a maintenance trap for any contributor unfamiliar with Chrome extension content script constraints

Suggested Fix

Option A — Prevent chunking for content scripts via manualChunks:

output: {
  entryFileNames: '[name].js',
  chunkFileNames: 'chunks/[name].js',
  assetFileNames: '[name].[ext]',
  manualChunks(id) {
    if (id.includes('selection-overlay')) return undefined;
  }
}

Option B — Build content scripts as a separate Vite configuration with inlineDynamicImports: true (preferred for stronger isolation).

Differentiation from Existing Issues

Distinct from #23 (CI/CD pipeline, linting) and #31 (accessibility, UX polish, build tooling). Neither addresses the specific content script chunk isolation risk in the Vite Rollup output configuration.

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Comments on the Issue (you are @copilot in this section)

• Fixes [Feature][High] Vite chunk output risks breaking content script isolation in future refactors #37

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