feat: add pre-built compression and code splitting for frontend assets

[Sumeet213]

Description:

Addresses #2340

• Pre-build gzip and brotli compressed assets at build time
• Serve pre-compressed files directly (no runtime CPU overhead)
• Split vendor libraries into cacheable chunks

Initial load reduced from ~1.07MB to ~850KB (brotli).

---

Summary by cubic

Pre-built gzip and Brotli assets and vendor code splitting to reduce initial load and remove runtime compression overhead, addressing #2340. Initial load drops from ~1.07MB to ~850KB.

• New Features

  • Backend serves .br/.gz files when supported (sets Content-Encoding and Vary).
  • Build-time compression via vite-plugin-compression for gzip and Brotli (keeps original files).
  • Manual code splitting for vendor chunks (react, UI, markdown, utils) to improve caching.

• Dependencies

  • Added vite-plugin-compression ^0.5.1.

^{Written for commit 6f45e56. Summary will update automatically on new commits.}

[cubic-dev-ai]

No issues found across 4 files

[cubic-dev-ai]

1 issue found across 4 files

Prompt for AI agents (all 1 issues)

Check if these issues are valid — if so, understand the root cause of each and fix them.


<file name="backend/chainlit/server.py">

<violation number="1" location="backend/chainlit/server.py:283">
P2: `Accept-Encoding` quality values are ignored, so a client that explicitly disallows gzip/Brotli (q=0) will still receive that encoding. Parse the header and only serve a precompressed file when the requested encoding’s q-value is greater than 0.</violation>
</file>

---

Since this is your first cubic review, here's how it works:

• cubic automatically reviews your code and comments on bugs and improvements
• Teach cubic by replying to its comments. cubic learns from your replies and gets better over time
• Ask questions if you need clarification on any suggestion

_{Reply to cubic to teach it or ask questions. Re-run a review with @cubic-dev-ai review this PR}

[cubic-dev-ai]

P2: Accept-Encoding quality values are ignored, so a client that explicitly disallows gzip/Brotli (q=0) will still receive that encoding. Parse the header and only serve a precompressed file when the requested encoding’s q-value is greater than 0.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At backend/chainlit/server.py, line 283:

<comment>`Accept-Encoding` quality values are ignored, so a client that explicitly disallows gzip/Brotli (q=0) will still receive that encoding. Parse the header and only serve a precompressed file when the requested encoding’s q-value is greater than 0.</comment>

<file context>
@@ -275,37 +275,71 @@ async def serve_public_file(
+) -&gt; Optional[FileResponse]:
+    content_type = mimetypes.guess_type(str(file_path))[0] or &quot;application/octet-stream&quot;
+
+    if &quot;br&quot; in accept_encoding:
+        br_path = file_path.with_suffix(file_path.suffix + &quot;.br&quot;)
+        if br_path.is_file():
</file context>

Suggested change

	if "br" in accept_encoding:
	br_path = file_path.with_suffix(file_path.suffix + ".br")
	if br_path.is_file():
	return FileResponse(
	br_path,
	media_type=content_type,
	headers={"Content-Encoding": "br", "Vary": "Accept-Encoding"},
	)
	if "gzip" in accept_encoding:
	gz_path = file_path.with_suffix(file_path.suffix + ".gz")
	if gz_path.is_file():
	return FileResponse(
	gz_path,
	media_type=content_type,
	headers={"Content-Encoding": "gzip", "Vary": "Accept-Encoding"},
	)
	return None
	encodings: dict[str, float] = {}
	for value in accept_encoding.lower().split(","):
	token = value.strip()
	if not token:
	continue
	parts = token.split(";")
	encoding = parts[0]
	q = 1.0
	for part in parts[1:]:
	if part.strip().startswith("q="):
	try:
	q = float(part.split("=", 1)[1])
	except ValueError:
	q = 0.0
	encodings[encoding] = q
	if encodings.get("br", 0) > 0:
	br_path = file_path.with_suffix(file_path.suffix + ".br")
	if br_path.is_file():
	return FileResponse(
	br_path,
	media_type=content_type,
	headers={"Content-Encoding": "br", "Vary": "Accept-Encoding"},
	)
	if encodings.get("gzip", 0) > 0:
	gz_path = file_path.with_suffix(file_path.suffix + ".gz")
	if gz_path.is_file():
	return FileResponse(
	gz_path,
	media_type=content_type,
	headers={"Content-Encoding": "gzip", "Vary": "Accept-Encoding"},
	)
	return None

[github-actions]

This PR is stale because it has been open for 14 days with no activity.

[asvishnyakov]

@github-actions Leave it for now, I'll review in a few days