perf(frontend): migrate cn to cnfast (#2527)

* perf(frontend): migrate cn to cnfast

Swap the vendored `cn` (redpanda-ui/lib/utils.tsx) from `twMerge(clsx(...))`
to cnfast — an optimized adaptation of clsx + tailwind-merge with
byte-identical output and the same `(...inputs: ClassValue[])` signature.
No call site changes.

- json-view: switch its direct `import clsx from 'clsx'` to cnfast's `clsx`
  export so clsx can be dropped as a direct dependency
- deps: drop clsx + tailwind-merge, add cnfast (class-variance-authority unchanged)
- bunfig: temporarily exclude cnfast from the 72h release-age gate
  (0.0.8 published 2026-06-22; remove the exclude once it ages past the gate)
- vendored redpanda-ui/lib/utils.tsx marked [upstream]; mirrors ui-registry #220
  and reconciles on the next registry sync

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* build(frontend): pin cnfast to exact 0.0.8

Address PR review: drop the caret so the intent is explicit. `^0.0.8`
already resolves to only 0.0.8 under semver (caret locks the patch on
0.0.x), so this is a no-op in resolution — just clearer for a pre-1.0
dependency.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: malinskibeniamin

frontend/bun.lock

@@ -1,5 +1,8 @@
 [install]
 minimumReleaseAge = 259200 # 72h supply-chain publish delay
+# Temporary: cnfast@0.0.8 (the `cn` migration) was published 2026-06-22, below
+# the 72h gate; remove from this list once it ages past the gate (~2026-06-25).
+minimumReleaseAgeExcludes = ["cnfast"]
 save = true
 saveTextLockfile = true
 print = "yarn"

frontend/bunfig.toml

@@ -97,8 +97,8 @@
     "ai": "^6.0.168",
     "array-move": "^4.0.0",
     "class-variance-authority": "^0.7.1",
-    "clsx": "^2.1.1",
     "cmdk": "^1.1.1",
+    "cnfast": "0.0.8",
     "date-fns": "^4.3.0",
     "dexie": "^4.2.1",
     "dotenv": "^17.2.3",
@@ -138,7 +138,6 @@
     "sql-formatter": "^15.8.1",
     "stacktrace-js": "^2.0.2",
     "streamdown": "^2.5.0",
-    "tailwind-merge": "^3.5.0",
     "tailwindcss": "^4.2.4",
     "tokenlens": "^1.3.1",
     "use-stick-to-bottom": "^1.1.1",

frontend/package.json

@@ -1,10 +1,14 @@
 import { cva } from 'class-variance-authority';
-import { type ClassValue, clsx } from 'clsx';
+import { type ClassValue, cn as cnfast } from 'cnfast';
 import React from 'react';
-import { twMerge } from 'tailwind-merge';
 
+/**
+ * [upstream] `cn` migrated to cnfast ahead of ui-registry PR #220 (byte-identical
+ * output, same `(...inputs: ClassValue[])` signature). Drop this marker on the
+ * next registry sync once #220 is released.
+ */
 export function cn(...inputs: ClassValue[]) {
-  return twMerge(clsx(inputs));
+  return cnfast(...inputs);
 }
 
 export function wrapStringChild(

frontend/src/components/redpanda-ui/lib/utils.tsx

@@ -1,6 +1,6 @@
 /** biome-ignore-all lint/suspicious/noArrayIndexKey: part of JSONNode implementation */
 /** biome-ignore-all lint/a11y/useKeyWithClickEvents: part of JSONNode implementation */
-import clsx from 'clsx';
+import { clsx } from 'cnfast';
 import { CopyButton } from 'components/redpanda-ui/components/copy-button';
 import { memo, useMemo, useState } from 'react';