claude-desktop-debian/docs/learnings/patching-minified-js.md

Patching minified JavaScript

Hard-won lessons from maintaining a long-lived patch suite against an actively re-minified upstream. Each section names a failure mode and the fix.

The verification recipes below use claude-desktop-debian-specific incantations (Claude-Setup.exe, nupkg extraction, build.sh --build appimage); substitute your own project's fetch/extract/build commands as needed.

Capturing identifiers: \w doesn't match $

JS identifiers allow $ and _; minifiers freely emit names like $e, C$i, g$x. The character class \w is [A-Za-z0-9_] — it does not match $. A (\w+) against $e captures the suffix e and returns a name that doesn't exist in the file. The failure is silent: regex matches, downstream sed runs against a truncated name, asar ships broken JS. Three recurrences (PRs #253, #421, #555) before the convention stuck.

Use [$\w]+ (repo convention; [\w$]+ is equivalent). Strict superset of \w+, so pre-$ versions still match. Live at cowork.sh:484-502:

const fsMatch = region.match(/([$\w]+)\.existsSync\(/);

The beautified false-negative trap

Testing a regex against build-reference/ is not verification. The beautified copy has whitespace the regex doesn't account for.

During PR #555, both \w+ and [\w$]+ tested false against the beautified file. Shipped minified bytes:

await new Promise(n=>setTimeout(n,g$x))

Beautified copy:

await new Promise((n) => setTimeout(n, g$x))

await new Promise\(([\w$]+)=>\s*setTimeout\(\1,\s*([\w$]+)\)\) fails the beautified version on the parens and spaces around =>. Always close the loop against shipped bytes.

Whitespace tolerance: \s* vs [ \t]*

\s matches newlines. A \s*-padded pattern is a license to span across structural boundaries the original line layout meant to keep apart — usually fine on minified bytes (no newlines to span), much looser on beautified.

Use [ \t]* when the intent is "spaces but stay on this line." Reserve \s* for crossing structural boundaries on purpose. The existing cowork.sh patches mix both — \s* where the surrounding context is bounded enough that newline-spanning is harmless, and literal token sequences (",b: etc.) when stricter adjacency is required.

Replacement-string escaping: \1, &, $1

A regex can match correctly and still produce corrupted output because the replacement string has its own metacharacters. Match debugging shows green; the asar still ships broken bytes. Three flavors:

sed & — the entire match. sed 's/foo/&_suffix/' is fine (foo_suffix). sed 's/foo/literal_&_dollar/' accidentally interpolates the match (literal_foo_dollar). Escape with \& if you want a literal ampersand:

sed 's/foo/literal_\&_dollar/'   # → literal_&_dollar

sed \1 — backreferences in the replacement. These work as expected in BRE/ERE. The footgun is the pattern side: in BRE, $ is the end-of-line anchor, so a literal $ in the search pattern needs \$. _common.sh:25 does exactly this for electron_var, which can be $e on newer upstream:

electron_var_re="${electron_var//\$/\\$}"

That escaping is for the sed pattern, not its replacement.

JS String.prototype.replace: $1, $&, $$ — the JS replacement DSL is its own thing. $& is the whole match; $1..$9 are capture groups; $$ is a literal $. Plain $ followed by an unrelated char is left alone, but $& and $N get interpolated:

code.replace(/foo/g, '$cost')   // → '$cost' (safe, no special)
code.replace(/foo/g, '$&_x')    // → 'foo_x' ($& = match)
code.replace(/foo/g, '$$cost')  // → '$cost' (escaped)

If the replacement is an injected JS snippet that happens to contain $1 or $& (template literals, jQuery, regex source), JS will eat them. Use $$ to escape, or build the string with concatenation so $ never sits next to a digit or &.

Idempotency: a re-run must be byte-identical

Without it, CI re-runs and partial builds layer mutations until something breaks visibly. Three patterns:

Re-key the guard to post-rename names. tray.sh:174-180 keys its fast-path guard on the post-rename ${tray_var}.setImage(${electron_var}.nativeImage.createFromPath(${path_var})) sequence, so the second run recognizes its own first-run output.

Negative lookbehind, inline. cowork.sh:102-106 — the (?<!...) prevents a second match against text the first run already wrapped:

const logRe = new RegExp(
    '(?<!\\|\\|process\\.platform==="linux"\\))' +
    win32Var.replace(/[.*+?^${}()|[\]\\]/g, '\\$&') +
    '(\\s*\\?\\s*"vmClient \\(TypeScript\\)")'
);

Explicit code.includes(...) check. cowork.sh:227-230 separates "anchor missing" from "already applied" in the build log:

} else if (code.includes(
    'getDownloadStatus(){return process.platform==="linux"?'
)) {
    console.log('  Cowork auto-nav suppression already applied');
}

PR #436 verified by running the patch twice and diffing the output.

Anchor selection: prefer literals over identifiers

The above sections cover making a patch work on first run. This one covers keeping it working release after release. A patch can apply cleanly today and silently no-op next month.

Minified identifiers churn every release. Developer strings — property names, log messages, IPC channel names — survive minification untouched (true for the upstream bundler used here; a --mangle-props build would invalidate property-name anchors). Anchor on those. A hardcoded minified name silently no-ops the next release; the build log still says "patched."

Three patterns from the suite:

• Quick-window (PR #390, fixing #144). Original patch: s/e.hide()/e.blur(),e.hide()/. When e became Sa, it no-oped. The rewrite anchors on "pop-up-menu" (quick-window.sh:17), the isWindowFocused property name (quick-window.sh:60), and the [QuickEntry] log strings (quick-window.sh:88-91).
• Cowork spawn (PR #436). Anchored on ,VAR.mountConda) (cowork.sh:741) — unique to the 12-arg call path, absent from the 10-arg one-shot. Asserts match count is exactly 1 and bails otherwise (cowork.sh:744), so a future second caller surfaces immediately.
• Tray (PR #515). tray.sh:16 uses the literal "menuBarEnabled" as a position anchor, then captures the surrounding minified identifier (\K\w+(?=\(\)\})) as the actual patch target. Two stages: stable literal → derived identifier. Every other tray name chains off that single dynamic extraction.

The lesson is about finding stable points to anchor on, not about what gets patched. The patch target is usually a minified identifier; the anchor should be a developer string nearby.

Multi-site coordinated patches: surface partial application

Site 1 patches, site 2 misses, the asar ships half-wired. The pattern: each sub-patch sets a per-site boolean flag on success, then a single named WARNING fires if any flag is false:

if (!siteADone || !siteBDone) {
    console.log('  WARNING: <ticket> partial — siteA=' + siteADone +
        ' siteB=' + siteBDone + '; <fallback consequence>');
}

CI greps the build log for WARNING: and fails the build. That catches the half-patched state even when individual sub-patches each log "applied." See cowork.sh:759-763 for a real instance — three-site sharedCwdPath forwarding, daemon fallback if any site misses.

Disambiguating non-unique anchors: lastIndexOf over indexOf

A string anchor can appear in source maps, dead exports, or chunk-merged duplicates alongside the live code. indexOf returns the first; that may be wrong.

cowork.sh:264 uses lastIndexOf(serviceErrorStr) to bias toward appended code. On 1.5354.0 the string occurs once, so the change is a no-op there — the defense is for a future upstream that reintroduces the string in onboarding text or sample data far from the live retry-loop site.

When neither side is reliable, narrow the search region first. cowork.sh:269-276 does this for the ENOENT check, scanning only a 300-character window before the error string.

Verifying a hypothesis before shipping a fix

Pull the pinned URL and SHA from scripts/setup/detect-host.sh, download, verify hash, extract without beautifying, and test the regex against the minified bytes:

url=$(grep -oP "claude_download_url='\K[^']+" \
    scripts/setup/detect-host.sh | head -1)
expected=$(grep -oP "claude_exe_sha256='\K[^']+" \
    scripts/setup/detect-host.sh | head -1)
mkdir -p /tmp/verify && cd /tmp/verify
wget -q -O Claude-Setup.exe "$url"
echo "$expected  Claude-Setup.exe" | sha256sum -c -

7z x -y Claude-Setup.exe -o exe
nupkg=$(find exe -name 'AnthropicClaude-*.nupkg' | head -1)
7z x -y "$nupkg" -o nupkg
npx asar extract nupkg/lib/net45/resources/app.asar app

node -e '
  const fs = require("fs");
  const code = fs.readFileSync(
    "app/.vite/build/index.js", "utf8");
  const re = /await new Promise\(([\w$]+)=>\s*setTimeout\(\1,\s*([\w$]+)\)\)/;
  const m = code.match(re);
  console.log(m ? `MATCH: ${m[0]}` : "NO MATCH");
'

NO MATCH means the regex is wrong. Verifying the SHA defends against stale URL pinning or server-side binary swap.

End-to-end verification (post-build)

Four layers: build log, syntactic validity, asar markers, runtime.

1. Check the patch-count line:

   ./build.sh --build appimage --clean no 2>&1 | tee build.log
   grep -E 'Applied [0-9]+ cowork patches' build.log
   

   Healthy 1.5354.0 build: Applied 12 cowork patches. A lower number, or any WARNING: in the cowork section, is a half-patched asar.

2. node --check on the patched index.js — catches malformed replacements that serialize but don't parse (PR #436 used this in dry-run validation):

   node --check test-build/.../app.asar.contents/.vite/build/index.js
   

3. Static-grep the shipped asar for the 9 cowork markers from PR #555. A verify-cowork-patches.sh helper that automates this is planned (issue #559 D6); prefer it once it lands.

4. Launch the AppImage and check runtime state:

   tail -20 ~/.config/Claude/logs/cowork_vm_daemon.log
   ls -la "${XDG_RUNTIME_DIR}/cowork-vm-service.sock"
   ss -lpx | grep cowork-vm-service.sock
   

   Daemon log should have lifecycle startup and lifecycle listening; socket should exist and be owned by the cowork-vm-service.js process listed by ss.

Cross-references

• tray-rebuild-race.md "Resilience to minifier churn" — prior art for dynamic extraction across a six-variable patch site and the post-rename idempotency-guard pattern.
• plugin-install.md "Getting the Minified Source for Any Shipped Version" — the reference-source.tar.gz release asset gives beautified asar contents of any prior version for diffing. Useful for spotting when an identifier renamed and which version did it.