fix(launcher): caller flags override ours; report the engine we actually run

[ralyodio]

Two launcher fixes that came out of chasing "TronBrowser got slow today."

1. Caller flags were silently ignored

FLAGS is placed before "$@", and Chromium honors the first occurrence of a switch. So tron --user-data-dir=/tmp/scratch produced two --user-data-dir flags and the browser opened the default profile anyway. A duplicated --user-data-dir can also fault the process — that is what a local SIGSEGV traced back to.

Now any switch of ours that the caller also passes is dropped, so theirs is the only one left.

--enable-features / --disable-features merge rather than being replaced — they're comma-separated lists, and dropping ours wholesale would re-enable the Manifest V2 kill switch (uBlock Origin stops loading) just because someone wanted one unrelated feature.

The dedupe deliberately runs before the Tor block. Tor's proxy flags are a guarantee, not a preference; appending them afterward keeps them first on the command line, where a caller-supplied --proxy-server cannot displace them.

2. Nothing recorded which engine actually ran

TronBrowser ships no engine — apps/desktop/launcher/tronbrowser drives whatever Ungoogled Chromium is on the system, and the bundled-binary branch ($DIR/chrome) is still a stub. On Linux that is usually the Flathub Flatpak, which updates itself.

So a Flathub push can change every user's browser overnight while TronBrowser's own history shows nothing, and the resulting regression in scrolling, video or compositing arrives as a TronBrowser bug against a release that touched none of it. There was no way to tell from the logs.

The launcher now prints the engine version and source on every launch, and when it differs from last launch says so explicitly:

TronBrowser: the browser engine CHANGED since your last launch.
  was: 141.0.7390.65 — flatpak io.github.ungoogled_software.ungoogled_chromium a1b2c3d4e5f6
  now: 149.0.7827.196 — flatpak io.github.ungoogled_software.ungoogled_chromium 9f8e7d6c5b4a
  TronBrowser did not do this — your system updated Chromium underneath it.
  If the browser now feels different (scrolling, video, GPU), start here.

Tests

The launcher had none — it is the one piece of TronBrowser with no compiler behind it. Added apps/desktop/test/launcher.test.ts, which runs the real script against a stub browser that records its argv.

• 8 new tests pass; 135 tests pass across apps/desktop
• Verified the new tests fail against the pre-fix launcher — it emits two --user-data-dir and two --enable-features
• sh -n and dash -n clean (shellcheck not installed here)

extensions/ai-sidebar/moshpit-drift.test.js fails to load in a fresh worktree because @moshcoder/moshpit-resolve isn't installed there. Pre-existing and unrelated; it resolves in a checkout that has run pnpm install.

Not included

This does not explain the specific slowdown that prompted it — that still points at a Flatpak engine update, which is being confirmed separately. These two fixes are correct regardless of what that turns up.

🤖 Generated with Claude Code

[github-actions]

vu1nz Security Review

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