fix(browser-control): bind the daemon on the main thread so sessions can start

[SandroHub013]

Issue for this PR

Closes #235

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Bun.WebView's chrome backend — the backend on every platform except macOS — throws
Bun.WebView with backend "chrome" is only available on the main thread when it is constructed off
the main thread. It throws at construction, so pointing it at an already-running Chrome through a
DevTools URL does not avoid it either.

The compiled binary hosts the browser-control daemon in-process, and nikcli runs sessions on a
worker thread, so that daemon bound its socket on a worker. list worked because it creates no
view; every start failed because it creates one. macOS was unaffected — it defaults to the
webkit backend — which is why the report was Windows-only.

The daemon no longer hosts itself on a worker. It delegates binding to the host's main thread via
setMainThreadDaemonHost(), and the worker then speaks to it over the same socket as any other
client, so views are created on a thread that is allowed to have them. nikcli registers that hook
over the RPC channel the TUI worker already has. With no host registered, ensureDaemon now fails
with a message naming the constraint instead of binding a daemon that cannot start a session.

createWebView() carries the same check, so any other caller gets an error with a fix in it rather
than Bun's bare message.

How did you verify your code works?

First reproduced it, on Windows 11 / Bun 1.4.0, by hosting the daemon on a worker and calling
start:

{"ok":false,"error":"Bun.WebView with backend \"chrome\" is only available on the main thread"}

Then, with hosting delegated to the main thread and the session driven from a worker through the
same Rpc util the nikcli wiring uses:

plan: delegate
main thread hosts daemon
worker start result: {"name":"page-1","url":"data:text/html,<title>via-worker</title>","status":"running", ...}

• bun test in packages/browser-control: 10 pass, including the new test/worker-hosting.test.ts,
  which covers the hosting rule and drives a main-thread-hosted daemon from a worker
• bun typecheck at the repo root: 35/35 packages
• bun src/cli.ts start --url https://example.com --viewport 1024x768, plus list and shutdown,
  behave as before — the CLI spawns its own daemon process, which was always on a main thread
• Built the binary from this branch (script/build.ts --single) and confirmed it boots. Its TUI
  smoke fails locally with EPERM: mkdir under the harness's synthetic HOME, but a binary built
  from live-main in the same tree fails identically, so that is a local build issue and not this
  change.

To confirm by hand: run start from a compiled binary's TUI on Windows or Linux. It returned the
WebView error before and returns session info now.

Screenshots / recordings

Not a UI change.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

Note for reviewers

The nikcli half touches the TUI worker/thread wiring (7 and 11 lines). If the delegation hook
belongs somewhere other than the existing Rpc.emit channel, say so and I will move it.

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[github-actions]

lgtm

[SandroHub013]

/nikcli review this

[github-actions]

Unable to connect. Is the computer able to access the url?

github run

[nikomatt69]

⚠️ CI Validation Failed

@nikomatt69 — validation failed on this commit.

Detail	Value
Failed step	Unknown step
Autofix status	⏭️ Autofix skipped
Run	View full logs

Failure Summary

(no summary available)

Please inspect the full Actions logs for complete output. Do not share this comment publicly — it may contain redacted paths.