feat: say why a browser start failed instead of just timing out

[nathanfallet]

Problem

When a browser never opens its debug port, all you get is a 30s wait and a generic FailedToConnectToBrowserException. There is no way to tell why it failed.

The reason is in fact already known — testConnection() catches the error on every attempt — but it is logged at debug level, so it never reaches production logs:

} catch (e: Exception) {
    logger.debug("Could not start: ${e.message}")
    false
}

And the info branch that gives up says it is "reading error" while the block that would actually read it is commented out.

Changes

1. Report the failure. start() now logs at error level: the port it waited on, how long, the process id, whether that process is still alive, and the last connection error.

Browser never opened its debug port on 127.0.0.1:52475 after 30500ms
  (pid=6220, alive=true). Last connection error: ConnectException: Connection refused

That last field is the useful one — it separates two causes that were indistinguishable:

• connection refused → nothing ever listened, the browser did not open the port;
• timeout / unexpected response → something answers, so another process holds it.

And alive=false would say the browser process died outright rather than hanging.

2. Discard the browser's stdio instead of piping it. Nothing reads those pipes today, and a pipe nobody drains fills up — once the OS buffer is full (a few KB on Windows) the browser blocks on its next write. If that happens before it opens its debug port, the port never opens and the start times out with no visible cause. This is also why the "read the error stream" block was commented out with "seems to block indefinitely on CI": reading a pipe that was never drained can hang.

Notes

No API change; both are internal. :core:jvmTest passes.

:core:build fails on kotlinStoreYarnLock here, as it does on main — unrelated.

[codecov]

Codecov Report

❌ Patch coverage is 6.66667% with 14 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../kotlin/dev/kdriver/core/browser/DefaultBrowser.kt	12.50%	7 Missing ⚠️
...ain/kotlin/dev/kdriver/core/browser/Process.jvm.kt	0.00%	7 Missing ⚠️

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