Allow callers to override smart_dialer_config.yml

[myleshorton]

Summary

Follow-up to #34. Lets callers replace the embedded smart_dialer_config.yml so a custom StreamDialer plumbed via WithStreamDialer is actually exercised by the smart strategy.

Why

The embedded config lists system: {} first under DNS. When the Outline-SDK strategy picks the system resolver (which it does whenever the probe path doesn't fail), it enforces this check at smart/stream_dialer.go:350:

if resolver == nil {  // resolver == nil means "system: {}" was selected
    if _, ok := f.StreamDialer.(*transport.TCPDialer); !ok {
        return nil, fmt.Errorf("cannot use system resolver with base dialer of type %T", f.StreamDialer)
    }
}

So any caller that supplies a StreamDialer that isn't exactly *transport.TCPDialer — e.g. radiance's bypass dialer, which is a FuncStreamDialer wrapping bypass.DialContext — sees the smart dialer fail at construction. findFallback is then called and errors out with "no fallback was specified" because the kindling config has no FALLBACK section.

Semantically this constraint is correct: system: {} uses the OS resolver, which routes through OS routing tables. For radiance, that means through its own VPN TUN — defeating the entire purpose of bypass. The strategy's type check is honest: "if you're using system DNS, you can't also be doing custom transport routing."

The fix is to let callers swap in a config that omits system: {} (using DoH/DoT entries that go through the StreamDialer) when they pass a custom dialer.

Changes

• WithSmartDialerConfig([]byte) Option — overrides the embedded YAML for the WithProxyless path. Order-independent with the other dialer options (same deferred-construction pattern as Allow callers to plug a custom dialer into the smart strategy #34).
• NewSmartHTTPTransportWithConfig(...) — same override for the standalone helper used by radiance/kindling/smart. NewSmartHTTPTransportWithDialer is preserved (delegates to the new helper with nil config).
• Empty-config validation matching the rest of the option family.
• Test coverage:
  • ProxylessConfigOrderIndependent — config supplied before and after WithProxyless reaches newSmartDialerFn.
  • WithSmartDialerConfig_Empty_ReturnsError — nil and empty []byte both rejected at option time.

Test plan

• go test ./... passes (existing ProxylessDialerOrderIndependent test updated for the new newSmartDialerFn signature)
• Radiance branch using NewSmartHTTPTransportWithConfig + a system-less YAML resolves the smart strategy through the bypass dialer — to be verified once this lands and radiance bumps the dep

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR adds support for overriding the embedded smart dialer YAML config so callers using custom dialers can avoid the default system: {} resolver path.

Changes:

• Adds WithSmartDialerConfig([]byte) for WithProxyless.
• Adds NewSmartHTTPTransportWithConfig(...) for standalone smart transport construction.
• Updates tests for deferred config plumbing and empty config rejection in the option path.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
kindling.go	Adds smart dialer config plumbing through options and standalone transport helper.
kindling_test.go	Updates smart dialer test hook signature and adds config-order/empty-config tests.

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