feat: add ConfigRequest.Capabilities for client capability negotiation

[myleshorton]

What

Add a Capabilities []string field to ConfigRequest and the first capability constant:

CapabilityNonSelectableOutbounds = "non_selectable_outbounds"

The client advertises capabilities it supports; the server enables optional behavior only for clients that report the matching capability — capability negotiation instead of version sniffing.

Why

lantern-cloud gates its new proxyless rule-set detour (an infrastructure outbound sent via ConfigResponse.NonSelectableOutbounds) on whether the client will treat that outbound as non-selectable. A client that doesn't (pre–getlantern/radiance#549) would let its URLTest auto-select the low-latency direct+frag dialer and route traffic through it — exposing the real IP.

The current gate is a hardcoded client-version floor (9.1.14-beta). A capability is strictly better:

• Correct signal. "Client honors NonSelectableOutbounds" is exactly the property that matters — not a version number that has to be kept in sync with whichever release happened to carry #549 (and breaks across forks/prereleases).
• Generalizes. #549 honors any tag in NonSelectableOutbounds. Gating on this one capability covers every future infra outbound with no new token and no client release — the whole point of NonSelectableOutbounds. Gating on "proxyless" specifically would need a new token per outbound.
• Symmetric. The client says "I understand non_selectable_outbounds" ↔ the server sends non_selectable_outbounds.

Note: the client already advertises the outline outbound type ("outline") via its auto-derived supported-protocols list, but that predates #549 — so it can't be used as the gate (old clients report it too). This new, explicitly-added capability is the safe signal.

Consumers

• radiance — advertises CapabilityNonSelectableOutbounds in config/fetcher.go (added in the same code that honors NonSelectableOutbounds, so advertising it ⟺ handling it safely).
• lantern-cloud#2936 — gates the proxyless detour on slices.Contains(req.Capabilities, common.CapabilityNonSelectableOutbounds), replacing the version floor.

Testing

go test ./... — TestCapabilitiesRoundTrip (key present, value round-trips, nil + empty-slice both omitted). Build + gofmt clean.

🤖 Generated with Claude Code

https://claude.ai/code/session_01WGpKfgkbfdJwwsTaouMDoR

Summary by CodeRabbit

• New Features

  • Added client capability support for configuration negotiation.
  • Introduced a capability flag for handling non-selectable outbounds, helping clients and servers agree on outbound behavior.
  • Added a new request field to send capability information during configuration requests.

• Tests

  • Added coverage to verify capability data is preserved through JSON serialization and omitted when empty.

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 8f594136-a9a4-4594-bb89-3832fe3949bd

📥 Commits

Reviewing files that changed from the base of the PR and between 57aaafd and de5009f.

📒 Files selected for processing (2)

• types.go
• types_test.go

📝 Walkthrough

Walkthrough

This PR adds a new CapabilityNonSelectableOutbounds constant and a Capabilities []string field to the ConfigRequest struct in types.go to support capability-based negotiation, along with a new test verifying JSON round-trip serialization behavior including omitempty handling.

Changes

Capabilities support

Layer / File(s)	Summary
Capability constant and struct field types.go	Adds CapabilityNonSelectableOutbounds constant and a Capabilities []string field (JSON tag capabilities,omitempty) to ConfigRequest, reordering fields and adding clarifying comments.
Round-trip serialization test types_test.go	Adds TestCapabilitiesRoundTrip verifying Capabilities serializes correctly and is omitted from JSON when nil or empty.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Related PRs: None found.

Suggested labels: enhancement

Suggested reviewers: None specified.

🐰 A whisker-twitch, a new field appears,
Capabilities hop in, dispelling version fears,
Non-selectable paths stay tucked away,
JSON round-trips tested — omitempty saves the day!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: adding ConfigRequest.Capabilities for client capability negotiation.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fisk/config-capabilities

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[Copilot]

Pull request overview

Adds explicit client capability negotiation to the shared common types so servers can safely enable optional behaviors based on what the client reports (instead of relying on version floors), starting with support for ConfigResponse.NonSelectableOutbounds.

Changes:

• Add ConfigRequest.Capabilities []string for client-advertised capabilities.
• Introduce CapabilityNonSelectableOutbounds = "non_selectable_outbounds" constant with documentation.
• Add a JSON round-trip test covering presence and omitempty behavior for Capabilities.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
types.go	Adds ConfigRequest.Capabilities plus the first capability constant used for negotiation.
types_test.go	Adds TestCapabilitiesRoundTrip to verify serialization/deserialization and omitempty omission behavior.

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[myleshorton]

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

[myleshorton]

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Full review finished.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.