Wire peer.Client into LocalBackend (Share My Connection PR 2/4)

[myleshorton]

Stacks on #458 (peer module + portforward). Targets fisk/peer-module; rebase onto main when #458 merges.

What's wired up

Dart toggle → FFI (PR 3) → backend.PatchSettings({PeerShareEnabledKey: true})
                                                          │
                                                          ▼
                                                  applyPeerShare(true)
                                                          │
                          ┌───────────────────────────────┼────────────────────────┐
                          ▼                               ▼                        ▼
                  peer.Client.Start             rollback setting            emit peer.StatusEvent
                   (UPnP → register             on Start failure           (subscribed by IPC SSE)
                    → sing-box → hb)

• common/settings: PeerShareEnabledKey (bool).
• peer.Client: emits peer.StatusEvent on Start success and Stop completion.
• backend.LocalBackend:
  • new peerController interface seam (so tests can inject a fake)
  • constructed in NewLocalBackend with kindling.HTTPClient() + common.GetBaseURL() + the device ID
  • new applyPeerShare helper, called from PatchSettings dispatch
  • new PeerStatus() accessor for the IPC handler
• ipc: GET /peer/status (snapshot) + GET /peer/status/events (SSE).

Three subtle behaviors worth flagging

1. Toggle calls are serialized by peerToggleMu. Without it, a fast off→on→off could see the second call's "already active" rollback racing the third call's Stop, and the persisted setting could end up disagreeing with runtime state.
2. Start runs under a 30s deadline. UPnP discovery + register + box build is normally single-digit seconds; the deadline caps the worst case so a hung router can't block the IPC toggle response indefinitely.
3. Auto-resume + Close synchronize via peerWG. If the user left the toggle on across restarts, LocalBackend.Start() resumes the session in a goroutine. Without the WG, a Close() racing the resume could cancel r.ctx mid-Start, leaving a registered route + open box behind on the cloud side.

Rollback semantics

Mirroring setBlockAds: write the setting, try the side effect, on failure roll the setting back AND return the error so the Dart toggle can re-render to "off" with a user-facing error. Stop errors are logged but not surfaced — the user wants the session off, and a partial teardown shouldn't keep the toggle on.

Test coverage

• TestApplyPeerShare_StartsOnEnable / _StopsOnDisable / _StartFailureRollsBackSetting
• TestResumePeerShare_NoopWhenSettingOff / _StartsWhenSettingOn
• TestClose_WaitsForResumeAndStopsActivePeer — exercises the WG race using a slowStartFake that blocks Start on a gate channel; asserts Close cannot return until the gate is released
• TestPatchSettings_PeerShareDispatches — PatchSettings({PeerShareEnabledKey: true}) → fake.startCalls == 1 (catches a typo'd dispatch key)
• TestClient_StatusEventEmittedOnStartAndStop in peer/ — Subscribe and assert both edges fire with the expected Status

go test -race ./peer/... ./backend/... ./common/settings/... ./ipc/... and golangci-lint run --new-from-rev=origin/main are both clean.

Out of scope (PR 3-4)

• PR 3 (lantern-core): setPeerProxyEnabled FFI export + ffigen regen.
• PR 4 (lantern): Dart setPeerProxy rewrite mirroring setBlockAds, optional status indicator using the new SSE.

Test plan

• go test -race ./peer/... ./backend/... ./common/settings/... ./ipc/...
• golangci-lint run --new-from-rev=origin/main
• Manual end-to-end deferred until PR 4 (when the Dart toggle lands)

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR wires the new peer.Client into LocalBackend so the persisted “Share My Connection” setting can start/stop the peer session and expose its state over IPC. It fits the second step of the stacked peer-share rollout by connecting the already-built peer module to backend settings and status reporting.

Changes:

• Added PeerShareEnabledKey and backend logic to start, stop, resume, and report peer-share state.
• Emitted peer lifecycle status events from peer.Client and exposed snapshot/SSE IPC handlers for that state.
• Added backend and peer tests covering enable/disable, resume-on-start, shutdown coordination, and status-event emission.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
peer/peer.go	Emits peer status events on successful start and stop.
peer/peer_test.go	Adds tests for peer status event emission.
ipc/server.go	Adds /peer/status and /peer/status/events IPC endpoints.
common/settings/settings.go	Introduces persisted peer_share_enabled setting key.
backend/radiance.go	Wires peer client construction, toggle handling, auto-resume, shutdown, and status accessors into LocalBackend.
backend/radiance_test.go	Adds tests for peer-share apply/resume/close/dispatch behavior.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.