env: forward shell RADIANCE_* vars from main app to system extension

[myleshorton]

Summary

macOS/iOS system extensions are sandboxed subprocesses launched by launchd, so they don't inherit the shell environment of the main Lantern app. That made it impossible to point the tunnel at staging with RADIANCE_ENV=staging Lantern — the main process hit staging, but the extension (which actually fetches /config-new) kept reading its ldflags-baked RADIANCE_VERSION and hitting prod constraints.

This PR wires the main app's RADIANCE_* env through to the extension:

• utils.Opts.EnvOverrides (JSON string — gomobile doesn't marshal maps) carries shell-set vars into gomobile calls.
• lantern-core/mobile.StartIPCServer and lantern-core/init_mobile.createClient parse the JSON and pass via backend.Options.EnvOverrides, which radiance applies with os.Setenv before common.Init reads them.
• Main-app Swift (macos/Runner/VPN/VPNManager.swift, ios/Runner/VPN/VPNManager.swift) filters ProcessInfo.environment for RADIANCE_*, serializes as JSON, and attaches to startVPNTunnel(options:) as netEx.EnvOverrides.
• Extension Swift (macos/PacketTunnel/..., ios/Tunnel/...) reads netEx.EnvOverrides out of startTunnel(options:) before MobileStartIPCServer, stashes it, and attaches to every subsequent opts() call.

Radiance bump (commit d7c8d9f)

Pulls in getlantern/radiance#429 (merged to refactor as 97ff9ac), which adds backend.Options.EnvOverrides plus the Unbounded signaling fix (direct-transport + streaming wrapper to freddie) and the transitive bumps of broflake and lantern-box. Pins qpack to v0.5.1 to match radiance and lantern-box.

Test plan

• `go build ./...` passes
• End-to-end verified 2026-04-21: desktop Lantern built against this branch + radiance Dashboard never comes up and no message appears in IE6 #429 connects through widget → egress; consumer state progresses to signaling-complete, datachannel opens, traffic flows.
• Build Lantern, launch with `RADIANCE_VERSION=9.1.1 RADIANCE_ENV=staging Lantern`, verify system extension's `X-Lantern-App-Version` header is 9.1.1 and traffic hits `api.staging.iantem.io`
• iOS parity

[Copilot]

Pull request overview

This PR forwards RADIANCE_* environment variables from the macOS/iOS host app into the sandboxed NetworkExtension process by serializing them as JSON and threading that string through the NETunnelProvider options and into lantern-core/radiance backend options.

Changes:

• Add utils.Opts.EnvOverrides (JSON string) for carrying RADIANCE_* overrides through gomobile.
• Pass netEx.EnvOverrides from the host app VPN managers into the extension providers and attach it to UtilsOpts on each gomobile call.
• Decode the JSON on the Go side and plumb it into backend.Options.EnvOverrides.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
macos/Runner/VPN/VPNManager.swift	Collect/encode RADIANCE_* env vars and include them in startVPNTunnel(options:).
ios/Runner/VPN/VPNManager.swift	Same as macOS host app: forward RADIANCE_* as JSON via tunnel start options.
macos/PacketTunnel/SingBox/ExtensionProvider.swift	Read netEx.EnvOverrides early and attach it to UtilsOpts for gomobile calls.
ios/Tunnel/SingBox/ExtensionProvider.swift	Same as macOS extension: capture/propagate netEx.EnvOverrides into UtilsOpts.
lantern-core/utils/common.go	Add EnvOverrides field to utils.Opts (JSON map string).
lantern-core/mobile/mobile.go	Parse JSON overrides and pass into backend.Options.EnvOverrides for IPC server backend creation.
lantern-core/init_mobile.go	Parse JSON overrides and pass into backend.Options.EnvOverrides for IPC client creation.

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[myleshorton]

Note this only solves this issue on MacOS and iOS. We'd need a followup PR(s) for other platforms.

[myleshorton]

Follow-up: unified IPC /bootstrap mechanism

Tracking in getlantern/engineering#3251.

This PR ships env propagation for macOS and iOS only because those are the sandboxed-system-extension platforms that actually need it today. It leaves gaps on Windows/Linux (lanternd runs as a service and ignores opts.EnvOverrides on the desktop path) and Android (backend plumbing compiled in, but no Kotlin/Java code populates it).

A file-based unified mechanism was considered and rejected — on macOS the main app and the network extension run as different users with incompatible sandbox restrictions, so a shared file is fragile.

The follow-up epic proposes replacing the Swift + gomobile + utils.Opts.EnvOverrides stack with a single IPC /bootstrap handshake that every platform uses identically:

Phase 1: daemon/extension opens IPC socket, blocks common.Init
Phase 2: GUI sends POST /bootstrap { env_overrides: {...} }
         → daemon applies os.Setenv → common.Init → ready

Merging this PR first unblocks the staging workflow immediately; the unified path lands as its own series on top.

[myleshorton]

FYI the radiance bump has been split out into #8686 so the Unbounded signaling fix can land without waiting on the env-propagation design discussion. This PR (#8683) continues to carry just the Swift/gomobile env-forwarding plumbing; it can be merged or left open independently of #8686.