Flight-track client defaults to MockClient and silently disables track history unless env is set

[tg12]

Summary

The client flight-track hook defaults to MockClient unless VITE_FLIGHT_PROVIDER is explicitly set to opensky. In that default branch, track history is unavailable because MockClient.track() always returns null.

Evidence

• client/src/modules/flights/hooks/useFlightTrack.ts#L7-L8 selects new MockClient() unless VITE_FLIGHT_PROVIDER === 'opensky'.
• client/src/core/providers/mock.client.ts#L37-L40 implements track() as return null.
• The fallback warning in the hook only logs and returns null, so the UI can degrade silently depending on environment configuration.

Why this matters

• A missing or mis-set client env var changes the frontend from live provider mode to mock mode.
• Track-history functionality can appear broken or absent even while the rest of the map renders, making the failure easy to miss.
• This creates environment-dependent behavior that is not obvious from the UI.

Attack or failure scenario

A deployment omits VITE_FLIGHT_PROVIDER or uses a non-opensky value. Snapshot and tracking behavior diverge: parts of the flight UI rely on mock data assumptions, and track history silently resolves to null for every aircraft.

Root cause

Provider selection is driven by a fragile client-side env gate with a mock implementation as the default branch.

Recommended fix

1. Make production provider selection explicit and fail closed when the configured provider is invalid.
2. Do not default to a mock provider in production builds.
3. Surface provider mode visibly in the UI or diagnostics.
4. Add tests for provider selection and invalid env configuration.

Acceptance criteria

• Production builds cannot silently default to MockClient.
• Invalid or missing provider config produces explicit failure or warning state.
• Track-history availability is deterministic across environments.

Suggested labels

• bug
• architecture
• production-readiness

Severity

High — a configuration slip can silently put the client on mock behavior and break track history without obvious operator feedback.

Confidence

Confirmed — the hook defaults to MockClient, and that client's track() implementation is a hardcoded null.