Let the location stream say why it has no fix

[RISCfuture]

The nearest-airport picker is the diversion path, and a pilot could get stuck on its
"Location Access Needed" screen until the view was torn down.

CoreLocationStreamer.init requested authorization eagerly, _start() hit
case .notDetermined: and returned with no resume path, and the only thing that could
have resumed it was locationManager(_:didChangeAuthorization:) — the pre-iOS-14
selector, which the modern SDK never calls. It was dead code. NearestView compensated
with two overlapping workarounds: a didBecomeActiveNotification handler and a 1 Hz
Timer.publish polling authorizationStatus on the main thread, each constructing a
throwaway CLLocationManager to read a status the app had no other way to learn.

Key design

Core Location already reports all of this on the updates themselves. CLLocationUpdate
carries authorizationRequestInProgress, authorizationDenied,
authorizationDeniedGlobally, authorizationRestricted and locationUnavailable (all
iOS 18; the floor here is 26), and per Configuring your app to use location services it
requests authorization on its own when iteration over the stream begins. Those flags
become a LocationAvailability the view switches on, so the prompt resolves in place.

What that retires: the eager requestWhenInUseAuthorization(), the CLLocationManager,
its delegate extension, the authorization switch, the inert desiredAccuracy assignment
that liveUpdates() never consulted, and both polls.

apply(_:) resolves a refusal first and only calls an update .available once a fix
actually arrives, so availability stays nil — a spinner, not an empty list — while
Core Location is still acquiring. insufficientlyInUse folds into .locationUnavailable;
accuracyLimited deliberately does not, because a coarse fix is ample for a 50 NM search.
No CLServiceSession (it is API_UNAVAILABLE(macos)) and no CLRequireExplicitServiceSession.

The subtlety worth catching in review

Deleting the didBecomeActiveNotification handler would have cost the one thing it was
also quietly doing: noticing that someone granted access in Settings and came back.
Without a replacement this would have traded one stuck screen for another. A scenePhase
change gated on a refusal now restarts the stream — one hook where there were two
polls, and it fires only when the state it repairs is actually present.

Also

• The Nearest tab no longer hides itself. AirportPicker gated it on
  CLLocationManager.locationServicesEnabled(), a blocking call that needed a detached
  task to stay off the main thread. .authorizationDeniedGlobally now explains the
  situation instead of vanishing the tab. (The app never used significant-location
  monitoring, the gate's other condition.)
• "Denied" is three situations, not one — this app refused, Location Services off
  device-wide, or a restriction from Screen Time or device management — and only the first
  is fixable at the Settings page the button opens. LocationDeniedView now says which,
  and hides the button where it cannot help.
• ContentView built a fresh streamer on every body evaluation, which would have reset
  the new state continuously. The environment default is already a single shared instance.
• That exposed a start/stop imbalance. NearestAirportViewModel started the streamer
  and never stopped it, and locationUpdates()'s self-start could drive the listener count
  negative — so the GPS ran for the life of the process after one visit to the tab.
  Subscribing now is the listener, and the view model can be cancelled. A release that
  arrives before its acquire (a view cancelled inside one runloop turn) is ignored
  rather than counted, since a tally below zero could never climb back to one and would
  wedge the stream permanently — a failure mode a sibling app of mine hit in production.
• Generate_Screenshots.swift waited 5 s for a springboard permission alert that only ever
  appeared because of the eager request from ContentView.body; that flow never opens the
  Nearest tab, so the block is gone.
• LocationError is deleted (its one case is subsumed, and it never conformed to
  LocalizedError as CLAUDE.md requires); the DocC topic list is updated to match, which
  matters because docbuild runs with warnings-as-errors.

Normalized with its siblings

This app reads location the same way as two sibling apps of mine, and they had diverged.
Two changes close that:

• liveUpdates(.airborne) — the configuration tuned for aircraft-rate motion, which both
  siblings already pass. The nearest-airport picker is the diversion path; it is used in flight.
• A UI-test seam. LOCATION=<lat>,<lon> and LOCATION-DENIED script a fix or a refusal,
  in the same shape UITestingHelper's weather and NOTAM stand-ins already use, so no UI test
  has to answer a system permission alert. This matters more after this PR, because the Nearest
  tab is now permanently visible and a future test will eventually reach it. The real streamer
  is still built lazily by the environment default, so a test that never opens the picker never
  constructs one.

Three differences from the siblings are deliberate and commented: accuracyLimited is treated
as available here (the fix is only a sort key, never displayed and never fed to a calculation),
serviceSessionRequired is not modelled (it can only be true under
CLRequireExplicitServiceSession, which this app does not adopt), and insufficientlyInUse
folds into .locationUnavailable (this app is foreground when-in-use on a visible screen).

Verification

On iPhone 17 Pro, app freshly installed with location privacy reset:

Check	Result
Prompt at launch	None — it now appears only on opening Nearest, per Apple's guidance
LocationPermissionPromptView reachable	Yes — visible behind the alert, confirming authorizationRequestInProgress fires
Grant → list populates without backgrounding	Yes — OAK, SQL, 1C9 by distance. This is the bug
Leaving the tab	Location indicator clears (it did not before)
Deny	App-specific copy + Open Settings
Grant in Settings, resume same pid	Denied screen replaced by the list — the scenePhase retry

• swift format lint --strict on changed files: clean
• swiftlint --strict: 0 violations (config-deprecation notices only)
• xcodebuild build: succeeded
• xcodebuild test -testPlan "SF50 Shared Unit Tests": 386/386 passed
• xcodebuild docbuild (warnings-as-errors): succeeded
• periphery scan --strict: No unused code detected
• Scripted-fix seam on a privacy-reset simulator: LOCATION=37.7214,-122.2208 populates the
  list with no permission prompt at all; LOCATION-DENIED renders the denied copy.
• Real stream re-verified after the .airborne switch: prompt on opening Nearest, list populates
  on grant.

No new unit tests: CLLocationUpdate has no public initializer, so the flag→availability
mapping cannot be constructed in a test without inventing an indirection that exists only
for the test. The mock now carries a settable availability, and NearestView gained
previews for the awaiting-permission and denied states.

🤖 Generated with Claude Code

https://claude.ai/code/session_01XgsEB3UyjyDLFn5duGQsSn