feat(scarfmon): instrument Nous model catalog + subscription path (beach-ball investigation)

User reported a remote-context beach-ball when opening the model
picker with Nous as the active provider. Existing measure points
showed loadProviders + loadModels at ~315ms each (fast). The
beach-ball must be in the uninstrumented Nous-overlay branch the
picker fires when nous is selected.

Adds four measure points covering every blocking call in that path:

- nous.subscription.loadState (interval, .diskIO) — auth.json read
  via NousSubscriptionService.loadState. Already known to do an SSH
  read; now precisely measurable.
- nous.readCache (interval, .diskIO) — nous_models cache read,
  TWO sequential SSH ops (fileExists + readFile).
- nous.bearerToken (interval, .diskIO) — auth.json read AGAIN inside
  fetchModels. **This is a duplicate read** — loadState already
  parsed the same file moments earlier. Comment-flagged as a
  caching candidate.
- nous.fetchModels (interval, .transport) + .bytes (event) — HTTP
  GET against the Nous /v1/models endpoint with the body byte count
  attached. The most likely beach-ball culprit if the endpoint is
  slow or hung.

After the next capture we'll know which of the four owns the user's
wall-clock; if `nous.bearerToken` shows up alongside
`nous.subscription.loadState` with similar duration, the duplicate
read is also a real cost worth fixing.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scarf/Packages/ScarfCore/Sources/ScarfCore/Services/NousModelCatalogService.swift

@@ -96,6 +96,7 @@ public struct NousModelCatalogService: Sendable {
     /// malformed cache → nil; the loader treats that as "no cache" and
     /// kicks off a fresh fetch.
     public func readCache() -> NousModelsCache? {
+        ScarfMon.measure(.diskIO, "nous.readCache") {
             let transport = context.makeTransport()
             guard transport.fileExists(cachePath) else { return nil }
             do {
@@ -113,6 +114,7 @@ public struct NousModelCatalogService: Sendable {
                 return nil
             }
         }
+    }
 
     private func writeCache(_ cache: NousModelsCache) {
         let transport = context.makeTransport()
@@ -148,6 +150,12 @@ public struct NousModelCatalogService: Sendable {
         // The subscription service already checks for `present`; we
         // re-read the raw token here because we need the actual string,
         // not just a Bool. Mirrors the SubscriptionService parse path.
+        // ScarfMon: separate `nous.bearerToken` measure point because
+        // this is the second auth.json read of the picker's open
+        // sequence (subscriptionService.loadState() did the first).
+        // Together with `nous.subscription.loadState`, total two SSH
+        // round-trips of the same file — candidate for caching.
+        ScarfMon.measure(.diskIO, "nous.bearerToken") {
             let transport = context.makeTransport()
             guard transport.fileExists(context.paths.authJSON) else { return nil }
             guard let data = try? transport.readFile(context.paths.authJSON) else { return nil }
@@ -158,12 +166,14 @@ public struct NousModelCatalogService: Sendable {
             guard let token, !token.isEmpty else { return nil }
             return token
         }
+    }
 
     /// Make the API call. Times out after `requestTimeout` so a hung
     /// network doesn't block the picker indefinitely. Returns the raw
     /// `[NousModel]` on success, throws on any HTTP / decode error so
     /// the caller can log + fall back.
     public func fetchModels() async throws -> [NousModel] {
+        try await ScarfMon.measureAsync(.transport, "nous.fetchModels") {
             guard let token = bearerToken() else {
                 throw NousModelCatalogError.notAuthenticated
             }
@@ -182,8 +192,10 @@ public struct NousModelCatalogService: Sendable {
             }
             struct Envelope: Decodable { let data: [NousModel] }
             let envelope = try JSONDecoder().decode(Envelope.self, from: data)
+            ScarfMon.event(.transport, "nous.fetchModels.bytes", count: envelope.data.count, bytes: data.count)
             return envelope.data
         }
+    }
 
     // MARK: - Public entry
 

scarf/scarf/Core/Services/NousSubscriptionService.swift

@@ -82,6 +82,7 @@ struct NousSubscriptionService: Sendable {
     /// on any read or parse failure — callers treat "absent" and "can't
     /// read" the same in UI (show a "not subscribed" CTA).
     nonisolated func loadState() -> NousSubscriptionState {
+        ScarfMon.measure(.diskIO, "nous.subscription.loadState") {
             guard let data = try? transport.readFile(authJSONPath) else {
                 return .absent
             }
@@ -108,4 +109,5 @@ struct NousSubscriptionService: Sendable {
                 updatedAt: updatedAt
             )
         }
+    }
 }