feat(scarfmon): B2 + B3 + iOS dashboard — file watcher, message hydration, dashboard load

Three areas instrumented in this batch. Both targets build clean.

B2 — Mac HermesFileWatcher (FSEvents + remote SSH poll)
- mac.fileWatcher.localFire (event) — every FSEvents change on a
  watched core or project path. High counts during streaming chats
  are normal (state.db-wal ticks per persisted message); high counts
  during idle suggest a runaway watcher install.
- mac.fileWatcher.remoteRestart (event, bytes=path-count) — fires
  once per SSH poller restart, with the union path count attached.
  Frequent restarts mean the project-list update path is churning.
- mac.fileWatcher.remoteDelta (event) — fires per non-empty change
  detected on the SSH poll. Pair with `ssh.streamScript` cadence to
  see actual poll latency.

B3 — Chat session boot + message hydration
- mac.fetchMessages (interval) + .rows (event) — bounded SQL
  fetch from HermesDataService. Catches slow paginated scrolls
  back through long sessions.
- mac.refreshSessionFromDB (interval) — RichChatViewModel's
  post-promptComplete refresh that picks up cost/token data.
- mac.hydrateMessages (interval) + .rows (event) — full session-boot
  hydration in RichChatViewModel.loadSessionHistory. Was the suspected
  trigger of the 22-bubble session-start storms in the Phase 3a
  baseline; now precisely measurable.

iOS Dashboard (resolves the original "out of sync" mystery)
- ios.loadDashboard (interval) — wraps the four dataService.fetch*
  Citadel SFTP round-trips in IOSDashboardViewModel.load().
- ios.allSessions.count (event) — sidebar list size after each
  load, correlates load latency with list growth.
- ios.dashboardRefresh.trigger (event) — fires only on
  pull-to-refresh, separates that entry path from initial appear.

**Architectural finding:** the original v2.6.0 user feedback
("chat out of sync iOS↔Mac on fast LAN") is now firmly attributable
to this — iOS does NOT subscribe to a file watcher. The dashboard
refresh path is appear-time + pull-to-refresh only.
`CitadelServerTransport.watchPaths()` is effectively dead code on
iOS today; nobody calls it. Earlier A1 instrumentation (commit
9df7142) put measure points on it, which is why captures showed
zero `ios.fileWatcher.tick` events. Future work: either add a
foregrounded poll loop to iOS, or thread the file watcher into
the dashboard subscription. Documented in the ScarfMon roadmap
memory.

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

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

@@ -188,6 +188,7 @@ public actor HermesDataService {
         limit: Int,
         before: Int? = nil
     ) async -> [HermesMessage] {
+        await ScarfMon.measureAsync(.sessionLoad, "mac.fetchMessages") {
             let sql: String
             let params: [SQLValue]
             if let before {
@@ -201,11 +202,14 @@ public actor HermesDataService {
                 let rows = try await backend.query(sql, params: params)
                 // Caller wants chronological (oldest-first) order; the SELECT
                 // is DESC for the LIMIT to bite the newest rows, so reverse.
-            return rows.map { messageFromRow($0) }.reversed()
+                let messages = rows.map { messageFromRow($0) }.reversed() as [HermesMessage]
+                ScarfMon.event(.sessionLoad, "mac.fetchMessages.rows", count: messages.count)
+                return messages
             } catch {
                 return []
             }
         }
+    }
 
     /// Legacy unbounded fetch retained for one release cycle so any
     /// out-of-tree consumers don't break. New code should use the

scarf/Packages/ScarfCore/Sources/ScarfCore/ViewModels/RichChatViewModel.swift

@@ -470,6 +470,7 @@ public final class RichChatViewModel {
 
     /// Re-fetch session metadata from DB to pick up cost/token updates.
     public func refreshSessionFromDB() async {
+        await ScarfMon.measureAsync(.sessionLoad, "mac.refreshSessionFromDB") {
             guard let sessionId else { return }
             let opened = await dataService.open()
             guard opened else { return }
@@ -478,6 +479,7 @@ public final class RichChatViewModel {
             }
             await dataService.close()
         }
+    }
 
     // MARK: - ACP Event Handling
 
@@ -1015,6 +1017,7 @@ public final class RichChatViewModel {
     /// Load message history from the DB, optionally combining an origin session
     /// (e.g., CLI session) with the current ACP session.
     public func loadSessionHistory(sessionId: String, acpSessionId: String? = nil) async {
+        await ScarfMon.measureAsync(.sessionLoad, "mac.hydrateMessages") {
         self.sessionId = sessionId
         // Force a fresh snapshot pull on remote contexts. An earlier open()
         // would have cached a stale copy — on resume we need whatever
@@ -1100,7 +1103,9 @@ public final class RichChatViewModel {
             .map(\.id)
             .min()
         hasMoreHistory = moreHistory
+        ScarfMon.event(.sessionLoad, "mac.hydrateMessages.rows", count: messages.count)
         buildMessageGroups()
+        } // end measureAsync(.sessionLoad, "mac.hydrateMessages")
     }
 
     // MARK: - Load Earlier (pagination)

scarf/Packages/ScarfIOS/Sources/ScarfIOS/IOSDashboardViewModel.swift

@@ -70,10 +70,13 @@ public final class IOSDashboardViewModel {
             return
         }
 
+        await ScarfMon.measureAsync(.sessionLoad, "ios.loadDashboard") {
             stats = await dataService.fetchStats()
             recentSessions = await dataService.fetchSessions(limit: 5)
             allSessions = await dataService.fetchSessions(limit: 25)
             sessionPreviews = await dataService.fetchSessionPreviews(limit: 25)
+        }
+        ScarfMon.event(.sessionLoad, "ios.allSessions.count", count: allSessions.count)
 
         // Attribution lookup (pass-2 UX): load the session→project
         // sidecar + project registry once so Dashboard rows can show
@@ -126,6 +129,7 @@ public final class IOSDashboardViewModel {
 
     /// Called from the pull-to-refresh gesture.
     public func refresh() async {
+        ScarfMon.event(.sessionLoad, "ios.dashboardRefresh.trigger", count: 1)
         await load()
     }
 }

scarf/scarf/Core/Services/HermesFileWatcher.swift

@@ -76,11 +76,21 @@ final class HermesFileWatcher {
     /// (Re)start the SSH polling stream over the union of `watchedCorePaths`
     /// and the current `remoteProjectPaths`. Called on initial start and
     /// whenever `updateProjectWatches` changes the project set.
+    ///
+    /// ScarfMon — `mac.fileWatcher.remoteRestart` (event) fires once per
+    /// poller restart with `bytes` carrying the path count. Frequent
+    /// restarts mean the project-list update path is churning; pair
+    /// with `mac.fileWatcher.remoteTick` from the upstream transport
+    /// (`ssh.streamScript` / `transport.watchPaths`) to see actual
+    /// poll cadence.
     private func startRemotePoller() {
         remotePollTask?.cancel()
-        let stream = transport.watchPaths(watchedCorePaths + remoteProjectPaths)
+        let pathSet = watchedCorePaths + remoteProjectPaths
+        ScarfMon.event(.transport, "mac.fileWatcher.remoteRestart", count: 1, bytes: pathSet.count)
+        let stream = transport.watchPaths(pathSet)
         remotePollTask = Task { [weak self] in
             for await _ in stream {
+                ScarfMon.event(.transport, "mac.fileWatcher.remoteDelta", count: 1)
                 await MainActor.run { [weak self] in
                     self?.lastChangeDate = Date()
                 }
@@ -146,6 +156,12 @@ final class HermesFileWatcher {
             queue: .main
         )
         source.setEventHandler { [weak self] in
+            // ScarfMon — fires every time FSEvents detects a change on
+            // a watched core or project path. High counts during
+            // streaming chats are normal (state.db-wal ticks per
+            // message persisted); high counts when nothing's happening
+            // suggest a runaway watcher install.
+            ScarfMon.event(.transport, "mac.fileWatcher.localFire", count: 1)
             self?.lastChangeDate = Date()
         }
         source.setCancelHandler {