Location notes: fix performance and UI issues (#774)

* Location notes: fix performance and UI issues

Performance fixes:
- Add Set-based duplicate detection (O(1) vs O(n) lookup)
- Eliminates lag when receiving 200+ notes during EOSE

Correctness fixes:
- Fix optimistic echo timestamp to match signed event timestamp
- Add echo IDs to noteIDs set for consistency

UI improvements:
- Remove duplicate "loading recent notes" text in header
- Simplify toolbar icon color logic for immediate green indication
- Icon now reliably turns green when notes exist in geohash

Tests: All 3 LocationNotes tests passing

* Location notes: add remaining robustness fixes

Additional improvements:
- Align counter/manager limits to 200 (prevents showing count higher than displayable)
- Set loading state before clearing notes to eliminate UI flicker on geohash change
- Add geohash validation for building-level precision (8 valid base32 chars)
- Add defensive 500-note memory cap with automatic trimming
- Clear stale notesGeohash state on sheet dismiss

Tests:
- Fix test geohashes to use valid base32 characters
- All 3 LocationNotes tests passing

---------

Co-authored-by: jack <jackjackbits@users.noreply.github.com>

bitchat/Services/LocationNotesManager.swift

@@ -74,7 +74,9 @@ final class LocationNotesManager: ObservableObject {
     @Published private(set) var state: State = .loading
     @Published private(set) var errorMessage: String?
     private var subscriptionID: String?
+    private var noteIDs = Set<String>() // O(1) duplicate detection
     private let dependencies: LocationNotesDependencies
+    private let maxNotesInMemory = 500 // Defensive cap (relay limit is 200)
 
     private enum Strings {
         static let noRelays = String(localized: "location_notes.error.no_relays", comment: "Shown when no geo relays are available near the selected location")
@@ -89,20 +91,35 @@ final class LocationNotesManager: ObservableObject {
     }
 
     init(geohash: String, dependencies: LocationNotesDependencies = .live) {
-        self.geohash = geohash.lowercased()
+        let norm = geohash.lowercased()
+        self.geohash = norm
         self.dependencies = dependencies
+        // Validate geohash (building-level precision: 8 chars)
+        if !Geohash.isValidBuildingGeohash(norm) {
+            SecureLogger.warning("LocationNotesManager: invalid geohash '\(norm)' (expected 8 valid base32 chars)", category: .session)
+        }
         subscribe()
     }
 
     func setGeohash(_ newGeohash: String) {
         let norm = newGeohash.lowercased()
         guard norm != geohash else { return }
+        // Validate geohash (building-level precision: 8 chars)
+        guard Geohash.isValidBuildingGeohash(norm) else {
+            SecureLogger.warning("LocationNotesManager: rejecting invalid geohash '\(norm)' (expected 8 valid base32 chars)", category: .session)
+            return
+        }
         if let sub = subscriptionID {
             dependencies.unsubscribe(sub)
             subscriptionID = nil
         }
+        // Set loading state before clearing to prevent empty state flicker
+        state = .loading
+        initialLoadComplete = false
+        errorMessage = nil
         geohash = norm
         notes.removeAll()
+        noteIDs.removeAll()
         subscribe()
     }
 
@@ -111,7 +128,12 @@ final class LocationNotesManager: ObservableObject {
             dependencies.unsubscribe(sub)
             subscriptionID = nil
         }
+        // Set loading state before clearing to prevent empty state flicker
+        state = .loading
+        initialLoadComplete = false
+        errorMessage = nil
         notes.removeAll()
+        noteIDs.removeAll()
         subscribe()
     }
 
@@ -147,12 +169,14 @@ final class LocationNotesManager: ObservableObject {
             guard event.kind == NostrProtocol.EventKind.textNote.rawValue else { return }
             // Ensure matching tag
             guard event.tags.contains(where: { $0.count >= 2 && $0[0].lowercased() == "g" && $0[1].lowercased() == self.geohash }) else { return }
-            if self.notes.contains(where: { $0.id == event.id }) { return }
+            guard !self.noteIDs.contains(event.id) else { return }
+            self.noteIDs.insert(event.id)
             let nick = event.tags.first(where: { $0.first?.lowercased() == "n" && $0.count >= 2 })?.dropFirst().first
             let ts = Date(timeIntervalSince1970: TimeInterval(event.created_at))
             let note = Note(id: event.id, pubkey: event.pubkey, content: event.content, createdAt: ts, nickname: nick)
             self.notes.append(note)
             self.notes.sort { $0.createdAt > $1.createdAt }
+            self.enforceMemoryCap()
             self.state = .ready
         }, { [weak self] in
             guard let self = self else { return }
@@ -188,10 +212,12 @@ final class LocationNotesManager: ObservableObject {
                 id: event.id,
                 pubkey: id.publicKeyHex,
                 content: trimmed,
-                createdAt: dependencies.now(),
+                createdAt: Date(timeIntervalSince1970: TimeInterval(event.created_at)),
                 nickname: nickname
             )
+            self.noteIDs.insert(event.id)
             self.notes.insert(echo, at: 0)
+            self.enforceMemoryCap()
             self.state = .ready
             self.errorMessage = nil
         } catch {
@@ -200,6 +226,15 @@ final class LocationNotesManager: ObservableObject {
         }
     }
 
+    /// Enforces defensive memory cap on notes array (keeps newest).
+    private func enforceMemoryCap() {
+        if notes.count > maxNotesInMemory {
+            let removed = notes.count - maxNotesInMemory
+            notes = Array(notes.prefix(maxNotesInMemory))
+            SecureLogger.debug("LocationNotesManager: trimmed \(removed) old notes (cap: \(maxNotesInMemory))", category: .session)
+        }
+    }
+
     /// Explicitly cancel subscription and release resources.
     func cancel() {
         if let sub = subscriptionID {