make sure cache saves to file properly

src/location/GeoCache.zig

@@ -6,6 +6,8 @@ const GeoCache = @This();
 allocator: std.mem.Allocator,
 cache: std.StringHashMap(CachedLocation),
 cache_file: ?[]const u8,
+dirty: bool,
+last_save: i64,
 
 pub const CachedLocation = struct {
     name: []const u8,
@@ -26,6 +28,8 @@ pub fn init(allocator: std.mem.Allocator, cache_file: ?[]const u8) !GeoCache {
         .allocator = allocator,
         .cache = cache,
         .cache_file = if (cache_file) |f| try allocator.dupe(u8, f) else null,
+        .dirty = false,
+        .last_save = std.time.milliTimestamp(),
     };
 }
 
@@ -47,6 +51,7 @@ pub fn deinit(self: *GeoCache) void {
 }
 
 pub fn get(self: *GeoCache, query: []const u8) ?CachedLocation {
+    self.saveIfNeeded();
     return self.cache.get(query);
 }
 
@@ -57,6 +62,28 @@ pub fn put(self: *GeoCache, query: []const u8, location: CachedLocation) !void {
         .coords = location.coords,
     };
     try self.cache.put(key, value);
+    self.dirty = true;
+}
+
+/// Save cache to disk if dirty and enough time has passed (15 minutes)
+pub fn saveIfNeeded(self: *GeoCache) void {
+    if (!self.dirty) return;
+
+    const cache_file = self.cache_file orelse return;
+
+    const now = std.time.milliTimestamp();
+    const elapsed_ms = now - self.last_save;
+    const fifteen_minutes_ms = 15 * std.time.ms_per_min;
+
+    if (elapsed_ms < fifteen_minutes_ms) return;
+
+    self.saveToFile(cache_file) catch |err| {
+        std.log.warn("Failed to save geocoding cache to {s}: {}", .{ cache_file, err });
+        return;
+    };
+
+    self.dirty = false;
+    self.last_save = now;
 }
 
 fn loadFromFile(allocator: std.mem.Allocator, cache: *std.StringHashMap(CachedLocation), file_path: []const u8) !void {