milestone 27: diagnostics — operational failures land in one curated log, resolved history purgeable

src/web/server.zig

@@ -32,6 +32,7 @@ const disk_monitor = @import("../storage/disk_monitor.zig");
 const dns_handler = @import("../server/handler.zig");
 const doh_server = @import("../server/doh_server.zig");
 const dot_server = @import("../server/dot_server.zig");
+const events_mod = @import("../storage/events.zig");
 const http_util = @import("http_util.zig");
 const listener_core = @import("../server/listener.zig");
 const local_tables_mod = @import("../server/local_tables.zig");
@@ -183,6 +184,11 @@ pub const WebState = struct {
     /// concurrent writes would misread each other's row counts.
     config_lock: std.Io.Mutex = .init,
     querylog_db: ?*db.Db = null,
+    /// The diagnostics event store, which owns a third connection of its own
+    /// and serializes every access — read and write — through its mutex. Null
+    /// when `Store.init` failed, which `/api/health` reports as `unavailable`
+    /// and treats as degraded.
+    events: ?*events_mod.Store = null,
 
     version: []const u8 = "",
     /// The `--admin-dev` asset directory, read by the dev-mode fallback. Empty