db-mode config changes apply live in-process

settings and upstream writes now follow a prepare, commit, publish, retire
contract: candidates are built and validated before the database transaction,
published as infallible pointer swaps, and old generations retire after their
readers drain. per-query policy values snapshot once per query; upstream pool,
cache, rate limiter, sessions, api limiter, log sink, blocklist scheduler and
the query-log queue each gained one named live operation. restart_required
shrinks from every scalar key to the bind keys and web.enabled; the admin ui
drops its restart notices for everything else. file mode is unchanged.

src/server/tcp_server_integration_test.zig

@@ -21,6 +21,7 @@ const header = @import("../dns/header.zig");
 const packet = @import("../dns/packet.zig");
 const types = @import("../dns/types.zig");
 const transport = @import("../upstream/transport.zig");
+const upstream_owner = @import("../upstream/owner.zig");
 
 const testing = std.testing;
 
@@ -37,11 +38,10 @@ const forward_timeout: std.Io.Clock.Duration = .{
 /// An upstream and nothing else optional: no filtering, no cache, no log. The
 /// listener is what these tests exercise, so the handler is the same bare one
 /// its own tests use.
-fn bareHandler(client: transport.Client) handler.Handler {
+fn bareHandler(up: *upstream_owner.Owner) handler.Handler {
     return .{
-        .upstream = client,
-        .blocking = blocking,
-        .forward_read_timeout = forward_timeout,
+        .upstream = up,
+        .policy = .{ .blocking = blocking, .forward_read_timeout = forward_timeout },
     };
 }
 
@@ -175,7 +175,8 @@ test "two length-prefixed queries share one connection" {
     const io = threaded.io();
 
     var fake: FakeUpstream = .{ .reply = response_bytes };
-    var h = bareHandler(fake.client());
+    var h_owner: upstream_owner.Borrowed = .{};
+    var h = bareHandler(h_owner.client(fake.client()));
 
     const listen_address: net.IpAddress = try .parse("127.0.0.1", 0);
     var server = try tcp_server.TcpServer.listen(gpa, io, listen_address, &h, .{ .max_connections = 2 });
@@ -205,7 +206,8 @@ test "the claimed slot records the connecting client" {
     const io = threaded.io();
 
     var fake: FakeUpstream = .{ .reply = response_bytes };
-    var h = bareHandler(fake.client());
+    var h_owner: upstream_owner.Borrowed = .{};
+    var h = bareHandler(h_owner.client(fake.client()));
 
     const listen_address: net.IpAddress = try .parse("127.0.0.1", 0);
     var server = try tcp_server.TcpServer.listen(gpa, io, listen_address, &h, .{ .max_connections = 2 });
@@ -282,7 +284,8 @@ test "a canceled serve does not wait for a live connection" {
     const io = threaded.io();
 
     var fake: FakeUpstream = .{ .reply = response_bytes };
-    var h = bareHandler(fake.client());
+    var h_owner: upstream_owner.Borrowed = .{};
+    var h = bareHandler(h_owner.client(fake.client()));
 
     const listen_address: net.IpAddress = try .parse("127.0.0.1", 0);
     // The idle budget is the whole time a drain would have to wait out, so it
@@ -344,7 +347,8 @@ test "an idle connection is closed and counted" {
     const io = threaded.io();
 
     var fake: FakeUpstream = .{ .reply = response_bytes };
-    var h = bareHandler(fake.client());
+    var h_owner: upstream_owner.Borrowed = .{};
+    var h = bareHandler(h_owner.client(fake.client()));
 
     const listen_address: net.IpAddress = try .parse("127.0.0.1", 0);
     var server = try tcp_server.TcpServer.listen(gpa, io, listen_address, &h, .{
@@ -377,7 +381,8 @@ test "a zero-length message is a connection error" {
     const io = threaded.io();
 
     var fake: FakeUpstream = .{ .reply = response_bytes };
-    var h = bareHandler(fake.client());
+    var h_owner: upstream_owner.Borrowed = .{};
+    var h = bareHandler(h_owner.client(fake.client()));
 
     const listen_address: net.IpAddress = try .parse("127.0.0.1", 0);
     var server = try tcp_server.TcpServer.listen(gpa, io, listen_address, &h, .{
@@ -429,7 +434,8 @@ test "deinit ends a serve loop that is blocked on accept" {
     const io = threaded.io();
 
     var fake: FakeUpstream = .{ .reply = response_bytes };
-    var h = bareHandler(fake.client());
+    var h_owner: upstream_owner.Borrowed = .{};
+    var h = bareHandler(h_owner.client(fake.client()));
 
     const listen_address: net.IpAddress = try .parse("127.0.0.1", 0);
     var server = try tcp_server.TcpServer.listen(gpa, io, listen_address, &h, .{ .max_connections = 2 });