diff --git a/src/server.zig b/src/server.zig
index 09c297a..c0677bb 100644
--- a/src/server.zig
+++ b/src/server.zig
@@ -6440,3 +6440,163 @@ test "enableCollTtlSweep periodically reaps due collections nobody ever touches
     var client = try client_mod.Client.connect(allocator, server.boundAddress());
     defer client.close();
 
+    _ = try collmod.ZSet.add(&db, allocator, "board", "alice", 10);
+    try client.collTtlExpire(.zset, "board", 0);
+
+    // Long enough for the collection to be due and for at least one sweep
+    // tick (every 50ms) to run past that point - nobody ever reads "board"
+    // again, so without the background sweeper it would sit there forever.
+    std.time.sleep(300 * std.time.ns_per_ms);
+
+    try std.testing.expect(!try collmod.collectionExists(&db, allocator, .zset, "board"));
+    try std.testing.expect(server.collTtlSweptTotal.get() >= 1);
+}
+
+test "a server with no coll ttl sweep interval never runs the coll ttl sweeper" {
+    const allocator = std.testing.allocator;
+    var tmp = std.testing.tmpDir(.{});
+    defer tmp.cleanup();
+    const path = try tmp.dir.realpathAlloc(allocator, ".");
+    defer allocator.free(path);
+
+    var db = try testDb(allocator, path);
+    defer db.close();
+
+    const address = try std.net.Address.parseIp("127.0.0.1", 0);
+    var server = try Server.init(allocator, &db, address);
+    try server.start();
+    defer server.stop();
+
+    const client_mod = @import("client.zig");
+    var client = try client_mod.Client.connect(allocator, server.boundAddress());
+    defer client.close();
+
+    _ = try collmod.Set.add(&db, allocator, "tags", "zig");
+    try client.collTtlExpire(.set, "tags", 0);
+    std.time.sleep(100 * std.time.ns_per_ms);
+
+    // Nothing swept it in the background, but the collection IS logically
+    // due - it is still physically present until something sweeps it.
+    try std.testing.expectEqual(@as(u64, 0), server.collTtlSweptTotal.get());
+    try std.testing.expect(try collmod.collectionExists(&db, allocator, .set, "tags"));
+}
+
+test "a server with the flat ttl sweeper and the coll ttl sweeper enabled at once runs both independently" {
+    // Every prior session's notes on both sweepers flagged the same gap:
+    // `enableTtlSweep` and `enableCollTtlSweep` start two structurally
+    // independent background threads on the same `Server` (separate
+    // fields, separate `std.Thread.spawn` calls, separate join calls in
+    // `stop()`), but nothing had ever exercised them running at the same
+    // time. This proves three things at once: a flat key due for
+    // expiry and a whole collection due for expiry both get reaped by
+    // their OWN sweeper without either one starving or double-counting
+    // the other's target, and `stop()` cleanly joins both sweeper threads
+    // (the exact bug class caught and fixed in session #28, where a
+    // missing join on one sweeper thread left it alive past `db.close()`
+    // and segfaulted the next test).
+    const allocator = std.testing.allocator;
+    var tmp = std.testing.tmpDir(.{});
+    defer tmp.cleanup();
+    const path = try tmp.dir.realpathAlloc(allocator, ".");
+    defer allocator.free(path);
+
+    var db = try testDb(allocator, path);
+    defer db.close();
+
+    const address = try std.net.Address.parseIp("127.0.0.1", 0);
+    var server = try Server.init(allocator, &db, address);
+    server.enableTtlSweep(50 * std.time.ns_per_ms);
+    server.enableCollTtlSweep(50 * std.time.ns_per_ms);
+    try server.start();
+    defer server.stop();
+
+    const client_mod = @import("client.zig");
+    var client = try client_mod.Client.connect(allocator, server.boundAddress());
+    defer client.close();
+
+    try client.set("flatkey", "1");
+    try client.ttlExpire("flatkey", 0);
+    _ = try collmod.Hash.set(&db, allocator, "session:1", "user", "ada");
+    try client.collTtlExpire(.hash, "session:1", 0);
+
+    // Poll rather than sleep a single fixed window: two background
+    // sweeper threads plus the accept/connection threads contending for
+    // `self.mutex` on a loaded host can occasionally push either sweeper's
+    // tick past a fixed 300ms, which is not a correctness bug in the
+    // sweeper - it is exactly the kind of host-load flakiness this
+    // project's own frostbyte sessions document repeatedly. Waiting up to
+    // 3s in 50ms increments keeps the assertion meaningful (still fails
+    // for real if a sweeper never runs) without being a coin flip on a
+    // busy machine.
+    var waited: u64 = 0;
+    while (waited < 3000 and (server.ttlSweptTotal.get() == 0 or server.collTtlSweptTotal.get() == 0)) {
+        std.time.sleep(50 * std.time.ns_per_ms);
+        waited += 50;
+    }
+
+    try std.testing.expectEqual(@as(?[]u8, null), try client.get(allocator, "flatkey"));
+    try std.testing.expect(!try collmod.collectionExists(&db, allocator, .hash, "session:1"));
+    try std.testing.expect(server.ttlSweptTotal.get() >= 1);
+    try std.testing.expect(server.collTtlSweptTotal.get() >= 1);
+
+    // Neither sweeper's counter absorbed the other's reap: exactly one
+    // flat key was due and exactly one collection was due, so each
+    // counter reads exactly 1, not a shared/blended total.
+    try std.testing.expectEqual(@as(u64, 1), server.ttlSweptTotal.get());
+    try std.testing.expectEqual(@as(u64, 1), server.collTtlSweptTotal.get());
+}
+
+test "coll_op over the wire exercises all five collection kinds against a real server" {
+    const allocator = std.testing.allocator;
+    var tmp = std.testing.tmpDir(.{});
+    defer tmp.cleanup();
+    const path = try tmp.dir.realpathAlloc(allocator, ".");
+    defer allocator.free(path);
+
+    var db = try testDb(allocator, path);
+    defer db.close();
+
+    const address = try std.net.Address.parseIp("127.0.0.1", 0);
+    var server = try Server.init(allocator, &db, address);
+    try server.start();
+    defer server.stop();
+
+    const client_mod = @import("client.zig");
+    var client = try client_mod.Client.connect(allocator, server.boundAddress());
+    defer client.close();
+
+    // Counter: get on a name nobody ever touched defaults to 0, set
+    // pins an exact value, incrby accumulates - the same three-step
+    // shape `collections.test.counter incrBy accumulates` already
+    // covers locally, now round-tripped over the wire.
+    {
+        var got = try client.collOp(allocator, .counter_get, "visits", &.{});
+        defer got.deinit(allocator);
+        try std.testing.expectEqual(@as(i64, 0), got.int);
+
+        var setReply = try client.collOp(allocator, .counter_set, "visits", &[_][]const u8{"10"});
+        defer setReply.deinit(allocator);
+        try std.testing.expect(setReply == .ok);
+
+        var incrReply = try client.collOp(allocator, .counter_incrby, "visits", &[_][]const u8{"5"});
+        defer incrReply.deinit(allocator);
+        try std.testing.expectEqual(@as(i64, 15), incrReply.int);
+    }
+
+    // Hash: set reports created vs updated as 1/0, get returns the
+    // value or nil, del removes a field, len/getall reflect what remains.
+    {
+        var created = try client.collOp(allocator, .hash_set, "profile", &[_][]const u8{ "name", "ada" });
+        defer created.deinit(allocator);
+        try std.testing.expectEqual(@as(i64, 1), created.int);
+
+        var updated = try client.collOp(allocator, .hash_set, "profile", &[_][]const u8{ "name", "grace" });
+        defer updated.deinit(allocator);
+        try std.testing.expectEqual(@as(i64, 0), updated.int);
+
+        _ = try client.collOp(allocator, .hash_set, "profile", &[_][]const u8{ "age", "36" });
+
+        var got = try client.collOp(allocator, .hash_get, "profile", &[_][]const u8{"name"});
+        defer got.deinit(allocator);
+        try std.testing.expectEqualStrings("grace", got.bytes);
+