test: speed up agent container websocket close test (#25559)

`TestWatchAgentContainers/CoderdWebSocketCanHandleClientClosing` spent
about 15 seconds waiting for the real websocket heartbeat ticker to
detect that the client closed.

Add a clock-aware `HeartbeatClose` wrapper and pass `api.Clock` through
the containers watch handler so the test can drive the heartbeat
deterministically with `quartz.Mock`. The test still verifies the same
client-close teardown path, but it advances the heartbeat tick instead
of waiting for wall-clock time.

Refs #25557


Discovered as part of the work on CODAGT-381.

coderd/httpapi/websocket.go

@@ -21,6 +21,12 @@ func HeartbeatClose(ctx context.Context, logger slog.Logger, exit func(), conn *
 	heartbeatCloseWith(ctx, logger, exit, conn, quartz.NewReal(), HeartbeatInterval)
 }
 
+// HeartbeatCloseWithClock is like HeartbeatClose, but uses the provided
+// clock so tests can drive heartbeat ticks deterministically.
+func HeartbeatCloseWithClock(ctx context.Context, logger slog.Logger, exit func(), conn *websocket.Conn, clk quartz.Clock) {
+	heartbeatCloseWith(ctx, logger, exit, conn, clk, HeartbeatInterval)
+}
+
 func heartbeatCloseWith(ctx context.Context, logger slog.Logger, exit func(), conn *websocket.Conn, clk quartz.Clock, interval time.Duration) {
 	ticker := clk.NewTicker(interval, "HeartbeatClose")
 	defer ticker.Stop()

coderd/workspaceagents.go

@@ -871,7 +871,7 @@ func (api *API) watchWorkspaceAgentContainers(rw http.ResponseWriter, r *http.Re
 	ctx, wsNetConn := codersdk.WebsocketNetConn(ctx, conn, websocket.MessageText)
 	defer wsNetConn.Close()
 
-	go httpapi.HeartbeatClose(ctx, logger, cancel, conn)
+	go httpapi.HeartbeatCloseWithClock(ctx, logger, cancel, conn, api.Clock)
 
 	encoder := json.NewEncoder(wsNetConn)
 

coderd/workspaceagents_internal_test.go

@@ -26,6 +26,7 @@ import (
 	"github.com/coder/coder/v2/coderd/database/dbauthz"
 	"github.com/coder/coder/v2/coderd/database/dbmock"
 	"github.com/coder/coder/v2/coderd/database/dbtime"
+	"github.com/coder/coder/v2/coderd/httpapi"
 	"github.com/coder/coder/v2/coderd/httpmw"
 	"github.com/coder/coder/v2/coderd/rbac"
 	"github.com/coder/coder/v2/coderd/rbac/policy"
@@ -37,6 +38,7 @@ import (
 	"github.com/coder/coder/v2/tailnet"
 	"github.com/coder/coder/v2/tailnet/tailnettest"
 	"github.com/coder/coder/v2/testutil"
+	"github.com/coder/quartz"
 	"github.com/coder/websocket"
 )
 
@@ -738,8 +740,9 @@ func TestWatchAgentContainers(t *testing.T) {
 		// response to this issue: https://github.com/coder/coder/issues/19449
 
 		var (
-			ctx    = testutil.Context(t, testutil.WaitLong)
+			ctx    = testutil.Context(t, testutil.WaitShort)
 			logger = slogtest.Make(t, &slogtest.Options{IgnoreErrors: true}).Leveled(slog.LevelDebug).Named("coderd")
+			mClock = quartz.NewMock(t)
 
 			mCtrl        = gomock.NewController(t)
 			mDB          = dbmock.NewMockStore(mCtrl)
@@ -766,12 +769,16 @@ func TestWatchAgentContainers(t *testing.T) {
 					AgentInactiveDisconnectTimeout: testutil.WaitShort,
 					Database:                       mDB,
 					Logger:                         logger,
+					Clock:                          mClock,
 					DeploymentValues:               &codersdk.DeploymentValues{},
 					TailnetCoordinator:             tailnettest.NewFakeCoordinator(),
 				},
 			}
 		)
 
+		trap := mClock.Trap().NewTicker("HeartbeatClose")
+		defer trap.Close()
+
 		var tailnetCoordinator tailnet.Coordinator = mCoordinator
 		api.TailnetCoordinator.Store(&tailnetCoordinator)
 		api.agentProvider = fAgentProvider
@@ -817,6 +824,8 @@ func TestWatchAgentContainers(t *testing.T) {
 			defer resp.Body.Close()
 		}
 
+		trap.MustWait(ctx).MustRelease(ctx)
+
 		// And: Create a streaming decoder
 		decoder := wsjson.NewDecoder[codersdk.WorkspaceAgentListContainersResponse](conn, websocket.MessageText, logger)
 		defer decoder.Close()
@@ -836,6 +845,7 @@ func TestWatchAgentContainers(t *testing.T) {
 
 		// When: We close the WebSocket
 		conn.Close(websocket.StatusNormalClosure, "test closing connection")
+		mClock.Advance(httpapi.HeartbeatInterval).MustWait(ctx)
 
 		// Then: We expect `containersCh` to be closed.
 		select {
@@ -883,6 +893,7 @@ func TestWatchAgentContainers(t *testing.T) {
 					AgentInactiveDisconnectTimeout: testutil.WaitShort,
 					Database:                       mDB,
 					Logger:                         logger,
+					Clock:                          quartz.NewReal(),
 					DeploymentValues:               &codersdk.DeploymentValues{},
 					TailnetCoordinator:             tailnettest.NewFakeCoordinator(),
 				},