diff --git a/internal/controller/codermcpserver_apply.go b/internal/controller/codermcpserver_apply.go
index e4bcb198..1493fa50 100644
--- a/internal/controller/codermcpserver_apply.go
+++ b/internal/controller/codermcpserver_apply.go
@@ -46,10 +46,12 @@ func (r *CoderMCPServerReconciler) syncMCPServer(
 	applied := server.Status.AppliedGeneration == server.Generation
 	found, err := sdk.MCPServerConfigByID(ctx, orgID, id)
 	switch {
-	case isCoderNotFound(err) && applied:
+	// Only Coder's own 404 proves that the config is gone. A proxy page or
+	// "Route not found." waits below and changes nothing (#337).
+	case isCoderResourceNotFound(err) && applied:
 		return mcpServerStalled(mcpServerResync, "DeletedExternally",
 			"MCP server config %s was deleted in Coder. The controller does not create it again until the spec changes.", id), false, nil
-	case isCoderNotFound(err):
+	case isCoderResourceNotFound(err):
 		server.Status.ConfigID, server.Status.Credentials = "", nil
 		r.sentCredentials.Delete(server.UID)
 		return nil, true, nil
diff --git a/internal/controller/codermcpserver_disable.go b/internal/controller/codermcpserver_disable.go
index 5da84c7f..e2fe0096 100644
--- a/internal/controller/codermcpserver_disable.go
+++ b/internal/controller/codermcpserver_disable.go
@@ -47,7 +47,8 @@ func (r *CoderMCPServerReconciler) disableMCPServerWithoutConsent(
 	}
 	found, err := sdk.MCPServerConfigByID(ctx, orgID, id)
 	switch {
-	case isCoderNotFound(err):
+	case isCoderResourceNotFound(err):
+		// Only Coder's own 404 proves that the config is gone (#337).
 		return stalled("MCP server config %s does not exist in Coder.", id), nil
 	case err != nil:
 		return unchecked("get MCP server config: %s", coderErrorSummary(err)), nil
diff --git a/internal/controller/codermcpserver_notfound_test.go b/internal/controller/codermcpserver_notfound_test.go
new file mode 100644
index 00000000..3d55ee85
--- /dev/null
+++ b/internal/controller/codermcpserver_notfound_test.go
@@ -0,0 +1,98 @@
+package controller_test
+
+import (
+	"context"
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+
+	"github.com/coder/coder-k8s/internal/credentialsecret"
+)
+
+// #337: in the sync, only Coder's own 404 proves that the config is gone. A
+// proxy page or "Route not found." waits with CoderUnavailable and changes
+// nothing, both for an applied config (no DeletedExternally kill switch) and
+// after a spec edit (no cleared config ID, no create).
+func TestCoderMCPServerSyncNotCoder404(t *testing.T) {
+	t.Parallel()
+	for name, fault := range notCoder404s {
+		for _, edited := range []bool{false, true} {
+			t.Run(fmt.Sprintf("%s/edited=%v", name, edited), func(t *testing.T) {
+				t.Parallel()
+				ctx := context.Background()
+				env := newMCPServerEnv(ctx, t, true)
+				env.keySecret(ctx, t, testMCPKey)
+				got, _ := env.applied(ctx, t, nil)
+				if edited {
+					require.NoError(t, k8sClient.Get(ctx, client.ObjectKeyFromObject(got), got))
+					got.Spec.Description = "edited"
+					require.NoError(t, k8sClient.Update(ctx, got))
+				}
+				before := got.Status.DeepCopy()
+				mark := len(env.writeRoutes())
+				env.fake.failNext(routeMCPServer, fault)
+				got, result := env.reconcile(ctx, t, got)
+				requireMCPServerStep(t, got, false, "CoderUnavailable")
+				require.Equal(t, 30*time.Second, result.RequeueAfter)
+				require.Equal(t, before.ConfigID, got.Status.ConfigID, "ownership is kept")
+				require.Equal(t, before.Credentials, got.Status.Credentials)
+				require.Empty(t, env.writesSince(mark), "no Coder write")
+
+				got, _ = env.reconcile(ctx, t, got)
+				requireMCPServerApplied(t, got)
+				require.Equal(t, 1, env.posts(), "the only create is the first one")
+			})
+		}
+	}
+}
+
+// #337: the read of the disable path also needs Coder's own 404 before the
+// config counts as gone. Another 404 waits, keeps the config ID, and the next
+// reconcile disables the config.
+func TestCoderMCPServerDisableNotCoder404(t *testing.T) {
+	t.Parallel()
+	for name, fault := range notCoder404s {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+			ctx := context.Background()
+			env := newMCPServerEnv(ctx, t, true)
+			secret := env.keySecret(ctx, t, testMCPKey)
+			got, _ := env.applied(ctx, t, nil)
+			require.NoError(t, k8sClient.Delete(ctx, secret))
+			before := got.Status.DeepCopy()
+			mark := len(env.writeRoutes())
+			env.fake.failNext(routeMCPServer, fault)
+			got, result := env.reconcile(ctx, t, got)
+			require.Contains(t, requireMCPServerStep(t, got, false, credentialsecret.ReasonSecretNotFound), "Coder can still send the credentials")
+			require.Equal(t, 30*time.Second, result.RequeueAfter)
+			require.Equal(t, before.ConfigID, got.Status.ConfigID, "ownership is kept")
+			require.Empty(t, env.writesSince(mark), "no Coder write")
+			require.True(t, env.stored(t, got).view.Enabled)
+
+			got, _ = env.reconcile(ctx, t, got)
+			require.Contains(t, requireMCPServerStep(t, got, true, credentialsecret.ReasonSecretNotFound), "The controller disabled MCP server config")
+			require.False(t, env.stored(t, got).view.Enabled)
+		})
+	}
+}
+
+// Coder's own 404 still counts as gone in the disable read, so the test
+// above cannot pass by never treating a 404 as gone. The sync read is
+// covered by TestCoderMCPServerSyncDeletedConfig.
+func TestCoderMCPServerDisableCoder404(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	env := newMCPServerEnv(ctx, t, true)
+	secret := env.keySecret(ctx, t, testMCPKey)
+	got, id := env.applied(ctx, t, nil)
+	require.NoError(t, env.dashboard(t).DeleteMCPServerConfig(ctx, env.orgID, id))
+	require.NoError(t, k8sClient.Delete(ctx, secret))
+	mark := len(env.writeRoutes())
+	got, result := env.reconcile(ctx, t, got)
+	require.Contains(t, requireMCPServerStep(t, got, true, credentialsecret.ReasonSecretNotFound), "does not exist in Coder")
+	require.Equal(t, 10*time.Minute, result.RequeueAfter)
+	require.Empty(t, env.writesSince(mark))
+}