chore: retire legacy v3 dev websocket + delete legacy self-hosting docs (#4198)

Follow-up to #4194 (v3 execution app + core-helper removal). The v3
(engine V1) is end-of-lifed and enforced off in prod, so this removes a
self-contained slice of the remaining dead v3 code while **keeping every
user-facing deprecation message** - a user still on v3 must still be
told to upgrade.

## Legacy dev websocket

`app/v3/handleWebsockets.server.ts` backs the `/ws` transport used
**only** by the legacy v3 `trigger dev` CLI (v4 dev uses a different
transport). It's now authenticate-then-close with
`V3_DEV_DEPRECATION_MESSAGE`, so an old CLI is still told what to do -
only the legacy `AuthenticatedSocketConnection` / `DevQueueConsumer`
execution behind it (which can no longer run) is removed.

- Deleted `app/v3/authenticatedSocketConnection.server.ts` (its only
consumer).
- `engineDeprecation.server.ts` and the deprecation message constants
are untouched.

## Docs

Deleted the intentionally-legacy "Docker (legacy)" self-hosting page
(`open-source-self-hosting.mdx`) and redirected
`/open-source-self-hosting` (+ the existing
`/v3/open-source-self-hosting` alias) to `/self-hosting/overview`;
repointed the two inbound links. The current `self-hosting/*` docs
already describe the v4 (single supervisor) setup.

## Deliberately out of scope

Despite the branch name, this PR does **not** touch MarQS or the
socket.io coordinator/provider namespaces. Investigation found MarQS is
entangled with **live v2** queue/metrics/concurrency/project-cleanup
code (`runQueue`, `queueSizeLimits`, `taskRunConcurrencyTracker`,
`EnvironmentQueuePresenter`, `registerProjectMetrics`, `deleteProject`),
so it needs a per-file reviewed pass, not a bulk delete. That remainder
stays on TRI-11883.

refs TRI-11883

Author: nicktrn

.server-changes/retire-legacy-v3-dev-websocket.md

@@ -0,0 +1,6 @@
+---
+area: webapp
+type: breaking
+---
+
+Removed support for the end-of-life v3 `trigger dev` CLI. Starting a dev session with an old v3 CLI now returns an upgrade message instead of connecting - upgrade to the v4 CLI to continue using `trigger dev`.

apps/webapp/app/v3/authenticatedSocketConnection.server.ts

@@ -3,31 +3,15 @@ import { WebSocketServer, type WebSocket } from "ws";
 import { authenticateApiKey } from "~/services/apiAuth.server";
 import { logger } from "~/services/logger.server";
 import { singleton } from "../utils/singleton";
-import { AuthenticatedSocketConnection } from "./authenticatedSocketConnection.server";
-import { Gauge } from "prom-client";
-import { metricsRegister } from "~/metrics.server";
-import { isV3Disabled, V3_DEV_DEPRECATION_MESSAGE } from "./engineDeprecation.server";
+import { V3_DEV_DEPRECATION_MESSAGE } from "./engineDeprecation.server";
 
 export const wss = singleton("wss", initalizeWebSocketServer);
 
-let authenticatedConnections: Map<string, AuthenticatedSocketConnection>;
-
 function initalizeWebSocketServer() {
   const server = new WebSocketServer({ noServer: true });
 
   server.on("connection", handleWebSocketConnection);
 
-  authenticatedConnections = new Map();
-
-  new Gauge({
-    name: "dev_authenticated_connections",
-    help: "Number of authenticated dev connections",
-    collect() {
-      this.set(authenticatedConnections.size);
-    },
-    registers: [metricsRegister],
-  });
-
   return server;
 }
 
@@ -59,35 +43,14 @@ async function handleWebSocketConnection(ws: WebSocket, req: IncomingMessage) {
 
   const authenticatedEnv = authenticationResult.environment;
 
-  // This legacy websocket is only used by the v3 `trigger dev` CLI (v4 uses a
-  // different dev transport). When the v3 shutdown is on, close it with a
-  // graceful reason instead of letting the CLI sit connected with no work.
-  if (isV3Disabled()) {
-    logger.warn("Rejected deprecated v3 dev CLI websocket connection", {
-      environmentId: authenticatedEnv.id,
-      projectId: authenticatedEnv.projectId,
-      organizationId: authenticatedEnv.organizationId,
-    });
-    ws.close(1008, V3_DEV_DEPRECATION_MESSAGE);
-    return;
-  }
-
-  const authenticatedConnection = new AuthenticatedSocketConnection(
-    ws,
-    authenticatedEnv,
-    req.headers["x-forwarded-for"] ?? req.socket.remoteAddress ?? "unknown"
-  );
-
-  authenticatedConnections.set(authenticatedConnection.id, authenticatedConnection);
-
-  authenticatedConnection.onClose.attachOnce((closeEvent) => {
-    logger.debug("Websocket closed", {
-      closeEvent,
-      authenticatedConnectionId: authenticatedConnection.id,
-    });
-
-    authenticatedConnections.delete(authenticatedConnection.id);
+  // This websocket is only used by the legacy v3 `trigger dev` CLI (v4 uses a
+  // different dev transport). The v3 engine is end-of-lifed, so there is no
+  // longer any work to run here — close with the graceful upgrade message so
+  // an old CLI is told what to do instead of sitting connected.
+  logger.warn("Rejected deprecated v3 dev CLI websocket connection", {
+    environmentId: authenticatedEnv.id,
+    projectId: authenticatedEnv.projectId,
+    organizationId: authenticatedEnv.organizationId,
   });
-
-  await authenticatedConnection.initialize();
+  ws.close(1008, V3_DEV_DEPRECATION_MESSAGE);
 }

apps/webapp/app/v3/handleWebsockets.server.ts

@@ -286,8 +286,7 @@
               {
                 "group": "Environment variables",
                 "pages": ["self-hosting/env/webapp", "self-hosting/env/supervisor"]
-              },
-              "open-source-self-hosting"
+              }
             ]
           },
           {
@@ -736,9 +735,13 @@
       "source": "/v3/upgrading-from-v2",
       "destination": "/guides/use-cases/upgrading-from-v2"
     },
+    {
+      "source": "/open-source-self-hosting",
+      "destination": "/self-hosting/overview"
+    },
     {
       "source": "/v3/open-source-self-hosting",
-      "destination": "/open-source-self-hosting"
+      "destination": "/self-hosting/overview"
     },
     {
       "source": "/v3/:slug*",

docs/docs.json

@@ -5,4 +5,4 @@ url: "https://github.com/triggerdotdev/trigger.dev"
 
 Trigger.dev is [Open Source on GitHub](https://github.com/triggerdotdev/trigger.dev). You can contribute to the project by submitting issues, pull requests, or simply by using it and providing feedback.
 
-You can also [self-host](/open-source-self-hosting) the project if you want to run it on your own infrastructure.
+You can also [self-host](/self-hosting/overview) the project if you want to run it on your own infrastructure.