docs: add "Running a local dev stand" guide + reference it from AGENTS.md

Captures the non-obvious gotchas that make bringing up a local instance
painful: the collaboration server is a THIRD process (pnpm dev starts only
API + client) that must be built before running (tsx/ts-node fail on NestJS
DI); APP_SECRET must be identical between the API and collab servers or every
realtime connection is rejected with "Invalid collab token"; Vite binds
localhost so LAN access needs --host; a stale @docmost/editor-ext white-
screens the client; pgvector is mandatory; migrations don't auto-run in dev.
Also documents that demo/test passwords should be a simple one-word
alphanumeric (no special chars, which get mangled through shells/JSON/URLs).

Referenced from AGENTS.md (Commands + Two-server-processes sections).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

AGENTS.md

@@ -197,6 +197,12 @@ pnpm workspace (`pnpm@10.4.0`) orchestrated by **Nx**. Four workspace packages:
 
 Run from the repo root unless noted. The dev workflow needs **Postgres (with the `pgvector` extension) and Redis** reachable per `.env` (copy `.env.example` → `.env`).
 
+> **Bringing up a full local stand** (API + client + the separate realtime
+> collaboration process) has several non-obvious gotchas — a missing collab
+> server, `APP_SECRET` mismatch between processes, a stale `editor-ext` white-
+> screening the client, LAN exposure. See **[docs/dev-stand.md](docs/dev-stand.md)**
+> for the step-by-step and the traps.
+
 ```bash
 pnpm install                 # install all workspaces (uses pnpm patches; see package.json `pnpm.patchedDependencies`)
 pnpm dev                     # client (Vite) + server (Nest watch) concurrently — primary dev loop
@@ -241,6 +247,8 @@ Migration files live in `apps/server/src/database/migrations/` and are named `YY
 - **API server** — `dist/main` (`apps/server/src/main.ts`), the Fastify HTTP app (`AppModule`).
 - **Collaboration server** — `dist/collaboration/server/collab-main` (`pnpm collab`), a Hocuspocus/Yjs WebSocket server (`apps/server/src/collaboration/`) handling real-time document editing, persistence, and page-history snapshots. It listens on `COLLAB_PORT` (default `3001`), separate from the API server's `PORT` (default `3000`), and shares state with the API server through Redis.
 
+`pnpm dev` starts **only** the API server + client — the collaboration process is separate and must be started too, or the editor never connects. See **[docs/dev-stand.md](docs/dev-stand.md)** for running both locally (and why `APP_SECRET` must match between them).
+
 The API server is a Fastify app with a global `/api` prefix (`main.ts` excludes `robots.txt`, public share pages, and `mcp` from the prefix). A `preHandler` hook enforces that a resolved `workspaceId` exists for most `/api` routes (multi-tenant by hostname/subdomain via `DomainMiddleware`). `GET /api/sb/:id` (the anonymous blob-sandbox read route) is listed in that preHandler's `excludedPaths`, so it is exempt from workspace resolution and carries no session auth at all (its capability is the unguessable UUID + TTL + TLS) — unlike `/api/files/public/...`, which still resolves a workspace and requires a workspace-bound attachment JWT. Auth is JWT (cookie + bearer); authorization is **CASL** (`core/casl`) — every data access is scoped to the user's abilities.
 
 ### Module structure (server)

docs/dev-stand.md

@@ -0,0 +1,135 @@
+# Running a local dev stand
+
+How to bring up a working local instance (API + client + realtime collaboration)
+and the non-obvious gotchas that will otherwise eat an hour. Written from real
+setup pain — read the **Gotchas** section before you start.
+
+## Prerequisites
+
+- **Node 20+ / pnpm 10+.**
+- **Postgres with pgvector.** Use the `pgvector/pgvector` image (e.g.
+  `pgvector/pgvector:pg18`). The stock `postgres` image will FAIL the
+  `CREATE EXTENSION vector` migration — the RAG feature stores embeddings in
+  `page_embeddings`.
+- **Redis** — backs caching, BullMQ queues, the Socket.IO adapter, and collab
+  sync.
+
+## 1. Environment (`.env`)
+
+The client (`apps/client/vite.config.ts`) and both server processes read env via
+`envPath` → the **workspace root `.env`**. Keep a single source of truth. Minimum:
+
+```dotenv
+APP_URL=http://localhost:3000
+PORT=3000
+APP_SECRET=<one long secret — SAME value everywhere, see gotcha #3>
+DATABASE_URL="postgresql://<user>:<pass>@localhost:5432/<db>?schema=public"
+REDIS_URL=redis://127.0.0.1:6379
+COLLAB_URL=http://localhost:3001      # where the CLIENT connects for realtime
+COLLAB_PORT=3001                      # where the COLLAB server listens
+STORAGE_DRIVER=local
+DISABLE_TELEMETRY=true
+```
+
+> If you also keep an `apps/server/.env`, its `APP_SECRET` **must match** the
+> root one (see gotcha #3).
+
+## 2. Migrations
+
+Migrations do **not** auto-run in local dev. After a fresh checkout or switching
+branches, apply them yourself or endpoints touching a new column/table will 500:
+
+```bash
+pnpm --filter server migration:latest
+```
+
+## 3. Bring it up — THREE processes, not two
+
+`pnpm dev` starts only the **API server** (Nest, `:3000`) and the **client**
+(Vite). Realtime collaboration is a **separate process** and `pnpm dev` does NOT
+start it. You need all three:
+
+```bash
+# 1) API + client (from the repo root)
+pnpm dev
+#    → API   http://localhost:3000
+#    → client http://localhost:5173  (Vite; localhost-only by default)
+
+# 2) Collaboration server — SEPARATE process. Build first (see gotcha #2), then:
+pnpm --filter server build          # produces dist/collaboration/server/collab-main.js
+pnpm collab:dev                     # node dist/.../collab-main → listens on :3001 (0.0.0.0)
+```
+
+Without step 2 the editor shows **"Real-time editor connection lost. Retrying…"**,
+stays in read-only *static* mode, and anything that only mounts in the *live*
+editor won't appear.
+
+## Seeding a login
+
+Register through the UI, or reset an existing user's password directly in the DB
+(the server hashes with `bcrypt`):
+
+```js
+// node -e '...'  with pg + bcrypt from the repo's node_modules
+const bcrypt = require("bcrypt");
+const { Client } = require("pg");
+(async () => {
+  const hash = await bcrypt.hash("demopass", 10);
+  const c = new Client({ /* DATABASE_URL parts */ });
+  await c.connect();
+  await c.query("update users set password=$1 where email=$2", [hash, "admin@example.com"]);
+  await c.end();
+})();
+```
+
+> **Use a simple one-word password with no special characters** (e.g. `demopass`,
+> not `Str0ng!Pass@2026`). Demo/test credentials get passed through shells, JSON
+> payloads, and URLs by scripts and automation, where `!` `@` `$` `&` etc. get
+> mangled or need escaping — a plain alphanumeric word avoids a whole class of
+> "wrong password" confusion.
+
+## Gotchas (the грабли)
+
+1. **Collaboration is a third process.** `pnpm dev` runs API + client only.
+   Start `pnpm collab:dev` (on `:3001`) separately or the live editor never
+   connects. The client connects to `COLLAB_URL` directly (default
+   `http://localhost:3001`), NOT through the Vite `/collab` proxy — the API
+   server on `:3000` does **not** serve the collab websocket.
+
+2. **The collab server must be built — you can't run it from source.**
+   `collab:dev` runs `node dist/collaboration/server/collab-main.js`, so run
+   `pnpm --filter server build` first. Running the entry via `tsx`/`ts-node`
+   fails with a NestJS DI error ("dependency … appears to be undefined at
+   runtime") because direct TS execution doesn't emit the decorator metadata the
+   built output has.
+
+3. **`APP_SECRET` must be identical for the API server and the collab server.**
+   The API issues a collab-token (JWT signed with `APP_SECRET`); the collab
+   server validates it with `APP_SECRET`. If they load different values (e.g. a
+   root `.env` and an `apps/server/.env` with different secrets), every realtime
+   connection is rejected with **`[onAuthenticate] Invalid collab token`** and
+   the editor shows "connection lost". Keep one secret everywhere.
+
+4. **Vite binds localhost only.** To reach the stand from another machine on the
+   LAN, start the client with `--host` (`pnpm --filter client exec vite --host`)
+   and use the box's LAN IP. The `/api`, `/socket.io`, and `/collab` Vite proxies
+   forward to `APP_URL`, so the API just works over the LAN; realtime needs
+   `COLLAB_URL` reachable from the browser (point it at the LAN IP:3001, and run
+   collab on `0.0.0.0` — it does by default).
+
+5. **A stale `@docmost/editor-ext` white-screens the client.** The client imports
+   from `@docmost/editor-ext` (a workspace package). If that package's source is
+   behind (missing a newer export, e.g. `Spoiler`), the client dies at load with
+   *"The requested module … does not provide an export named 'Spoiler'"* → blank
+   page. Make sure the workspace `packages/editor-ext` is current for the branch
+   you're running (a stale sibling checkout resolved through a shared
+   `node_modules` symlink is the usual cause).
+
+6. **pgvector, not stock postgres** (see Prerequisites) — the `vector` extension
+   migration fails otherwise.
+
+7. **Migrations don't auto-run in dev** — run `migration:latest` after every pull
+   or branch switch.
+
+See also the **Commands** and **Architecture → Two server processes** sections in
+[`AGENTS.md`](../AGENTS.md).