triggershell/docs/ARCHITECTURE.md

# Architecture

```
 triggershell (Node CLI, src/cli)               server.ts + src/ (Next.js, all server logic)
 ───────────────────────────────                ─────────────────────────────────────────
 triggershell start                              server.ts (custom Node server)
   1. resolve + validate the config (loadConfig)    ├─ Next.js request handler (pages, API routes)
   2. check the port is free                        ├─ ws.WebSocketServer on /ws/runs
   3. set TRIGGERSHELL_CONFIG_PATH/PORT/HOST/        └─ boot: migrate DB, sync auth, reconcile runs
      NODE_ENV
   4. import("./server.ts") — same process                    │
   5. poll /api/healthz, open browser                          │
                                                    ┌──────────┴──────────┐
                                              REST API                 WebSocket
                                          (src/app/api/**)          (src/lib/ws/server.ts)
                                                    │                       │
                                                    └───────────┬───────────┘
                                                                │
                                                    src/lib/runner/engine.ts
                                                       execa(argv, env) — never a shell string
                                                                │
                                                    child process (the configured script)
```

## Why a custom Node server

Next.js Route Handlers can't host a persistent WebSocket server, so `server.ts` wraps Next's
request handler in a plain `http.createServer` and attaches a `ws.WebSocketServer` via the
`upgrade` event, scoped to `/ws/runs` with its own auth check (Route Handlers get auth via
`next/headers`'s `cookies()`, which isn't available on a raw `http.IncomingMessage`).

## Why the CLI and server share one process

`triggershell start` (`src/cli/commands/start.ts`) doesn't spawn `server.ts` as a child process —
it sets `process.env` (`TRIGGERSHELL_CONFIG_PATH`, `PORT`, `HOST`, `NODE_ENV`) and then dynamically
`import()`s `server.ts` directly, in the same Node process. `server.ts` reads that env and installs
its own `SIGTERM`/`SIGINT` handlers, so once it's imported, `Ctrl-C` or `systemctl stop` just work —
there's no parent process relaying signals to a child, no separate lifecycle to manage. The CLI's
`bin/triggershell.js` entry point registers `tsx`'s loader once for the whole process
(`tsx/esm/api`'s `register()`), so both the CLI's own `.ts` command files and `server.ts` run
straight from source, with no compile/bundle step for either.

## Running as a systemd service

`triggershell service install` renders a unit file (`src/cli/lib/systemd.ts`) whose `ExecStart`
line pins the exact `node` binary (`process.execPath`) and the exact, symlink-resolved path to the
installed CLI (`fs.realpathSync(process.argv[1])`) at install time — necessary because systemd
services run with a minimal `PATH` that may not include wherever Node actually lives. By default it
installs a per-user unit (`~/.config/systemd/user/triggershell.service`, no root required); `--system`
targets `/etc/systemd/system/` instead and prints the `sudo` commands to run if not already root.
`install` reloads the systemd daemon but does not enable/start the unit itself — that's a separate,
explicit `systemctl --user enable --now triggershell`, since it's the point where the service
actually starts listening and running scripts. `triggershell service status`/`uninstall` are thin
wrappers around `systemctl`; log tailing is just `journalctl --user -u triggershell -f` — not
reimplemented.

## Cross-module-graph state

Next compiles Route Handlers and Server Components through its own build/module graph, which is a
*separate* module instantiation from whatever `server.ts` imports directly via `tsx` at startup —
even though both run in the same OS process. A plain module-level singleton (e.g. `new Map()` at
the top of a file) ends up duplicated, one copy per graph, which silently breaks anything that
needs to be shared across that boundary (the WebSocket subscriber registry, the live-run-handle
registry used for cancellation, the config/DB singletons). These are anchored on `globalThis`
instead, which is the one truly process-wide object regardless of which graph loaded the file —
see the comment in `src/lib/runner/events.ts` for the canonical explanation.

## Run lifecycle

```
queued → running → succeeded | failed | cancelled | timed_out
                  ↘ interrupted   (set at boot for any row still queued/running - see below)
```

- `src/lib/runner/build-args.ts` turns validated variable values into `{argv, env, stdin}` per
  each variable's `passAs` — this is the only place variable values become process arguments, and
  it never builds a shell string.
- `src/lib/runner/engine.ts` spawns via `execa`, streams stdout/stderr chunks to both the run's log
  file (`logs.dir/<runId>.log`) and `runEvents` (for WS broadcast), and updates the `runs` row's
  status as the child process progresses.
- `src/lib/runner/registry.ts` holds an in-memory `Map<runId, {controller: AbortController}>` for
  live runs, used to route a cancel request (REST or WS) to the right process. This can't survive
  a restart, so `reconcileOrphanedRuns()` marks any DB row still `queued`/`running` at boot as
  `interrupted` — its output can't be re-attached, only its final state corrected.

## Auth

- Session: `iron-session` — a stateless, encrypted+signed cookie (no session-store table).
- Config is the source of truth for *who* is allowed in; `src/lib/auth/sync.ts` upserts config
  users/tokens into SQLite on boot, giving a single DB-backed check path plus `lastLoginAt` tracking.
- `src/proxy.ts` (Next's Proxy, formerly "Middleware") does a fast, cookie-only redirect for
  unauthenticated page/API requests — explicitly *not* the real security boundary. Every Route
  Handler also calls `requireAuth()` itself; this is the actual auth check.
- The WS `upgrade` handler is outside Next's request pipeline entirely, so it authenticates by hand
  (parsing the cookie header, or a `?token=` query param) via `authenticateUpgrade()`.

## Build-time vs. runtime config

Every server file that reads the config/DB at request time (`getConfig()`, `getDb()`,
`requireAuth()`) sets `export const dynamic = "force-dynamic"`. Without it, `next build` tries to
statically prerender pages like `/` at build time, which fails because there's no config file to
read yet (the config only exists at `triggershell start` runtime, in the user's own project
directory, not the package's).