# Architecture

Self-hosted clinical documentation platform. Dockerized Node.js server, PostgreSQL, Redis, and vanilla-JS SPA. No build step on the frontend.

## Stack

| Layer | Technology |
|---|---|
| Runtime | Node.js 24 (Alpine, digest-pinned) + Express 4 |
| Database | PostgreSQL 16 via the digest-pinned `pgvector/pgvector:pg16` image |
| Cache / state | Redis for operational cache, prompt suggestions, and queue groundwork |
| Frontend | Vanilla JavaScript SPA, service-worker cache |
| Mobile | Capacitor 6 wrapper (Android + iOS) |
| Container | Docker Compose (app + db + Redis) |
| Observability | Prometheus metrics at `/metrics`; structured app logs in files, Postgres, and optional Loki |
| Reverse proxy | External (Caddy, Nginx, Traefik — any) |

## Repository layout

```
server.js                        # Express entry
Dockerfile                       # node:24-alpine base, plus pandoc, python3/python-pptx/python-docx, poppler
docker-compose.yml               # app + postgres
migrations/                      # node-pg-migrate files (versioned)
scripts/
  maintenance.js                 # REINDEX / collation-drift CLI
  release.sh                     # semver bump + tag + push

src/
  db/
    database.js                  # pg pool, idempotent baseline init, helpers
    migrate.js                   # programmatic node-pg-migrate runner
  middleware/
    auth.js                      # JWT + session-table validation, sliding idle
    logging.js                   # request log
  utils/
    ai.js                        # callAI() multi-provider router
    models.js                    # model registry + server-side whitelist
    prompts.js                   # prompt templates (DB-overridable)
    crypto.js                    # AES-256-GCM (PHI at rest)
    passwords.js                 # argon2id with bcrypt fallback + rehash
    sessions.js                  # token hashing, UA parser, session-id gen
    platform.js                  # isMobileClient() detection
    redact.js                    # PHI redactor for audit details
    auditQueue.js                # batched audit/api/access log writer
    fileType.js                  # magic-byte upload verification
    promptSafe.js                # <UNTRUSTED_*> LLM prompt wrapper
    logger.js                    # audit/api/access + Loki shipper
    errors.js                    # generic 500 responder
    sttProvider.js, ttsProvider.js  # speech-to-text and text-to-speech routing
    documentExport.js            # pptx/docx/pdf export
    slideSpec.js, docSpec.js     # markdown -> typed spec for the renderers
    deckSchema.js, deckBuild.js  # the deck a presentation is designed as
    deckReview.js                # optional vision pass over a rendered deck
  routes/                        # Express routers (auth, hpi, soap, patient education, …)

public/                          # SPA
  index.html                     # shell, loads components on demand
  sw.js                          # service worker (cache shell, network-first API)
  js/                            # vanilla JS modules, no build step
  components/                    # per-tab HTML fragments
  css/styles.css

.forgejo/workflows/
  docker-build.yml               # dev + main: tests, image; main also publishes
  deploy.yml                     # manual dispatch: deploy.sh against the host
```

## Request pipeline

```
request
  → helmet          (CSP, HSTS, X-Content-Type-Options, …)
  → CORS            (APP_URL + CORS_ORIGINS whitelist, fail-closed in prod)
  → cookieParser
  → express.json    (10 MB cap)
  → rate limiters   (general 200 req/min, per-endpoint tighter on auth)
  → static          (public/ with no-cache on HTML, 1h on JS/CSS; ?v=BUILD_ID busts cache per deploy)
  → route           (feature routers under /api/*)
    → authMiddleware (on protected routes: JWT, DB session check, 24h idle, last_activity update)
  → handler
  → response
```

On boot, `server.js`:
- Validates `JWT_SECRET` and `DATA_ENCRYPTION_KEY` — refuses to start in production without them.
- Runs `initDatabase()` (idempotent baseline) then `node-pg-migrate` (versioned delta).
- Checks `pg_database` collation version; auto-REINDEXes + refreshes on drift.
- Reads git HEAD for `BUILD_ID`; injects `?v=BUILD_ID` into every local `/js/*.js` and `/css/*.css` reference in `index.html`.
- Registers SIGTERM/SIGINT handlers that drain the audit queue and close the pool before exit.

## Auth model

Hybrid, runtime-selected by User-Agent and `X-Client` header:

| Client | Token transport | Persistence | Idle policy |
|---|---|---|---|
| Web browser | `ped_auth` httpOnly cookie, `sameSite=lax` | 30 d maxAge (sliding) | 24 h from last write request |
| Capacitor app (`PedScribe-Android` / `Capacitor` UA) | `Authorization: Bearer <jwt>` | iOS Keychain / Android EncryptedSharedPreferences via `capacitor-secure-storage-plugin` | No server-side idle check (persistent) |

Sessions are validated against `user_sessions.token_hash` on every request. Any
logout / password-change / admin-revoke drops the row and the next request gets
401. The service worker clears its caches on logout so a stale shell never
shows PHI on a shared workstation.

Conventional-commits auto-tag workflow can push a new semver tag using a
`RELEASE_PAT` PAT secret so downstream release workflows fire on the tag push
(the default `GITHUB_TOKEN` is blocked from triggering other workflows by
design).

## Frontend

Single HTML document with `#auth-screen` and `#main-app` sections. Tabs are
per-feature HTML fragments under `public/components/` fetched on demand. JS
modules talk via `window` globals and `CustomEvent` on `document` — no
bundler, no framework. Loader order is fixed in `index.html`.

Post-note helpers such as billing suggestions, don't-miss review, and patient
education handouts are reusable browser-side actions backed by authenticated
JSON APIs. The patient education helper generates a parent-facing plain-text
draft from the edited note and keeps the clinician in the review loop before
copying or sharing.

`authFetch.js` installs a global `fetch` interceptor that treats any 401 on an
authenticated request as a signal to clear local session state and redirect to
login. A `BroadcastChannel('pedscribe-auth')` pushes that signal to sibling
tabs so logging out in one tab drops UI in every open tab.

## Docker topology

| Container | Image | Internal port | External |
|---|---|---|---|
| `pediatric-ai-scribe` | `ped-ai-local:latest` (built from repo) | 3000 | 127.0.0.1:3552 |
| `pedscribe-db` | `pgvector/pgvector:pg16` | 5432 | not exposed |
| `ped-ai-redis` | Redis | 6379 | not exposed |

Named volumes: `pgdata` (database), `scribe-logs` (filesystem audit logs), and Redis data if persistence is enabled by compose.
Application health-check polls `GET /api/health`.

A reverse proxy terminates TLS and forwards to `127.0.0.1:3552`. The app is
never bound to a public interface directly.

## Service worker

`sw.js` implements two strategies:

- **Shell assets** (`/`, `/js/*`, `/css/*`, `/components/*`) — cache-first.
- **`/api/*`** — network-first with cached fallback. Ensures fresh data online,
  last-known-good when offline.

Precached on install: `index.html`, core JS, main stylesheet, login component.
Cleared on logout (`caches.keys() → caches.delete()`).

## Clinical Assistant And MCP

The clinical assistant can call an external MCP-backed retrieval service. Ped-AI remains responsible for the user workflow, provider selection, prompts, and display. MCP remains responsible for Nextcloud access, indexing, retrieval, and vector search. Clinical answer response caching is intentionally disabled; Redis is used for operational metadata and prompt suggestions, not answer reuse.

## Speech

Browser Whisper and browser-local Whisper model downloads are removed from runtime. Speech-to-text routes through LiteLLM; upstream provider choice belongs in LiteLLM config. Browser-native Web Speech remains available only when explicitly enabled by user settings and browser support.

## Operational map

The sections above describe the code. These describe the running system: who
owns what, what crosses each boundary, and where the truth lives when two
places disagree.

### Ownership

Ped-AI is a self-hosted Express application with a browser frontend, PostgreSQL storage, Redis operational state, LiteLLM model routing, and optional MCP-backed clinical retrieval.

| Area | Owner | Notes |
|---|---|---|
| Web app | Ped-AI | Auth, UI, clinical workflows, admin settings, notes, My Resources, bedside tools |
| Database | PostgreSQL | Users, sessions, settings, saved app data, audit/API/access logs |
| Operational cache | Redis | Prompt suggestions, lightweight state, queue groundwork; not clinical answer caching |
| Model gateway | LiteLLM | Text, speech and image model discovery and routing |
| Clinical retrieval | MCP service | Nextcloud access, indexing, search, rerank, source metadata |
| Reverse proxy | Caddy or equivalent | TLS and public routing |

### Request Flow

Normal app request:

```txt
browser
  -> reverse proxy
  -> Express middleware
  -> auth/session check when protected
  -> route handler
  -> PostgreSQL/Redis/provider calls as needed
  -> JSON or HTML fragment response
```

Clinical Assistant request:

```txt
browser
  -> Ped-AI clinical assistant route
  -> MCP semantic search for indexed clinical sources
  -> Ped-AI builds grounded answer prompt
  -> LiteLLM chat model
  -> Ped-AI returns answer plus source metadata
  -> browser renders markdown, citations, and source cards
```

Ped-AI owns the user workflow and rendering. MCP owns retrieval and indexed source metadata. LiteLLM owns model routing.

### Runtime Boundaries

| Boundary | Main Risk | Current Direction |
|---|---|---|
| Browser to Ped-AI | XSS, stale shell, session handling | Sanitized rendering, httpOnly cookie for web, cache busting |
| Ped-AI to PostgreSQL | schema drift, slow queries | migrations, maintenance checks, indexes where needed |
| Ped-AI to Redis | unavailable operational state | Redis is useful but should not hold required clinical answers |
| Ped-AI to LiteLLM | provider downtime, wrong model mode | metadata-based model discovery and timeouts |
| Ped-AI to MCP | retrieval latency/failure | explicit MCP client layer and graceful fallback messages |
| MCP to Nextcloud | stale indexed metadata | scanner/indexer updates source metadata over time |

### Source Of Truth

| Data | Source Of Truth |
|---|---|
| User accounts and sessions | Ped-AI PostgreSQL |
| Admin app settings | Ped-AI PostgreSQL `app_settings` |
| Clinical source documents | Nextcloud and MCP index |
| Clinical source title/path shown to users | MCP result metadata, especially indexed `file_path` |
| Clinical answer text | Generated per request; intentionally not cached |
| Model availability | LiteLLM metadata and configured fallbacks |

### Deployment Shape

Production usually runs:

```txt
Caddy/TLS
  -> pediatric-ai-scribe container
     -> pedscribe-db container
     -> ped-ai-redis container
     -> LiteLLM endpoint
     -> MCP endpoint
```

The app should stay private behind the reverse proxy. Do not expose PostgreSQL, Redis, MCP internals, or provider keys publicly.

### Design Principles

- Keep Ped-AI stateless enough to run more than one app container.
- Keep clinical answer generation live and source-grounded; do not cache final clinical answers.
- Prefer model capability metadata over model-name regexes.
- Prefer indexed file names and paths over embedded PDF metadata for source titles.
- Keep renderer fixes narrow and tested because LLM markdown is messy.
- Keep old frontend globals working until the affected feature is intentionally converted to ESM.