T-HUB/docs/engineering-guide.md

Tactical Media Broadcast Hub — Engineering Guide

Covers: everything built as of 499c9fe (WP0–WP3-in-flight), plus Level-2 systems as marked (planned). Companion docs: admin-guide.md · user-guide.md.

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1. System overview

Tactical Media Broadcast Hub is a self-hosted, multi-tenant social-media management platform (Level 1: post & schedule) growing into a video/livestream master-control system (Level 2, planned). Three planes:

CONTROL PLANE                     MEDIA PLANE (planned, WP9+)
  apps/web  (Next.js UI)            media-worker: ingest → compositor →
  apps/api  (NestJS)                  persistent encoder → outputs
  apps/scheduler (Temporal)        FFmpeg-first; never through the API
  PostgreSQL · Redis · Temporal
STORAGE PLANE
  S3-compatible object storage (MinIO dev / any S3 prod)
  ALL media client-side encrypted; content-addressed

Hard rules enforced in code: media bytes never transit API processes; provider branching outside connector packages fails lint; passwords never transit the system (OAuth tokens / bot tokens only); every tenant table is RLS-isolated with FORCE ROW LEVEL SECURITY.

2. Repository layout

apps/
  web/            Next.js 14 App Router frontend (all screens, mock-registry layer)
  api/            NestJS control plane (health, auth, rbac, vault, audit, publishing, storage)
  scheduler/      Temporal worker (publish workflow + activities)
  media-worker/   health-only stub (WP9 fills it)
packages/
  core/           normalized domain types (permissions, connections, publishing, VC family)
  connector-sdk/  PlatformConnector interface, manifest, registry, HTTP client, contract kits
  connector-example/ connector-mock-social/ connector-mock-video/ connector-mock-livestream/
  connector-mastodon/ connector-telegram/          (WP3, in flight)
  testing/        live-source simulator (dod-flap scenario) + mock RTMP sink
infra/            docker-compose (postgres:5433, redis, temporal, minio, otel, prometheus, grafana)
docs/             this documentation set

Monorepo: pnpm workspaces + Turborepo. pnpm lint|typecheck|build|test at root runs all 13+ packages.

3. Identity, tenancy & security (WP2)

3.1 Database roles — two-pool discipline

• Owner pool (SUPER_DATABASE_URL, the postgres superuser in dev): runs migrations, provisions. Never serves requests.
• App pool (DATABASE_URL, role sp_app): neither superuser nor table owner → FORCE ROW LEVEL SECURITY binds for real. Created by migration 003_app_role.sql with table/sequence grants + default privileges.

3.2 Row-level security

Every tenant table (memberships, connections, credentials, audit_log, drafts, publications, scheduled_publications) has:

USING (workspace_id = NULLIF(current_setting('app.workspace_id', true), '')::uuid)

NULLIF matters: pooled sessions carry an empty-string GUC placeholder after SET LOCAL commits; without it the cast throws instead of failing closed. Tenant context is set per-transaction via withTenant(workspaceId, fn) (apps/api/src/db/client.ts) using set_config(..., true) — transaction-local, cannot leak.

3.3 SECURITY DEFINER discipline (audit finding #3)

Cross-tenant functions take an explicit p_workspace_id and call fn_assert_tenant(), which asserts the parameter against the session's tenant context. No unguarded EXECUTE grants for sp_app.

3.4 Continuous authorization (audit finding #2)

Any membership insert/update/delete fires bump_authz_epoch() — COALESCE(NEW.workspace_id, OLD.workspace_id) (OLD is NULL on INSERT; the original bug silently no-oped). Sessions embed the epoch at issue; RbacGuard compares against the live workspaces.authz_epoch and fails closed (401, epoch stale) on mismatch. Revocation propagates to live sessions without waiting for re-login.

3.5 Sessions & OIDC

HMAC-SHA256 signed tokens (apps/api/src/auth/session.ts), 12h TTL, constant-time verify. OIDC: generic code flow + PKCE S256, discovery-document driven (auth/oidc.ts) — Authentik/Keycloak/any compliant issuer via OIDC_* env.

3.6 Credential vault

Envelope encryption (vault/vault.ts): per-workspace DEK (AES-256-GCM) wrapped by master KEK (SUPERPOSTER_KEK, 32B base64; production-required). Rotation re-wraps; old DEK dropped → pre-rotation ciphertext unreadable (tested). Connectors receive opaque CredentialRef handles via CredentialAccessor — never ciphertext, never raw tokens.

3.7 Audit log

Hash-chained per branch (audit_append for tenant rows, audit_append_system for workspaceless events). Branch selection is by tenant-context presence, never by role (findings #1/#6 — sp_scheduler with tenant context appends to the tenant chain). audit_verify_chain(workspace) recomputes hashes — tampering is detectable (tested). Secret-shaped keys are scrubbed to [REDACTED] before append (audit/audit.service.ts).

3.8 Storage encryption (user mandate)

storage/storage.ts — client-side envelope: body = SPENC1 | iv(12) | KEK-wrapped CEK(48) | AES-256-GCM ciphertext+tag. S3_KEK required in production. SSE-at-rest header set additionally. Keys are the plaintext sha256 (sha256/<hash>.<ext>), so put-dedup survives; getObject re-verifies the hash → storage tampering throws. Cross-workspace media dedup is storage-level only; row visibility stays tenant-scoped.

4. Connector architecture (WP1)

4.1 The contract

PlatformConnector (connector-sdk/src/types.ts): manifest(), authorize(), getIdentity(), optional publish/uploadMedia/uploadVideo/getFeed/getComments/reply/getMessages/amplify/unamplify/subscribeWebhooks/handleWebhook/.... Every list method returns Page<T, cursor>.

4.2 Manifest & capabilities

ConnectorManifest declares id, displayName, capabilities (30+ booleans incl. amplifyRepost/amplifyQuote/amplifyShare), connectionFields (e.g. Mastodon instanceUrl, Telegram botToken secret), oauth flavor. The manifest validator rejects password fields outright. UI renders strictly from capabilities — an undeclared capability renders nothing, never a grayed-out lie.

4.3 Registry & the no-branching rule

ConnectorRegistry.register/get — unknown provider throws UnknownProviderError. The ESLint rule no-restricted-syntax (root eslint.config.mjs) fails any provider string literal outside packages/connector-*/, packages/testing/, and apps/web/src/lib/ (the mock-registry boundary standing in for the real registry until the API wires up — same discipline, documented in the config).

4.4 HTTP discipline

RateLimitedHttpClient: per-host token bucket (default 1 rps; Mastodon 0.5), exponential backoff with jitter on 429/5xx, Retry-After honored.

4.5 Amplify truth table (verified per platform, 2026)

Platform	Repost	Quote	Share	Notes
Mastodon	✅ reblog	✅ quoted_status_id (≥4.5)	—	native scheduling via scheduled_at
Telegram	—	—	✅ forward/copy	has_protected_content blocks
Facebook	⚠️ no native reshare API	—	link-share approximation	manifest marks degraded
Instagram	❌	❌	own-media stories only	API exposes no amplify
Bluesky / Threads / LinkedIn	✅ / ✅ / ✅(reshare w/ commentary)	✅ / ✅ / —	—	Level 1b wave
Reddit	—	—	crosspost (stable-but-undocumented) + vote	no vote automation ever
X	✅ (metered)	❌ self-serve (Apr 2026)	—	deferred; pay-per-post model when added

4.6 Contract test kits

connectorContractTests / videoConnectorContractTests / livestreamConnectorContractTests — capability-aware: declared capability without implementing method = FAIL; methods behind undeclared capabilities must be absent. Kits caught two real violations during development.

5. Publishing pipeline (WP3, sol-delivered & verified)

• State machine (publishing.service.ts): editing → in_review → approved → scheduled → published (+ rejected, cancelled). Every transition permission-checked (approval.request / approval.grant / publication.schedule) and audited.
• Durability (006_publishing.sql): scheduled_publications carries a UNIQUE idempotency_key; the DB row commits first; if Temporal is unreachable the row stays pending and the worker's startup sweep picks it up.
• Temporal (scheduler/src/workflows/publish.workflow.ts): scheduledPublish(id) activity (5-min timeout) claims pending-only, resolves the connector via registry, publishes, records the publication, idempotent on re-run.

6. Frontend (apps/web)

Tailwind v4 @theme tokens (dark-first OKLCH, @theme inline brand hook for tenant theming), hand-rolled primitives, cmdk palette, TanStack Virtual streams (500+ items/column, scroll-into-view), Tiptap compose with per-platform char counters/previews. Streams flagship: capability-gated amplify bars, keyboard j/k navigate, r repost, q quote. All data from src/lib/ mock-registry (fixtures are seeded-deterministic). QA: apps/web/scripts/visual-qa.mjs — 14 states, 0 console errors; byte-diff confirms every interaction renders.

7. Testing strategy

Suite	What it proves	Runs
connector contract kits	connectors don't lie about capabilities	CI, always
pure units (vault, session, oidc, scrub, storage-crypto, key-scheme)	crypto/format invariants incl. tamper detection	CI, always
tenancy.integration.test.ts	RLS isolation, tenant-branch audit, epoch bump, chain tamper, immutability triggers	needs DATABASE_URL (sp_app) + SUPER_DATABASE_URL (owner), else skips
storage.integration.test.ts	S3 roundtrip, dedup, presign	needs S3_ENDPOINT, else skips
visual-qa (playwright)	screens render, interactions fire, console clean	local/CI with chromium

Live-DB invocation (from repo root, postgres on :5433):

DATABASE_URL='postgresql://sp_app:sp_app_dev@localhost:5433/tmbh' \
SUPER_DATABASE_URL='postgresql://tmbh:tmbh_dev@localhost:5433/tmbh' \
pnpm --filter @tactical-media-broadcast-hub/api test

8. Observability & ops surface

/healthz (liveness), /readyz (TCP probes: postgres/redis/temporal with per-component status). OTel OTLP tracing skeleton (disabled-safe without collector). Structured pino logs with credential-key redaction. Grafana (3001) provisioned against Prometheus (9090). Full metrics rollout is WP14.

9. Level 2 systems (planned — designs in proposal.md §4.4)

Live Source Monitor (adaptive polling, anti-flapping, per-host budgets); media engine (persistent encoder, graph-rewire switching, GStreamer decision gate); Auto Director (policies/rules/override/program-lock); control room (Preview/Program, TAKE/CUT); archive/grabber/crosspost (S3-mandated, encrypted, content-deduped).

10. Key file map

Concern	Path
Tenant context / pools	apps/api/src/db/client.ts
Migrations 001–006	apps/api/migrations/
Vault / storage crypto	apps/api/src/vault/vault.ts, apps/api/src/storage/storage.ts
Sessions / OIDC	apps/api/src/auth/
RBAC guard	apps/api/src/rbac/rbac.guard.ts
Audit chain	migrations/001_tenants.sql (SQL) + apps/api/src/audit/
Publishing	apps/api/src/publishing/, apps/scheduler/src/
Connector SDK	packages/connector-sdk/src/
Frontend mock-registry	apps/web/src/lib/
Lint: no-provider-branching	eslint.config.mjs