# V4 — Architecture (Page Index)

This directory holds the V4 (a UE5 tactical-action universe of multiple
game-style "cells" — tactical FPS, stealth, action-RPG, RTS, 2D run-and-gun — on
a shared engine) architecture reference, decomposed from the single
[`../V4_ARCHITECTURE.md`](../V4_ARCHITECTURE.md) hub into focused, in-depth,
code-grounded pages. The hub remains the canonical entry point and preserves
every section heading; each page below expands one part of the system with
richer, code-grounded detail and an honest implemented / spec-only status. The
companion feature map lives in [`../V4_features.md`](../V4_features.md).

> **Cross-reference convention.** Page-to-page links are relative
> (`./<slug>.md`). Platform-foundation links point at the shared
> [`platform/`](../../platform/overview.html) space.

## Architecture landscape

```mermaid
flowchart TB
  Host[V4 game host] --> Plugins[Cell and mode plugins]
  Plugins --> Gameplay[GAS animation input and cell specialization]
  Gameplay --> AI[Perception stealth crowds and AI director]
  Gameplay --> Authority[Networking determinism online and persistence]
  AI --> World[World streaming procgen maps and content]
  Authority --> World
  World --> Presentation[Audio VFX cinematics UI accessibility and hardware]
  Plugins --> Data[(Versioned cell mode asset save and progression data)]
  Authority --> Evidence[(Replays telemetry receipts and audits)]
  Data --> Build[Build cook performance security compliance and launch]
  Presentation --> Build
  Evidence --> Build
```

The host controls compatible composition; plugins own cell/mode specialization;
shared systems own reusable contracts; server or deterministic authority owns
effects; and build/operations own deployability. An arrow does not authorize a
cell to bypass another layer's version, safety, or persistence boundary.

Trace an affected behavior from plugin activation and canonical data through
input/GAS/animation, AI/world, authority/persistence, presentation, telemetry,
build, and recovery evidence. Pair that trace with the
[feature index](../features/README.md) and name the target cells—one cell's
functional or performance result cannot certify the others.

Every focused architecture topic appears exactly once below. The
[V4 documentation guide](../docs/README.md) provides the status vocabulary and
role paths; the [diagram atlas](../docs/diagram-atlas.md) supplies cross-system
models. Backlog, dependencies, decisions, current code/assets/tests/builds,
verification, and platform release evidence remain authoritative.

## Orientation

- [V4 Product Promise & Architectural Overview](./product-promise.md) — what V4
  commits to and the multi-cell-on-one-engine thesis.
- [Subsystem Glossary & Module Map](./glossary.md) — every V4 module mapped to
  code.
- [High-Level Architecture](./high-level-architecture.md) — the runtime topology
  and the cell-hosting model.

## Combat, Character & Input Systems

- [Gameplay Ability System (GAS) Layout](./gas-layout.md) — attribute sets,
  abilities, and effects across the cells.
- [Animation Pipeline](./animation-pipeline.md) — state machines, blending, and
  per-cell specialization.
- [Input Pipeline](./input-pipeline.md) — Enhanced Input, contexts, and per-cell
  input schemes.

## AI, Stealth & Per-Cell Combat

- [AI, Perception & Stealth](./ai-perception-stealth.md) — the AI architecture,
  perception, and the stealth systems.
- [Per-Cell Architecture Deep-Dives](./per-cell-deep-dives.md) — how each
  game-style cell is built on the shared engine.

## Netcode, Modes & World

- [Networking & Determinism](./networking-determinism.md) — the netcode model,
  replication, and determinism.
- [Game Modes & Live Service](./game-modes-live-service.md) — the mode
  architecture across cells and live service.
- [World Streaming & Procedural Generation](./world-streaming-procgen.md) —
  world streaming, procgen, and crowds.

## Online, Persistence & Platform

- [Online Services & Persistence](./online-services-persistence.md) — online
  services and the persistence/save layer.

## Presentation, Production & Launch

- [Presentation Pipelines: Audio, VFX, Cinematics & UI](./presentation-pipelines.md)
  — the audio, VFX, cinematic, and UI/HUD pipelines.
- [Build, Data & Content Pipeline](./build-data-content.md) — build/cook/patch,
  data architecture, and the content pipeline.
- [Telemetry, Observability & Performance](./telemetry-observability-performance.md)
  — telemetry, observability, and performance budgets.
- [Security, Compliance & Launch](./security-compliance-launch.md) — security,
  compliance, testing/cert, and launch readiness.