# quic_ecs_dt — Project Guide for Claude

## What & why

Source repo for **"QUIC + ECS as Complementary Transport and Runtime Substrates for Industrial Digital Twins"** — UCAmI 2026 (Plantevin & Francillette, UQAC). Third paper in a sequence; the first two are at IEEE SWC 2026:

- `plantevin2026ecs` — ECS as runtime substrate for industrial DT (200k assets @ 114 Hz on Pi 5).
- `plantevin2026quic` — QUIC partial reliability for DT sensor streams (94% P99 reduction vs TCP at 5% loss).

**UCAmI hypothesis (the composition question):** prior work shows ECS and QUIC each work as substrates *independently*. Does integrating real QUIC traffic into a Bevy ECS ingest path introduce coupling that degrades either one's claimed properties? The paper argues no, and measures it.

## Architecture

Three-tier QUIC ↔ ECS bridge, headless Bevy runtime:

| Tier | QUIC primitive | Use case | Channel cap | Tx newtype |
|------|----------------|----------|-------------|------------|
| T1 | Unreliable datagrams (RFC 9221) | High-freq ephemeral telemetry; drops OK | 1024 | `T1Sender::send_lossy` (try_send, drop on full) |
| T2 | Unidirectional streams | Ordered threshold events; reliable | 512 | `T2Sender::send` (await, backpressure) |
| T3 | Bidirectional streams | Actuator commands w/ ACK; per-command oneshot reply | 256 | `T3Sender::send` of `T3Inbound { command, reply }` |

QUIC server runs on a dedicated OS thread with a Tokio multi-thread runtime; pushes decoded `QuicMessage` (UUID + sensor_id + f64 + ts + seq, 38 B fixed LE) into `tokio::sync::mpsc` per tier via the `T1Sender / T2Sender / T3Sender` newtypes (in [substrate/src/transport/mod.rs](substrate/src/transport/mod.rs)) so misuse is a type error. Bevy `ingest_system` drains in `PreUpdate`, gated by `run_if(in_state(ServerState::Started))`. Pattern is in [substrate/src/transport/ecs.rs](substrate/src/transport/ecs.rs).

**T3 ack protocol.** A device opens a bi-stream and writes one `QuicMessage` (the command). The demux task reads it, builds a `T3Inbound { command, reply: oneshot::Sender<QuicMessage> }`, and sends it on the T3 mpsc. The ECS handler writes the ack into `reply`; the demux task awaits `reply_rx` and writes the resulting `QuicMessage` back on the bi-stream. Dropping the oneshot signals "no handler" and propagates as a stream close — used by the placeholder ingest until M4 installs real handlers.

**Target hardware:** CM5 (BCM2712, Cortex-A76, 4 GB) as DT runtime; M4 Max as traffic generator; 1 Gbps direct Ethernet. Both rigs are in hand.

## Repo map

```
quic_ecs_dt/
├── paper/                Quarto + LNCS source — single index.qmd, refs in references.bib
├── substrate/            Rust crate: Bevy 0.18 + Quinn 0.11 + rustls 0.23 + Tokio
│   └── src/
│       ├── main.rs       App::new, MinimalPlugins, EcsQuicTransportPlugin
│       ├── config.rs     figment chain: defaults → config.toml → APP_* env
│       └── transport/
│           ├── mod.rs    QuicMessage struct
│           ├── ecs.rs    Plugin: tokio thread + 3 mpsc + PreUpdate ingest
│           └── server.rs run_substrate_server (EMPTY STUB)
├── simulator/            Rust crate: stub today; will be Quinn client + Bevy sensor generators
├── data/                 (created by M6) loopback/, two_machine/ — raw CSVs committed, *_processed ignored
├── Cargo.toml            workspace
└── Makefile              render, preview, build, build-cm5, deploy-cm5
```

## Status

| Area | State |
|------|-------|
| `AppConfig` figment loader (defaults → TOML → env) | Done — [substrate/src/config.rs:42](substrate/src/config.rs#L42) |
| 3-tier MPSC bridge scaffolding (Tokio thread + Bevy plugin) | Done — [substrate/src/transport/ecs.rs](substrate/src/transport/ecs.rs) |
| `QuicMessage` struct (no codec yet) | Defined — [substrate/src/transport/mod.rs:4](substrate/src/transport/mod.rs#L4) |
| Quinn server lifecycle | Listener up — `ServerState{Starting,Started}` in [substrate/src/transport/state.rs](substrate/src/transport/state.rs); `OnEnter(Starting)` → bind + accept loop in [substrate/src/transport/ecs.rs](substrate/src/transport/ecs.rs). Explicit `TransportConfig` w/ tuned datagram recv buffer (256 KiB) in [substrate/src/transport/server.rs](substrate/src/transport/server.rs). Per-tier sender newtypes (`T1Sender::send_lossy`, `T2Sender::send`, `T3Sender::send`) in [substrate/src/transport/mod.rs](substrate/src/transport/mod.rs) |
| T1 demux (datagrams → ECS) | Done — `handle_incoming` orchestrator + `read_datagrams` reader in [substrate/src/transport/server.rs](substrate/src/transport/server.rs); decode errors logged but non-fatal; channel-full drops silent at trace; received/dropped/decode_errors counters in the end-of-stream debug line |
| T2 demux (uni streams → ECS) | Done — `read_uni_streams` accepts streams in [substrate/src/transport/server.rs](substrate/src/transport/server.rs), spawns one task per stream that reads 38 B chunks until EOF; decode failure resets the stream via `recv.stop(0)` (one bad stream doesn't kill the connection); `t2.send().await` honours backpressure |
| T3 demux (bi streams ↔ ECS) | Done — `accept_bi_streams` + `read_one_bi_stream` in [substrate/src/transport/server.rs](substrate/src/transport/server.rs); reads 38 B command, ships `T3Inbound { command, reply: oneshot::Sender }` to the ECS, awaits the reply, writes 38 B ack and finishes. If the ECS drops the oneshot (no handler installed yet — the M4 placeholder) `send.reset(0)` gives the client a clean signal instead of a half-open stream. `handle_incoming` joins all three readers on close |
| TLS / self-signed cert | Done (M1) — `certs/server.{crt,key}` via `make certs`, gitignored. PEM loader in [substrate/src/transport/server.rs:15](substrate/src/transport/server.rs#L15); rustls `aws-lc-rs` default provider installed in [substrate/src/main.rs](substrate/src/main.rs) |
| Wire codec for `QuicMessage` (39 B fixed LE, incl. `sensor_type: u8`) | Done — [substrate/src/transport/mod.rs](substrate/src/transport/mod.rs); 5 unit tests passing. `SensorType` enum: `Generic / Temperature / Humidity / Pressure / Voltage / Current` |
| `tracing-subscriber` init w/ `RUST_LOG` | Done (M1) — [substrate/src/main.rs:8-12](substrate/src/main.rs#L8-L12) |
| ECS components (`RawSensorData`, `SmoothedValue`) + 5 systems (Ingest/Sim/Export/FaultInjection/Diagnostics) | Done — entities = `(DeviceId, SensorId, SensorTypeTag, RawSensorData, SmoothedValue, Asset)` per (device, sensor); `SensorRegistry` upserts via `HashMap<(Uuid, u16), Entity>` in [substrate/src/world.rs](substrate/src/world.rs). `IngestSystem` drains all three tiers; T3 ack preserves command's `sensor_type` and returns the device's most recent `raw_value`. `SimulationSystem` maintains a 16-sample rolling mean per entity and emits `substrate_threshold_crossings_total{type, direction}` when the smoothed mean crosses a per-type threshold (`Changed<RawSensorData>` query so cost scales with ingress, not fleet size). `ExportSystem` samples `substrate_{entities,channel_depth,channel_capacity,rss_bytes}` + `sensor_aggregate{type, stat}` once per second. `FaultInjection` is still a stub awaiting M6. `Diagnostics` logs `tick_hz` once per second |
| Schedule rate-gating | Done (M4) — `MinimalPlugins.set(ScheduleRunnerPlugin::run_loop(1/tick_rate_hz))` in [substrate/src/main.rs](substrate/src/main.rs); replaces the default busy-loop with the configured period |
| Prometheus exporter + Grafana dashboards | Done (M5) — `ObservabilityPlugin` in [substrate/src/observability.rs](substrate/src/observability.rs) installs `metrics-exporter-prometheus` on the existing tokio runtime. **Runtime surface** (paper §Evaluation): counters `substrate_received_total{tier}`, `dropped_total{tier=t1}`, `decode_errors_total{tier}`, `t3_no_handler_total`; latency histograms `substrate_latency_us{tier}`; gauges `substrate_tick_hz`, `substrate_entities`, `substrate_channel_depth{tier}`, `substrate_channel_capacity{tier}`, `substrate_rss_bytes`. **Sensor data surface** (operator dashboard): per-type aggregates `sensor_aggregate{type, stat=count|mean|min|max}` computed once per second over the live world, cardinality bounded by `\|SensorType\| × 4` so it scales to thousands of sensors. Two dashboards: [dashboards/runtime.json](dashboards/runtime.json) and [dashboards/sensors.json](dashboards/sensors.json) (thermometer/gauge/stat panels per type) |
| Simulator (Quinn client + sensor generators) | `SimulatorClient` lib in [simulator/src/client.rs](simulator/src/client.rs) — connects, trusts the substrate's PEM cert via custom `ServerCertVerifier` (sidesteps `CaUsedAsEndEntity`); `send_datagram(QuicMessage)` for T1, `send_uni_stream(&[QuicMessage])` for T2, `request(&QuicMessage) -> QuicMessage` for T3. CLI driver in [simulator/src/main.rs](simulator/src/main.rs) with clap flags (`--addr`, `--rate-hz`, `--t2-rate-hz`, `--t3-rate-hz`, `--t3-timeout-ms`, `--count`, `--devices`, `--sensor-id`, `--sensor-type`, `--profile`, `--cert`, `--server-name`); parallel T1+T2+T3 emitters, per-(device,sensor) sequence counters, type-appropriate waveform generators (sin/cos curves centred on realistic sensor ranges), 1-Hz combined progress logs, Ctrl-C drain. `--profile industrial` fans out to 5 sensors per device (Temperature/Humidity/Pressure/Voltage/Current). Bevy-driven sensor generator still pending |
| End-to-end test harness | Six integration tests across [simulator/tests/end_to_end_t1.rs](simulator/tests/end_to_end_t1.rs), [simulator/tests/end_to_end_t2.rs](simulator/tests/end_to_end_t2.rs), [simulator/tests/end_to_end_t3.rs](simulator/tests/end_to_end_t3.rs): T1 single-datagram round-trip + 32-msg burst order; T2 single-stream order-preservation + 4-stream concurrent per-device ordering; T3 round-trip with fake-ECS handler + no-handler stream-reset. Each test calls `bind_endpoint` + `accept_loop` in-process with channels owned by the test |
| `config.toml` at repo root | Done (M1) — [config.toml](config.toml); loaded by [substrate/src/main.rs:9](substrate/src/main.rs#L9) |
| Benchmark harness (sweep + CSV writer) | Missing |
| CM5 cross-compile / deploy | Wired in [Makefile:30](Makefile#L30); not exercised |

`cargo run -p substrate` boots, prints the loaded config, and idles on the (still-empty) Quinn server. `MinimalPlugins` busy-loops the ECS schedule by default — expected, will gate to `tick_rate_hz` in M4.

## Roadmap

Each milestone has one verification gate. Update Status here as we go.

- **M1 — Wire codec & root config.** ✅ Done 2026-05-04. Hand-rolled little-endian codec on `QuicMessage` (38 B fixed: 16 UUID + 2 stream_id + 8 f64 + 8 ts_us + 4 seq) with roundtrip + layout + length-error tests; `config.toml` at repo root; dev TLS via `make certs`; structured `tracing-subscriber` init reads `RUST_LOG` (default `info`).
- **M2 — Quinn server + self-signed TLS.** ✅ Done 2026-05-06. Listener up under `ServerState::Starting/Started`; type-system tier semantics + T3 oneshot ack protocol; per-connection `handle_incoming` orchestrator joining T1 datagram, T2 uni-stream, and T3 bi-stream readers. T1 has dropped/decoded counters; T2 resets a stream on decode failure without killing the connection; T3 ships `T3Inbound { command, reply }` to the ECS and resets the stream when no handler answers. End-to-end coverage: 6 integration tests in [simulator/tests/](simulator/tests/) plus 4 codec unit tests, all green.
- **M3 — Simulator client.** Replace [simulator/src/main.rs](simulator/src/main.rs) with a Bevy app: Quinn client, N synthetic devices, configurable per-tier rates. *Verify:* end-to-end loopback drains messages on all three tiers. **Status (2026-05-05):** simulator made into a lib + bin; `SimulatorClient::{connect,send_datagram,close}` plus a manual smoke runner in `simulator/src/main.rs`. Two integration tests in `simulator/tests/end_to_end_t1.rs` exercise the full T1 path against an in-process substrate. Bevy-driven generator + T2/T3 helpers + load profiles still pending.
- **M4 — ECS world.** ✅ Done. `Asset` + `DeviceId` + `SensorId` + `SensorTypeTag` + `RawSensorData` + `SmoothedValue` components in [substrate/src/world.rs](substrate/src/world.rs); `SensorRegistry` resource for O(1) `(Uuid, u16) → Entity`. `IngestSystem` drains all three tiers (T1 batched, T2/T3 fully); T3 handler returns the latest sensor value as ack. `SimulationSystem` runs a per-entity 16-sample rolling mean and emits `substrate_threshold_crossings_total{type, direction}` on per-type threshold crossings — gives the ECS observable digital-twin work, not just write-through ingest. `ExportSystem` samples `substrate_{entities,channel_depth,channel_capacity,rss_bytes}` + `sensor_aggregate{type, stat}` once per second. `FaultInjection` still a stub (M6). `DiagnosticsSystem` logs tick rate once per second. Schedule rate-gated via `ScheduleRunnerPlugin::run_loop(1/tick_rate_hz)`. 8 unit tests passing (entity create, in-place update, T3 ack, SmoothedValue push/window/non-finite/full-roll, threshold-crossing transition).
- **M5 — Observability (VictoriaMetrics + Grafana).** ✅ Done. Wire format extended to carry `sensor_type: u8` (38 → 39 B, decoded into `SensorType` enum). Two metric surfaces over `metrics-exporter-prometheus`:
  - **Runtime** (paper §Evaluation): `substrate_received_total{tier}`, `dropped_total{tier=t1}`, `decode_errors_total{tier}`, `t3_no_handler_total`, `latency_us{tier}` histograms, `tick_hz` / `entities` / `channel_depth{tier}` / `rss_bytes` gauges.
  - **Sensor data** (operator surface): `sensor_aggregate{type, stat=count|mean|min|max}` aggregated per second across the live ECS world. Cardinality bounded to `\|SensorType\| × 4` series independent of physical sensor count.
  - Dashboards: [dashboards/runtime.json](dashboards/runtime.json) + [dashboards/sensors.json](dashboards/sensors.json).
  - Verified: `--profile industrial --devices 2 --count 200` yields 10 entities and all 5 type aggregates with realistic values (T=20.5°C, RH=51%, P=1018 hPa, V=230.2 V, I=12 A).
- **M6 — Benchmark harness.** Sweep `entity_count ∈ {10k, 50k, 100k, 200k}` × `loss_rate ∈ {0%, 1%, 5%}` with 2k warmup + 5k measurement ticks. Loss via `tc netem` or in-app injection. Writes `data/loopback/final_table.csv`. *Verify:* one full sweep on M4 Max produces a CSV the Quarto figures consume.
- **M7 — CM5 cross-compile & deploy.** Exercise [Makefile:30](Makefile#L30) (`build-cm5`, `deploy-cm5`); set real `CM5_HOST`. *Verify:* binary runs on CM5 with a feed from M4 Max over 1 Gbps Ethernet.
- **M8 — Two-machine run + paper render.** Sweep with simulator on M4 Max → substrate on CM5; populate `data/two_machine/final_table.csv`; `make render` produces a PDF. **Update §Evaluation prose to reflect actual numbers.** Current paper figures (241 Hz, 64 µs / 15.8 ms P99, 2.6 µs jitter, 1.02 MB/1k, R²=0.9999) are **aspirational placeholders** — they may move and the conclusions may shift; that's expected.

## Conventions

- **Rust:** edition 2024; workspace at root with `simulator` + `substrate`; `opt-level=1` dev, `opt-level=3` for deps.
- **Pinned crates:** Bevy 0.18, Quinn 0.11, rustls 0.23, Tokio 1 (full), figment 0.10 (toml + env), uuid 1.23 (v4), serde 1.
- **Config:** `figment` chain — defaults in [substrate/src/config.rs:25](substrate/src/config.rs#L25) → `config.toml` → env `APP_*` (double-underscore for nesting, e.g. `APP_NETWORK__SERVER_PORT=9000`).
- **Bevy:** headless — `MinimalPlugins` only; do not pull rendering plugins.
- **Tokio↔Bevy:** keep the dedicated-thread + mpsc pattern in [substrate/src/transport/ecs.rs:49](substrate/src/transport/ecs.rs#L49); do not block the ECS schedule on async work.
- **Paper:** Quarto + LNCS template ([paper/_extensions/template.tex](paper/_extensions/template.tex), [paper/_quarto.yml](paper/_quarto.yml)). **Never commit `llncs.cls` or `splncs04.bst`** — CTAN licensing; download per [README.md:25-34](README.md#L25-L34).
- **Data:** raw CSVs under `data/` are committed; `*_processed.csv` is gitignored. Paper figures consume `data/loopback/final_table.csv` and `data/two_machine/final_table.csv`.
- **Build artifacts:** `target/`, `paper/_output/`, `paper/figures/`, `paper/.quarto/`, `paper/index.tex` all gitignored.
- **Errors:** `anyhow` (with `.context()`) for internal startup paths where the error type is uninteresting; `thiserror` for boundary types we want to match against (e.g. `WireError` in the codec).
- **Warnings:** let real warnings show. No `#[allow(dead_code)]`, `_var` blanket suppression, or `PhantomData` shims to silence the compiler — warnings are honest TODO markers and disappear when the consuming code lands. See [feedback memory](../../.claude/projects/-Users-vplantevin-Projects-Research-quic-ecs-dt/memory/feedback_no_warning_hacks.md).

## Known deferrals

- **Channel ownership is per-host, not per-connection.** All connections share the same three mpsc channels. Fairness under N-device load relies on tokio scheduling. Acceptable for the "one ECS world per host" model the paper describes; revisit if many-device benchmarks show starvation.
- **No graceful shutdown.** The `quic-runtime` thread is parked on `pending()`; spawned tasks (accept loop, per-conn demux) are orphaned at process exit. Fine for research runs; we'll need an `OnExit(Started)` (or a `Stopping` state) when M5 observability needs clean drain or M8 wants finalised CSV writes.
- **Bind failure is fatal.** `OnEnter(Starting)` panics if `bind_endpoint` fails. A `ServerState::Failed` variant joins when we wire proper error surfacing.
- **T3 ack semantics are minimal.** The current handler echoes the device's most recent `raw_value` with a server timestamp — adequate for "read sensor" commands, not for actuator-write semantics. A future iteration may introduce an `ActuatorState` component and a setpoint-apply path; for now T3 is best framed as "reliable read/query RPC" in the paper.
- **`FaultInjectionSystem` is still empty.** Runs on schedule but does nothing. M6 fills it with rate-controlled in-app drop so loss sweeps don't depend on external `tc netem`.
- **Schedule rate-gating is approximate.** `ScheduleRunnerPlugin::run_loop(period)` honours `period` as a minimum; observed `tick_hz` runs ~85% of target on macOS dev (target 60 → ~50). Should be tighter on the CM5; revisit if M6 sweeps depend on a steady tick.

## Run / verify

```bash
make certs              # generate certs/server.{crt,key} (ECDSA P-256, SAN: localhost/cm5.local/127.0.0.1/::1)
make build              # cargo build --release (native, depends on certs)
make build-cm5          # aarch64 cross-build for the CM5 (depends on certs)
make deploy-cm5         # scp to $CM5_HOST (set in env or override Makefile var)
make render             # build the paper PDF
make preview            # live-reload paper preview at :4848
make clean              # cargo clean + drop generated paper outputs
```

`certs/` is gitignored; `make build` regenerates the dev cert if missing. From the repo root: `cargo run -p substrate` boots, prints the loaded `AppConfig`, and idles. `config.toml` and cert paths are resolved relative to the cwd — always launch from the repo root.

**Tests.** `cargo test --workspace` runs the codec unit tests in `substrate` plus the end-to-end integration tests in [simulator/tests/](simulator/tests/). Each integration test calls `bind_endpoint` + `accept_loop` in-process on `127.0.0.1:0` (OS-assigned port), connects a `SimulatorClient` against it, and asserts what arrives on the test-owned T1 receiver. Add a new `simulator/tests/end_to_end_*.rs` for each new wire path (T2 uni, T3 bi) as the substrate-side demux lands.

**Metrics scrape.** With `metrics_enabled = true` (default), the substrate exposes a Prometheus-format endpoint:

```bash
curl http://127.0.0.1:9100/metrics
```

A docker-compose stack under [monitoring/](monitoring/) brings up VictoriaMetrics + Grafana auto-provisioned: `make monitoring-up` then Grafana at <http://localhost:3000> (admin / admin), both dashboards under the `quic_ecs_dt` folder. The compose mounts [dashboards/](dashboards/) directly so any edit to the JSON files re-imports within 10 s.

Two Grafana dashboards under [dashboards/](dashboards/):

- [`runtime.json`](dashboards/runtime.json) — tick rate, RSS, per-tier received/dropped/latency, channel depth (paper §Evaluation surface).
- [`sensors.json`](dashboards/sensors.json) — thermometer + gauges + stat panels per `SensorType`, driven by `sensor_aggregate{type, stat}` (operator-facing surface).

Both use the `${datasource}` template variable so you can point them at any Prometheus-compatible source.

**Manual two-process run.** From the repo root, in two shells:

```bash
# shell 1 — server (use RUST_LOG=substrate=debug to see the per-conn summary)
cargo run -p substrate

# shell 2 — client; --help shows all flags
cargo run -p simulator -- --rate-hz 100 --count 0 --devices 4
```

Simulator flags (see `cargo run -p simulator -- --help`): `--addr`, `--server-name`, `--cert`, `--rate-hz` (T1 datagram rate; `0` disables T1), `--t2-rate-hz` / `--t3-rate-hz` (per-tier event rate; `0` disables), `--t3-timeout-ms` (T3 ack wait, default `2000`), `--count` (T1 count; `0` = until Ctrl-C), `--devices`, `--sensor-id`, `--sensor-type` (one of `generic|temperature|humidity|pressure|voltage|current`), `--profile` (`single` or `industrial` — 5 sensors per device on ids 0..4 covering all types). The client logs a one-second `progress` line with `t1_sent`/`t2_sent`/`t3_sent`/`t3_timeouts`/per-tier observed Hz, and a final `simulator done` line with elapsed time on exit.

## Key references

- Prior self-citations: `plantevin2026ecs`, `plantevin2026quic` (both IEEE SWC 2026, "to appear").
- QUIC: RFC 9000 (core), RFC 9221 (unreliable datagrams).
- DT foundations: Tao et al. 2019; Grieves & Vickers 2017; Minerva et al. 2020.
- ECS: Nystrom 2014, *Game Programming Patterns*.
- Mixed-reliability transport: Peeck et al. (W2RP for DDS).
- DT sync metrics: Çakır et al. 2023 (Twin Alignment Ratio); Bellavista et al. 2023 (ODTE).
- Industrial QUIC/IIoT: Fernández et al. 2021; Boeding et al. 2025.
- Full bibliography: [paper/references.bib](paper/references.bib).