mikkeli
73eff1c5d6
The app<->svc-gw channels have no wire format yet. Measured USB link drops (~3 s per power change, sleeping tablet invisible at link level) and yukart decision 24 already fix the required fields: heartbeat, command idempotency key, and utterance id/sequence/terminator/expiry. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
55 lines
2.1 KiB
Markdown
55 lines
2.1 KiB
Markdown
---
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type: plan
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status: active
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updated: 2026-10-09
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---
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# Initial plan
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## What is defined
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The envelope, the topic namespace, and the standard OBD-II signals — the ones
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whose names, units and ranges are fixed by the standard rather than by the car.
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## What is not
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**Z27AG-specific signals.** They do not exist until Phase 2 identifies them from
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observed traffic. They arrive as DBC entries plus registry rows with
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`source: "z27ag"`, one at a time as each is confirmed.
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**Composite payload shapes.** `gnss/fix`, `nav/guidance`, `nav/route` and
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`system/<service>` have their fields named in `topics.json` but no JSON Schema
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yet. They get one when a publisher exists to constrain.
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**The app ↔ `svc-gw` boundary protocol.** Bus topics are defined here, but the
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two channels across the boundary (latest-wins state down, acknowledged commands
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up) have no wire format yet. Project-yukart decision 24 (proposed) already
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fixes what it must carry, because the USB link drops for ~3 s at every power
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change and a sleeping tablet looks alive at the link layer:
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- a **heartbeat** in both directions, with an agreed interval and timeout, so the
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Orin reaps a silent client instead of trusting TCP or link state;
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- an **idempotency key** on every upstream command, so retries across a
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reconnect never act twice;
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- for TTS, **utterance id + chunk sequence + terminator + an expiry**, so a
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reconnect can resume or drop an utterance rather than replay it blindly.
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Defined when `svc-gw` and `app-flutter` first talk, not before.
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## Order
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1. Schema validation available to all three languages — the Rust services, the
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Python fixtures and the Dart client must reject a malformed message
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identically, or the contract is decorative.
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2. `gnss/fix` schema, driven by what `tool-mock` replays.
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3. Z27AG signals, as Phase 2 confirms them.
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## Consumers
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| Repo | Reads |
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|---|---|
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| `svc-core` | signals, envelope, DBC |
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| `svc-gw` | topics, envelope |
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| `svc-nav` | topics, envelope |
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| `app-flutter` | topics, envelope, signals (for display units) |
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| `tool-mock` | all of it — fixtures publish the real schema |
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