Define the envelope, topic namespace and OBD-II signal registry

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013kj58Jugkic783b8ZrtTVZ

schema/envelope.json

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+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://yukart/schema/envelope.json",
+  "title": "Signal envelope",
+  "description": "Every decoded signal published on yukart/vehicle/* and yukart/gnss/*. Raw CAN uses the binary frame encoding instead.",
+  "type": "object",
+  "required": [
+    "timestamp",
+    "monotonic",
+    "value",
+    "unit"
+  ],
+  "additionalProperties": false,
+  "properties": {
+    "timestamp": {
+      "type": "integer",
+      "description": "UTC epoch microseconds. Absolute reference. Subject to NTP steps; use monotonic for ordering."
+    },
+    "monotonic": {
+      "type": "integer",
+      "description": "Nanoseconds from CLOCK_MONOTONIC. Authoritative for ordering and for any interval within a session. Not comparable across boots."
+    },
+    "value": {
+      "type": [
+        "number",
+        "string",
+        "boolean",
+        "null"
+      ],
+      "description": "null means the signal is known but currently has no value."
+    },
+    "unit": {
+      "type": "string",
+      "description": "Derived from signals.json. Never authored per message."
+    },
+    "quality": {
+      "enum": [
+        "ok",
+        "stale",
+        "invalid"
+      ],
+      "default": "ok",
+      "description": "Omitted when ok."
+    },
+    "mock": {
+      "type": "boolean",
+      "default": false,
+      "description": "Present and true when synthesised. Must be rendered visibly by any display."
+    }
+  }
+}

schema/signals.json

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+{
+  "$comment": "Single source for signal identity. Topic name and envelope unit are both derived from these entries and are never authored separately. source=obd2 is standardised; source=z27ag is reverse-engineered and lives in the DBC.",
+  "signals": {
+    "engine_rpm": {
+      "unit": "rpm",
+      "type": "number",
+      "source": "obd2",
+      "description": "Engine speed",
+      "range": [
+        0,
+        8000
+      ]
+    },
+    "vehicle_speed_kph": {
+      "unit": "kph",
+      "type": "number",
+      "source": "obd2",
+      "description": "Road speed",
+      "range": [
+        0,
+        255
+      ]
+    },
+    "coolant_temp_c": {
+      "unit": "celsius",
+      "type": "number",
+      "source": "obd2",
+      "description": "Engine coolant temperature",
+      "range": [
+        -40,
+        215
+      ]
+    },
+    "intake_air_temp_c": {
+      "unit": "celsius",
+      "type": "number",
+      "source": "obd2",
+      "description": "Intake air temperature",
+      "range": [
+        -40,
+        215
+      ]
+    },
+    "throttle_pct": {
+      "unit": "percent",
+      "type": "number",
+      "source": "obd2",
+      "description": "Throttle position",
+      "range": [
+        0,
+        100
+      ]
+    },
+    "engine_load_pct": {
+      "unit": "percent",
+      "type": "number",
+      "source": "obd2",
+      "description": "Calculated engine load",
+      "range": [
+        0,
+        100
+      ]
+    },
+    "fuel_level_pct": {
+      "unit": "percent",
+      "type": "number",
+      "source": "obd2",
+      "description": "Fuel tank level",
+      "range": [
+        0,
+        100
+      ]
+    },
+    "intake_pressure_kpa": {
+      "unit": "kpa",
+      "type": "number",
+      "source": "obd2",
+      "description": "Intake manifold absolute pressure",
+      "range": [
+        0,
+        255
+      ]
+    },
+    "maf_gps": {
+      "unit": "g/s",
+      "type": "number",
+      "source": "obd2",
+      "description": "Mass air flow rate",
+      "range": [
+        0,
+        656
+      ]
+    }
+  }
+}

schema/topics.json

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+{
+  "root": "yukart",
+  "topics": {
+    "yukart/can/raw": {
+      "payload": "binary",
+      "retained": false,
+      "rate": "1000-3000/s",
+      "publisher": "can-bridge",
+      "description": "Timestamped raw frames. Binary, not the JSON envelope."
+    },
+    "yukart/vehicle/<signal>": {
+      "payload": "envelope",
+      "retained": true,
+      "rate": "1-50/s",
+      "publisher": "decoder",
+      "description": "One topic per signal, named exactly as in signals.json."
+    },
+    "yukart/gnss/fix": {
+      "payload": "envelope",
+      "retained": true,
+      "rate": "1-10/s",
+      "publisher": "gnss",
+      "description": "value is an object: lat, lon, alt_m, speed_kph, heading_deg, fix, satellites."
+    },
+    "yukart/system/<service>": {
+      "payload": "json",
+      "retained": true,
+      "rate": "on change",
+      "publisher": "every service",
+      "description": "state: starting|ready|degraded|stopping, plus service-specific detail."
+    },
+    "yukart/nav/guidance": {
+      "payload": "json",
+      "retained": true,
+      "rate": "on change",
+      "publisher": "svc-nav",
+      "description": "Next manoeuvre, distance, street name."
+    },
+    "yukart/nav/route": {
+      "payload": "json",
+      "retained": true,
+      "rate": "on change",
+      "publisher": "svc-nav",
+      "description": "Active route geometry."
+    },
+    "yukart/session/mark": {
+      "payload": "json",
+      "retained": false,
+      "rate": "human",
+      "publisher": "svc-gw",
+      "description": "Operator event stamped into the recording. Carries both clocks like the envelope."
+    }
+  }
+}