Write down the backend <-> ai-worker contract

`stream:camera_frames` and `channel:print_alerts` are the only interface
between `continuum-backend` and `continuum-ai-worker`, and there was
nothing specifying either. They had drifted completely: the backend
wrote `farmId`, `printerId`, `r2ObjectKey` and `capturedAt`; the worker
read a single field called `printer_id` and ignored the rest. Every task
was delivered, acknowledged, and attributed to a printer called
"unknown" - and nothing errored, because a stream entry is a flat string
map and asking it for a field that is not there is not a failure. Same
shape as the /ws/edge/v1 drift, found the same way.

`schemas/continuum/v1/ai/` is now canonical, with a TypeBox mirror in
ts-types and a Rust mirror in the worker.

Two things the schemas have to say that JSON Schema does not naturally
express, both of which caused real bugs:

- A Valkey stream entry is a flat field/value map of *strings*. No
  nesting, no numbers, no null. So FrameTask has no numeric or nested
  properties, and a field with no value is omitted from the XADD rather
  than written as `""` - an empty string is a value, and the producer
  was writing one for `print_job_id`, which a consumer would carry into
  a lookup or a uuid column.
- PrintAlert, by contrast, *is* a JSON document, because PUBLISH carries
  one opaque string. It is also fire-and-forget with no persistence, so
  it can only ever be a live-console feed and never the record of a
  detection.

The README's layout section was stale (it still listed four DTOs that
were removed in 2026-09) and did not mention `edge/` or `ai/` at all. It
now names both, says why the inter-service protocols live here, and
notes that their Rust mirrors sit in the single repo that consumes each
rather than in `packages/rust-types`.

schemas/continuum/v1/ai/frame_task.schema.json

@@ -0,0 +1,43 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://git.octoturge.com/Continuum/continuum-schemas/raw/branch/main/schemas/continuum/v1/ai/frame_task.schema.json",
+  "title": "FrameTask",
+  "description": "One camera still, handed from continuum-backend to continuum-ai-worker for print-failure scoring. Produced by XADD onto the stream named below; consumed by XREADGROUP.\n\nThis is a Valkey stream entry, not a JSON document: the wire form is a flat field/value map and EVERY value is a string. That is why there are no numeric or boolean properties here and why a field with no value is omitted from the XADD rather than written as an empty string - an empty string is a value, and a consumer that treats it as one ends up looking up the object key \"\".\n\nField names are snake_case, matching every other schema in this repository. The backend's HTTP routes are camelCase; this wire is not an HTTP route, and the consumer on the other end is serde-derived Rust.",
+  "x-stream": "stream:camera_frames",
+  "x-consumer-group": "ai-worker",
+  "type": "object",
+  "properties": {
+    "farm_id": {
+      "type": "string",
+      "format": "uuid",
+      "description": "`farms.id`. Carried so a consumer can attribute load and alerts per farm without a database round trip."
+    },
+    "printer_id": {
+      "type": "string",
+      "format": "uuid",
+      "description": "`printers.id` - the backend's own UUID, already resolved from the gateway's printer id. NOT the gateway's `printers.toml` id, which means nothing outside its own farm."
+    },
+    "print_job_id": {
+      "type": "string",
+      "format": "uuid",
+      "description": "`print_jobs.id`, when the frame belongs to a tracked job. Omitted entirely when it does not - a printer may be streaming while idle, or running something queued outside Continuum. Consumers must treat an absent key and an empty value alike, and must not fabricate a job id."
+    },
+    "r2_object_key": {
+      "type": "string",
+      "minLength": 1,
+      "description": "Where the frame actually is, in the R2 bucket. The frame bytes are deliberately NOT in the stream: a stream entry is held in memory by the server and replayed to every consumer group, and a JPEG per printer per second would make the stream the largest thing in the deployment."
+    },
+    "captured_at": {
+      "type": "string",
+      "format": "date-time",
+      "description": "When the camera took the frame, from the gateway's clock - not when the backend enqueued it. These can differ by a lot: a gateway buffers frames while its uplink is down, so a task may arrive minutes after the moment it describes."
+    }
+  },
+  "required": [
+    "farm_id",
+    "printer_id",
+    "r2_object_key",
+    "captured_at"
+  ],
+  "additionalProperties": false
+}

schemas/continuum/v1/ai/print_alert.schema.json

@@ -0,0 +1,47 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://git.octoturge.com/Continuum/continuum-schemas/raw/branch/main/schemas/continuum/v1/ai/print_alert.schema.json",
+  "title": "PrintAlert",
+  "description": "A print-failure detection, published by continuum-ai-worker for live operator consoles.\n\nUnlike FrameTask this one IS a JSON document: it travels as the payload of a Valkey PUBLISH, which carries a single opaque string, so the structure has to be inside it.\n\nPUBLISH is fire-and-forget with no persistence and no delivery guarantee: an alert published while nothing is subscribed is gone. That is acceptable for the live-console path it feeds and is NOT acceptable as the record of a detection, which belongs in Postgres. As of 2026-10-11 nothing subscribes to this channel and nothing persists it - see the README section on the AI path.",
+  "x-channel": "channel:print_alerts",
+  "type": "object",
+  "properties": {
+    "printer_id": {
+      "type": "string",
+      "format": "uuid",
+      "description": "`printers.id`, taken from the frame task that produced the detection."
+    },
+    "print_job_id": {
+      "type": "string",
+      "format": "uuid",
+      "description": "Omitted when the frame was not attributed to a tracked job."
+    },
+    "label": {
+      "type": "string",
+      "description": "What the model thinks it saw, e.g. \"spaghetti\", \"layer_shift\", \"detachment\". A free string rather than an enum on purpose: the label set is a property of the model file, which changes without this schema changing."
+    },
+    "confidence": {
+      "type": "number",
+      "minimum": 0,
+      "maximum": 1,
+      "description": "The model's own score. Whether it is high enough to act on is the consumer's policy decision, not the worker's - the worker publishes what it found and does not threshold on behalf of an operator who may want to see near-misses."
+    },
+    "captured_at": {
+      "type": "string",
+      "format": "date-time",
+      "description": "From the frame, not from the detection. An operator needs to know when the printer looked like this, not when a GPU got round to looking."
+    },
+    "r2_object_key": {
+      "type": "string",
+      "description": "The frame the detection came from, so a console can show the operator the picture rather than only a label."
+    }
+  },
+  "required": [
+    "printer_id",
+    "label",
+    "confidence",
+    "captured_at",
+    "r2_object_key"
+  ],
+  "additionalProperties": false
+}