Wake Approvisionnement on a stock event instead of a clock
The reactive half of the agent. It consumes product.stock_changed from the catalog topic and reports only a crossing of the threshold — every further order line on an already-low reference would otherwise raise the same alarm, and an agent that repeats itself is one a human learns to ignore. A stock-out is treated as its own fact even when the reference was already low. The detection lands on a watchlist readable over a webhook, because a proposal that reached only an execution log would be lost between two nightly runs. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
Stéphane Tailland
@@ -176,3 +176,26 @@ endpoints and the known blockers.
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Deliverables in English. Export workflows as JSON and commit them; do not rely
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on the n8n instance as the source of truth.
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## The Kafka credential is created by hand
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`kafka-classic-models` in n8n holds the SCRAM password of the
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`classic-models-agent-approvisionnement` KafkaUser and the Strimzi cluster CA.
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It is not in this repo and must not be: n8n encrypts stored credentials with
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`N8N_ENCRYPTION_KEY`, and the committed workflow JSON references it by id only.
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To recreate it after a rebuild:
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```
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kubectl -n kafka get secret classic-models-agent-approvisionnement \
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-o jsonpath='{.data.password}' | base64 -d
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kubectl -n kafka get secret kafka-cluster-ca-cert \
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-o jsonpath='{.data.ca\.crt}' | base64 -d
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```
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then POST to `/rest/credentials` with type `kafka`, `ssl: true`, the CA in the
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`ca` field, `saslMechanism: scram-sha-512`, brokers
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`kafka-kafka-bootstrap.kafka.svc.cluster.local:9093`. The workflow's
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`credentials.kafka.id` then needs the new id.
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The KafkaUser itself lives in `infra-kafka/kafka-users.yaml`.
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@@ -147,3 +147,75 @@ looks exactly like one computed from all of it, so the difference has to be in
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the output. A catalog that outgrows one page needs a paging loop **and** the
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read-volume cap this repo already lists as mandatory for autonomous agents.
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## approvisionnement-stock-watch
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The reactive half, and the one the design had been waiting on. It is woken by
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`product.stock_changed` on `classic-models.catalog` rather than by a clock, so a
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reference that runs low at 14:32 is noticed at 14:32 instead of being reported
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at 06:00 the next morning.
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Verified end to end against the live catalog:
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```
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S12_1099 68 → 38 detected: "fell from 68 to 38, below the threshold of 50"
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38 → 30 not detected — already below, figures refreshed instead
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30 → 0 detected: "is out of stock. Nothing can be promised."
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0 → 68 not detected, entry refreshed (a correction, not demand)
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POST {"clear":["S12_1099"]} → watching: 0
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```
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### Only a crossing is news
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`before >= threshold && after < threshold`. Without that test, every further
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order line on an already-low reference raises the same alarm again, and an agent
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that repeats itself is one a human learns to ignore.
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A stock-out is treated as its own fact even when the reference was already below
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the threshold: *low* and *nothing left to promise* are different problems.
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A movement that changes nothing newsworthy still **refreshes** an entry already
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being watched. Otherwise the watchlist would show the figure from the moment of
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detection, which is the number least likely to still be true.
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`reason` carries `order:<n>` for demand and `manual-adjustment` for someone
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correcting the books. Both can justify a purchase order; only demand says
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anything about the future, so the distinction is recorded rather than filtered
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on.
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### The detection has somewhere to go
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`$getWorkflowStaticData('global')`, keyed by reference, readable over
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`GET /webhook/stock-watchlist` and cleared with
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`POST {"clear": ["S24_2000"]}`. The purchase *proposal* still has nowhere to be
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written — the domain has no purchase order and no supplier entity — but a
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detection that only reached an execution log would be lost between two nightly
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runs, which would make the reactive half pointless.
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The obvious next consumer is `check-availability`: "can we promise X?" is a
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better answer when it knows X crossed the threshold at 14:32.
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### Kafka details worth keeping
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- **The offset moves only on success** (`resolveOffset: onCompletion`,
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`allowedStatuses: ["success"]`). A failed execution replays its event rather
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than losing it — for an autonomous agent a detection dropped in silence is
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worse than one made twice.
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- **`fromBeginning: false`.** Otherwise every restart replays the whole
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retention window and re-detects crossings dealt with days ago.
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- Most messages on the topic are not `stock_changed`, and the workflow says so
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explicitly and succeeds. A workflow that threw on an uninteresting event would
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replay it forever.
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- The consumer has its **own** SCRAM account,
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`classic-models-agent-approvisionnement`: Read on that one topic and that one
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consumer-group prefix. It cannot read sales or payments, and it cannot write —
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so a compromised workflow can raise no event another agent would act on.
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### Two traps
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- **n8n's Kafka credential has a `ca` field.** The cluster CA goes there, so
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there was no need to touch `NODE_EXTRA_CA_CERTS` or to disable verification.
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Not obvious from the node's UI, which shows it only once `ssl` is on.
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- **A webhook declaring several methods has one output per method**, in the
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order declared. Wiring only the first silently drops every POST: the execution
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reports **success** and n8n answers `No item to return was found`.
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@@ -0,0 +1,115 @@
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{
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"name": "Approvisionnement \u2014 stock watch",
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"nodes": [
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{
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"parameters": {
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"topic": "classic-models.catalog",
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"groupId": "approvisionnement-stock-watch",
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"resolveOffset": "onCompletion",
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"allowedStatuses": [
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"success"
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],
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"options": {
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"jsonParseMessage": true,
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"onlyMessage": true,
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"fromBeginning": false
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}
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},
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"type": "n8n-nodes-base.kafkaTrigger",
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"typeVersion": 2,
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"position": [
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0,
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0
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],
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"id": "kafka-trigger-stock-watch",
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"name": "Catalog events",
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"credentials": {
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"kafka": {
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"id": "8qNZXLzvdx5rWQ0V",
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"name": "kafka-classic-models"
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}
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}
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},
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{
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"parameters": {
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"jsCode": "// A stock movement, judged the moment it happens.\n//\n// This is the reactive half of Approvisionnement. The 06:00 run proposes\n// purchase orders on a buying cycle, which is genuinely periodic; noticing that\n// a reference is about to run out is not, and a nightly sweep would report at\n// 06:00 what was true at 14:32 the previous afternoon.\n//\n// What it reacts to is a fact the API published, not a row it went looking for.\nconst THRESHOLD = 50;\nconst COVER = 3; // a proposal covers three times the threshold\nconst STOCK_CHANGED = 'com.sttlab.classicmodels.product.stock_changed.v1';\n\nconst event = $json ?? {};\n\n// The topic carries every catalog event, so most messages are not ours. Saying\n// so explicitly keeps the offset moving: a workflow that threw on an\n// uninteresting event would replay it forever.\nif (event.type !== STOCK_CHANGED) {\n return [{ json: { considered: false, type: event.type ?? 'unreadable' } }];\n}\n\nconst data = event.data ?? {};\nconst before = Number(data.before?.quantityinstock);\nconst after = Number(data.after?.quantityinstock);\nif (!Number.isFinite(before) || !Number.isFinite(after)) {\n return [{ json: {\n considered: false,\n escalate: true,\n reason: `${event.subject}: the movement carried no readable quantities.`,\n }}];\n}\n\n// Only a *crossing* is news. Without this, every further order line on an\n// already-low reference raises the same alarm again, and an agent that repeats\n// itself is one a human learns to ignore.\nconst crossed = before >= THRESHOLD && after < THRESHOLD;\n// A stock-out is a different fact from a low stock, even when the reference was\n// already below the threshold \u2014 nothing can be promised at all.\nconst emptied = after === 0 && before > 0;\n\n// `order:` means demand; anything else is someone correcting the books. Both\n// justify a purchase order, but only demand is a signal about the future.\nconst fromDemand = String(data.reason ?? '').startsWith('order:');\n\nconst store = $getWorkflowStaticData('global');\nstore.watchlist = store.watchlist ?? {};\n\nif (!crossed && !emptied) {\n // Not news, but if this reference is already being watched its figures have\n // just moved. Refresh them rather than leaving a human reading the number it\n // held at the moment of detection, which is the number least likely to still\n // be true.\n const watched = store.watchlist[event.subject];\n if (watched) {\n watched.on_hand = after;\n watched.propose_order = THRESHOLD * COVER - after;\n watched.last_movement_at = event.time ?? new Date().toISOString();\n }\n return [{ json: {\n considered: true,\n detected: false,\n watching: Boolean(watched),\n productcode: event.subject,\n on_hand: after,\n }}];\n}\n\nconst state = { detected: true, escalate: true,\n productcode: event.subject,\n on_hand: after,\n was: before,\n threshold: THRESHOLD,\n stock_out: after === 0,\n driver: fromDemand ? 'demand' : 'correction',\n movement: data.reason ?? null,\n propose_order: THRESHOLD * COVER - after,\n observed_at: event.time ?? new Date().toISOString(),\n // Kept so this detection can be joined to the request that caused it. It is\n // the only link back \u2014 the event deliberately names no actor.\n traceparent: event.traceparent ?? null,\n};\n\nstate.reason = state.stock_out\n ? `${state.productcode} is out of stock (was ${before}). Nothing can be promised.`\n : `${state.productcode} fell from ${before} to ${after}, below the threshold of ${THRESHOLD}.`;\n\n// The watchlist is the destination, and it is a real one: the proposal still\n// has nowhere to be written \u2014 the domain has no purchase order and no supplier\n// entity \u2014 so a detection that only logged would be lost between two nightly\n// runs. Here it survives, keyed by reference so a reference cannot appear twice.\nstore.watchlist[state.productcode] = state;\n\nreturn [{ json: state }];\n"
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},
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"type": "n8n-nodes-base.code",
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"typeVersion": 2,
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"position": [
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220,
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0
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],
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"id": "detect-crossing",
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"name": "Judge the movement"
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},
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{
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"parameters": {
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"httpMethod": [
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"GET",
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"POST"
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],
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"path": "stock-watchlist",
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"responseMode": "lastNode",
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"options": {},
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"multipleMethods": true
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},
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"type": "n8n-nodes-base.webhook",
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"typeVersion": 2,
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"position": [
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0,
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200
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],
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"id": "watchlist-read",
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"name": "Watchlist",
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"webhookId": "stock-watchlist-get"
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},
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{
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"parameters": {
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"jsCode": "// What has been detected and not yet dealt with.\n//\n// A detection that goes only into an execution log is one nobody reads. This\n// makes the watchlist readable \u2014 by the periodic run, which can start from what\n// was already noticed rather than rediscovering it, and by a human.\n//\n// GET /webhook/stock-watchlist \u2192 the current list\n// POST /webhook/stock-watchlist {\"clear\": [\"S24_2000\"]} \u2192 drop entries\nconst store = $getWorkflowStaticData('global');\nstore.watchlist = store.watchlist ?? {};\n\n// GET carries no body; the node still runs, and clear is then empty.\nconst body = $json.body ?? {};\nconst clear = Array.isArray(body.clear) ? body.clear : [];\nfor (const code of clear) delete store.watchlist[code];\n\nconst entries = Object.values(store.watchlist);\nreturn [{ json: {\n watching: entries.length,\n cleared: clear,\n // Worst first: an out-of-stock reference is not the same problem as one that\n // merely crossed the threshold.\n entries: entries.sort((a, b) => a.on_hand - b.on_hand),\n}}];\n"
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},
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"type": "n8n-nodes-base.code",
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"typeVersion": 2,
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"position": [
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220,
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200
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],
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"id": "watchlist-render",
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"name": "Render the watchlist"
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}
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],
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"connections": {
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"Catalog events": {
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"main": [
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[
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{
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"node": "Judge the movement",
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"type": "main",
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"index": 0
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}
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]
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]
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},
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"Watchlist": {
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"main": [
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[
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{
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"node": "Render the watchlist",
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"type": "main",
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"index": 0
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}
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],
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[
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{
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"node": "Render the watchlist",
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"type": "main",
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"index": 0
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}
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]
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]
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}
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},
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"settings": {
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"executionOrder": "v1"
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}
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}
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Reference in New Issue
Block a user