feat: an A2A facade for the n8n agents, and Approvisionnement's first workflow
The adapter is written once and parameterised, so both n8n agents get the same A2A surface and differ only in the workflow behind the webhook. It owns the protocol and nothing else: no Keycloak client, no credentials, and the end user's token forwarded in a header so a workflow that logs its input does not log the token with it. escalate: true fails the task rather than completing it, because an autonomous agent meeting a rule that needs approval must hand it back, not decide. Serving this from the gateway was the repo's stated preference and does not reach: A2A returns a Task with a lifecycle, and a proxy cannot synthesise that from a webhook's single reply. The check_availability workflow does the token exchange itself, using the agent's client secret from the pod environment so the committed JSON holds no secret, then talks MCP in two calls — initialize to obtain the session id from a response header, then tools/call. It reads the product code with a regex rather than a model: this agent's critical path is rules, and a question naming no product escalates instead of being guessed at. MCP rather than the REST route, which would have been one HTTP call instead of two: the per-tool ACL by consumer group lives on the MCP route only. Going through REST would give an autonomous agent broader access than a conversational one, which is exactly backwards. Status: the adapter is tested (13 tests) and the identity chain is verified by hand, but the workflow fails at its token exchange and is not yet working — see the note in workflows/. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
This commit is contained in:
Stéphane Tailland
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{
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"name": "Approvisionnement \u2014 check_availability",
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"nodes": [
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{
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"parameters": {
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"httpMethod": "POST",
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"path": "check-availability",
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"responseMode": "responseNode",
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"options": {}
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},
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"id": "webhook",
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"name": "Webhook",
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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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0
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],
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"webhookId": "check-availability"
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},
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{
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"parameters": {
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"method": "POST",
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"url": "https://keycloak.sttlab.local/realms/classic-models/protocol/openid-connect/token",
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"sendBody": true,
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"contentType": "form-urlencoded",
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"bodyParameters": {
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"parameters": [
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{
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"name": "grant_type",
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"value": "urn:ietf:params:oauth:grant-type:token-exchange"
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},
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{
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"name": "client_id",
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"value": "classic-models-agent-approvisionnement"
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},
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{
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"name": "client_secret",
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"value": "={{ $env.APPROVISIONNEMENT_CLIENT_SECRET }}"
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},
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{
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"name": "subject_token",
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"value": "={{ $('Webhook').item.json.headers['x-subject-token'] }}"
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},
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{
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"name": "subject_token_type",
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"value": "urn:ietf:params:oauth:token-type:access_token"
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},
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{
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"name": "scope",
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"value": "openid mcp-catalog-audience token-exchange-broker-audience"
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}
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]
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},
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"options": {}
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},
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"id": "exchange-token",
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"name": "Exchange token",
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"type": "n8n-nodes-base.httpRequest",
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"typeVersion": 4.2,
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"position": [
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220,
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0
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]
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},
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{
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"parameters": {
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"method": "POST",
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"url": "https://catalog-dev.sttlab.local/catalog-mcp",
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"sendHeaders": true,
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"headerParameters": {
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"parameters": [
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{
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"name": "Authorization",
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"value": "=Bearer {{ $json.access_token }}"
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},
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{
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"name": "Accept",
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"value": "application/json, text/event-stream"
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}
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]
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},
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"sendBody": true,
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"specifyBody": "json",
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"jsonBody": "{\"jsonrpc\": \"2.0\", \"id\": 1, \"method\": \"initialize\", \"params\": {\"protocolVersion\": \"2025-06-18\", \"capabilities\": {}, \"clientInfo\": {\"name\": \"approvisionnement\", \"version\": \"0.1.0\"}}}",
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"options": {
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"response": {
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"response": {
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"fullResponse": true
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}
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}
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}
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},
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"id": "mcp-initialize",
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"name": "MCP initialize",
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"type": "n8n-nodes-base.httpRequest",
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"typeVersion": 4.2,
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"position": [
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440,
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0
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]
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},
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{
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"parameters": {
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"method": "POST",
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"url": "https://catalog-dev.sttlab.local/catalog-mcp",
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"sendHeaders": true,
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"headerParameters": {
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"parameters": [
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{
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"name": "Authorization",
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"value": "=Bearer {{ $('Exchange token').item.json.access_token }}"
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},
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{
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"name": "Accept",
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"value": "application/json, text/event-stream"
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},
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{
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"name": "mcp-session-id",
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"value": "={{ $json.headers['mcp-session-id'] }}"
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}
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]
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},
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"sendBody": true,
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"specifyBody": "json",
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"jsonBody": "={{ JSON.stringify({ jsonrpc: '2.0', id: 2, method: 'tools/call', params: { name: 'get-product', arguments: { path_productcode: $('Decide the product').item.json.productcode } } }) }}",
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"options": {
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"response": {
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"response": {
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"neverError": true
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}
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}
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}
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},
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"id": "read-stock",
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"name": "Read stock",
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"type": "n8n-nodes-base.httpRequest",
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"typeVersion": 4.2,
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"position": [
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660,
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0
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]
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},
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{
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"parameters": {
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"jsCode": "// Pull the product code out of the question.\n//\n// A regex rather than a model: this agent's critical path is rules, and putting\n// an LLM on it would make a nightly job both slower and less predictable. If the\n// question does not name a product, the agent escalates instead of guessing \u2014\n// an autonomous agent that meets an ambiguity must hand it back, never resolve\n// it on its own.\nconst question = $('Webhook').first().json.body?.question ?? '';\nconst match = question.match(/\\bS\\d+_\\d+[A-Za-z]*\\b/);\nif (!match) {\n return [{ json: { productcode: null, question } }];\n}\nreturn [{ json: { productcode: match[0], question } }];\n"
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},
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"id": "decide-the-product",
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"name": "Decide the product",
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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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180
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]
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},
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{
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"parameters": {
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"jsCode": "// Turn the MCP reply into a decision.\n//\n// An A2A call returns an answer, not data: the caller learns whether the stock\n// covers what it asked about, and never receives the stock table. That is what\n// keeps this agent from becoming a read proxy onto the catalog domain.\nconst THRESHOLD = 50; // below this, a reorder is due before promising anything\n\nconst decided = $('Decide the product').first().json;\nif (!decided.productcode) {\n return [{ json: {\n answer: 'No product reference in the question. Name one as S10_1949 and ask again.',\n escalate: true,\n }}];\n}\n\nconst raw = $input.first().json;\nconst body = typeof raw === 'string' ? raw : (raw.data ?? JSON.stringify(raw));\n\n// The endpoint answers as an SSE event, so the JSON sits on a `data:` line.\nconst line = String(body).split('\\n').find((l) => l.startsWith('data:'));\nif (!line) {\n return [{ json: {\n answer: `Could not read the catalog's reply for ${decided.productcode}.`,\n escalate: true,\n }}];\n}\n\nconst rpc = JSON.parse(line.slice(5).trim());\nif (rpc.error) {\n // A refusal is the caller's own permissions being applied. Reported, never\n // worked around.\n return [{ json: {\n answer: `The catalog refused the read for ${decided.productcode}: ${rpc.error.message}.`,\n escalate: true,\n }}];\n}\n\nconst product = JSON.parse(rpc.result.content[0].text);\nconst stock = Number(product.quantityinstock);\nconst available = stock >= THRESHOLD;\n\nreturn [{ json: {\n answer: available\n ? `Yes \u2014 ${product.productname} (${product.productcode}) can be promised: `\n + `${stock} in stock, above the reorder threshold of ${THRESHOLD}.`\n : `No \u2014 ${product.productname} (${product.productcode}) is down to ${stock}, `\n + `below the reorder threshold of ${THRESHOLD}. A reorder is due before it can be promised.`,\n escalate: false,\n}}];\n"
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},
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"id": "answer",
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"name": "Answer",
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"type": "n8n-nodes-base.code",
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"typeVersion": 2,
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"position": [
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880,
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0
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]
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},
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{
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"parameters": {
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"respondWith": "json",
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"responseBody": "={{ JSON.stringify($json) }}",
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"options": {}
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},
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"id": "respond",
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"name": "Respond",
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"type": "n8n-nodes-base.respondToWebhook",
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"typeVersion": 1.1,
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"position": [
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1100,
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0
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]
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}
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],
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"connections": {
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"Webhook": {
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"main": [
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[
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{
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"node": "Decide the product",
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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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"Decide the product": {
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"main": [
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[
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{
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"node": "Exchange token",
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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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"Exchange token": {
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"main": [
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[
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{
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"node": "MCP initialize",
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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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"MCP initialize": {
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"main": [
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[
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{
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"node": "Read stock",
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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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"Read stock": {
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"main": [
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[
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{
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"node": "Answer",
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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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"Answer": {
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"main": [
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[
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{
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"node": "Respond",
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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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