fix(workflow): answer when the product does not exist

MCP does not report a tool failure as a JSON-RPC error. It reports it as a
successful result carrying isError: true, with the reason as text. The node
only checked `error`, so it read the failure as data and went on to JSON.parse
the sentence "HTTP call failed with status 404" as a product. The throw is what
made the webhook answer nothing at all.

Now checks result.isError, distinguishes a missing product from any other tool
failure, and guards every parse of a payload it did not construct. Through the
facade, escalate: true becomes a task in state failed rather than a completed
one.

Also corrects this file: the earlier note said the run completed in success
with every node executing. It did not — that was the wrong execution. n8n's
executions list did not return them newest-first as assumed, and the conclusion
drawn from it sent the search to the wrong place.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

workflows/README.md

@@ -51,13 +51,40 @@ The regex is loose after the underscore on purpose — a reference that looks
 valid but does not exist must reach the catalog and come back as "no such
 product", because answering "you named no product" would be false.
 
-### Known gap
+### The one that took longest
 
-A product code that does not exist returns an **empty body** rather than that
-message. The run completes, every node executes including the one that composes
-the answer, and the response is still empty — so the fault is between the
-composing node and the webhook response, not in the decision logic.
-`alwaysOutputData` on the read node did not change it.
+A product code that does not exist returned an **empty body**, and the reason is
+worth keeping.
 
-For an autonomous agent, silence is the worst possible answer. Not shipped as
-acceptable — recorded as unfinished.
+MCP does not report a tool failure as a JSON-RPC `error`. It reports it as a
+perfectly successful **result** carrying `isError: true`, with the reason as
+text:
+
+```
+data: {"jsonrpc":"2.0","result":{"content":[{"type":"text",
+       "text":"HTTP call failed with status 404: {\"detail\":\"Not found.\"}"}],
+       "isError":true},"id":2}
+```
+
+A client that only checks `rpc.error` therefore reads a failure as data. This
+one went on to `JSON.parse` the sentence "HTTP call failed with status 404" as
+if it were a product, threw, and the webhook answered nothing at all.
+
+Two lessons, both now in the node:
+
+- **check `result.isError`, not just `error`** — they mean different things: a
+  protocol failure versus a tool that ran and failed;
+- **guard every `JSON.parse` of a payload you did not construct.** The throw is
+  what turned a wrong answer into no answer, which for an autonomous agent is
+  the worse of the two.
+
+Now:
+
+```
+"Peut-on promettre S99_NOPE ?"
+  → {"answer":"There is no product S99_NOPE in the catalog.","escalate":true}
+```
+
+and through the A2A facade, `escalate: true` becomes a task in state **failed**
+rather than a completed one — the honest shape for "a human has to look at
+this".

workflows/approvisionnement-check-availability.json

@@ -157,7 +157,7 @@
     },
     {
       "parameters": {
-        "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 item = $input.first();\nif (!item) {\n  return [{ json: {\n    answer: `The catalog returned nothing for ${decided.productcode}. It may not exist.`,\n    escalate: true,\n  }}];\n}\nconst raw = item.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"
+        "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 item = $input.first();\nif (!item) {\n  return [{ json: {\n    answer: `The catalog returned nothing for ${decided.productcode}. It may not exist.`,\n    escalate: true,\n  }}];\n}\nconst raw = item.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\nlet rpc;\ntry {\n  rpc = JSON.parse(line.slice(5).trim());\n} catch (e) {\n  return [{ json: {\n    answer: `The catalog's reply for ${decided.productcode} could not be read.`,\n    escalate: true,\n  }}];\n}\n\n// A JSON-RPC `error` is a protocol failure \u2014 a malformed call, a session gone.\nif (rpc.error) {\n  return [{ json: {\n    answer: `The catalog refused the read for ${decided.productcode}: ${rpc.error.message}.`,\n    escalate: true,\n  }}];\n}\n\n// A *tool* failure is not that. MCP reports it as a perfectly successful result\n// carrying `isError: true`, with the reason as text \u2014 so a client that only\n// checks `error` reads a failure as data and tries to parse \"HTTP call failed\n// with status 404\" as a product. Which is exactly what this did.\nconst text = rpc.result?.content?.[0]?.text ?? '';\nif (rpc.result?.isError) {\n  const missing = text.includes('404');\n  return [{ json: {\n    answer: missing\n      ? `There is no product ${decided.productcode} in the catalog.`\n      : `The catalog could not answer for ${decided.productcode}: ${text}`,\n    escalate: true,\n  }}];\n}\n\nlet product;\ntry {\n  product = JSON.parse(text);\n} catch (e) {\n  return [{ json: {\n    answer: `The catalog returned something unreadable for ${decided.productcode}.`,\n    escalate: true,\n  }}];\n}\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"
       },
       "id": "answer",
       "name": "Answer",