A 404 on a URL you guessed is not "the capability doesn't exist"

The incident

Looking for the path to correct a record, two names were guessed and tried.

POST .../invoices/correction   -> 404
POST .../invoices/update       -> 404

From that, the conclusion was "this platform has no correction API; it is irreversible." That conclusion drove a plan for manual recovery, went into the documentation as "irreversible", and was reported to someone else as fact.

It was wrong. One search produced the real path.

POST .../orders/updateInvoices

★ The write is .../invoices; the correction is .../updateInvoices.

The assumption was that a verb would hang off the same noun. In reality it was a separate verb path. The whole judgement rested on believing the other side follows resource-tree REST conventions.

★★ Rules

1. If you guessed the path, a 404 is not evidence. Before concluding, ask "did I invent this URL?"
2. "The capability doesn't exist" may be said only after docs, search and asking
3. ★ "Irreversible" is an unusually expensive verdict. That one word produces manual work, design changes, and apologies. Search once more before saying it

★★★ Aside — this rule was already written down

Two days earlier, after a 404 on a different endpoint, this had been recorded:

Do not read a 404 as "no such capability". You have not found the path yet.

Two days later it was broken. Three similar things happened that same week — a validator passed the defect it existed to catch, a format rule was agreed and then violated by hand, and here a judgement rule was written down and not retrieved at the moment of judging.

★★ Writing a rule down and retrieving it at the moment of judgement are two different capabilities.

Recording it is not enough; it has to sit somewhere that fires automatically just before the judgement — a checklist, a lint, a review question — to actually work.

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