7.30Therefore retries require idempotency

This is why these belong together:

TIMEOUT
   ↓
RETRY
   ↓
IDEMPOTENT OPERATION

For Salesforce:

CREATE

may be unsafe.

UPSERT using stable External ID

is much safer.

Interview phrase worth memorizing:

“I treat ambiguous failures like timeouts differently from known business failures because a timeout doesn't prove the downstream operation wasn't committed. Retries therefore need idempotent semantics.”

Excellent.