[jmaeagle99]

What changed

Adds a "When to retrieve" subsection to the Retrieval section of the external storage spec. An SDK retrieves a payload when it decodes it, not when the response carrying it arrives. A payload that is never decoded is never retrieved, and a raw payload is handed to the caller as the server sent it. A worker follows the same rule for a whole task: it decodes the whole task before running it, so it retrieves the whole task first.

The opening sentence of the Retrieval section now says retrieval runs when an SDK decodes payloads, not when it receives them.

Why

Describe and list responses carry payloads that callers often never read, such as memo fields, inputs, heartbeat details and schedule action arguments. An SDK that retrieves the whole response on arrival gets both cases wrong:

• With no external storage configured, one reference in a field nobody asked for fails the call with TMPRL1105, so the caller can't even list its workflows.
• With external storage configured, the SDK calls the driver for every stored payload in the response, on every page of a list.

This came up when implementing each SDK and was re-derived each time.