mark AgentSessionState snapshot and delta optional

[longcw]

cloud to worker:

• version: require worker to have the same version of state
• version + empty snapshot: new session
• version + snapshot: cold start

worker to cloud:

• version + delta: update the cloud state to new version

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[paulwe]

it will always be one or the other so maybe oneof?

[paulwe]

the new session state should be a db with empty tables. if the schema the sdk needs changes in later versions this avoids ongoing maintenance to keep them synced

[longcw]

it will always be one or the other

when cloud thinks the work has the full state, it should only set the version but not snapshot and delta?

[paulwe]

oh, right... undefined is a valid oneof state (optional is syntactic sugar over oneof { T })

[longcw]

we will have a schema version in the db, if the schema version from the snapshot is not matched to the one in agent sdk, either we raise an error or automatically convert it to the new schema and sync a new snapshot to the cloud. so the cloud doesn't need to care about the schema of the db.

[longcw]

so the new session state can be an empty byte? it make the sdk easier to determine it's a new session

[paulwe]

no, it can't be empty bytes... that's what i wanted to clarify since you were disambiguating the zero and undefined states

[longcw]

why it cannot be empty bytes... can we distinguish "not set" and empty value if we check the field with HasField or WhichOneof before accessing it? or you mean by design you don't want it to be empty bytes?

[paulwe]

cloud to worker:

• version - undefined oneof indicates new session
• version + snapshot - cold start from ongoing session

worker to cloud

• version + snapshot - new session / new schema
• version + delta - update to version-1

[longcw]

I was thinking "version - undefined oneof" means the hot sync that only a version is sent to the worker and "version + empty snapshot" means a new session (or discard previous data if any)

[paulwe]

we would only need this if we planned to reuse session ids but they should always be distinct right?

[paulwe]

you're right. maybe this? - cloud to worker:

• undefined (no state) - new session
• version - resume ongoing session
• version + snapshot - cold start from ongoing session

[paulwe]

messages are always optional it doesn't have to be explicitly optional