feat(app-server, threadstore): Thread pagination APIs and ThreadStore contract

[owenlin0]

Why

The goal of this PR is to align on app-server and ThreadStore API updates for paginating through large threads.

app-server

thread/turns/list

• Updates thread/turns/list to support itemsView?: "notLoaded" | "summary" | "full" | null, defaulting to summary.
• Implements the current thread/turns/list behavior over the existing persisted rollout-history fallback:
  • notLoaded returns turn envelopes with empty items.
  • summary returns the first user message and final assistant message when available.
  • full preserves the existing full item behavior.

Note that this method still uses the naive approach of loading the entire rollout file, and returns just the filtered slice of the data. Real pagination will come later by leveraging SQLite.

thread/turns/items/list

• Adds the experimental thread/turns/items/list protocol, schema, dispatcher, and processor stub. The app-server currently returns JSON-RPC -32601 with thread/turns/items/list is not supported yet.

ThreadStore

• Adds the experimental thread/turns/items/list protocol, schema, dispatcher, and processor stub. The app-server currently returns JSON-RPC -32601 with thread/turns/items/list is not supported yet.
• Adds ThreadStore contract types and stubbed methods for listing thread turns and listing items within a turn.
• Adds a typed StoredTurnStatus and StoredTurnError to avoid baking app-server API enums or lossy string status values into the store-facing turn contract.
• Adds a typed StoredTurnStatus and StoredTurnError to avoid baking app-server API enums or lossy string status values into the store-facing turn contract.

This also sketches the storage abstraction we expect to need once turns are indexed/stored. In particular, notLoaded is useful only if ThreadStore can eventually list turn metadata without loading every persisted item for each turn.

Validation

• Added/updated protocol serialization coverage for the new request and response shapes.
• Added app-server integration coverage for thread/turns/list default summary behavior and all three itemsView modes.
• Added app-server integration coverage that thread/turns/items/list returns the expected unsupported JSON-RPC error when experimental APIs are enabled.
• Added thread-store coverage that the default trait methods return ThreadStoreError::Unsupported.

No developers.openai.com documentation update is needed for this internal experimental app-server API surface.

[wiltzius-openai]

the threadstore API change looks right to me

for the local store implementation it will definitely be easier to do this if we move the rollout history into sqlite because you can get indexes more or less for free

the remote store this is going to be challenging to implement but I don't think that's the fault of the contract

[wiltzius-openai]

what does the Vec look like if the request items_view is Summary or NotLoaded? In the NotLoaded case I guess it can be an empty vector, but for Summary what's the return type?

[owenlin0]

good question!

• for items_view: summary we will have pretty much always have a vector of two items: [<InitialUserMessage item>, <FinalAssistantMessageItem>] (for a successfully completed turn)
• for items_view: not_loaded we will just have items: []

I'll make sure it's documented clearly once I have this implemented more