Structured cross-session reference requests and prepared message contexts. The [package contract](../../packages/context/session-reference) owns canonical URIs, current-surface projection, tag-safe JSON and byte retention, stable errors, and the untrusted model prompt. Host adapters use these types instead of passing their UI mention syntax into the agent core.
`SessionReferenceCandidate` is host-facing discovery output. Its label uses the latest session title when present, while filtering still searches only session id and cwd and never transcript text.
/** Source session working directory, when recorded. */
cwd?: string
/** Source session creation time in Unix epoch milliseconds. */
createdAt: number
}
```
## Prepared messages
Preparation preserves readable current-message content and returns at most one aggregated context. The host binds `contexts` to that exact `send()` or `steer()` call.
```ts type-equiv
/** Message payload and the zero-or-one durable snapshot contexts bound to it. */
interface PreparedReferencedMessage {
/** Readable message content after host mention tokens are removed. */
content: ContentBlock[]
/** Empty without references; otherwise one aggregated untrusted context. */
contexts: HookContext[]
}
```
## Errors
`SessionReferenceError.code` separates invalid configuration or input, self-reference, count limits, source-read failure, budget failure, and cancellation. Host protocols map these codes to their own error envelopes without inspecting prompt bytes.
```ts type-equiv
/** Stable failure codes exposed to host adapters. */
