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//! The canonical, versioned compaction receipt.
//!
//! A single transcript compaction is one lifecycle fact. Historically that fact
//! was reconstructed independently in three places — the persisted transcript
//! `compaction` event metadata, the live `AgentEvent::TranscriptCompacted`
//! payload, and `RunObservabilityRecord.compaction_events` (which reparsed the
//! transcript JSON key-by-key and dropped `reason`/`recap`). ACP consumers had
//! no stable identity to key on and synthesized host-local UUIDs.
//!
//! [`CompactionReceipt`] is the one owner of that fact. It is constructed once
//! at the lifecycle boundary (`run_compaction_lifecycle`) or, for host-script
//! driven compaction, normalized once at the `__host_agent_record_compaction`
//! builtin boundary. It is then:
//!
//! * embedded verbatim under `metadata.receipt` on the transcript event, whose
//! event `id` is set to [`CompactionReceipt::receipt_id`];
//! * carried on `AgentEvent::TranscriptCompacted` and forwarded through ACP;
//! * deserialized (typed, not scraped) into `CompactionEventRecord`.
//!
//! So one compaction operation yields exactly one `receipt_id` across all four
//! projections, and `reason`, `recap`, snapshot provenance, and policy survive
//! every projection without a host synthesizing identity.
use serde::{Deserialize, Serialize};
use super::RecapMetrics;
/// Current on-the-wire schema version for [`CompactionReceipt`]. Bump this when
/// the receipt's meaning changes in a way readers must branch on; additive
/// optional fields do not require a bump because `#[serde(default)]` fills them.
pub const COMPACTION_RECEIPT_SCHEMA_VERSION: u32 = 1;
fn default_schema_version() -> u32 {
COMPACTION_RECEIPT_SCHEMA_VERSION
}
/// One serializable, versioned record of a single transcript compaction. See the
/// module docs for how it flows through every projection.
#[derive(Clone, Debug, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(default)]
pub struct CompactionReceipt {
/// Schema version. Lets readers migrate: a receipt read from an older
/// persisted transcript that predates a meaning change carries its original
/// version, and a transcript with no embedded receipt at all is migrated by
/// the record builder (see `compaction_events_from_transcript`).
#[serde(default = "default_schema_version")]
pub schema_version: u32,
/// Stable identity for this compaction operation, shared verbatim across the
/// transcript event id, the live event, ACP, and the observability record.
pub receipt_id: String,
/// Owning agent session, when the compaction ran against one.
pub session_id: Option<String>,
/// Owning transcript, when known. Best-effort provenance; the record's
/// `transcript_id` is sourced authoritatively from the transcript itself.
pub transcript_id: Option<String>,
/// Call-site surface that initiated compaction (`CompactMode::as_str`).
pub mode: String,
/// Why compaction fired (`CompactionTrigger::as_str`, or a host-supplied
/// reason such as `context_overflow`).
pub reason: String,
/// User-facing policy label (may be broader than the engine strategy).
pub strategy: String,
/// Engine strategy actually used after honoring any PreCompact `Modify`.
pub engine_strategy: String,
pub archived_messages: usize,
pub estimated_tokens_before: usize,
pub estimated_tokens_after: usize,
/// Id of the pre-compaction snapshot asset, when one was built.
pub snapshot_asset_id: Option<String>,
pub instruction_mode: Option<String>,
pub instruction_source: Option<String>,
pub compaction_policy: Option<serde_json::Value>,
/// Observation-mask recap metrics; `None` for the LLM/truncate/custom
/// strategies, which do not spend a recap budget.
pub recap: Option<RecapMetrics>,
}
/// Generate a fresh, unique compaction receipt id.
pub fn new_compaction_receipt_id() -> String {
format!("compaction-{}", uuid::Uuid::now_v7())
}
impl CompactionReceipt {
/// Serialize the receipt for verbatim embedding under `metadata.receipt` on
/// the transcript event.
pub fn to_json(&self) -> serde_json::Value {
serde_json::to_value(self).unwrap_or(serde_json::Value::Null)
}
/// Read a receipt embedded under `metadata.receipt` on a transcript
/// `compaction` event. Returns `None` when the key is absent (a legacy
/// transcript written before receipts existed) or malformed, so the caller
/// can fall back to the legacy flat-metadata migration path.
pub fn from_event_metadata(metadata: Option<&serde_json::Value>) -> Option<Self> {
let receipt = metadata?.get("receipt")?;
serde_json::from_value(receipt.clone()).ok()
}
/// Normalize a host-script compaction payload — the dict `.harn` code hands
/// to `agent_record_compaction` / `__host_agent_record_compaction` — into a
/// receipt at the builtin boundary, minting a fresh `receipt_id`. This is the
/// one place the host-driven shape is validated, so the `.harn` auto-compact
/// path yields the same unified receipt as the Rust lifecycle paths.
pub fn from_host_payload(session_id: &str, payload: &serde_json::Value) -> Self {
let str_field = |key: &str| {
payload
.get(key)
.and_then(serde_json::Value::as_str)
.map(str::to_string)
};
let usize_field = |key: &str| {
payload
.get(key)
.and_then(serde_json::Value::as_u64)
.unwrap_or(0) as usize
};
let strategy = str_field("strategy")
.or_else(|| str_field("engine_strategy"))
.unwrap_or_default();
let engine_strategy = str_field("engine_strategy").unwrap_or_else(|| strategy.clone());
Self {
schema_version: COMPACTION_RECEIPT_SCHEMA_VERSION,
receipt_id: new_compaction_receipt_id(),
session_id: Some(session_id.to_string()),
transcript_id: None,
mode: str_field("mode").unwrap_or_else(|| "auto".to_string()),
reason: str_field("reason").unwrap_or_else(|| "threshold".to_string()),
strategy,
engine_strategy,
archived_messages: usize_field("archived_messages"),
estimated_tokens_before: usize_field("estimated_tokens_before"),
estimated_tokens_after: usize_field("estimated_tokens_after"),
snapshot_asset_id: str_field("snapshot_asset_id"),
instruction_mode: str_field("instruction_mode"),
instruction_source: str_field("instruction_source"),
compaction_policy: payload.get("compaction_policy").cloned(),
recap: payload
.get("recap")
.and_then(|value| serde_json::from_value::<RecapMetrics>(value.clone()).ok()),
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn receipt_round_trips_through_json_with_recap_and_policy() {
let receipt = CompactionReceipt {
schema_version: COMPACTION_RECEIPT_SCHEMA_VERSION,
receipt_id: "compaction-abc".to_string(),
session_id: Some("session-1".to_string()),
transcript_id: Some("session-1".to_string()),
mode: "auto".to_string(),
reason: "threshold".to_string(),
strategy: "hybrid".to_string(),
engine_strategy: "observation_mask".to_string(),
archived_messages: 7,
estimated_tokens_before: 4000,
estimated_tokens_after: 1200,
snapshot_asset_id: Some("snapshot-9".to_string()),
instruction_mode: Some("extend".to_string()),
instruction_source: Some("author".to_string()),
compaction_policy: Some(serde_json::json!({"scope": "summary"})),
recap: Some(RecapMetrics {
recap_bytes: 512,
budget_bytes: 16_000,
kept_results_count: 3,
dropped_count: 1,
carried_prior_recap: true,
}),
};
let json = receipt.to_json();
let decoded = CompactionReceipt::from_event_metadata(Some(&serde_json::json!({
"receipt": json,
})))
.expect("embedded receipt decodes");
assert_eq!(decoded, receipt);
}
#[test]
fn absent_receipt_key_yields_none_for_legacy_migration() {
let legacy = serde_json::json!({
"mode": "manual",
"strategy": "truncate",
"archived_messages": 3,
});
assert!(CompactionReceipt::from_event_metadata(Some(&legacy)).is_none());
assert!(CompactionReceipt::from_event_metadata(None).is_none());
}
#[test]
fn missing_schema_version_defaults_to_current() {
let receipt: CompactionReceipt = serde_json::from_value(serde_json::json!({
"receipt_id": "compaction-xyz",
"mode": "manual",
}))
.expect("partial receipt loads");
assert_eq!(receipt.schema_version, COMPACTION_RECEIPT_SCHEMA_VERSION);
assert_eq!(receipt.receipt_id, "compaction-xyz");
assert!(receipt.recap.is_none());
}
}