fix(console): reconcile history around lineage anchors

crates/protocol/src/lib.rs

@@ -842,6 +842,16 @@ pub struct SessionConversationTurn {
     pub entries: Vec<SessionSnapshotEntry>,
 }
 
+/// The immediate parent lineage and the stable real-user boundary adopted from it.
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[cfg_attr(feature = "typescript", derive(ts_rs::TS))]
+#[cfg_attr(feature = "json-schema", derive(schemars::JsonSchema))]
+pub struct SessionHistoryLineageBoundary {
+    pub lineage_id: String,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub adopted_through_turn_id: Option<String>,
+}
+
 /// Bounded backward page over the adopted conversation lineage.
 ///
 /// Turns remain chronological within a page. `next_cursor` is an opaque,
@@ -859,6 +869,10 @@ pub struct SessionHistoryPage {
     /// cursor with this page's boundary.
     #[serde(default, skip_serializing_if = "Vec::is_empty")]
     pub compact_ancestor_lineage_ids: Vec<String>,
+    /// Immediate parent relationship used to retain only the adopted prefix
+    /// across fork/rewind refreshes that have no newest-page overlap.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub parent_lineage: Option<SessionHistoryLineageBoundary>,
     pub turns: Vec<SessionConversationTurn>,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub next_cursor: Option<String>,

crates/protocol/src/typescript.rs

@@ -12,10 +12,10 @@ use crate::{
     PasteArtifactAvailability, PasteArtifactMediaType, PasteArtifactRef, PendingSubmissionSummary,
     PendingSubmissionsSnapshot, Permission, RewindSummary, RewindTarget, RewindTargetId, RunResult,
     ScopeRule, Segment, SessionContentPart, SessionConversationTurn, SessionEntryProvenance,
-    SessionHistoryPage, SessionMessageRole, SessionSnapshot, SessionSnapshotEntry,
-    SessionSnapshotEntryData, SessionToolAttachment, SubmissionDisposition, SymlinkPolicy,
-    ToolResultDisposition, TurnResult, UploadedFileAvailability, UploadedFileRef, WorkerBusyState,
-    WorkerCommandAcknowledgement, WorkerCommandDisposition, WorkerCommandEnvelope,
+    SessionHistoryLineageBoundary, SessionHistoryPage, SessionMessageRole, SessionSnapshot,
+    SessionSnapshotEntry, SessionSnapshotEntryData, SessionToolAttachment, SubmissionDisposition,
+    SymlinkPolicy, ToolResultDisposition, TurnResult, UploadedFileAvailability, UploadedFileRef,
+    WorkerBusyState, WorkerCommandAcknowledgement, WorkerCommandDisposition, WorkerCommandEnvelope,
     WorkerCommandKind, WorkerEvent, WorkerMaintenanceState, WorkerRunState, WorkerState,
     WorkerStateSnapshot, WorkerStatus,
     subscription::{
@@ -106,6 +106,7 @@ pub fn generated_protocol_types() -> String {
     push_decl::<SessionSnapshotEntryData>(&cfg, &mut output);
     push_decl::<SessionSnapshotEntry>(&cfg, &mut output);
     push_decl::<SessionConversationTurn>(&cfg, &mut output);
+    push_decl::<SessionHistoryLineageBoundary>(&cfg, &mut output);
     push_decl::<SessionHistoryPage>(&cfg, &mut output);
     push_decl::<PendingSubmissionSummary>(&cfg, &mut output);
     push_decl::<PendingSubmissionsSnapshot>(&cfg, &mut output);

crates/session-store/src/public_snapshot.rs

@@ -4,8 +4,8 @@ use base64::{
 };
 use protocol::{
     Segment, SessionContentPart, SessionConversationTurn, SessionEntryProvenance,
-    SessionHistoryPage, SessionMessageRole, SessionSnapshot, SessionSnapshotEntry,
-    SessionSnapshotEntryData, SessionToolAttachment,
+    SessionHistoryLineageBoundary, SessionHistoryPage, SessionMessageRole, SessionSnapshot,
+    SessionSnapshotEntry, SessionSnapshotEntryData, SessionToolAttachment,
 };
 use serde::{Deserialize, Serialize};
 use sha2::{Digest, Sha256};
@@ -261,6 +261,28 @@ pub fn read_retained_session_history_page(
     } else {
         None
     };
+    let parent_lineage = if lineage.len() > 1 {
+        let parent_turns = read_history_turns_backward(
+            &store,
+            active.session_id,
+            &lineage[1..],
+            None,
+            1,
+            RetainedHistoryReadLimits {
+                max_scan_bytes: limits.max_scan_bytes.saturating_sub(metadata_bytes),
+                max_entries: limits.max_entries.saturating_sub(metadata_entries),
+                ..limits
+            },
+        )?;
+        Some(SessionHistoryLineageBoundary {
+            lineage_id: lineage_identity(active.session_id, &lineage[1..]),
+            adopted_through_turn_id: parent_turns
+                .first()
+                .map(|positioned| positioned.turn.turn_id.clone()),
+        })
+    } else {
+        None
+    };
     let mut turns = read_history_turns_backward(
         &store,
         active.session_id,
@@ -302,6 +324,7 @@ pub fn read_retained_session_history_page(
         session_id: active.session_id.to_string(),
         lineage_id,
         compact_ancestor_lineage_ids,
+        parent_lineage,
         turns: turns
             .into_iter()
             .map(|positioned| positioned.turn)
@@ -1735,6 +1758,21 @@ mod tests {
                 .all(|entry| entry.entry_id != "assistant-1-unadopted")
         }));
         assert!(page.turns.iter().all(|turn| turn.turn_id != "user-2"));
+        let store = WorkerSessionStore::open_read_only(aggregate_root.join("session")).unwrap();
+        let (_, source_lineage_id, _, _) = load_adopted_lineage(
+            &store,
+            session_id,
+            source_segment,
+            RetainedHistoryReadLimits::default(),
+        )
+        .unwrap();
+        assert_eq!(
+            page.parent_lineage,
+            Some(SessionHistoryLineageBoundary {
+                lineage_id: source_lineage_id,
+                adopted_through_turn_id: Some("user-1".to_string()),
+            })
+        );
     }
 
     #[test]