feat(core): persist v2 session context epochs (#30789)

packages/core/src/session/sql.ts

@@ -11,6 +11,7 @@ import type { SessionSchema } from "./schema"
 import type { MessageID, PartID, SessionV1 } from "../v1/session"
 import { WorkspaceV2 } from "../workspace"
 import { Timestamps } from "../database/schema.sql"
+import type { SystemContext } from "../system-context"
 
 type SessionMessageData = Omit<(typeof SessionMessage.Message)["Encoded"], "type" | "id">
 type V1MessageData = Omit<SessionV1.Info, "id" | "sessionID">
@@ -161,3 +162,15 @@ export const SessionInputTable = sqliteTable(
     uniqueIndex("session_input_session_promoted_seq_idx").on(table.session_id, table.promoted_seq),
   ],
 )
+
+export const SessionContextEpochTable = sqliteTable("session_context_epoch", {
+  session_id: text()
+    .$type<SessionSchema.ID>()
+    .primaryKey()
+    .references(() => SessionTable.id, { onDelete: "cascade" }),
+  baseline: text().notNull(),
+  snapshot: text({ mode: "json" }).notNull().$type<SystemContext.Snapshot>(),
+  baseline_seq: integer().notNull(),
+  replacement_seq: integer(),
+  revision: integer().notNull().default(0),
+})