feat(tui): improve session fork handling

packages/core/src/database/migration.gen.ts

@@ -46,5 +46,6 @@ export const migrations = (
     import("./migration/20260703190000_reset_v2_shell_event_payloads"),
     import("./migration/20260703200000_reset_v2_session_events"),
     import("./migration/20260705180000_rename_instructions"),
+    import("./migration/20260706223930_add-session-fork"),
   ])
 ).map((module) => module.default) satisfies DatabaseMigration.Migration[]

packages/core/src/database/migration/20260706223930_add-session-fork.ts

@@ -0,0 +1,39 @@
+import { Effect } from "effect"
+import type { DatabaseMigration } from "../migration"
+
+export default {
+  id: "20260706223930_add-session-fork",
+  up(tx) {
+    return Effect.gen(function* () {
+      yield* tx.run(`ALTER TABLE \`session\` ADD \`fork_session_id\` text;`)
+      yield* tx.run(`ALTER TABLE \`session\` ADD \`fork_message_id\` text;`)
+      yield* tx.run(`
+        UPDATE \`session\`
+        SET
+          \`parent_id\` = NULL,
+          \`fork_session_id\` = (
+            SELECT json_extract(\`event\`.\`data\`, '$.parentID')
+            FROM \`event\`
+            WHERE \`event\`.\`aggregate_id\` = \`session\`.\`id\`
+              AND \`event\`.\`type\` = 'session.forked'
+            ORDER BY \`event\`.\`seq\`
+            LIMIT 1
+          ),
+          \`fork_message_id\` = (
+            SELECT json_extract(\`event\`.\`data\`, '$.from')
+            FROM \`event\`
+            WHERE \`event\`.\`aggregate_id\` = \`session\`.\`id\`
+              AND \`event\`.\`type\` = 'session.forked'
+            ORDER BY \`event\`.\`seq\`
+            LIMIT 1
+          )
+        WHERE EXISTS (
+          SELECT 1
+          FROM \`event\`
+          WHERE \`event\`.\`aggregate_id\` = \`session\`.\`id\`
+            AND \`event\`.\`type\` = 'session.forked'
+        );
+      `)
+    })
+  },
+} satisfies DatabaseMigration.Migration

packages/core/src/database/schema.gen.ts

@@ -196,6 +196,8 @@ export default {
           \`project_id\` text NOT NULL,
           \`workspace_id\` text,
           \`parent_id\` text,
+          \`fork_session_id\` text,
+          \`fork_message_id\` text,
           \`slug\` text NOT NULL,
           \`directory\` text NOT NULL,
           \`path\` text,