fix: complete immutable message migration

packages/session-query/session-query/src/index.ts

@@ -45,6 +45,7 @@ import {
   materializeSessionResultFilters,
 } from './filters.ts'
 import * as tracing from './tracing.ts'
+import { snapshotEvent } from './snapshot.ts'
 
 export type * from './types.ts'
 export { SessionSearchCursor } from './cursor.ts'
@@ -146,7 +147,7 @@ export abstract class SessionQueryService extends Service {
     new Session(sessionId, loaded.events, loaded.header)
     return {
       session: structuredClone(loaded.header),
-      events: loaded.events.map(event => structuredClone(event)),
+      events: loaded.events.map(snapshotEvent),
     }
   }
 
@@ -330,10 +331,13 @@ export abstract class SessionQueryService extends Service {
     }
     const startSeq = Math.max(0, seq - before)
     const endSeq = Math.min(loaded.events.length - 1, seq + after)
+    const targetSnapshot = snapshotEvent(target)
+    const events = loaded.events.slice(startSeq, endSeq + 1)
+      .map(event => event === target ? targetSnapshot : snapshotEvent(event))
     return {
-      session: loaded.header,
-      target,
-      events: loaded.events.slice(startSeq, endSeq + 1),
+      session: structuredClone(loaded.header),
+      target: targetSnapshot,
+      events,
       startSeq,
       endSeq,
     }

packages/session-query/session-query/src/snapshot.ts

@@ -0,0 +1,27 @@
+/** Detached session-query snapshots that preserve message immutability. */
+
+import { deepFreeze } from '@deepseek-ai/dsh-llm'
+import type { SessionEvent } from '@deepseek-ai/dsh-session'
+
+/**
+ * Clone one event while retaining the invariant that every identified message is frozen.
+ * @param event - source event from one corpus observation.
+ * @returns a detached event whose message value, if any, is deeply frozen.
+ */
+export function snapshotEvent<T extends SessionEvent>(event: T): T {
+  const snapshot = structuredClone(event)
+  switch (snapshot.type) {
+    case 'user/message':
+      deepFreeze(snapshot.data)
+      break
+    case 'assistant/message':
+    case 'tool/result':
+    case 'steering/message':
+      deepFreeze(snapshot.data.message)
+      break
+    default:
+      // SessionEventMap is merge-extensible; plugin-owned log-only events carry no core message.
+      break
+  }
+  return snapshot
+}

packages/session-query/session-query/src/tracing.ts

@@ -10,6 +10,7 @@ import type {
   SessionLineageTrace,
   SessionRecord,
 } from './types.ts'
+import { snapshotEvent } from './snapshot.ts'
 
 interface EventLogAnalysis {
   records: SessionEventRecord[]
@@ -51,7 +52,7 @@ export function currentSurfaceEvents(
         'SESSION_QUERY_INVALID_SURFACE',
       )
     }
-    return structuredClone(event)
+    return snapshotEvent(event)
   })
 }