diff --git a/apps/server/src/provider/Layers/ClaudeAdapter.test.ts b/apps/server/src/provider/Layers/ClaudeAdapter.test.ts
index 502620359836..295926b26644 100644
--- a/apps/server/src/provider/Layers/ClaudeAdapter.test.ts
+++ b/apps/server/src/provider/Layers/ClaudeAdapter.test.ts
@@ -6691,6 +6691,56 @@ describe("ClaudeAdapterLive", () => {
     );
   });
 
+  it.effect("completed turns keep their ids but not the SDK messages", () => {
+    const harness = makeHarness();
+    return Effect.gen(function* () {
+      const adapter = yield* ClaudeAdapter;
+      const session = yield* adapter.startSession({
+        threadId: THREAD_ID,
+        provider: ProviderDriverKind.make("claudeAgent"),
+        runtimeMode: "full-access",
+      });
+      const turn = yield* adapter.sendTurn({
+        threadId: session.threadId,
+        input: "hello",
+        attachments: [],
+      });
+      const completedFiber = yield* Stream.filter(
+        adapter.streamEvents,
+        (event) => event.type === "turn.completed",
+      ).pipe(Stream.runHead, Effect.forkChild);
+
+      harness.query.emit({
+        type: "assistant",
+        session_id: "sdk-session-1",
+        uuid: "assistant-1",
+        parent_tool_use_id: null,
+        message: {
+          id: "assistant-message-1",
+          content: [{ type: "text", text: "Hi" }],
+        },
+      } as unknown as SDKMessage);
+      harness.query.emit({
+        type: "result",
+        subtype: "success",
+        is_error: false,
+        errors: [],
+        session_id: "sdk-session-1",
+        uuid: "result-1",
+      } as unknown as SDKMessage);
+      yield* Fiber.join(completedFiber);
+
+      const snapshot = yield* adapter.readThread(session.threadId);
+      assert.deepEqual(
+        snapshot.turns.map((entry) => ({ id: String(entry.id), items: entry.items })),
+        [{ id: String(turn.turnId), items: [] }],
+      );
+    }).pipe(
+      Effect.provideService(Random.Random, makeDeterministicRandomService()),
+      Effect.provide(harness.layer),
+    );
+  });
+
   it.effect("rewinds Claude history when the fork omits retained system messages", () => {
     const forkCalls: Array<Parameters<NonNullable<ClaudeAdapterLiveOptions["forkSession"]>>> = [];
     let firstTurnId = "";
diff --git a/apps/server/src/provider/Layers/ClaudeAdapter.ts b/apps/server/src/provider/Layers/ClaudeAdapter.ts
index 11a5322b4eee..6e30f5241780 100644
--- a/apps/server/src/provider/Layers/ClaudeAdapter.ts
+++ b/apps/server/src/provider/Layers/ClaudeAdapter.ts
@@ -267,7 +267,6 @@ interface ClaudeTurnState {
    * steered instead (the queued message continues the same turn).
    */
   readonly synthetic?: boolean;
-  readonly items: Array<unknown>;
   readonly assistantTextBlocks: Map<number, AssistantTextBlockState>;
   readonly assistantTextBlockOrder: Array<AssistantTextBlockState>;
   readonly capturedProposedPlanKeys: Set<string>;
@@ -422,10 +421,11 @@ interface ClaudeSessionContext {
   resumeSessionId: string | undefined;
   readonly pendingApprovals: Map<ApprovalRequestId, PendingApproval>;
   readonly pendingUserInputs: Map<ApprovalRequestId, PendingUserInput>;
-  readonly turns: Array<{
-    id: TurnId;
-    items: Array<unknown>;
-  }>;
+  /** Completed turn ids, reported by readThread and trimmed on rollback.
+   * SDK messages are not kept: rollback reads Claude's own history through
+   * turnStartMessageIds, and a long-lived session would otherwise hold every
+   * message it ever produced. */
+  readonly turns: Array<{ readonly id: TurnId }>;
   readonly inFlightTools: Map<number, ToolInFlight>;
   readonly claudeTasks: Map<string, ClaudeTaskState>;
   readonly taskAgents: Map<string, ClaudeTaskAgentState>;
@@ -2176,10 +2176,7 @@ export const makeClaudeAdapter = Effect.fn("makeClaudeAdapter")(function* (
     }
     return {
       threadId,
-      turns: context.turns.map((turn) => ({
-        id: turn.id,
-        items: [...turn.items],
-      })),
+      turns: context.turns.map((turn) => ({ id: turn.id, items: [] })),
     };
   });
 
@@ -2808,10 +2805,7 @@ export const makeClaudeAdapter = Effect.fn("makeClaudeAdapter")(function* (
       });
     }
 
-    context.turns.push({
-      id: turnState.turnId,
-      items: [...turnState.items],
-    });
+    context.turns.push({ id: turnState.turnId });
 
     yield* emitThreadTokenUsage(context, usageSnapshot, {
       rawMethod: "claude/result",
@@ -3175,10 +3169,6 @@ export const makeClaudeAdapter = Effect.fn("makeClaudeAdapter")(function* (
       return;
     }
 
-    if (context.turnState) {
-      context.turnState.items.push(message.message);
-    }
-
     for (const toolResult of toolResultBlocksFromUserMessage(message)) {
       const toolEntry = Array.from(context.inFlightTools.entries()).find(
         ([, tool]) => tool.itemId === toolResult.toolUseId,
@@ -3378,7 +3368,6 @@ export const makeClaudeAdapter = Effect.fn("makeClaudeAdapter")(function* (
         turnId,
         startedAt,
         synthetic: true,
-        items: [],
         assistantTextBlocks: new Map(),
         assistantTextBlockOrder: [],
         capturedProposedPlanKeys: new Set(),
@@ -3461,7 +3450,6 @@ export const makeClaudeAdapter = Effect.fn("makeClaudeAdapter")(function* (
           cwd: path.resolve(context.session.cwd ?? "."),
         });
       }
-      context.turnState.items.push(message.message);
       if (
         normalizeClaudeActiveTokenUsage(
           message.message.usage,
@@ -5205,7 +5193,6 @@ export const makeClaudeAdapter = Effect.fn("makeClaudeAdapter")(function* (
       const turnState: ClaudeTurnState = {
         turnId,
         startedAt: yield* nowIso,
-        items: [],
         assistantTextBlocks: new Map(),
         assistantTextBlockOrder: [],
         capturedProposedPlanKeys: new Set(),