From 35d5df3bc0ac5d9406a13d14c8d0ee2da756e198 Mon Sep 17 00:00:00 2001
From: kolaworld <kolaawe@pm.me>
Date: Sat, 15 Aug 2026 13:40:18 -0400
Subject: [PATCH 1/2] fix(ai): preserve existing message ids on interrupt
 snapshots

Keep ModelMessage.id on MESSAGES_SNAPSHOT so interrupt boundaries do not rewrite stable identity. Generate snapshot_<run>_<index> only when an id is missing.

Fixes #1107
---
 .changeset/fix-1107-snapshot-message-ids.md |  5 +++
 packages/ai/src/activities/chat/index.ts    |  4 ++-
 packages/ai/tests/chat.test.ts              | 36 +++++++++++++++++++++
 3 files changed, 44 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/fix-1107-snapshot-message-ids.md

diff --git a/.changeset/fix-1107-snapshot-message-ids.md b/.changeset/fix-1107-snapshot-message-ids.md
new file mode 100644
index 0000000000..82f1e30e7a
--- /dev/null
+++ b/.changeset/fix-1107-snapshot-message-ids.md
@@ -0,0 +1,5 @@
+---
+'@tanstack/ai': patch
+---
+
+Preserve existing message IDs on interrupt `MESSAGES_SNAPSHOT` events.
diff --git a/packages/ai/src/activities/chat/index.ts b/packages/ai/src/activities/chat/index.ts
index 15fb215ba0..2130c6be03 100644
--- a/packages/ai/src/activities/chat/index.ts
+++ b/packages/ai/src/activities/chat/index.ts
@@ -2177,7 +2177,9 @@ class TextEngine<
               ? undefined
               : JSON.stringify(message.content)
         return {
-          id: `snapshot_${this.runIdOverride ?? this.requestId}_${index}`,
+          id:
+            message.id ||
+            `snapshot_${this.runIdOverride ?? this.requestId}_${index}`,
           role: message.role,
           ...(content !== undefined ? { content } : {}),
           ...('toolCalls' in message && message.toolCalls
diff --git a/packages/ai/tests/chat.test.ts b/packages/ai/tests/chat.test.ts
index 0e362875c9..cc72fbab60 100644
--- a/packages/ai/tests/chat.test.ts
+++ b/packages/ai/tests/chat.test.ts
@@ -678,6 +678,42 @@ describe('chat()', () => {
       })
     })
 
+    it('preserves existing message ids on the interrupt MESSAGES_SNAPSHOT', async () => {
+      const { adapter } = createMockAdapter({
+        iterations: [
+          [
+            ev.runStarted(),
+            ev.textStart('stream-assistant'),
+            {
+              ...ev.toolStart('call_1', 'clientSearch'),
+              parentMessageId: 'stream-assistant',
+            },
+            ev.toolArgs('call_1', '{"query":"test"}'),
+            ev.runFinished('tool_calls'),
+          ],
+        ],
+      })
+
+      const chunks = await collectChunks(
+        chat({
+          adapter,
+          runId: 'interrupt-run',
+          messages: [{ id: 'user-1', role: 'user', content: 'Search' }],
+          tools: [clientTool('clientSearch')],
+        }) as AsyncIterable<StreamChunk>,
+      )
+
+      const snapshot = chunks.find(
+        (chunk) => chunk.type === EventType.MESSAGES_SNAPSHOT,
+      )
+      expect(snapshot).toMatchObject({
+        messages: [
+          { id: 'user-1', role: 'user', content: 'Search' },
+          { id: 'stream-assistant', role: 'assistant' },
+        ],
+      })
+    })
+
     it('should yield an interrupt outcome for client tools', async () => {
       const { adapter } = createMockAdapter({
         iterations: [

From b6c9128a25d50b2ae9ff13f367a4ebcd298fa033 Mon Sep 17 00:00:00 2001
From: kolaworld <kolaawe@pm.me>
Date: Sat, 15 Aug 2026 13:57:16 -0400
Subject: [PATCH 2/2] test(ai): cover snapshot id fallback when a message has
 no id

---
 packages/ai/tests/chat.test.ts | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/packages/ai/tests/chat.test.ts b/packages/ai/tests/chat.test.ts
index cc72fbab60..dac3497b4e 100644
--- a/packages/ai/tests/chat.test.ts
+++ b/packages/ai/tests/chat.test.ts
@@ -714,6 +714,36 @@ describe('chat()', () => {
       })
     })
 
+    it('generates a snapshot id on the interrupt MESSAGES_SNAPSHOT when a message has no id', async () => {
+      const { adapter } = createMockAdapter({
+        iterations: [
+          [
+            ev.runStarted(),
+            ev.toolStart('call_1', 'clientSearch'),
+            ev.toolArgs('call_1', '{"query":"test"}'),
+            ev.runFinished('tool_calls'),
+          ],
+        ],
+      })
+
+      const chunks = await collectChunks(
+        chat({
+          adapter,
+          runId: 'interrupt-run',
+          messages: [{ role: 'user', content: 'Search' }],
+          tools: [clientTool('clientSearch')],
+        }) as AsyncIterable<StreamChunk>,
+      )
+
+      const snapshot = chunks.find(
+        (chunk) => chunk.type === EventType.MESSAGES_SNAPSHOT,
+      )
+      expect(snapshot?.messages[0]).toMatchObject({
+        id: 'snapshot_interrupt-run_0',
+        role: 'user',
+      })
+    })
+
     it('should yield an interrupt outcome for client tools', async () => {
       const { adapter } = createMockAdapter({
         iterations: [