From 8830d2a8ddf51c1ae044fa76f60881c1901469d2 Mon Sep 17 00:00:00 2001
From: Shoaib Akhtar Ansari <shoaib.ansari5398@gmail.com>
Date: Fri, 16 Jan 2026 19:11:19 +0530
Subject: [PATCH 1/2] fix(session): safeguard message conversion against
 invalid prompts (#8862)

---
 packages/opencode/src/session/message-v2.ts | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/packages/opencode/src/session/message-v2.ts b/packages/opencode/src/session/message-v2.ts
index 4b081b5b44e..5e8326ac330 100644
--- a/packages/opencode/src/session/message-v2.ts
+++ b/packages/opencode/src/session/message-v2.ts
@@ -517,8 +517,11 @@ export namespace MessageV2 {
                 input: part.state.input,
                 output: part.state.time.compacted
                   ? "[Old tool result content cleared]"
-                  : { output: part.state.output, attachments: part.state.attachments },
-                callProviderMetadata: part.metadata,
+                  : {
+                      output: part.state.output,
+                      attachments: part.state.attachments?.filter((x) => x) ?? [],
+                    },
+                callProviderMetadata: part.metadata ?? {},
               })
             }
             if (part.state.status === "error")
@@ -556,12 +559,12 @@ export namespace MessageV2 {
       }
     }
 
-    return convertToModelMessages(
-      result.filter((msg) => msg.parts.some((part) => part.type !== "step-start")),
-      {
-        tools: options?.tools,
-      },
-    )
+    const filtered = result
+      .filter((msg) => msg.parts.length > 0)
+      .filter((msg) => msg.parts.some((part) => part.type !== "step-start"))
+    return convertToModelMessages(filtered, {
+      tools: options?.tools,
+    })
   }
 
   export const stream = fn(Identifier.schema("session"), async function* (sessionID) {

From deac3fd3db05f4f8cd0a734a96f11b62ad2e9153 Mon Sep 17 00:00:00 2001
From: Shoaib Akhtar Ansari <shoaib.ansari5398@gmail.com>
Date: Sat, 17 Jan 2026 13:24:40 +0530
Subject: [PATCH 2/2] fix(session): combine filters and add regression test

---
 packages/opencode/src/session/message-v2.ts   |  6 +-
 .../opencode/test/session/issue-8862.test.ts  | 99 +++++++++++++++++++
 2 files changed, 102 insertions(+), 3 deletions(-)
 create mode 100644 packages/opencode/test/session/issue-8862.test.ts

diff --git a/packages/opencode/src/session/message-v2.ts b/packages/opencode/src/session/message-v2.ts
index 5e8326ac330..fbdfd1bc477 100644
--- a/packages/opencode/src/session/message-v2.ts
+++ b/packages/opencode/src/session/message-v2.ts
@@ -559,9 +559,9 @@ export namespace MessageV2 {
       }
     }
 
-    const filtered = result
-      .filter((msg) => msg.parts.length > 0)
-      .filter((msg) => msg.parts.some((part) => part.type !== "step-start"))
+    const filtered = result.filter(
+      (msg) => msg.parts.length > 0 && msg.parts.some((part) => part.type !== "step-start"),
+    )
     return convertToModelMessages(filtered, {
       tools: options?.tools,
     })
diff --git a/packages/opencode/test/session/issue-8862.test.ts b/packages/opencode/test/session/issue-8862.test.ts
new file mode 100644
index 00000000000..f5e7d876c1c
--- /dev/null
+++ b/packages/opencode/test/session/issue-8862.test.ts
@@ -0,0 +1,99 @@
+import { describe, expect, test } from "bun:test"
+import { MessageV2 } from "../../src/session/message-v2"
+
+const sessionID = "session"
+
+function assistantInfo(id: string, parentID: string): MessageV2.Assistant {
+  return {
+    id,
+    sessionID,
+    role: "assistant",
+    time: { created: 0 },
+    parentID,
+    modelID: "model",
+    providerID: "provider",
+    mode: "",
+    agent: "agent",
+    path: { cwd: "/", root: "/" },
+    cost: 0,
+    tokens: {
+      input: 0,
+      output: 0,
+      reasoning: 0,
+      cache: { read: 0, write: 0 },
+    },
+  } as unknown as MessageV2.Assistant
+}
+
+function basePart(messageID: string, id: string) {
+  return {
+    id,
+    sessionID,
+    messageID,
+  }
+}
+
+describe("issue-8862 regression test", () => {
+  test("successfully converts tool results with undefined metadata/attachments", () => {
+    const userID = "m-user"
+    const assistantID = "m-assistant"
+
+    const input: MessageV2.WithParts[] = [
+      {
+        info: assistantInfo(assistantID, userID),
+        parts: [
+          {
+            ...basePart(assistantID, "a2"),
+            type: "tool",
+            callID: "call-1",
+            tool: "bash",
+            state: {
+              status: "completed",
+              input: { cmd: "ls" },
+              output: "ok",
+              title: "Bash",
+              metadata: undefined as any,
+              time: { start: 0, end: 1 },
+              attachments: undefined as any,
+            } as any,
+            metadata: undefined as any,
+          },
+        ] as MessageV2.Part[],
+      },
+    ]
+
+    expect(MessageV2.toModelMessage(input)).toStrictEqual([
+      {
+        role: "assistant",
+        content: [
+          {
+            type: "tool-call",
+            toolCallId: "call-1",
+            toolName: "bash",
+            input: { cmd: "ls" },
+            providerExecuted: undefined,
+            providerOptions: {},
+          },
+        ],
+      },
+      {
+        role: "tool",
+        content: [
+          {
+            type: "tool-result",
+            toolCallId: "call-1",
+            toolName: "bash",
+            output: {
+              type: "json",
+              value: {
+                output: "ok",
+                attachments: [],
+              },
+            },
+            providerOptions: {},
+          },
+        ],
+      },
+    ])
+  })
+})