fix(opencode): forward parent attachments to subagents

packages/opencode/src/tool/task.ts

@@ -21,6 +21,35 @@ export interface TaskPromptOps {
   prompt(input: SessionPrompt.PromptInput): Effect.Effect<SessionV1.WithParts>
 }
 
+type ForwardedFilePart = Extract<SessionPrompt.PromptInput["parts"][number], { type: "file" }>
+
+function parentAttachments(
+  messages: SessionV1.WithParts[],
+  parentMessageID: MessageID,
+  subagent: string,
+): ForwardedFilePart[] {
+  const parent = messages.find((message) => message.info.role === "user" && message.info.id === parentMessageID)
+  // Only forward attachments when the parent message explicitly targets this subagent.
+  if (!parent || !parent.parts.some((part) => part.type === "agent" && part.name === subagent)) return []
+
+  const seen = new Set<string>()
+  return parent.parts.flatMap((part) => {
+    if (part.type !== "file") return []
+    const key = [part.url, part.mime, part.filename ?? ""].join("\n")
+    if (seen.has(key)) return []
+    seen.add(key)
+    return [
+      {
+        type: "file" as const,
+        mime: part.mime,
+        filename: part.filename,
+        url: part.url,
+        source: part.source,
+      },
+    ]
+  })
+}
+
 const id = "task"
 const BACKGROUND_DESCRIPTION = [
   "Background mode: background=true launches the subagent asynchronously and returns immediately.",
@@ -162,11 +191,12 @@ export const TaskTool = Tool.define(
         Effect.orDie,
       )
       if (msg.info.role !== "assistant") return yield* Effect.fail(new Error("Not an assistant message"))
-      const variant = msg.info.variant
+      const assistant = msg.info
+      const variant = assistant.variant
 
       const model = next.model ?? {
-        modelID: msg.info.modelID,
-        providerID: msg.info.providerID,
+        modelID: assistant.modelID,
+        providerID: assistant.providerID,
       }
       const metadata = {
         parentSessionId: ctx.sessionID,
@@ -185,6 +215,23 @@ export const TaskTool = Tool.define(
 
       const runTask = Effect.fn("TaskTool.runTask")(function* () {
         const parts = yield* ops.resolvePromptParts(params.prompt)
+        const forwarded = parentAttachments(ctx.messages, assistant.parentID, next.name)
+        const promptParts =
+          forwarded.length === 0
+            ? parts
+            : [
+                ...parts,
+                ...forwarded.filter(
+                  (candidate) =>
+                    !parts.some(
+                      (part) =>
+                        part.type === "file" &&
+                        part.url === candidate.url &&
+                        part.mime === candidate.mime &&
+                        part.filename === candidate.filename,
+                    ),
+                ),
+              ]
         const result = yield* ops.prompt({
           messageID: MessageID.ascending(),
           sessionID: nextSession.id,
@@ -194,7 +241,7 @@ export const TaskTool = Tool.define(
           },
           variant: next.model ? undefined : variant,
           agent: next.name,
-          parts,
+          parts: promptParts,
         })
         return result.parts.findLast((item) => item.type === "text")?.text ?? ""
       })

packages/opencode/test/tool/task.test.ts

@@ -248,6 +248,62 @@ describe("tool.task", () => {
     }),
   )
 
+  it.instance("execute forwards parent user file parts for matching agent handoff", () =>
+    Effect.gen(function* () {
+      const sessions = yield* Session.Service
+      const { chat, assistant } = yield* seed()
+      yield* sessions.updatePart({
+        id: PartID.ascending(),
+        messageID: assistant.parentID,
+        sessionID: chat.id,
+        type: "agent",
+        name: "general",
+        source: {
+          value: "@general",
+          start: 0,
+          end: 8,
+        },
+      })
+      yield* sessions.updatePart({
+        id: PartID.ascending(),
+        messageID: assistant.parentID,
+        sessionID: chat.id,
+        type: "file",
+        mime: "image/png",
+        filename: "image.png",
+        url: "data:image/png;base64,AAAA",
+      })
+
+      const tool = yield* TaskTool
+      const def = yield* tool.init()
+      let seen: SessionPrompt.PromptInput | undefined
+      const promptOps = stubOps({ onPrompt: (input) => (seen = input) })
+
+      yield* def.execute(
+        {
+          description: "inspect image",
+          prompt: "describe this image",
+          subagent_type: "general",
+        },
+        {
+          sessionID: chat.id,
+          messageID: assistant.id,
+          agent: "build",
+          abort: new AbortController().signal,
+          extra: { promptOps },
+          messages: yield* sessions.messages({ sessionID: chat.id }),
+          metadata: () => Effect.void,
+          ask: () => Effect.void,
+        },
+      )
+
+      expect(seen?.parts).toEqual([
+        { type: "text", text: "describe this image" },
+        { type: "file", mime: "image/png", filename: "image.png", url: "data:image/png;base64,AAAA" },
+      ])
+    }),
+  )
+
   it.instance("execute asks by default and skips checks when bypassed", () =>
     Effect.gen(function* () {
       const { chat, assistant } = yield* seed()