fix(core): bound outbound image history (#39929)

packages/core/test/session-model-request.test.ts

@@ -1,6 +1,6 @@
 import { describe, expect, test } from "bun:test"
 import { Message, ToolResultPart } from "@opencode-ai/ai"
-import { unsupportedParts } from "@opencode-ai/core/session/model-request"
+import { boundImages, unsupportedParts } from "@opencode-ai/core/session/model-request"
 
 const capabilities = (input: string[]) => ({ tools: true, input, output: ["text"] })
 
@@ -62,3 +62,51 @@ describe("SessionModelRequest.unsupportedParts", () => {
     expect(unsupportedParts([message], capabilities(["text", "image"]))[0]?.content).toEqual(message.content)
   })
 })
+
+describe("SessionModelRequest.boundImages", () => {
+  test("preserves images below the trigger", () => {
+    const messages = [Message.user({ type: "media", mediaType: "image/png", data: "aGVsbG8=" })]
+    expect(boundImages(messages)).toBe(messages)
+  })
+
+  test("replaces oldest images until the retained payload reaches the target", () => {
+    const image = "a".repeat(9 * 1024 * 1024)
+    const messages = [
+      Message.user({ type: "media", mediaType: "image/png", data: image, filename: "first.png" }),
+      Message.user({ type: "media", mediaType: "image/png", data: image, filename: "second.png" }),
+      Message.user({ type: "media", mediaType: "image/png", data: image, filename: "third.png" }),
+    ]
+    const result = boundImages(messages)
+
+    expect(result[0]?.content[0]).toMatchObject({ type: "text" })
+    expect(result[1]?.content[0]).toMatchObject({ type: "text" })
+    expect(result[2]?.content[0]).toMatchObject({ type: "media", filename: "third.png" })
+  })
+
+  test("replaces images nested in tool results", () => {
+    const image = "a".repeat(13 * 1024 * 1024)
+    const result = boundImages([
+      Message.tool(
+        ToolResultPart.make({
+          id: "call_1",
+          name: "read",
+          result: {
+            type: "content",
+            value: [
+              { type: "file", uri: `data:image/png;base64,${image}`, mime: "image/png", name: "first.png" },
+              { type: "file", uri: `data:image/png;base64,${image}`, mime: "image/png", name: "second.png" },
+            ],
+          },
+        }),
+      ),
+    ])
+
+    expect(result[0]?.content[0]).toMatchObject({
+      type: "tool-result",
+      result: {
+        type: "content",
+        value: [{ type: "text" }, { type: "file", name: "second.png" }],
+      },
+    })
+  })
+})