diff --git a/packages/opencode/src/plugin/copilot.ts b/packages/opencode/src/plugin/copilot.ts
index 0be1345871fd..535238a74944 100644
--- a/packages/opencode/src/plugin/copilot.ts
+++ b/packages/opencode/src/plugin/copilot.ts
@@ -68,12 +68,15 @@ export async function CopilotAuthPlugin(input: PluginInput): Promise<Hooks> {
                 // Completions API
                 if (body?.messages) {
                   const last = body.messages[body.messages.length - 1]
+                  // check for sneaky anthropic tool_result
+                  const hasToolResult =
+                    Array.isArray(last?.content) && last.content.some((part: any) => part.type === "tool_result")
                   return {
                     isVision: body.messages.some(
                       (msg: any) =>
                         Array.isArray(msg.content) && msg.content.some((part: any) => part.type === "image_url"),
                     ),
-                    isAgent: last?.role !== "user",
+                    isAgent: hasToolResult || last?.role !== "user",
                   }
                 }
 
@@ -88,7 +91,7 @@ export async function CopilotAuthPlugin(input: PluginInput): Promise<Hooks> {
                     isAgent: last?.role !== "user",
                   }
                 }
-              } catch {}
+              } catch { }
               return { isVision: false, isAgent: false }
             })
 
diff --git a/packages/opencode/test/plugin/copilot-initiator.test.ts b/packages/opencode/test/plugin/copilot-initiator.test.ts
new file mode 100644
index 000000000000..5133d79311d3
--- /dev/null
+++ b/packages/opencode/test/plugin/copilot-initiator.test.ts
@@ -0,0 +1,153 @@
+import { test, expect, afterAll } from "bun:test"
+import { CopilotAuthPlugin } from "../../src/plugin/copilot"
+
+// Capture server to verify request headers
+let capturedHeaders: Headers | null = null
+const server = Bun.serve({
+  port: 0,
+  fetch(req) {
+    capturedHeaders = req.headers
+    return new Response(JSON.stringify({ id: "msg_123", content: [], type: "message" }), {
+      status: 200,
+      headers: { "Content-Type": "application/json" },
+    })
+  },
+})
+
+afterAll(() => {
+  server.stop()
+})
+
+async function getWrappedFetch() {
+  const hooks = await CopilotAuthPlugin({
+    client: {} as any,
+    project: {} as any,
+    worktree: {} as any,
+    directory: new URL("file:///tmp") as any,
+    serverUrl: new URL("http://localhost:4096") as any,
+    $: Bun.$,
+  })
+
+  const auth = await hooks.auth!.loader!(
+    async () => ({ type: "oauth" as const, refresh: "test-token", access: "test-token", expires: 0 }),
+    undefined as any,
+  )
+
+  return auth.fetch!
+}
+
+test("tool_result in last user message sets x-initiator: agent", async () => {
+  const wrappedFetch = await getWrappedFetch()
+  capturedHeaders = null
+
+  const body = JSON.stringify({
+    model: "claude-sonnet-4-5-20250929",
+    messages: [
+      { role: "user", content: [{ type: "text", text: "Use the tool" }] },
+      {
+        role: "assistant",
+        content: [{ type: "tool_use", id: "toolu_123", name: "bash", input: { command: "ls" } }],
+      },
+      {
+        role: "user",
+        content: [{ type: "tool_result", tool_use_id: "toolu_123", content: "file1.txt\nfile2.txt" }],
+      },
+    ],
+  })
+
+  await wrappedFetch(`${server.url.origin}/v1/messages`, {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body,
+  })
+
+  expect(capturedHeaders).not.toBeNull()
+  expect(capturedHeaders!.get("x-initiator")).toBe("agent")
+})
+
+test("mixed text + tool_result sets x-initiator: agent", async () => {
+  const wrappedFetch = await getWrappedFetch()
+  capturedHeaders = null
+
+  const body = JSON.stringify({
+    model: "claude-sonnet-4-5-20250929",
+    messages: [
+      {
+        role: "user",
+        content: [
+          { type: "tool_result", tool_use_id: "toolu_123", content: "done" },
+          { type: "text", text: "continue please" },
+        ],
+      },
+    ],
+  })
+
+  await wrappedFetch(`${server.url.origin}/v1/messages`, {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body,
+  })
+
+  expect(capturedHeaders).not.toBeNull()
+  expect(capturedHeaders!.get("x-initiator")).toBe("agent")
+})
+
+test("normal user text sets x-initiator: user", async () => {
+  const wrappedFetch = await getWrappedFetch()
+  capturedHeaders = null
+
+  const body = JSON.stringify({
+    model: "claude-sonnet-4-5-20250929",
+    messages: [{ role: "user", content: [{ type: "text", text: "Hello world" }] }],
+  })
+
+  await wrappedFetch(`${server.url.origin}/v1/messages`, {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body,
+  })
+
+  expect(capturedHeaders).not.toBeNull()
+  expect(capturedHeaders!.get("x-initiator")).toBe("user")
+})
+
+test("string content sets x-initiator: user", async () => {
+  const wrappedFetch = await getWrappedFetch()
+  capturedHeaders = null
+
+  const body = JSON.stringify({
+    model: "claude-sonnet-4-5-20250929",
+    messages: [{ role: "user", content: "Hello world" }],
+  })
+
+  await wrappedFetch(`${server.url.origin}/v1/messages`, {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body,
+  })
+
+  expect(capturedHeaders).not.toBeNull()
+  expect(capturedHeaders!.get("x-initiator")).toBe("user")
+})
+
+test("assistant last message should set x-initiator: agent", async () => {
+  const wrappedFetch = await getWrappedFetch()
+  capturedHeaders = null
+
+  const body = JSON.stringify({
+    model: "claude-sonnet-4-5-20250929",
+    messages: [
+      { role: "user", content: "Hello" },
+      { role: "assistant", content: [{ type: "text", text: "Hi there" }] },
+    ],
+  })
+
+  await wrappedFetch(`${server.url.origin}/v1/messages`, {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body,
+  })
+
+  expect(capturedHeaders).not.toBeNull()
+  expect(capturedHeaders!.get("x-initiator")).toBe("agent")
+})