@@ -257,6 +257,8 @@ export interface SlotMap {
   readonly "session.message.user": SessionMessageInput
   /** The agent, model and duration line closing an assistant turn. */
   readonly "session.message.assistant.footer": SessionMessageInput
+  /** A background subagent's or shell's completion notice (`↳ Subagent finished · …`). */
+  readonly "session.message.completion": SessionMessageInput
   readonly "session.part.text": SessionPartInput
   readonly "session.part.reasoning": SessionPartInput
   /** One tool call; `tool` is the canonical tool name (shell, patch, subagent, read, ...). */
@@ -553,7 +555,8 @@ export interface Keymap {
 }
 
 /** The kind of one transcript row, as layout rules see it. */
-export type TranscriptRowKind = "user" | "text" | "reasoning" | "tool" | "group" | "footer" | "other"
+/** A "notice" is a system or synthetic message: a completion, an instruction load, a goal update. */
+export type TranscriptRowKind = "user" | "text" | "reasoning" | "tool" | "group" | "footer" | "notice" | "other"
 
 /**
  * Host layout knobs a plugin may set. Every field is optional; an unset field
 
@@ -1685,7 +1685,11 @@ function transcriptRowKind(
 ): TranscriptRowKind {
   if (row.type === "group") return "group"
   if (row.type === "assistant-footer") return "footer"
-  if (row.type === "message") return message(row.messageID)?.type === "user" ? "user" : "other"
+  if (row.type === "message") {
+    const type = message(row.messageID)?.type
+    if (type === "user") return "user"
+    return type === "system" || type === "synthetic" ? "notice" : "other"
+  }
   if (row.type !== "part") return "other"
   const item = message(row.ref.messageID)
   if (item?.type !== "assistant") return "other"
@@ -2193,21 +2197,23 @@ function SessionNoticeMessageV2(props: { message: SessionMessageInfo }) {
         </InlineToolRow>
       }
     >
-      <box
-        marginLeft={3}
-        onMouseOver={() => childID() && setHover(true)}
-        onMouseOut={() => setHover(false)}
-        onMouseUp={() => {
-          if (renderer.getSelection()?.getSelectedText()) return
-          const id = childID()
-          if (id) navigate({ type: "session", sessionID: id })
-        }}
-      >
-        <text wrapMode="none">
-          <span style={{ fg: color() }}>{heading()}</span>
-          <span style={{ fg: theme.text.muted }}>{suffix()}</span>
-        </text>
-      </box>
+      <Slot path="session.message.completion" input={{ sessionID: ctx.sessionID, messageID: props.message.id }}>
+        <box
+          marginLeft={3}
+          onMouseOver={() => childID() && setHover(true)}
+          onMouseOut={() => setHover(false)}
+          onMouseUp={() => {
+            if (renderer.getSelection()?.getSelectedText()) return
+            const id = childID()
+            if (id) navigate({ type: "session", sessionID: id })
+          }}
+        >
+          <text wrapMode="none">
+            <span style={{ fg: color() }}>{heading()}</span>
+            <span style={{ fg: theme.text.muted }}>{suffix()}</span>
+          </text>
+        </box>
+      </Slot>
     </Show>
   )
 }
 
@@ -0,0 +1,13 @@
+import { Plugin } from "@opencode/plugin/tui"
+
+// Claims completion notices and stacks notices tight.
+export default Plugin.define({
+  id: "fixture.completion-notice",
+  setup(context) {
+    context.ui.layout({ rowGap: (row) => (row.kind === "notice" && row.previous === "notice" ? 0 : 1) })
+    context.ui.slot({
+      replace: "session.message.completion",
+      render: (input) => <text>Completion claimed: {input.messageID}</text>,
+    })
+  },
+})
@@ -55,7 +55,7 @@ const goal = {
   updatedAt: 0,
 }
 
-async function openSession(plugin: string) {
+async function openSession(plugin: string, history: ReadonlyArray<unknown> = messages) {
   const fixture = await copyPlugin(plugin)
   const setup = await createAppFixture({
     width: 100,
@@ -65,7 +65,7 @@ async function openSession(plugin: string) {
     fetch: (url) => {
       if (url.pathname === "/api/session") return json({ data: [session], cursor: {} })
       if (url.pathname === `/api/session/${session.id}`) return json({ data: session })
-      if (url.pathname === `/api/session/${session.id}/message`) return json({ data: messages, cursor: {} })
+      if (url.pathname === `/api/session/${session.id}/message`) return json({ data: history, cursor: {} })
       if (/^\/api\/session\/[^/]+\/(inbox|permission)$/.test(url.pathname)) return json({ data: [] })
       if (url.pathname === "/api/model")
         return json({
@@ -205,3 +205,35 @@ test("a plugin picks the bare rail composer", async () => {
   const prose = spans.findIndex((line) => line.spans.some((span) => span.text.includes("is fixed")))
   expect(rgbToHex(color(rail, "┃"))).toBe(rgbToHex(color(prose, "is fixed")))
 })
+
+test("a plugin claims completion notices, and layout rules see notices as their own kind", async () => {
+  const notice = (id: string, created: number, metadata: Record<string, unknown>, description: string) => ({
+    type: "synthetic",
+    id,
+    text: "Notice",
+    description,
+    metadata,
+    time: { created },
+  })
+  // Newest first, as the server pages them.
+  const history = [
+    notice("msg_goal", 6, { source: "goal" }, "Goal updated"),
+    notice("msg_done_b", 5, { source: "subagent", state: "completed", agent: "worker", childID: "ses_b" }, "Fix b"),
+    notice("msg_done_a", 4, { source: "subagent", state: "completed", agent: "worker", childID: "ses_a" }, "Fix a"),
+    ...messages,
+  ]
+  await using app = await openSession("completion-notice", history)
+  await app.ready
+  const frame = await waitForHighlightedFrame(
+    app,
+    (frame) => frame.includes("Completion claimed: msg_done_b") && frame.includes("Goal updated"),
+  )
+  const lines = frame.split("\n")
+  const first = lines.findIndex((line) => line.includes("Completion claimed: msg_done_a"))
+  // Each completion is the plugin's; notices after notices stack with no blank row between them.
+  expect(first).toBeGreaterThan(lines.findIndex((line) => line.includes("The parser is fixed.")))
+  expect(lines[first + 1]).toContain("Completion claimed: msg_done_b")
+  // Other notices keep the host's own row.
+  expect(lines[first + 2]).toContain("Goal updated")
+  expect(frame).not.toContain("Worker finished")
+})