diff --git a/packages/opencode/src/cli/cmd/tui/i18n/en.ts b/packages/opencode/src/cli/cmd/tui/i18n/en.ts
index 039767425..5154882f4 100644
--- a/packages/opencode/src/cli/cmd/tui/i18n/en.ts
+++ b/packages/opencode/src/cli/cmd/tui/i18n/en.ts
@@ -560,6 +560,10 @@ export const dict: Record<string, string> = {
   // Session badges
   "tui.session.badge.auto": "Auto",
 
+  // Context rebuild boundary marker (inserted by /rebuild)
+  "tui.session.rebuild_boundary.label": "context rebuilt",
+  "tui.session.rebuild_boundary.detail": "earlier messages summarized",
+
   // Workspace trust
   "trust.title": "Accessing workspace:",
   "trust.safety_check": "Quick safety check: Is this a project you created or one you trust? (Like your own code, a well-known open source project, or work from your team). If not, take a moment to review what's in this folder first.",
diff --git a/packages/opencode/src/cli/cmd/tui/i18n/zh.ts b/packages/opencode/src/cli/cmd/tui/i18n/zh.ts
index 7347d5fe4..c067ca8f6 100644
--- a/packages/opencode/src/cli/cmd/tui/i18n/zh.ts
+++ b/packages/opencode/src/cli/cmd/tui/i18n/zh.ts
@@ -581,6 +581,10 @@ export const dict = {
   // Session badges
   "tui.session.badge.auto": "自动",
 
+  // Context rebuild boundary marker (inserted by /rebuild)
+  "tui.session.rebuild_boundary.label": "上下文已重建",
+  "tui.session.rebuild_boundary.detail": "较早消息已摘要",
+
   // Workspace trust
   "trust.title": "访问工作区：",
   "trust.safety_check": "安全确认：这是你自己创建或信任的项目吗？（如你自己的代码、知名开源项目或团队内部项目）。如果不是，请先检查此目录下的内容。",
diff --git a/packages/opencode/src/cli/cmd/tui/i18n/zht.ts b/packages/opencode/src/cli/cmd/tui/i18n/zht.ts
index 23cc47497..e74894971 100644
--- a/packages/opencode/src/cli/cmd/tui/i18n/zht.ts
+++ b/packages/opencode/src/cli/cmd/tui/i18n/zht.ts
@@ -550,6 +550,10 @@ export const dict = {
   // Session badges
   "tui.session.badge.auto": "自動",
 
+  // Context rebuild boundary marker (inserted by /rebuild)
+  "tui.session.rebuild_boundary.label": "上下文已重建",
+  "tui.session.rebuild_boundary.detail": "較早訊息已摘要",
+
   // Workspace trust
   "trust.title": "存取工作區：",
   "trust.safety_check": "安全確認：這是你自己建立或信任的專案嗎？（如你自己的程式碼、知名開源專案或團隊內部專案）。如果不是，請先檢查此目錄下的內容。",
diff --git a/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx b/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
index bc38ccb43..201167b53 100644
--- a/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
+++ b/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
@@ -1536,7 +1536,16 @@ function UserMessage(props: {
       return parsed ? [parsed] : []
     })[0]
   })
+  // A context rebuild (`/rebuild`) inserts a single user message carrying a
+  // `checkpoint` part plus `synthetic: true` text parts (the rendered context
+  // and index). Neither renders — `checkpoint` has no PART_MAPPING entry and
+  // synthetic text is excluded from `text()` above — so the boundary used to be
+  // completely invisible in the transcript, unlike compaction which at least
+  // leaves a visible summary message behind. Surface it as a one-line marker
+  // row so the user can see that a rebuild happened and where.
+  const rebuildBoundary = createMemo(() => props.parts.some((x) => x.type === "checkpoint"))
   const { theme } = useTheme()
+  const t = useLanguage().t
   const [hover, setHover] = createSignal(false)
   const queued = createMemo(() => props.pending && props.message.id > props.pending)
   const color = createMemo(() => local.agent.color(props.message.agent))
@@ -1603,6 +1612,17 @@ function UserMessage(props: {
           )
         }}
       </Show>
+      <Show when={rebuildBoundary()}>
+        <box id={props.message.id} marginTop={props.index === 0 ? 0 : 1} paddingLeft={2} flexDirection="row" gap={1}>
+          <text fg={theme.textMuted}>
+            <span style={{ bg: theme.backgroundElement, fg: theme.primary, bold: true }}>
+              {" "}
+              ⟲ {t("tui.session.rebuild_boundary.label")}{" "}
+            </span>
+            <span style={{ fg: theme.textMuted }}> {t("tui.session.rebuild_boundary.detail")}</span>
+          </text>
+        </box>
+      </Show>
       <Show when={text() && !actorNotification()}>
         <box
           id={props.message.id}
diff --git a/packages/opencode/test/cli/cmd/tui/rebuild-boundary-marker.test.ts b/packages/opencode/test/cli/cmd/tui/rebuild-boundary-marker.test.ts
new file mode 100644
index 000000000..948c69189
--- /dev/null
+++ b/packages/opencode/test/cli/cmd/tui/rebuild-boundary-marker.test.ts
@@ -0,0 +1,31 @@
+import { describe, expect, test } from "bun:test"
+import { dict as en } from "../../../../src/cli/cmd/tui/i18n/en"
+import { dict as zh } from "../../../../src/cli/cmd/tui/i18n/zh"
+import { dict as zht } from "../../../../src/cli/cmd/tui/i18n/zht"
+
+// A `/rebuild` inserts one user message carrying a `checkpoint` part plus
+// synthetic text parts. The TUI renders it as a one-line marker row in
+// UserMessage (routes/session/index.tsx) so the boundary is visible in the
+// transcript. The label copy is localized; the marker row would render an empty
+// badge if these keys ever went missing, so pin them here.
+const KEYS = ["tui.session.rebuild_boundary.label", "tui.session.rebuild_boundary.detail"] as const
+
+describe("rebuild boundary marker copy", () => {
+  test("english copy names the rebuild and what happened to earlier messages", () => {
+    expect(en["tui.session.rebuild_boundary.label"]).toBe("context rebuilt")
+    expect(en["tui.session.rebuild_boundary.detail"]).toBe("earlier messages summarized")
+  })
+
+  test("localized dictionaries define the marker copy", () => {
+    for (const key of KEYS) {
+      for (const [name, dict] of Object.entries({ en, zh, zht })) {
+        expect(dict[key], `${name} is missing ${key}`).toBeTruthy()
+      }
+      // Untranslated keys silently fall back to English via the `base` merge in
+      // context/language.tsx, so an English string here means a missed
+      // translation rather than a crash — assert it is actually translated.
+      expect(zh[key]).not.toBe(en[key])
+      expect(zht[key]).not.toBe(en[key])
+    }
+  })
+})