diff --git a/packages/ui-mac/src/renderer/alpha-ui/session-rail/terminal/terminal-rail-core.ts b/packages/ui-mac/src/renderer/alpha-ui/session-rail/terminal/terminal-rail-core.ts
new file mode 100644
index 000000000000..34de87b4e080
--- /dev/null
+++ b/packages/ui-mac/src/renderer/alpha-ui/session-rail/terminal/terminal-rail-core.ts
@@ -0,0 +1,94 @@
+// REQ-125 C3-term(#550)—— 右栏终端面板的纯模型与引擎通道 seam。
+//
+// 边界(seam 基线 §② 白名单 / §③ I1):终端仿真与 PTY 数据通道属可复用的非布局内核,
+// alpha 只自持外壳(页签条 / 圆角深底输出区外框 / 脚条)。引擎经下方
+// `AlphaTerminalEngineChannel` typed seam 进入,本目录零 import 上游模块。
+//
+// 地面真相(2026-07-24 勘破):上游引擎 = `packages/app/src/components/terminal.tsx`
+// (ghostty-web WASM + PTY WebSocket 数据通道)+ `packages/app/src/context/terminal.tsx`
+// (workspace 级 PTY 页签状态,`SessionProviders` 已将其挂在 alpha session 叶之上)。
+// 两者今日均不在 `@opencode-ai/app` 公开面上 —— exports map 被
+// `surface-seam-contract.test.ts` 钉死为仅 `./surface/session`(ADR-027)。接入真实引擎
+// 需要一次窄 export(ADR-027 修订 + alpha-frontend.patch),归 owner 决策,不在本票擅动;
+// 在此之前 channel 缺席,面板 fail-closed 落空态。
+//
+// I8:本面板不自持任何会话/工作区异步状态 —— 一切数据都是 channel 访问器的同步派生。
+// 但同 workspace 的会话切换不会重挂本子树,同步 accessor 本身证明不了背后的 PTY 状态
+// 属于当前会话:channel 投影必须在铸造时盖上 `serverKey+directory+sessionID` 三元身份
+// (`identity`),消费侧经 C1 `live.accepts(identity)` 校验;身份不符或校验器缺席一律
+// fail-closed 视为 channel 缺席(`acceptedEngineChannel`),旧 channel 无法继续渲染。
+import type { Component } from "solid-js"
+import type { AlphaSessionIdentity } from "../../session-workspace/session-workspace-core"
+
+/** 一条终端实例(引擎侧 PTY)的页签视图模型。 */
+export interface AlphaTerminalInstance {
+  id: string
+  title: string
+  /** 该实例是否有任务在跑(面板页签呼吸点;缺数据 = false,不伪造)。 */
+  running: boolean
+}
+
+/** 脚条状态明细:运行状态 + 环境 + 尺寸(缺项即不渲染对应段,不伪造)。 */
+export interface AlphaTerminalFootStatus {
+  running: boolean
+  shell?: string
+  cols?: number
+  rows?: number
+}
+
+/**
+ * 引擎通道 typed seam —— 面板消费的全部外部能力。
+ * 未来适配器把上游 `useTerminal()`(状态)与 `Terminal`(Ghostty 嵌入)收敛成本形状。
+ * 适配器在投影时盖 `identity`(I8 三元组);消费侧必须经 `acceptedEngineChannel` 校验。
+ */
+export interface AlphaTerminalEngineChannel {
+  /** 本 channel 投影所属的会话三元身份(serverKey+directory+sessionID),铸造时固定。 */
+  identity: AlphaSessionIdentity
+  ready(): boolean
+  instances(): AlphaTerminalInstance[]
+  activeID(): string | undefined
+  open(id: string): void
+  close(id: string): void
+  create(): void
+  footStatus(id: string): AlphaTerminalFootStatus
+  /** 引擎渲染的输出区内容;alpha 只提供圆角深底外框。 */
+  EngineOutput: Component<{ instanceID: string }>
+}
+
+/**
+ * I8 fail-closed 闸:channel 只有携带被当前 live 上下文接受的三元身份才可被消费。
+ * channel 缺席、校验器缺席、身份不符 —— 一律返回 undefined(面板落空态),
+ * 同 workspace 切会话后旧 channel 立即失效,直到适配器按新身份重投影。
+ */
+export function acceptedEngineChannel(
+  channel: AlphaTerminalEngineChannel | undefined,
+  accepts: ((identity: AlphaSessionIdentity) => boolean) | undefined,
+): AlphaTerminalEngineChannel | undefined {
+  if (!channel || !accepts) return undefined
+  if (!accepts(channel.identity)) return undefined
+  return channel
+}
+
+/** 激活实例解析:空列表 → undefined;activeID 失效(已关闭)→ 回落首个实例。 */
+export function resolveActiveInstance(
+  instances: AlphaTerminalInstance[],
+  activeID: string | undefined,
+): AlphaTerminalInstance | undefined {
+  if (instances.length === 0) return undefined
+  return instances.find((instance) => instance.id === activeID) ?? instances[0]
+}
+
+/** 运行指示三层中的最外层输入:任一实例在跑(右栏 tab 呼吸点数据源)。 */
+export function anyTerminalRunning(instances: AlphaTerminalInstance[]): boolean {
+  return instances.some((instance) => instance.running)
+}
+
+function isPositiveSize(value: number | undefined): value is number {
+  return typeof value === "number" && Number.isSafeInteger(value) && value > 0
+}
+
+/** 脚条尺寸段:`80×24`;任一维缺失或非法 → undefined(整段不渲染)。 */
+export function formatTerminalSize(cols: number | undefined, rows: number | undefined): string | undefined {
+  if (!isPositiveSize(cols) || !isPositiveSize(rows)) return undefined
+  return `${cols}×${rows}`
+}
diff --git a/packages/ui-mac/src/renderer/alpha-ui/session-rail/terminal/terminal-rail-panel.tsx b/packages/ui-mac/src/renderer/alpha-ui/session-rail/terminal/terminal-rail-panel.tsx
new file mode 100644
index 000000000000..167560b2568c
--- /dev/null
+++ b/packages/ui-mac/src/renderer/alpha-ui/session-rail/terminal/terminal-rail-panel.tsx
@@ -0,0 +1,172 @@
+// REQ-125 C3-term(#550)—— 右栏终端面板外壳(已批稿 session-workspace §终端)。
+// alpha 自持:实例页签条(白卡浮起 + 运行呼吸点 + 新建/关闭)、圆角深底输出区外框
+// (双主题恒深底)、脚条(运行状态 · 环境 · 尺寸)。输出区内容由引擎经
+// `AlphaTerminalEngineChannel` 渲染;channel 缺席或未就绪 → fail-closed 空态。
+import { For, Show, createMemo } from "solid-js"
+import { t } from "../../../i18n"
+import type { AlphaSessionIdentity } from "../../session-workspace/session-workspace-core"
+import {
+  acceptedEngineChannel,
+  anyTerminalRunning,
+  formatTerminalSize,
+  resolveActiveInstance,
+  type AlphaTerminalEngineChannel,
+} from "./terminal-rail-core"
+import "./terminal-rail.css"
+
+const STAGE_ID = "alpha-terminal-stage"
+
+function PlusIcon() {
+  return (
+    <svg class="a-term-icon" viewBox="0 0 24 24" aria-hidden="true">
+      <path d="M12 5v14M5 12h14" />
+    </svg>
+  )
+}
+
+export function TerminalRailPanel(props: {
+  channel?: AlphaTerminalEngineChannel
+  /** C1 live 上下文的身份校验(`live.accepts`);缺席 = fail-closed,channel 视为不存在。 */
+  accepts?: (identity: AlphaSessionIdentity) => boolean
+}) {
+  // I8:channel 必须携带被当前会话接受的三元身份,且 ready;任一不满足即落空态。
+  const engine = () => {
+    const channel = acceptedEngineChannel(props.channel, props.accepts)
+    return channel?.ready() ? channel : undefined
+  }
+  const instances = createMemo(() => engine()?.instances() ?? [])
+  const active = createMemo(() => resolveActiveInstance(instances(), engine()?.activeID()))
+  const foot = createMemo(() => {
+    const current = active()
+    const channel = engine()
+    if (!current || !channel) return undefined
+    return channel.footStatus(current.id)
+  })
+
+  return (
+    <section
+      class="a-term-panel"
+      data-alpha-terminal-panel
+      data-alpha-terminal-any-running={anyTerminalRunning(instances()) ? "true" : undefined}
+      aria-label={t("alpha.session.terminal")}
+    >
+      <Show
+        when={active()}
+        fallback={
+          <div class="a-term-empty" data-alpha-terminal-empty>
+            <span class="a-term-empty-icon" aria-hidden="true">
+              <svg class="a-term-icon" viewBox="0 0 24 24">
+                <path d="M4 17l6-6-6-6M12 19h8" />
+              </svg>
+            </span>
+            <b>{t("alpha.terminal.emptyTitle")}</b>
+            <p>{t("alpha.terminal.emptyBody")}</p>
+            <button
+              type="button"
+              class="a-term-empty-new"
+              data-alpha-terminal-new
+              disabled={engine() === undefined}
+              onClick={() => engine()?.create()}
+            >
+              <PlusIcon />
+              {t("alpha.terminal.new")}
+            </button>
+          </div>
+        }
+      >
+        {(current) => (
+          <>
+            <div class="a-term-tabs" role="tablist" aria-label={t("alpha.terminal.tabs")}>
+              <For each={instances()}>
+                {(instance) => (
+                  <span
+                    class="a-term-tab"
+                    classList={{ "a-term-tab--on": instance.id === current().id }}
+                    role="presentation"
+                    data-alpha-terminal-tab={instance.id}
+                    data-alpha-terminal-running={instance.running ? "true" : undefined}
+                  >
+                    <button
+                      type="button"
+                      role="tab"
+                      class="a-term-tab-open"
+                      aria-selected={instance.id === current().id}
+                      aria-controls={STAGE_ID}
+                      onClick={() => engine()?.open(instance.id)}
+                    >
+                      <Show when={instance.running}>
+                        <span class="a-term-rundot" aria-hidden="true" />
+                      </Show>
+                      <span class="a-term-tab-label">{instance.title}</span>
+                    </button>
+                    <button
+                      type="button"
+                      class="a-term-tab-close"
+                      data-alpha-terminal-close={instance.id}
+                      aria-label={t("alpha.terminal.close", { title: instance.title })}
+                      onClick={() => engine()?.close(instance.id)}
+                    >
+                      <svg class="a-term-icon" viewBox="0 0 24 24" aria-hidden="true">
+                        <path d="M6 6l12 12M18 6L6 18" />
+                      </svg>
+                    </button>
+                  </span>
+                )}
+              </For>
+              <button
+                type="button"
+                class="a-term-add"
+                data-alpha-terminal-new
+                aria-label={t("alpha.terminal.new")}
+                onClick={() => engine()?.create()}
+              >
+                <PlusIcon />
+              </button>
+            </div>
+            <div class="a-term-stage" id={STAGE_ID} role="tabpanel" aria-label={t("alpha.session.terminal")}>
+              <div class="a-term-output" data-alpha-terminal-output>
+                <Show when={engine()} keyed>
+                  {(channel) => {
+                    const EngineOutput = channel.EngineOutput
+                    return (
+                      <Show when={current().id} keyed>
+                        {(instanceID) => <EngineOutput instanceID={instanceID} />}
+                      </Show>
+                    )
+                  }}
+                </Show>
+              </div>
+              <Show when={foot()}>
+                {(status) => (
+                  <div class="a-term-foot" data-alpha-terminal-foot>
+                    <span
+                      class="a-term-foot-state"
+                      classList={{ "a-term-foot-state--running": status().running }}
+                      data-alpha-terminal-foot-state={status().running ? "running" : "idle"}
+                    >
+                      <i aria-hidden="true" />
+                      {status().running ? t("alpha.terminal.footRunning") : t("alpha.terminal.footIdle")}
+                    </span>
+                    <Show when={status().shell}>
+                      {(shell) => (
+                        <>
+                          <span class="a-term-foot-sep" aria-hidden="true">
+                            ·
+                          </span>
+                          <span>{shell()}</span>
+                        </>
+                      )}
+                    </Show>
+                    <Show when={formatTerminalSize(status().cols, status().rows)}>
+                      {(size) => <span class="a-term-foot-size">{size()}</span>}
+                    </Show>
+                  </div>
+                )}
+              </Show>
+            </div>
+          </>
+        )}
+      </Show>
+    </section>
+  )
+}
diff --git a/packages/ui-mac/src/renderer/alpha-ui/session-rail/terminal/terminal-rail-test-runtime.tsx b/packages/ui-mac/src/renderer/alpha-ui/session-rail/terminal/terminal-rail-test-runtime.tsx
new file mode 100644
index 000000000000..3b875e67a2cb
--- /dev/null
+++ b/packages/ui-mac/src/renderer/alpha-ui/session-rail/terminal/terminal-rail-test-runtime.tsx
@@ -0,0 +1,127 @@
+// REQ-125 C3-term(#550)—— 组件测试 runtime:假引擎通道驱动面板(形态同
+// session-workspace-test-runtime)。假通道只实现 seam 形状,行为与上游语义对齐:
+// open 切激活、close 移除并回落激活、create 追加并激活。
+// I8:channel 投影铸造时盖三元身份;accepts 用真 sameSessionIdentity 对当前 live
+// 身份校验 —— 同 workspace 切会话即拒收旧投影,重投影后恢复。
+import { createSignal } from "solid-js"
+import { render } from "solid-js/web"
+import { sameSessionIdentity, type AlphaSessionIdentity } from "../../session-workspace/session-workspace-core"
+import {
+  type AlphaTerminalEngineChannel,
+  type AlphaTerminalFootStatus,
+  type AlphaTerminalInstance,
+} from "./terminal-rail-core"
+import { TerminalRailPanel } from "./terminal-rail-panel"
+
+export { render }
+
+interface FakeInstance extends AlphaTerminalInstance {
+  foot: AlphaTerminalFootStatus
+}
+
+const WORKSPACE = { serverKey: "sidecar", directory: "/tmp/workspace" }
+
+const identityOf = (sessionID: string): AlphaSessionIdentity => ({ ...WORKSPACE, sessionID })
+
+const initialInstances: FakeInstance[] = [
+  {
+    id: "pty_1",
+    title: "终端 1",
+    running: true,
+    foot: { running: true, shell: "zsh", cols: 80, rows: 24 },
+  },
+  {
+    id: "pty_2",
+    title: "终端 2",
+    running: false,
+    foot: { running: false, shell: "zsh", cols: 80, rows: 24 },
+  },
+]
+
+const [instances, setInstances] = createSignal<FakeInstance[]>(initialInstances)
+const [activeID, setActiveID] = createSignal<string | undefined>("pty_1")
+const [ready, setReady] = createSignal(true)
+const [liveIdentity, setLiveIdentity] = createSignal<AlphaSessionIdentity>(identityOf("ses_a"))
+
+export const channelCalls: string[] = []
+
+let nextCreated = 3
+
+function makeChannel(identity: AlphaSessionIdentity): AlphaTerminalEngineChannel {
+  return {
+    identity,
+    ready,
+    instances,
+    activeID,
+    open(id) {
+      channelCalls.push(`open:${id}`)
+      setActiveID(id)
+    },
+    close(id) {
+      channelCalls.push(`close:${id}`)
+      setInstances((all) => all.filter((instance) => instance.id !== id))
+      setActiveID((current) => (current === id ? instances()[0]?.id : current))
+    },
+    create() {
+      channelCalls.push("create")
+      const id = `pty_${nextCreated}`
+      nextCreated += 1
+      const created: FakeInstance = {
+        id,
+        title: `终端 ${nextCreated - 1}`,
+        running: false,
+        foot: { running: false, shell: "zsh", cols: 80, rows: 24 },
+      }
+      setInstances((all) => [...all, created])
+      setActiveID(id)
+    },
+    footStatus(id) {
+      return instances().find((instance) => instance.id === id)?.foot ?? { running: false }
+    },
+    EngineOutput: (props) => <div data-alpha-terminal-engine-output={props.instanceID} />,
+  }
+}
+
+const [channel, setChannel] = createSignal<AlphaTerminalEngineChannel>(makeChannel(identityOf("ses_a")))
+
+const accepts = (identity: AlphaSessionIdentity) => sameSessionIdentity(identity, liveIdentity())
+
+export function TerminalRailHarness() {
+  return <TerminalRailPanel channel={channel()} accepts={accepts} />
+}
+
+export function TerminalRailHarnessWithoutEngine() {
+  return <TerminalRailPanel accepts={accepts} />
+}
+
+/** 同 workspace 切会话:只换 live 三元组的 sessionID(serverKey+directory 不变)。 */
+export function setTerminalLiveSession(sessionID: string) {
+  setLiveIdentity(identityOf(sessionID))
+}
+
+/** 适配器语义:按给定会话身份重投影 channel(共享同一 workspace 级 PTY 状态)。 */
+export function projectTerminalChannel(sessionID: string) {
+  setChannel(makeChannel(identityOf(sessionID)))
+}
+
+export function setTerminalInstances(next: FakeInstance[]) {
+  setInstances(next)
+}
+
+export function setTerminalActiveID(next: string | undefined) {
+  setActiveID(next)
+}
+
+export function setTerminalChannelReady(next: boolean) {
+  setReady(next)
+}
+
+export function resetTerminalRailHarness() {
+  setInstances(initialInstances)
+  setActiveID("pty_1")
+  setReady(true)
+  setLiveIdentity(identityOf("ses_a"))
+  setChannel(makeChannel(identityOf("ses_a")))
+  nextCreated = 3
+  channelCalls.splice(0)
+}
diff --git a/packages/ui-mac/src/renderer/alpha-ui/session-rail/terminal/terminal-rail.css b/packages/ui-mac/src/renderer/alpha-ui/session-rail/terminal/terminal-rail.css
new file mode 100644
index 000000000000..188859978f7b
--- /dev/null
+++ b/packages/ui-mac/src/renderer/alpha-ui/session-rail/terminal/terminal-rail.css
@@ -0,0 +1,299 @@
+/* REQ-125 C3-term(#550)· 右栏终端面板外壳 —— 已批稿 session-workspace §终端。
+ * 令牌纪律(I5):全部 var() 引用为 --a-*;唯一例外是 .a-term-stage 上定义的
+ * --a-term-stage-* 局部锚 —— 终端可读性约定要求输出区双主题恒深底(已批稿明文),
+ * 这些值不进全局主题、不受 [data-theme] 条件、不染 alpha chrome。
+ * 依赖全局 tokens.css/base.css(经 session-workspace.css 于 .a-ui 根注入)。 */
+
+.a-term-panel {
+  display: flex;
+  flex: 1;
+  flex-direction: column;
+  width: 100%;
+  height: 100%;
+  min-height: 0;
+}
+
+/* ── 实例页签条 ─────────────────────────────────────────────── */
+
+.a-term-tabs {
+  display: flex;
+  align-items: center;
+  gap: 4px;
+  flex: none;
+  min-width: 0;
+  padding: 8px 10px 0;
+  overflow-x: auto;
+}
+
+.a-term-tab {
+  position: relative;
+  display: inline-flex;
+  align-items: center;
+  flex: none;
+  height: 28px;
+  border: 1px solid transparent;
+  border-radius: var(--a-radius-md);
+  color: var(--a-text-secondary);
+  font-size: var(--a-text-sm);
+  font-weight: var(--a-weight-medium);
+}
+
+.a-term-tab:hover {
+  background: var(--a-bg-muted);
+}
+
+.a-term-tab--on {
+  border-color: var(--a-border);
+  background: var(--a-surface);
+  box-shadow: var(--a-shadow-xs);
+  color: var(--a-text);
+}
+
+.a-term-tab-open {
+  display: inline-flex;
+  align-items: center;
+  gap: 7px;
+  min-width: 0;
+  height: 100%;
+  padding: 0 3px 0 11px;
+  border: 0;
+  background: transparent;
+  color: inherit;
+  font: inherit;
+  cursor: pointer;
+}
+
+.a-term-tab-label {
+  overflow: hidden;
+  max-width: 140px;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+.a-term-tab-close {
+  display: grid;
+  place-items: center;
+  flex: none;
+  width: 18px;
+  height: 18px;
+  margin-right: 5px;
+  padding: 0;
+  border: 0;
+  border-radius: var(--a-radius-xs);
+  background: transparent;
+  color: var(--a-text-tertiary);
+  cursor: pointer;
+  opacity: 0;
+  transition: opacity var(--a-dur-fast) var(--a-ease-out);
+}
+
+.a-term-tab:hover .a-term-tab-close,
+.a-term-tab--on .a-term-tab-close,
+.a-term-tab-close:focus-visible {
+  opacity: 1;
+}
+
+.a-term-tab-close:hover {
+  background: var(--a-bg-muted);
+  color: var(--a-text);
+}
+
+.a-term-rundot {
+  flex: none;
+  width: 6px;
+  height: 6px;
+  border-radius: var(--a-radius-full);
+  background: var(--a-success);
+  animation: a-term-pulse 1.4s var(--a-ease-in-out) infinite;
+}
+
+.a-term-add {
+  display: grid;
+  place-items: center;
+  flex: none;
+  width: 26px;
+  height: 26px;
+  padding: 0;
+  border: 0;
+  border-radius: var(--a-radius-md);
+  background: transparent;
+  color: var(--a-text-tertiary);
+  cursor: pointer;
+}
+
+.a-term-add:hover {
+  background: var(--a-bg-muted);
+  color: var(--a-text);
+}
+
+.a-term-icon {
+  width: 15px;
+  height: 15px;
+  fill: none;
+  stroke: currentColor;
+  stroke-linecap: round;
+  stroke-linejoin: round;
+  stroke-width: 1.8;
+}
+
+.a-term-tab-close .a-term-icon {
+  width: 11px;
+  height: 11px;
+}
+
+/* ── 输出区外框:圆角容器,双主题恒深底(引擎在内渲染)────────── */
+
+.a-term-stage {
+  --a-term-stage-bg: #0a0b0d;
+  --a-term-stage-text: #d4d4d8;
+  --a-term-stage-text-dim: #71727a;
+  --a-term-stage-border: rgba(255, 255, 255, 0.08);
+  --a-term-stage-success: #4ade80;
+
+  display: flex;
+  flex: 1;
+  flex-direction: column;
+  min-height: 0;
+  margin: 8px 10px 10px;
+  border: 1px solid var(--a-border);
+  border-radius: var(--a-radius-lg);
+  overflow: hidden;
+  background: var(--a-term-stage-bg);
+}
+
+.a-term-output {
+  position: relative;
+  flex: 1;
+  min-height: 0;
+  color: var(--a-term-stage-text);
+  font-family: var(--a-font-mono);
+  font-size: var(--a-text-sm);
+}
+
+/* ── 脚条:运行状态 · 环境 · 尺寸(mono 小字,恒居深底内)────── */
+
+.a-term-foot {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  flex: none;
+  padding: 6px 10px;
+  border-top: 1px solid var(--a-term-stage-border);
+  color: var(--a-term-stage-text-dim);
+  font-family: var(--a-font-mono);
+  font-size: var(--a-text-2xs);
+}
+
+.a-term-foot-state {
+  display: inline-flex;
+  align-items: center;
+  gap: 5px;
+}
+
+.a-term-foot-state i {
+  width: 6px;
+  height: 6px;
+  border-radius: var(--a-radius-full);
+  background: var(--a-term-stage-text-dim);
+}
+
+.a-term-foot-state--running {
+  color: var(--a-term-stage-success);
+}
+
+.a-term-foot-state--running i {
+  background: var(--a-term-stage-success);
+  animation: a-term-pulse 1.4s var(--a-ease-in-out) infinite;
+}
+
+.a-term-foot-size {
+  margin-left: auto;
+}
+
+/* ── 空态(无实例 / 引擎通道缺席 fail-closed)──────────────── */
+
+.a-term-empty {
+  display: flex;
+  flex: 1;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  gap: 10px;
+  padding: 30px;
+  text-align: center;
+}
+
+.a-term-empty-icon {
+  display: grid;
+  place-items: center;
+  width: 40px;
+  height: 40px;
+  border-radius: var(--a-radius-lg);
+  background: var(--a-bg-muted);
+  color: var(--a-text-tertiary);
+}
+
+.a-term-empty-icon .a-term-icon {
+  width: 19px;
+  height: 19px;
+}
+
+.a-term-empty b {
+  color: var(--a-text);
+  font-size: var(--a-text-sm);
+  font-weight: var(--a-weight-medium);
+}
+
+.a-term-empty p {
+  margin: 0;
+  max-width: 30ch;
+  color: var(--a-text-tertiary);
+  font-size: var(--a-text-xs);
+  line-height: var(--a-leading-snug);
+}
+
+.a-term-empty-new {
+  display: inline-flex;
+  align-items: center;
+  gap: 5px;
+  height: 28px;
+  padding: 0 12px;
+  border: 1px solid var(--a-border);
+  border-radius: var(--a-radius-md);
+  background: var(--a-surface);
+  color: var(--a-text);
+  font-size: var(--a-text-sm);
+  font-weight: var(--a-weight-medium);
+  cursor: pointer;
+}
+
+.a-term-empty-new:hover:not(:disabled) {
+  background: var(--a-bg-muted);
+}
+
+.a-term-empty-new:disabled {
+  color: var(--a-text-disabled);
+  cursor: default;
+}
+
+@keyframes a-term-pulse {
+  0%,
+  100% {
+    opacity: 1;
+  }
+
+  50% {
+    opacity: 0.35;
+  }
+}
+
+@media (prefers-reduced-motion: reduce) {
+  .a-term-rundot,
+  .a-term-foot-state--running i {
+    animation: none;
+  }
+
+  .a-term-tab-close {
+    transition: none;
+  }
+}
diff --git a/packages/ui-mac/src/renderer/alpha-ui/session-rail/terminal/terminal-rail.test.ts b/packages/ui-mac/src/renderer/alpha-ui/session-rail/terminal/terminal-rail.test.ts
new file mode 100644
index 000000000000..37d5238650db
--- /dev/null
+++ b/packages/ui-mac/src/renderer/alpha-ui/session-rail/terminal/terminal-rail.test.ts
@@ -0,0 +1,162 @@
+// REQ-125 C3-term(#550)—— 终端面板:页签状态机(纯模型)+ 真 Solid 挂载外壳 + I1/I5 静态断言。
+import { describe, expect, test } from "bun:test"
+import { readFileSync } from "node:fs"
+import { join, resolve } from "node:path"
+import { sameSessionIdentity, type AlphaSessionIdentity } from "../../session-workspace/session-workspace-core"
+import {
+  acceptedEngineChannel,
+  anyTerminalRunning,
+  formatTerminalSize,
+  resolveActiveInstance,
+  type AlphaTerminalEngineChannel,
+  type AlphaTerminalInstance,
+} from "./terminal-rail-core"
+
+const panel = readFileSync(join(import.meta.dir, "terminal-rail-panel.tsx"), "utf8")
+const core = readFileSync(join(import.meta.dir, "terminal-rail-core.ts"), "utf8")
+const runtimeSource = readFileSync(join(import.meta.dir, "terminal-rail-test-runtime.tsx"), "utf8")
+const css = readFileSync(join(import.meta.dir, "terminal-rail.css"), "utf8")
+const shell = readFileSync(join(import.meta.dir, "../../session-workspace/session-workspace-shell.tsx"), "utf8")
+
+const instance = (id: string, running = false): AlphaTerminalInstance => ({ id, title: id, running })
+
+// 剥掉注释行:静态断言约束的是代码;注释里允许指名上游落点(勘破记录)。
+const codeLines = (source: string) =>
+  source
+    .split("\n")
+    .filter((line) => !/^\s*(\/\/|\/?\*)/.test(line))
+    .join("\n")
+
+describe("REQ-125 C3-term tab state machine", () => {
+  test("active resolution: empty list, stale active, and direct hit", () => {
+    expect(resolveActiveInstance([], "pty_1")).toBeUndefined()
+    expect(resolveActiveInstance([], undefined)).toBeUndefined()
+
+    const all = [instance("pty_1"), instance("pty_2")]
+    expect(resolveActiveInstance(all, "pty_2")?.id).toBe("pty_2")
+    expect(resolveActiveInstance(all, undefined)?.id).toBe("pty_1")
+    expect(resolveActiveInstance(all, "pty_gone")?.id).toBe("pty_1")
+  })
+
+  test("any-running rolls up per-instance run indicators", () => {
+    expect(anyTerminalRunning([])).toBe(false)
+    expect(anyTerminalRunning([instance("a"), instance("b")])).toBe(false)
+    expect(anyTerminalRunning([instance("a"), instance("b", true)])).toBe(true)
+  })
+
+  test("engine channel is only consumable with an accepted identity triple (I8 fail-closed)", () => {
+    const identity: AlphaSessionIdentity = { serverKey: "sidecar", directory: "/tmp/workspace", sessionID: "ses_a" }
+    const channel = { identity } as AlphaTerminalEngineChannel
+    const acceptsOnly = (live: AlphaSessionIdentity) => (candidate: AlphaSessionIdentity) =>
+      sameSessionIdentity(candidate, live)
+
+    // channel 缺席 / 校验器缺席 → 一律拒绝(fail-closed)。
+    expect(acceptedEngineChannel(undefined, acceptsOnly(identity))).toBeUndefined()
+    expect(acceptedEngineChannel(channel, undefined)).toBeUndefined()
+
+    // 三元组任一维不符 → 拒绝;完全一致才放行。
+    expect(acceptedEngineChannel(channel, acceptsOnly({ ...identity, sessionID: "ses_b" }))).toBeUndefined()
+    expect(acceptedEngineChannel(channel, acceptsOnly({ ...identity, directory: "/tmp/other" }))).toBeUndefined()
+    expect(acceptedEngineChannel(channel, acceptsOnly({ ...identity, serverKey: "remote" }))).toBeUndefined()
+    expect(acceptedEngineChannel(channel, acceptsOnly(identity))).toBe(channel)
+  })
+
+  test("foot size renders only from sane cols×rows", () => {
+    expect(formatTerminalSize(80, 24)).toBe("80×24")
+    expect(formatTerminalSize(undefined, 24)).toBeUndefined()
+    expect(formatTerminalSize(80, undefined)).toBeUndefined()
+    expect(formatTerminalSize(0, 24)).toBeUndefined()
+    expect(formatTerminalSize(-80, 24)).toBeUndefined()
+    expect(formatTerminalSize(80.5, 24)).toBeUndefined()
+    expect(formatTerminalSize(Number.NaN, 24)).toBeUndefined()
+  })
+})
+
+describe("REQ-125 C3-term real Solid mount", () => {
+  test("component cases cover tabs, run indicators, engine embed, foot, and fail-closed states", () => {
+    const result = Bun.spawnSync({
+      cmd: [process.execPath, "test", resolve(import.meta.dir, "../../../../../test-component/terminal-rail.cases.ts")],
+      cwd: resolve(import.meta.dir, "../../../../.."),
+      env: process.env,
+    })
+    const output = `${result.stdout.toString()}${result.stderr.toString()}`
+    if (result.exitCode !== 0) throw new Error(output)
+    expect(output).toContain("8 pass")
+    expect(output).toContain("0 fail")
+  })
+})
+
+describe("REQ-125 C3-term I1/I5 static ratchets", () => {
+  test("terminal shell imports no upstream module and hand-rolls no engine or data channel", () => {
+    const sources = codeLines(`${panel}\n${core}\n${runtimeSource}`)
+    const forbidden = [
+      // I1:零上游 import —— 引擎只能经 typed seam(AlphaTerminalEngineChannel)进入。
+      "@opencode-ai/app",
+      "@opencode-ai/ui",
+      "@opencode-ai/session-ui",
+      "app/src/",
+      "MessageTimeline",
+      "MessagePart",
+      "SessionPage",
+      // 零查询上游 DOM。
+      "querySelector",
+      "MutationObserver",
+      // 引擎与数据通道不得在 alpha 侧重实现(白名单 = 复用,不是重写)。
+      "ghostty-web",
+      "new WebSocket",
+      "window.api",
+    ]
+    forbidden.forEach((token) => expect(sources).not.toContain(token))
+    expect(panel).toContain("AlphaTerminalEngineChannel")
+    // I8:channel 消费必须走身份闸,seam 上必须携带三元身份。
+    expect(panel).toContain("acceptedEngineChannel(props.channel, props.accepts)")
+    expect(core).toContain("identity: AlphaSessionIdentity")
+  })
+
+  test("panel copy is fully externalized to i18n with en/zh parity", () => {
+    // 产品面无硬编码文案(CJK 只允许出现在注释外的字符串 = 0;此处直接禁全文件 CJK,注释亦用可审计中文?
+    // —— 注释允许中文,故只扫 JSX/字符串行:粗粒度为「非注释行不得含 CJK」。
+    const cjkLines = panel
+      .split("\n")
+      .filter((line) => !line.trim().startsWith("//") && !line.trim().startsWith("*") && !line.trim().startsWith("/*"))
+      .filter((line) => /[㐀-鿿]/.test(line))
+    expect(cjkLines).toEqual([])
+
+    const en = readFileSync(join(import.meta.dir, "../../../i18n/en.ts"), "utf8")
+    const zh = readFileSync(join(import.meta.dir, "../../../i18n/zh.ts"), "utf8")
+    const keys = [...panel.matchAll(/t\("(alpha\.[a-z.A-Z]+)"/g)].map((match) => match[1])
+    expect(keys.length).toBeGreaterThan(0)
+    keys.forEach((key) => {
+      expect(en).toContain(`"${key}"`)
+      expect(zh).toContain(`"${key}"`)
+    })
+  })
+
+  test("css uses only --a-* tokens; raw colors live only in the theme-invariant stage anchors", () => {
+    // I5:一切 var() 引用是 --a-*。
+    expect(
+      [...css.matchAll(/var\((--[^,)]+)/g)].map((match) => match[1]).filter((token) => !token.startsWith("--a-")),
+    ).toEqual([])
+
+    // 颜色字面量只允许出现在 --a-term-stage-* 定义行(双主题恒深底的局部锚)。
+    const rawColorLines = codeLines(css)
+      .split("\n")
+      .filter((line) => /#[0-9a-f]{3,8}\b|rgba?\(|oklch\(/i.test(line))
+      .filter((line) => !/^\s*--a-term-stage-[a-z-]+:/.test(line))
+    expect(rawColorLines).toEqual([])
+
+    // 深底不随主题条件翻转:文件内禁任何主题条件选择器。
+    expect(codeLines(css)).not.toContain("data-theme")
+    expect(codeLines(css)).not.toContain("prefers-color-scheme")
+    expect(css.match(/\.a-term-stage \{[^}]*\}/s)?.[0]).toContain("background: var(--a-term-stage-bg)")
+
+    // 呼吸点动效在 reduced-motion 下静止。
+    expect(css).toContain("@media (prefers-reduced-motion: reduce)")
+    expect(css.match(/@media \(prefers-reduced-motion: reduce\) \{[\s\S]*$/)?.[0]).toContain("animation: none")
+  })
+
+  test("shell mounts the terminal panel only for the terminal rail state, gated by live.accepts", () => {
+    expect(shell).toContain(`import { TerminalRailPanel } from "../session-rail/terminal/terminal-rail-panel"`)
+    expect(shell).toMatch(/activePanel\(\) === "terminal"[\s\S]{0,300}<TerminalRailPanel accepts=\{props\.live\.accepts\} \/>/)
+  })
+})
diff --git a/packages/ui-mac/src/renderer/alpha-ui/session-workspace/session-workspace-shell.tsx b/packages/ui-mac/src/renderer/alpha-ui/session-workspace/session-workspace-shell.tsx
index 88a83ea4d04e..dd84b011200e 100644
--- a/packages/ui-mac/src/renderer/alpha-ui/session-workspace/session-workspace-shell.tsx
+++ b/packages/ui-mac/src/renderer/alpha-ui/session-workspace/session-workspace-shell.tsx
@@ -1,5 +1,6 @@
 import { createSignal, type Accessor, Show } from "solid-js"
 import { t } from "../../i18n"
+import { TerminalRailPanel } from "../session-rail/terminal/terminal-rail-panel"
 import type { AlphaSessionIdentity, AlphaSessionLiveSnapshot } from "./session-workspace-core"
 
 export interface AlphaSessionLiveContext {
@@ -118,7 +119,13 @@ export function SessionWorkspaceShell(props: { live: AlphaSessionLiveContext })
             data-alpha-session-rail-host
             data-alpha-session-rail-panel={activePanel()}
             aria-label={t("alpha.session.railHost")}
-          />
+          >
+            <Show when={activePanel() === "terminal"}>
+              {/* C3-term(#550):引擎通道待窄 export 落地后接入;缺席时面板 fail-closed 空态。
+                  I8:channel 身份必须过 live.accepts,会话切换后旧投影即刻失效。 */}
+              <TerminalRailPanel accepts={props.live.accepts} />
+            </Show>
+          </aside>
         )}
       </Show>
     </div>
diff --git a/packages/ui-mac/src/renderer/alpha-ui/session-workspace/session-workspace.css b/packages/ui-mac/src/renderer/alpha-ui/session-workspace/session-workspace.css
index 4ef9febdbaf3..a7e9c91caf9e 100644
--- a/packages/ui-mac/src/renderer/alpha-ui/session-workspace/session-workspace.css
+++ b/packages/ui-mac/src/renderer/alpha-ui/session-workspace/session-workspace.css
@@ -191,7 +191,9 @@
 }
 
 .a-swk-rail-host {
+  display: flex;
   flex: none;
+  flex-direction: column;
   width: min(400px, 38vw);
   min-width: 320px;
   min-height: 0;
diff --git a/packages/ui-mac/src/renderer/i18n/en.ts b/packages/ui-mac/src/renderer/i18n/en.ts
index 811c69dd25ae..52c8fac40865 100644
--- a/packages/ui-mac/src/renderer/i18n/en.ts
+++ b/packages/ui-mac/src/renderer/i18n/en.ts
@@ -1134,6 +1134,14 @@ export const dict = {
   "alpha.session.crossServerDetail": "The Alpha sidebar shows local-engine sessions. This window is connected to another server, so the session cannot open here. Return home and choose a local session.",
   "alpha.session.backHome": "Back to home",
 
+  "alpha.terminal.tabs": "Terminal tabs",
+  "alpha.terminal.new": "New terminal",
+  "alpha.terminal.close": "Close {{title}}",
+  "alpha.terminal.emptyTitle": "No terminals yet",
+  "alpha.terminal.emptyBody": "Create one, or ask the assistant to run commands for you from the composer.",
+  "alpha.terminal.footRunning": "Running",
+  "alpha.terminal.footIdle": "Idle",
+
   "alpha.sidebar.appearance": "Appearance",
   "alpha.sidebar.themeLight": "Light",
   "alpha.sidebar.themeDark": "Dark",
diff --git a/packages/ui-mac/src/renderer/i18n/locale-regression.test.ts b/packages/ui-mac/src/renderer/i18n/locale-regression.test.ts
index 187b76610a31..3610a0160d03 100644
--- a/packages/ui-mac/src/renderer/i18n/locale-regression.test.ts
+++ b/packages/ui-mac/src/renderer/i18n/locale-regression.test.ts
@@ -47,6 +47,7 @@ const EXTERNALIZED_SURFACES = [
   "alpha-ui/composer-autocomplete.tsx",
   "alpha-ui/model-picker-add.tsx",
   "alpha-ui/model-picker-core.ts",
+  "alpha-ui/session-rail/terminal/terminal-rail-panel.tsx",
   "alpha-ui/session-workspace/alpha-session-workspace.tsx",
   "alpha-ui/settings.tsx",
   "alpha-ui/surface-boundary.tsx",
diff --git a/packages/ui-mac/src/renderer/i18n/zh.ts b/packages/ui-mac/src/renderer/i18n/zh.ts
index d947c9fddf98..cd3401553845 100644
--- a/packages/ui-mac/src/renderer/i18n/zh.ts
+++ b/packages/ui-mac/src/renderer/i18n/zh.ts
@@ -1123,6 +1123,13 @@ export const dict = {
   "alpha.session.crossServerTitle": "此会话不属于当前连接的服务器",
   "alpha.session.crossServerDetail": "Alpha 侧栏固定显示本地引擎的会话;当前窗口已切换到其他服务器,无法在这里打开它。请返回首页后重新选择本地会话。",
   "alpha.session.backHome": "返回首页",
+  "alpha.terminal.tabs": "终端页签",
+  "alpha.terminal.new": "新建终端",
+  "alpha.terminal.close": "关闭 {{title}}",
+  "alpha.terminal.emptyTitle": "还没有终端",
+  "alpha.terminal.emptyBody": "新建一个,或在输入框里让助手替你跑命令。",
+  "alpha.terminal.footRunning": "运行中",
+  "alpha.terminal.footIdle": "空闲",
   "alpha.sidebar.appearance": "外观",
   "alpha.sidebar.themeLight": "浅色",
   "alpha.sidebar.themeDark": "深色",
diff --git a/packages/ui-mac/test-component/terminal-rail.cases.ts b/packages/ui-mac/test-component/terminal-rail.cases.ts
new file mode 100644
index 000000000000..1dfdb5ec9d44
--- /dev/null
+++ b/packages/ui-mac/test-component/terminal-rail.cases.ts
@@ -0,0 +1,227 @@
+import { transformAsync } from "@babel/core"
+import presetTypescript from "@babel/preset-typescript"
+import { GlobalRegistrator } from "@happy-dom/global-registrator"
+import { afterAll, afterEach, beforeEach, describe, expect, mock, test } from "bun:test"
+import presetSolid from "babel-preset-solid"
+
+GlobalRegistrator.register()
+const solid = await import("solid-js/dist/solid.js")
+mock.module("solid-js", () => solid)
+const solidWeb = await import("solid-js/web/dist/web.js")
+mock.module("solid-js/web", () => solidWeb)
+
+Bun.plugin({
+  name: "terminal-rail-component-test",
+  setup(builder) {
+    builder.onLoad({ filter: /packages\/ui-mac\/src\/.*\.tsx$/ }, async (args) => {
+      const transformed = await transformAsync(await Bun.file(args.path).text(), {
+        filename: args.path,
+        presets: [
+          [presetSolid, { generate: "dom", hydratable: false }],
+          [presetTypescript, { allExtensions: true, isTSX: true, onlyRemoveTypeImports: true }],
+        ],
+        sourceMaps: "inline",
+      })
+      return { contents: transformed?.code ?? "", loader: "js" }
+    })
+  },
+})
+
+const runtime = await import("../src/renderer/alpha-ui/session-rail/terminal/terminal-rail-test-runtime")
+const disposers: Array<() => void> = []
+
+beforeEach(() => {
+  runtime.resetTerminalRailHarness()
+  document.body.replaceChildren()
+})
+
+afterEach(() =>
+  disposers
+    .splice(0)
+    .reverse()
+    .forEach((dispose) => dispose()),
+)
+
+afterAll(() => GlobalRegistrator.unregister())
+
+async function flush() {
+  await Promise.resolve()
+  await Promise.resolve()
+}
+
+function mount(component: () => unknown) {
+  const host = document.createElement("div")
+  document.body.append(host)
+  disposers.push(solidWeb.render(() => component(), host))
+  return host
+}
+
+const tab = (host: HTMLElement, id: string) => host.querySelector<HTMLElement>(`[data-alpha-terminal-tab="${id}"]`)
+const tabButton = (host: HTMLElement, id: string) => tab(host, id)?.querySelector<HTMLButtonElement>("[role='tab']")
+
+describe("REQ-125 terminal rail panel real Solid mount", () => {
+  test("renders instance tabs, run indicators, engine output, and the foot from the channel", async () => {
+    const host = mount(() => runtime.TerminalRailHarness())
+    await flush()
+
+    expect(host.querySelectorAll("[data-alpha-terminal-tab]")).toHaveLength(2)
+    expect(tabButton(host, "pty_1")?.getAttribute("aria-selected")).toBe("true")
+    expect(tabButton(host, "pty_2")?.getAttribute("aria-selected")).toBe("false")
+
+    // 运行指示:仅在跑的实例带呼吸点;面板根暴露「任一在跑」供右栏 tab 层消费。
+    expect(tab(host, "pty_1")?.querySelector(".a-term-rundot")).not.toBeNull()
+    expect(tab(host, "pty_2")?.querySelector(".a-term-rundot")).toBeNull()
+    expect(host.querySelector("[data-alpha-terminal-panel]")?.getAttribute("data-alpha-terminal-any-running")).toBe(
+      "true",
+    )
+
+    // 引擎输出:激活实例挂进输出区外框;脚条 = 运行中 · zsh · 80×24。
+    expect(
+      host.querySelector("[data-alpha-terminal-output] [data-alpha-terminal-engine-output='pty_1']"),
+    ).not.toBeNull()
+    const foot = host.querySelector<HTMLElement>("[data-alpha-terminal-foot]")!
+    expect(foot.querySelector("[data-alpha-terminal-foot-state]")?.getAttribute("data-alpha-terminal-foot-state")).toBe(
+      "running",
+    )
+    expect(foot.textContent).toContain("运行中")
+    expect(foot.textContent).toContain("zsh")
+    expect(foot.textContent).toContain("80×24")
+
+    // 运行结束 → 呼吸点与「任一在跑」一起消失(状态驱动,非一次性渲染)。
+    runtime.setTerminalInstances([
+      { id: "pty_1", title: "终端 1", running: false, foot: { running: false, shell: "zsh", cols: 80, rows: 24 } },
+    ])
+    await flush()
+    expect(tab(host, "pty_1")?.querySelector(".a-term-rundot")).toBeNull()
+    expect(
+      host.querySelector("[data-alpha-terminal-panel]")?.getAttribute("data-alpha-terminal-any-running"),
+    ).toBeNull()
+  })
+
+  test("switching tabs goes through the channel and remounts the engine output", async () => {
+    const host = mount(() => runtime.TerminalRailHarness())
+    await flush()
+
+    tabButton(host, "pty_2")!.click()
+    await flush()
+
+    expect(runtime.channelCalls).toContain("open:pty_2")
+    expect(tabButton(host, "pty_2")?.getAttribute("aria-selected")).toBe("true")
+    expect(tabButton(host, "pty_1")?.getAttribute("aria-selected")).toBe("false")
+    expect(
+      host.querySelector("[data-alpha-terminal-output] [data-alpha-terminal-engine-output='pty_2']"),
+    ).not.toBeNull()
+    expect(host.querySelector("[data-alpha-terminal-engine-output='pty_1']")).toBeNull()
+    expect(
+      host
+        .querySelector("[data-alpha-terminal-foot] [data-alpha-terminal-foot-state]")
+        ?.getAttribute("data-alpha-terminal-foot-state"),
+    ).toBe("idle")
+  })
+
+  test("create and close go through the channel and the active tab follows", async () => {
+    const host = mount(() => runtime.TerminalRailHarness())
+    await flush()
+
+    host.querySelector<HTMLButtonElement>(".a-term-add")!.click()
+    await flush()
+    expect(runtime.channelCalls).toContain("create")
+    expect(host.querySelectorAll("[data-alpha-terminal-tab]")).toHaveLength(3)
+    expect(tabButton(host, "pty_3")?.getAttribute("aria-selected")).toBe("true")
+
+    host.querySelector<HTMLButtonElement>("[data-alpha-terminal-close='pty_3']")!.click()
+    await flush()
+    expect(runtime.channelCalls).toContain("close:pty_3")
+    expect(host.querySelectorAll("[data-alpha-terminal-tab]")).toHaveLength(2)
+    expect(tabButton(host, "pty_1")?.getAttribute("aria-selected")).toBe("true")
+    expect(
+      host.querySelector("[data-alpha-terminal-output] [data-alpha-terminal-engine-output='pty_1']"),
+    ).not.toBeNull()
+  })
+
+  test("stale activeID falls back to the first instance instead of a blank stage", async () => {
+    runtime.setTerminalActiveID("pty_gone")
+    const host = mount(() => runtime.TerminalRailHarness())
+    await flush()
+
+    expect(tabButton(host, "pty_1")?.getAttribute("aria-selected")).toBe("true")
+    expect(
+      host.querySelector("[data-alpha-terminal-output] [data-alpha-terminal-engine-output='pty_1']"),
+    ).not.toBeNull()
+  })
+
+  test("no instances shows the approved empty state with a working create entry", async () => {
+    runtime.setTerminalInstances([])
+    runtime.setTerminalActiveID(undefined)
+    const host = mount(() => runtime.TerminalRailHarness())
+    await flush()
+
+    expect(host.querySelector("[data-alpha-terminal-empty]")).not.toBeNull()
+    expect(host.querySelector("[role='tablist']")).toBeNull()
+    expect(host.querySelector("[data-alpha-terminal-empty]")?.textContent).toContain("还没有终端")
+
+    const create = host.querySelector<HTMLButtonElement>("[data-alpha-terminal-empty] [data-alpha-terminal-new]")!
+    expect(create.disabled).toBe(false)
+    create.click()
+    await flush()
+    expect(runtime.channelCalls).toContain("create")
+    expect(host.querySelectorAll("[data-alpha-terminal-tab]")).toHaveLength(1)
+  })
+
+  test("without an engine channel the panel fails closed to the empty state", async () => {
+    const host = mount(() => runtime.TerminalRailHarnessWithoutEngine())
+    await flush()
+
+    expect(host.querySelector("[data-alpha-terminal-empty]")).not.toBeNull()
+    expect(host.querySelector("[role='tablist']")).toBeNull()
+    expect(host.querySelector("[data-alpha-terminal-output]")).toBeNull()
+    expect(host.querySelector(".a-term-rundot")).toBeNull()
+    expect(
+      host.querySelector<HTMLButtonElement>("[data-alpha-terminal-empty] [data-alpha-terminal-new]")?.disabled,
+    ).toBe(true)
+  })
+
+  test("same-directory session switch rejects the stale channel until re-projection (I8)", async () => {
+    const host = mount(() => runtime.TerminalRailHarness())
+    await flush()
+    expect(host.querySelectorAll("[data-alpha-terminal-tab]")).toHaveLength(2)
+
+    // 同 workspace(serverKey+directory 不变)切到另一会话:旧 channel 身份不再被 live.accepts
+    // 接受 → 面板即刻按 channel 缺席处理(空态 + 新建禁用),旧投影不得继续渲染。
+    runtime.setTerminalLiveSession("ses_b")
+    await flush()
+    expect(host.querySelector("[data-alpha-terminal-empty]")).not.toBeNull()
+    expect(host.querySelector("[role='tablist']")).toBeNull()
+    expect(host.querySelector("[data-alpha-terminal-output]")).toBeNull()
+    expect(host.querySelector("[data-alpha-terminal-engine-output='pty_1']")).toBeNull()
+    expect(
+      host.querySelector<HTMLButtonElement>("[data-alpha-terminal-empty] [data-alpha-terminal-new]")?.disabled,
+    ).toBe(true)
+
+    // 适配器按新会话身份重投影 → 面板恢复实例形态(workspace 级 PTY 状态共享)。
+    runtime.projectTerminalChannel("ses_b")
+    await flush()
+    expect(host.querySelector("[data-alpha-terminal-empty]")).toBeNull()
+    expect(host.querySelectorAll("[data-alpha-terminal-tab]")).toHaveLength(2)
+    expect(
+      host.querySelector("[data-alpha-terminal-output] [data-alpha-terminal-engine-output='pty_1']"),
+    ).not.toBeNull()
+  })
+
+  test("a channel that is not ready is treated the same as absent (fail closed)", async () => {
+    runtime.setTerminalChannelReady(false)
+    const host = mount(() => runtime.TerminalRailHarness())
+    await flush()
+
+    expect(host.querySelector("[data-alpha-terminal-empty]")).not.toBeNull()
+    expect(
+      host.querySelector<HTMLButtonElement>("[data-alpha-terminal-empty] [data-alpha-terminal-new]")?.disabled,
+    ).toBe(true)
+
+    // 引擎就绪后无需重挂:同一面板切换到实例形态。
+    runtime.setTerminalChannelReady(true)
+    await flush()
+    expect(host.querySelector("[data-alpha-terminal-empty]")).toBeNull()
+    expect(host.querySelectorAll("[data-alpha-terminal-tab]")).toHaveLength(2)
+  })
+})