diff --git a/web/hwlab-cloud-web/src/components/workbench/SessionRail.vue b/web/hwlab-cloud-web/src/components/workbench/SessionRail.vue
index b57519f1..4e673694 100644
--- a/web/hwlab-cloud-web/src/components/workbench/SessionRail.vue
+++ b/web/hwlab-cloud-web/src/components/workbench/SessionRail.vue
@@ -1,4 +1,7 @@
 <script setup lang="ts">
+// SPEC: PJ2026-010401 Web工作台 draft-2026-06-18-r1; PJ2026-01040104 响应布局; PJ2026-01040106 Trace阅读.
+// Responsibility: Session rail list, low-noise session details, local resize, and collapse UI state.
+
 import { computed, ref } from "vue";
 import { useWorkbenchStore } from "@/stores/workbench";
 import { useClipboard } from "@/composables/useClipboard";
@@ -7,15 +10,20 @@ import { workbenchSessionPath } from "@/utils";
 
 const workbench = useWorkbenchStore();
 const { copied, copy } = useClipboard();
+const COLLAPSED_STORAGE_KEY = "hwlab.workbench.sessionRailCollapsed.v1";
 const width = ref(readWidth());
+const collapsed = ref(readCollapsed());
 const dragging = ref(false);
+const detailOpen = ref(false);
 const activeTab = computed(() => workbench.sessionTabs.find((tab) => tab.active) ?? null);
+const activeSessionUrl = computed(() => activeTab.value ? sessionUrl(activeTab.value) : "");
+const railStyle = computed(() => ({ width: collapsed.value ? "48px" : `${width.value}px` }));
 const showSessionListLoading = computed(() => workbench.sessionListLoading);
 
 function copyActive(): void {
   const tab = activeTab.value;
   if (!tab) return;
-  void copy(`url=${sessionUrl(tab)}\nsession=${tab.sessionId ?? ''}\nthread=${tab.threadId ?? ''}\ntrace=${tab.lastTraceId ?? ''}`);
+  void copy(`url=${sessionUrl(tab)}\nsessionId=${tab.sessionId ?? ''}\nthreadId=${tab.threadId ?? ''}\ntraceId=${tab.lastTraceId ?? ''}\nstatus=${tab.status ?? ''}\nupdatedAt=${tab.updatedAt ?? tab.startedAt ?? ''}`);
 }
 
 function sessionUrl(tab: { sessionId?: string | null }): string {
@@ -24,6 +32,7 @@ function sessionUrl(tab: { sessionId?: string | null }): string {
 }
 
 function startResize(event: PointerEvent): void {
+  if (collapsed.value) return;
   dragging.value = true;
   const startX = event.clientX;
   const startWidth = width.value;
@@ -38,6 +47,7 @@ function startResize(event: PointerEvent): void {
 }
 
 function keyResize(event: KeyboardEvent): void {
+  if (collapsed.value) return;
   const step = event.shiftKey ? 32 : 8;
   if (event.key === "ArrowLeft") { event.preventDefault(); setWidth(width.value - step); }
   if (event.key === "ArrowRight") { event.preventDefault(); setWidth(width.value + step); }
@@ -59,6 +69,19 @@ function readWidth(): number {
   }
 }
 
+function toggleCollapsed(): void {
+  collapsed.value = !collapsed.value;
+  try { localStorage.setItem(COLLAPSED_STORAGE_KEY, collapsed.value ? "true" : "false"); } catch { /* ignore */ }
+}
+
+function readCollapsed(): boolean {
+  try {
+    return localStorage.getItem(COLLAPSED_STORAGE_KEY) === "true";
+  } catch {
+    return false;
+  }
+}
+
 function formatSessionUpdatedTime(value: string | null | undefined): string {
   if (!value) return "未记录";
   const date = new Date(value);
@@ -73,16 +96,19 @@ function formatSessionUpdatedTime(value: string | null | undefined): string {
 </script>
 
 <template>
-  <aside class="session-rail" id="session-sidebar" :class="{ 'is-resizing': dragging }" :style="{ width: `${width}px` }">
+  <aside class="session-rail" id="session-sidebar" :class="{ 'is-resizing': dragging, 'is-collapsed': collapsed }" :data-collapsed="collapsed" :style="railStyle">
     <div class="panel-header compact">
-      <div>
+      <div v-if="!collapsed">
         <p class="page-eyebrow">Sessions</p>
         <h2>显式会话</h2>
       </div>
-      <button id="session-create" class="btn btn-primary btn-sm" type="button" @click="workbench.createSession">新建</button>
+      <div class="session-rail-header-actions">
+        <button v-if="!collapsed" id="session-detail-toggle" class="message-detail-button session-detail-button" type="button" aria-label="Session 详情" title="Session 详情" :disabled="showSessionListLoading || !activeTab" @click="detailOpen = true">!</button>
+        <button v-if="!collapsed" id="session-create" class="btn btn-primary btn-sm" type="button" @click="workbench.createSession">新建</button>
+        <button id="session-collapse-toggle" class="btn btn-secondary btn-sm session-collapse-toggle" type="button" :aria-label="collapsed ? '展开 Sessions' : '折叠 Sessions'" :title="collapsed ? '展开 Sessions' : '折叠 Sessions'" :aria-expanded="!collapsed" @click="toggleCollapsed">{{ collapsed ? '›' : '‹' }}</button>
+      </div>
     </div>
-    <div class="session-model-channel" id="session-model-channel">模型通道：{{ workbench.providerProfile }}</div>
-    <div class="session-list" id="session-tabs" :data-loading="showSessionListLoading">
+    <div v-if="!collapsed" class="session-list" id="session-tabs" :data-loading="showSessionListLoading">
       <LoadingState v-if="showSessionListLoading" class="session-list-loading" label="加载中" />
       <template v-else>
         <button v-for="tab in workbench.sessionTabs" :key="tab.sessionId || tab.key" class="session-tab" :data-active="tab.active" :data-running="tab.running" :data-status="tab.status || undefined" :data-session-id="tab.sessionId || undefined" type="button" :title="tab.label || tab.sessionId || tab.key" @click="workbench.selectSession(tab)">
@@ -99,16 +125,35 @@ function formatSessionUpdatedTime(value: string | null | undefined): string {
         </div>
       </template>
     </div>
-    <div class="session-active-metadata" id="session-status">
-      <span>{{ showSessionListLoading ? '加载中' : activeTab ? `当前 ${activeTab.sessionId}` : '等待 session' }}</span>
-      <small v-if="!showSessionListLoading && activeTab?.lastTraceId">trace {{ activeTab.lastTraceId }}</small>
-      <small v-if="copied">已复制</small>
-    </div>
-    <div class="session-rail-actions">
+    <div v-if="!collapsed" class="session-rail-actions">
       <button id="session-copy" class="btn btn-secondary btn-sm" type="button" :disabled="showSessionListLoading || !activeTab" @click="copyActive">复制</button>
       <button id="session-delete" class="btn btn-secondary btn-sm" type="button" :disabled="showSessionListLoading || !activeTab" @click="workbench.deleteCurrentSession">删除当前</button>
     </div>
+    <div v-if="detailOpen && activeTab" class="workbench-dialog-backdrop" role="presentation" @click.self="detailOpen = false">
+      <section id="session-detail-dialog" class="workbench-dialog" role="dialog" aria-modal="true" aria-labelledby="session-detail-title">
+        <header>
+          <div class="dialog-title-stack">
+            <h2 id="session-detail-title">Session 详情</h2>
+            <p>{{ activeTab.sessionId || '未选择' }}</p>
+          </div>
+          <button type="button" class="dialog-close" aria-label="关闭" @click="detailOpen = false">x</button>
+        </header>
+        <dl class="session-detail-grid">
+          <div><dt>sessionId</dt><dd>{{ activeTab.sessionId || '-' }}</dd></div>
+          <div><dt>threadId</dt><dd>{{ activeTab.threadId || '-' }}</dd></div>
+          <div><dt>lastTraceId</dt><dd>{{ activeTab.lastTraceId || '-' }}</dd></div>
+          <div><dt>URL</dt><dd>{{ activeSessionUrl || '-' }}</dd></div>
+          <div><dt>status</dt><dd>{{ activeTab.status || 'unknown' }}</dd></div>
+          <div><dt>updatedAt</dt><dd>{{ activeTab.updatedAt || activeTab.startedAt || '未记录' }}</dd></div>
+        </dl>
+        <div class="session-detail-actions">
+          <button id="session-detail-copy" class="btn btn-secondary btn-sm" type="button" @click="copyActive">复制</button>
+          <span v-if="copied">已复制</span>
+        </div>
+      </section>
+    </div>
     <div
+      v-if="!collapsed"
       class="session-resize-handle"
       role="separator"
       tabindex="0"
diff --git a/web/hwlab-cloud-web/src/styles/workbench.css b/web/hwlab-cloud-web/src/styles/workbench.css
index c7c11900..ac543b72 100644
--- a/web/hwlab-cloud-web/src/styles/workbench.css
+++ b/web/hwlab-cloud-web/src/styles/workbench.css
@@ -566,7 +566,44 @@
 }
 
 .session-rail {
-  grid-template-rows: auto auto minmax(0, 1fr) auto auto;
+  grid-template-rows: auto minmax(0, 1fr) auto;
+}
+
+.session-rail-header-actions {
+  display: inline-flex;
+  flex: 0 0 auto;
+  align-items: center;
+  justify-content: flex-end;
+  gap: 6px;
+}
+
+.session-detail-button:disabled {
+  cursor: not-allowed;
+  opacity: 0.45;
+}
+
+.session-collapse-toggle {
+  min-width: 30px;
+  padding: 0 8px;
+  font-size: 16px;
+  line-height: 1;
+}
+
+.session-rail.is-collapsed {
+  width: 48px !important;
+  grid-template-rows: auto;
+  justify-items: center;
+  padding: 8px;
+}
+
+.session-rail.is-collapsed .panel-header.compact {
+  width: 100%;
+  justify-content: center;
+}
+
+.session-rail.is-collapsed .session-rail-header-actions {
+  width: 100%;
+  justify-content: center;
 }
 
 .hwpod-panel {
@@ -1476,26 +1513,42 @@
   text-align: left;
 }
 
-.session-model-channel,
-.session-active-metadata {
+.session-detail-grid {
   display: grid;
-  gap: 3px;
+  grid-template-columns: repeat(2, minmax(0, 1fr));
+  gap: 8px;
+  margin: 0;
+}
+
+.session-detail-grid div {
+  min-width: 0;
   border: 1px solid #d8e1eb;
   border-radius: 8px;
   background: #f8fafc;
   padding: 8px;
-  color: #475569;
+}
+
+.session-detail-grid dt {
+  color: #64748b;
+  font-size: 11px;
+  font-weight: 800;
+}
+
+.session-detail-grid dd {
+  margin: 3px 0 0;
+  color: #0f172a;
+  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
   font-size: 12px;
   overflow-wrap: anywhere;
 }
 
-.session-active-metadata span {
-  color: #0f172a;
-  font-weight: 750;
-}
-
-.session-active-metadata small {
+.session-detail-actions {
+  display: flex;
+  align-items: center;
+  justify-content: flex-end;
+  gap: 8px;
   color: #64748b;
+  font-size: 12px;
 }
 
 .session-resize-handle {
@@ -2591,17 +2644,26 @@
     overflow: hidden;
   }
 
+  .session-rail.is-collapsed {
+    width: 100% !important;
+    max-height: 44px;
+    grid-template-rows: auto;
+    justify-items: stretch;
+  }
+
   .session-rail .panel-header.compact {
     min-height: 34px;
   }
 
   .session-rail .panel-header.compact .page-eyebrow,
-  .session-rail .session-model-channel,
-  .session-rail .session-active-metadata,
   .session-rail .session-resize-handle {
     display: none;
   }
 
+  .session-rail.is-collapsed .panel-header.compact {
+    justify-content: flex-end;
+  }
+
   .session-rail .session-rail-actions {
     display: flex;
     justify-content: flex-end;
diff --git a/web/hwlab-cloud-web/tests/workbench-e2e/fixtures/selectors.ts b/web/hwlab-cloud-web/tests/workbench-e2e/fixtures/selectors.ts
index ed3fa996..ca48d2e0 100644
--- a/web/hwlab-cloud-web/tests/workbench-e2e/fixtures/selectors.ts
+++ b/web/hwlab-cloud-web/tests/workbench-e2e/fixtures/selectors.ts
@@ -4,10 +4,13 @@
 export const selectors = {
   workspace: "#workspace",
   sessionCreate: "#session-create",
+  sessionDetailToggle: "#session-detail-toggle",
+  sessionDetailDialog: "#session-detail-dialog",
+  sessionDetailCopy: "#session-detail-copy",
+  sessionCollapseToggle: "#session-collapse-toggle",
   sessionCopy: "#session-copy",
   sessionDelete: "#session-delete",
   sessionTabs: "#session-tabs",
-  sessionStatus: "#session-status",
   commandInput: "#command-input",
   commandSend: "#command-send",
   conversationList: "#conversation-list",
diff --git a/web/hwlab-cloud-web/tests/workbench-e2e/specs/deep-link.spec.ts b/web/hwlab-cloud-web/tests/workbench-e2e/specs/deep-link.spec.ts
index 72fe969d..958c9eae 100644
--- a/web/hwlab-cloud-web/tests/workbench-e2e/specs/deep-link.spec.ts
+++ b/web/hwlab-cloud-web/tests/workbench-e2e/specs/deep-link.spec.ts
@@ -44,7 +44,8 @@ test.describe("legacy cnv deep link canonical authority", () => {
 
   test("cnv route reflects canonical URL as soon as canonical content is visible", async ({ page }) => {
     await gotoWorkbench(page, "/workbench/sessions/cnv_c5e1330558c94d8e");
-    await expect(page.locator(selectors.sessionStatus)).toContainText("当前 ses_c5e1330558c94d8e");
+    await page.locator(selectors.sessionDetailToggle).click();
+    await expect(page.locator(selectors.sessionDetailDialog)).toContainText("ses_c5e1330558c94d8e");
     await expect(page).toHaveURL(/\/workbench\/sessions\/ses_c5e1330558c94d8e$/u, { timeout: 500 });
     const state = await fakeServerState(page);
     const legacyGets = (state.requestLedger as Array<{ method?: string; path?: string }>).filter((item) => item.method === "GET" && /^\/v1\/agent\/sessions\/[^/]+$/u.test(item.path ?? ""));
diff --git a/web/hwlab-cloud-web/tests/workbench-e2e/specs/session-rail-details-collapse.spec.ts b/web/hwlab-cloud-web/tests/workbench-e2e/specs/session-rail-details-collapse.spec.ts
new file mode 100644
index 00000000..3a29d9dd
--- /dev/null
+++ b/web/hwlab-cloud-web/tests/workbench-e2e/specs/session-rail-details-collapse.spec.ts
@@ -0,0 +1,66 @@
+import { expect, gotoWorkbench, saveScreenshot, test } from "../fixtures/test";
+import { selectors, sessionTab } from "../fixtures/selectors";
+
+test("session rail keeps low-frequency metadata behind details and preserves active session while collapsed", async ({ page }, testInfo) => {
+  await gotoWorkbench(page);
+  await expect(page.locator(sessionTab("ses_running"))).toHaveAttribute("data-active", "true");
+  await expect(page.locator("#session-model-channel")).toHaveCount(0);
+  await expect(page.locator("#session-status")).toHaveCount(0);
+  await expect(page.locator("#session-sidebar")).not.toContainText("模型通道：codex");
+  await expect(page.locator("#session-sidebar")).not.toContainText(/当前\s+ses_/u);
+  await expect(page.locator("#session-sidebar")).not.toContainText(/trace\s+trc_/u);
+  await saveScreenshot(page, testInfo, "session-rail-default");
+
+  await page.locator(selectors.sessionDetailToggle).click();
+  const detail = page.locator(selectors.sessionDetailDialog);
+  await expect(detail).toBeVisible();
+  await expect(detail).toContainText("sessionId");
+  await expect(detail).toContainText("ses_running");
+  await expect(detail).toContainText("threadId");
+  await expect(detail).toContainText("thr_running");
+  await expect(detail).toContainText("lastTraceId");
+  await expect(detail).toContainText("trc_running");
+  await expect(page.locator(selectors.sessionDetailCopy)).toBeVisible();
+  await saveScreenshot(page, testInfo, "session-rail-detail-dialog");
+  await page.keyboard.press("Escape");
+  await page.locator(`${selectors.sessionDetailDialog} .dialog-close`).click();
+
+  const rail = page.locator("#session-sidebar");
+  const center = page.locator(".workbench-center");
+  const beforeRail = await rail.boundingBox();
+  const beforeCenter = await center.boundingBox();
+  await page.locator(selectors.sessionCollapseToggle).click();
+  await expect(rail).toHaveAttribute("data-collapsed", "true");
+  const collapsedRail = await rail.boundingBox();
+  const collapsedCenter = await center.boundingBox();
+  expect(collapsedRail?.width ?? 0).toBeLessThan(80);
+  expect(collapsedCenter?.width ?? 0).toBeGreaterThan((beforeCenter?.width ?? 0) + 100);
+  expect(collapsedRail?.width ?? 0).toBeLessThan((beforeRail?.width ?? 0) - 120);
+  await expect(page).toHaveURL(/\/workbench\/sessions\/ses_running/u);
+  await expect(page.locator(`${selectors.messageCard}[data-role="agent"][data-status="running"]`)).toBeVisible();
+  await expect(page.locator(selectors.commandInput)).toBeVisible();
+  await saveScreenshot(page, testInfo, "session-rail-collapsed");
+
+  await page.locator(selectors.sessionCollapseToggle).click();
+  await expect(rail).toHaveAttribute("data-collapsed", "false");
+  await expect(page.locator(sessionTab("ses_running"))).toHaveAttribute("data-active", "true");
+  await expect(page.locator(`${selectors.messageCard}[data-role="agent"][data-status="running"]`)).toBeVisible();
+  const expandedRail = await rail.boundingBox();
+  expect(expandedRail?.width ?? 0).toBeGreaterThan(200);
+  await saveScreenshot(page, testInfo, "session-rail-expanded-after-collapse");
+});
+
+test.describe("mobile session rail collapse", () => {
+  test.use({ viewport: { width: 390, height: 844 } });
+
+  test("collapse toggle remains reachable on narrow screens", async ({ page }, testInfo) => {
+    await gotoWorkbench(page);
+    await expect(page.locator(selectors.sessionCollapseToggle)).toBeVisible();
+    await page.locator(selectors.sessionCollapseToggle).click();
+    await expect(page.locator("#session-sidebar")).toHaveAttribute("data-collapsed", "true");
+    await expect(page.locator(selectors.commandInput)).toBeVisible();
+    await saveScreenshot(page, testInfo, "session-rail-mobile-collapsed");
+    await page.locator(selectors.sessionCollapseToggle).click();
+    await expect(page.locator(selectors.sessionTabs)).toBeVisible();
+  });
+});
diff --git a/web/hwlab-cloud-web/tests/workbench-e2e/specs/session-switch-reload.spec.ts b/web/hwlab-cloud-web/tests/workbench-e2e/specs/session-switch-reload.spec.ts
index d516cd3e..822ffbd1 100644
--- a/web/hwlab-cloud-web/tests/workbench-e2e/specs/session-switch-reload.spec.ts
+++ b/web/hwlab-cloud-web/tests/workbench-e2e/specs/session-switch-reload.spec.ts
@@ -30,7 +30,8 @@ test("session switch persists active session after reload", async ({ page }, tes
 
   await page.reload();
   await expect(page.locator(sessionTab("ses_completed"))).toHaveAttribute("data-active", "true");
-  await expect(page.locator(selectors.sessionStatus)).toContainText("ses_completed");
+  await page.locator(selectors.sessionDetailToggle).click();
+  await expect(page.locator(selectors.sessionDetailDialog)).toContainText("ses_completed");
   await expect(page.locator(`${selectors.traceTimeline}[data-status="completed"]`)).toBeVisible();
   await saveScreenshot(page, testInfo, "session-switch-reload");
 });