feat(knowledge): folder-path breadcrumb above the space header

Inside a folder the header only showed the current folder's name — no
sense of depth, and getting back up meant repeated back-clicks. A
breadcrumb row (design 2075:8134) now sits above the header on desktop:
space name, then the ancestor chain, leaf last.

- Parent segments are clickable, capped at 8 CJK chars (96px @12px)
  with a full-name tooltip only when actually truncated.
- Chains deeper than 5 levels collapse the middle into an ellipsis
  whose hover card lists the hidden folders.
- Hidden at the space root so the single-level page keeps its layout;
  when shown, the leaf title drops to font-normal — the breadcrumb
  carries the hierarchy, the title no longer has to.

Suppressions: pruned entries the header edit and the latest merge made
stale (shrink-only).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/frontend/client/eslint-suppressions.json

@@ -741,11 +741,6 @@
       "count": 1
     }
   },
-  "src/components/Chat/Messages/DeepThinkingGroup.tsx": {
-    "no-restricted-syntax": {
-      "count": 6
-    }
-  },
   "src/components/Chat/Messages/HoverButtons.tsx": {
     "@typescript-eslint/no-explicit-any": {
       "count": 2
@@ -808,9 +803,6 @@
     }
   },
   "src/components/Chat/Messages/ThinkingContent.tsx": {
-    "no-restricted-imports": {
-      "count": 1
-    },
     "no-restricted-syntax": {
       "count": 1
     }
@@ -3345,7 +3337,7 @@
   },
   "src/pages/knowledge/SpaceDetail/KnowledgeSpaceHeader.tsx": {
     "@typescript-eslint/no-unused-vars": {
-      "count": 5
+      "count": 4
     }
   },
   "src/pages/knowledge/SpaceDetail/KnowledgeSpaceShareDialog.tsx": {
@@ -3436,7 +3428,7 @@
   },
   "src/pages/knowledge/index.tsx": {
     "@typescript-eslint/no-unused-vars": {
-      "count": 3
+      "count": 2
     },
     "no-console": {
       "count": 3

src/frontend/client/src/pages/knowledge/SpaceDetail/KnowledgeBreadcrumb.tsx

@@ -0,0 +1,120 @@
+import { useState } from "react";
+import { Outlined } from "bisheng-icons";
+import { cn } from "~/utils";
+import { Tooltip, TooltipContent, TooltipTrigger } from "~/components/ui/Tooltip2";
+import { HoverCard, HoverCardContent, HoverCardTrigger } from "~/components/ui/HoverCard";
+
+interface BreadcrumbNode {
+    id?: string;
+    name: string;
+}
+
+interface KnowledgeBreadcrumbProps {
+    spaceName: string;
+    /** Ancestor chain from root folder to the current folder (leaf last); space root NOT included. */
+    currentPath: BreadcrumbNode[];
+    onNavigateFolder: (folderId?: string) => void;
+    className?: string;
+}
+
+/** Parent segment width cap: 8 CJK characters at 12px (design "最大长度为8个中文字符"). */
+const PARENT_MAX_WIDTH = "max-w-[96px]";
+/** When the chain exceeds 5 levels, collapse the middle into an ellipsis (design 2075:8134). */
+const COLLAPSE_THRESHOLD = 5;
+
+function Separator() {
+    return <Outlined.Right className="size-4 shrink-0 text-text-4" aria-hidden />;
+}
+
+/** Clickable parent segment: hover highlights with the brand color; long names truncate with a tooltip. */
+function ParentCrumb({ node, onNavigate }: { node: BreadcrumbNode; onNavigate: (folderId?: string) => void }) {
+    // The full-name tooltip only shows when the name actually overflows the width cap.
+    const [overflowing, setOverflowing] = useState(false);
+
+    const button = (
+        <button
+            type="button"
+            onClick={() => onNavigate(node.id)}
+            onMouseEnter={(e) => setOverflowing(e.currentTarget.scrollWidth > e.currentTarget.clientWidth)}
+            className={cn(
+                "shrink-0 truncate text-text-3 transition-colors hover:text-blue-600",
+                PARENT_MAX_WIDTH,
+            )}
+        >
+            {node.name}
+        </button>
+    );
+
+    return (
+        <Tooltip>
+            <TooltipTrigger asChild>{button}</TooltipTrigger>
+            {overflowing && (
+                <TooltipContent noArrow side="bottom" className="z-[999] bg-white px-3 py-2 text-sm text-[#4e5969] shadow-md">
+                    {node.name}
+                </TooltipContent>
+            )}
+        </Tooltip>
+    );
+}
+
+/**
+ * Folder path breadcrumb above the knowledge-space header title (desktop only; design 2075:8134).
+ * Hidden at the space root ("single level" case) — the caller only renders it inside a folder.
+ */
+export function KnowledgeBreadcrumb({ spaceName, currentPath, onNavigateFolder, className }: KnowledgeBreadcrumbProps) {
+    // Full chain: space root first, current folder last.
+    const items: BreadcrumbNode[] = [{ id: undefined, name: spaceName }, ...currentPath];
+    const current = items[items.length - 1];
+    const collapse = items.length > COLLAPSE_THRESHOLD;
+    // Collapsed layout keeps the first item and the last two; the rest hide behind an ellipsis.
+    const headParents = collapse ? [items[0]] : items.slice(0, -1);
+    const hiddenParents = collapse ? items.slice(1, -2) : [];
+    const tailParents = collapse ? [items[items.length - 2]] : [];
+
+    return (
+        <nav
+            aria-label="breadcrumb"
+            className={cn("flex min-w-0 items-center gap-0.5 text-caption leading-6 text-text-3", className)}
+        >
+            {headParents.map((node) => (
+                <span key={node.id ?? "space-root"} className="flex shrink-0 items-center gap-0.5">
+                    <ParentCrumb node={node} onNavigate={onNavigateFolder} />
+                    <Separator />
+                </span>
+            ))}
+            {collapse && (
+                <span className="flex shrink-0 items-center gap-0.5">
+                    <HoverCard openDelay={100} closeDelay={150}>
+                        <HoverCardTrigger asChild>
+                            <span className="cursor-pointer px-0.5 text-text-3 transition-colors hover:text-blue-600">
+                                ...
+                            </span>
+                        </HoverCardTrigger>
+                        <HoverCardContent
+                            align="start"
+                            className="flex w-auto max-w-[420px] flex-wrap items-center gap-x-0.5 gap-y-1 rounded-lg border border-border-base bg-white px-4 py-2 text-caption leading-6 text-text-3 shadow-md"
+                        >
+                            {hiddenParents.map((node, idx) => (
+                                <span key={node.id} className="flex shrink-0 items-center gap-0.5">
+                                    {idx > 0 && <Separator />}
+                                    <ParentCrumb node={node} onNavigate={onNavigateFolder} />
+                                </span>
+                            ))}
+                        </HoverCardContent>
+                    </HoverCard>
+                    <Separator />
+                </span>
+            )}
+            {tailParents.map((node) => (
+                <span key={node.id ?? "space-root"} className="flex shrink-0 items-center gap-0.5">
+                    <ParentCrumb node={node} onNavigate={onNavigateFolder} />
+                    <Separator />
+                </span>
+            ))}
+            {/* Current page: not clickable, no hover effect, only limited by the row width. */}
+            <span aria-current="page" className="min-w-0 truncate whitespace-nowrap">
+                {current.name}
+            </span>
+        </nav>
+    );
+}

src/frontend/client/src/pages/knowledge/SpaceDetail/KnowledgeSpaceHeader.tsx

@@ -20,6 +20,7 @@ import {
 import { Button } from "~/components/ui/Button";
 import { Tooltip, TooltipContent, TooltipTrigger } from "~/components/ui/Tooltip2";
 import { CopyShareLinkButton } from "~/components/CopyShareLinkButton";
+import { KnowledgeBreadcrumb } from "./KnowledgeBreadcrumb";
 import { useLocalize, useMediaQuery, usePrefersMobileLayout } from "~/hooks";
 import { knowledgeUploadCapabilities } from "../knowledgeUploadCapabilities";
 
@@ -383,7 +384,21 @@ export function KnowledgeSpaceHeader({
     );
 
     return (
-        <div className="flex min-h-8 items-center justify-between gap-3 pt-4 pb-4 max-[767px]:gap-2 max-[767px]:pb-3">
+        <div className="flex flex-col">
+            {/* Folder-path breadcrumb (desktop only — this header never renders on mobile).
+                Hidden at the space root: with a single level the page content shifts up (design 2075:8134). */}
+            {currentPath.length > 0 && (
+                <KnowledgeBreadcrumb
+                    className="pt-3"
+                    spaceName={space.name}
+                    currentPath={currentPath}
+                    onNavigateFolder={onNavigateFolder}
+                />
+            )}
+        <div className={cn(
+            "flex min-h-8 items-center justify-between gap-3 pb-4 max-[767px]:gap-2 max-[767px]:pb-3",
+            currentPath.length > 0 ? "pt-1" : "pt-4",
+        )}>
 
                     {/* 左侧：根目录显示空间标题 + 信息 + 分享；进入文件夹后显示返回按钮 + 分隔线 + 当前文件夹名（设计稿 11772:70584） */}
                     <div className="flex min-w-0 flex-1 items-center gap-1 text-sm">
@@ -403,7 +418,7 @@ export function KnowledgeSpaceHeader({
                                 </button>
                                 <div className="mx-1 h-4 w-px shrink-0 bg-[#e5e6eb]" aria-hidden />
                                 */}
-                                <h1 className="min-w-0 truncate text-base font-medium text-[#1d2129] max-[767px]:text-[16px] max-[767px]:leading-6">
+                                <h1 className="min-w-0 truncate text-base font-normal text-[#1d2129] max-[767px]:text-[16px] max-[767px]:leading-6">
                                     {currentPath[currentPath.length - 1]?.name || space.name}
                                 </h1>
                             </>
@@ -460,5 +475,6 @@ export function KnowledgeSpaceHeader({
                         {batchAndAddActions}
                     </div>
         </div>
+        </div>
     );
 }