diff --git a/2.Design/API.md b/2.Design/API.md
index 50f20cb..64cfa02 100644
--- a/2.Design/API.md
+++ b/2.Design/API.md
@@ -342,22 +342,30 @@ Web 端未读数由 `AppShell` 每 30 秒轮询一次；在通知页标已读后
 | `status` | 可重复；`draft`/`in_review`/`published`/`archived`，不传为全部 |
 | `doc_type` | `note`/`howto`/`faq`/`postmortem`/`decision` |
 | `source_item_id` | 按来源事项筛 |
+| `category_id` | 按分类筛，**包含子分类** |
+| `uncategorized` | `true` 只看未分类 |
+| `tag` | 按标签名筛（不区分大小写） |
 | `q` | 标题 / 正文 / 摘要子串 |
 | `limit` | 1–100，默认 30 |
 | `cursor` | 上一页的 `next_cursor` |
 
-返回 `{items, next_cursor, has_more}`。每条是 `item` 字段 + `knowledge` + `source`：
+返回 `{items, next_cursor, has_more}`。每条是 `item` 字段 + `knowledge` + `category` + `source`：
 
 ```json
 {
   "id": "…", "kind": "knowledge", "title": "发票原件必须一起寄",
-  "body_md": "…", "status": "published", "tags": [],
+  "body_md": "…", "status": "published", "tags": [{"id": "…", "name": "财务"}],
   "knowledge": {
     "doc_type": "howto", "summary": "…", "status_hint": "published",
     "source_kind": "task", "source_item_id": "…", "generated_by": "human",
     "published_at": "2026-10-28T05:54:44Z", "archived_at": null,
     "chunk_count": 0, "author_id": "…"
   },
+  "category": {
+    "id": "…", "parent_id": "…", "name": "回滚", "depth": 3,
+    "sort_order": 0, "version": 1,
+    "path": ["研发", "部署", "回滚"], "full_path": "研发 / 部署 / 回滚"
+  },
   "source": {"id": "…", "kind": "task", "title": "发票原件必须一起寄", "status": "done"}
 }
 ```
@@ -374,19 +382,43 @@ Web 端未读数由 `AppShell` 每 30 秒轮询一次；在通知页标已读后
 
 ```json
 {"title": "报销单要贴发票原件", "body_md": "…", "doc_type": "note",
+ "tag_names": ["财务", "报销"], "category_id": "可选的分类 id",
  "source_item_id": "可选的来源事项 id"}
 ```
 
 - 不带 `source_item_id` → `source_kind=manual`（手记），允许没有来源。
 - 带 → 来源必须是同工作区的 `task`/`ticket`，否则 `7005`。
+- `category_id` 可省（未分类）；跨工作区的分类一律按不存在处理（`7006`）。
+- `tag_names` 按名字去重创建，空格/逗号分隔由前端拆好再传。
 - 新知识一律 `draft`，不会直接对外可见。
 
 ### 5.4 `PATCH /knowledge/{item_id}` — 修改内容
 
-必须带 `version`（乐观锁，冲突 `4009`）。可改 `title`/`body_md`/`summary`/`doc_type`。
+必须带 `version`（乐观锁，冲突 `4009`）。可改 `title`/`body_md`/`summary`/`doc_type`/`tag_names`/`category_id`；
+传 `clear_category: true` 表示移到未分类。
 **已发布的不许直接改**（`7003`，先撤回审议或归档），避免"发布后被悄悄改写"。
 
-### 5.5 `POST /knowledge/{item_id}/status` — 状态动作
+### 5.5 知识分类 `/knowledge/categories`
+
+分类是工作区级的三级小树，用来给知识安一个位置；它**不是权限边界**，只是归类。
+
+| 方法 | 路径 | 说明 |
+|---|---|---|
+| GET | `/knowledge/categories` | 扁平列表（按 depth/sort_order 排好），每条带 `doc_count`、`path`、`full_path`；另有 `max_depth=3` |
+| POST | `/knowledge/categories` | `{name, parent_id?, sort_order?}` |
+| PATCH | `/knowledge/categories/{id}` | `{name?, parent_id?, move?, sort_order?, version}` |
+| DELETE | `/knowledge/categories/{id}?force=false` | 有子分类不让删；有知识要 `force=true`，删后知识变未分类 |
+
+三条规则：
+
+1. **最多三级**。第四级不是"更细"，是"找不到"，创建/移动越界一律 `7007`。
+2. **同一层不能重名**（不区分大小写），否则 `7008`；不同层可以同名。
+3. **移动带着子树走**：把一棵三层树挪到第二层下面会让最深节点到第五层，这种移动直接拒绝（`7007`），
+   不静默改层级。
+
+`PATCH` 里 `move=true` 才处理 `parent_id`，避免"只改名字"被误当成移动。改名的 `version` 冲突是 `4009`。
+
+### 5.6 `POST /knowledge/{item_id}/status` — 状态动作
 
 | action | 允许的前置状态 | 结果 | 谁能做 |
 |---|---|---|---|
@@ -401,7 +433,7 @@ Web 端未读数由 `AppShell` 每 30 秒轮询一次；在通知页标已读后
 
 **发布要 owner/admin 的理由**：发布等于团队为这条结论背书，不能谁都能推。
 
-### 5.6 `POST /items/{item_id}/knowledge` — 把一件事沉淀成知识
+### 5.7 `POST /items/{item_id}/knowledge` — 把一件事沉淀成知识
 
 Query：`doc_type`（默认 `postmortem`）。来源可以是任务或工单；工单会带出验收结论。
 返回与 5.2 相同的知识对象；同一来源重复沉淀 → `7002`。
@@ -409,7 +441,7 @@ Query：`doc_type`（默认 `postmortem`）。来源可以是任务或工单；
 **工单验收通过时，后端会自动调用这条逻辑**（`generated_by=rule`，`doc_type=postmortem`，
 正文开头固定一句"这份草稿由系统根据来源自动整理，请先核对再发布"），所以用户不需要记得点。
 
-### 5.7 检索 `GET /knowledge/search`
+### 5.8 检索 `GET /knowledge/search`
 
 Query：
 | 参数 | 说明 |
@@ -434,7 +466,7 @@ Query：
 2. **结果必须带来源**，能点回原文。这是 D3（知识必须有来源）的延伸：不给"出处不存在"的答案。
 3. **宁可返回空，也不凑数**。检索失败比误导便宜。
 
-发布（`5.5` 的 `publish`）时会自动重建索引，用户发布完立刻能搜到；
+发布（`5.6` 的 `publish`）时会自动重建索引，用户发布完立刻能搜到；
 但改完正文不会自动重建，需要调用下面这条。
 
 ### `POST /knowledge/{item_id}/reindex` — 重建切片
@@ -447,7 +479,7 @@ Query：
 将来换 pgvector 只改列类型与索引，接口不变。换 embedding 模型（`EMBEDDING_PROVIDER`）后
 **必须整体重建**，否则新旧向量混在一张表里，分数没法比较。
 
-### 5.8 知识的错误码
+### 5.9 知识的错误码
 
 | 码 | HTTP | 含义 |
 |---|---|---|
@@ -456,6 +488,9 @@ Query：
 | 7003 | 409 | 当前状态不允许这个动作 |
 | 7004 | 403 | 权限不足（如非管理员发布） |
 | 7005 | 409 | 来源事项无效或缺失 |
+| 7006 | 404 | 分类不存在，或不是本工作区的 |
+| 7007 | 422 | 分类层级超过三级，或移动后会让子树超过三级 |
+| 7008 | 409 | 分类重名 / 还有子分类 / 分类下还有知识（需 `force`） |
 
 ---
 
diff --git a/2.Design/ROADMAP-M0-M1.md b/2.Design/ROADMAP-M0-M1.md
index d9b2e13..3bf1f70 100644
--- a/2.Design/ROADMAP-M0-M1.md
+++ b/2.Design/ROADMAP-M0-M1.md
@@ -291,11 +291,14 @@
 | 3.8.4 | 索引生命周期：发布自动建、改正文需 `reindex`、换模型整体重建 | 0.5 | [x] `POST /knowledge/{id}/reindex` |
 | 3.9 | 安卓知识列表 | 1.0 | [x] 只读列表 + 详情动作（编辑正文走安卓编辑器） |
 | 3.10 | 文档与 e2e | 1.0 | [x] `knowledge.mjs` 7 项 + `retrieval.mjs` 6 项 |
+| 3.11 | 知识分类：工作区三级小树（`knowledge_category` + 迁移 0007 + RLS），知识可归一类，列表按分类子树 / 未分类 / 标签筛选 | 1.0 | [x] 增删改移 + 重名 `7008`、超三级 `7007`、删分类要 `force` |
+| 3.12 | 备忘录形态：新建知识一次写全（标题/类型/分类/标签/正文），不再是"填个标题就完成"；抽屉加宽 + 可整屏 | 1.0 | [x] Web `KnowledgeComposer` + 安卓大对话框；`Sheet` 增 `size="md/lg/xl"` 与展开按钮；截图 `2.Design/screens/knowledge-composer.png`、`knowledge-categories.png` |
 
 ### M3 完成定义（DOD）
 - [x] 一件事办完 → 自动出现一份草稿 → 核对 → 发布，全程不用手动复制粘贴
 - [x] 每条知识都能追到来源（除手记），点开能看到来源事项
 - [x] 非管理员发布被拒；跨租户看不到别人的知识
+- [x] 知识是备忘录：标题、正文、标签、三级分类、搜索；新建时就能把这些一次填完（Web 与安卓一致）
 - [x] 切片与语义检索跑通（`real[]` + SQL 余弦；pgvector 仍待独立实例）
 - [ ] 真实用两周：新同事靠知识库自己解决过一次问题（需要真实团队）
 
diff --git a/2.Design/screens/knowledge-categories.png b/2.Design/screens/knowledge-categories.png
new file mode 100644
index 0000000..03e003e
Binary files /dev/null and b/2.Design/screens/knowledge-categories.png differ
diff --git a/2.Design/screens/knowledge-composer.png b/2.Design/screens/knowledge-composer.png
new file mode 100644
index 0000000..5d41f43
Binary files /dev/null and b/2.Design/screens/knowledge-composer.png differ
diff --git a/android/app/src/main/java/com/dadao/task/data/Api.kt b/android/app/src/main/java/com/dadao/task/data/Api.kt
index 97761f5..ee2c9c4 100644
--- a/android/app/src/main/java/com/dadao/task/data/Api.kt
+++ b/android/app/src/main/java/com/dadao/task/data/Api.kt
@@ -236,6 +236,26 @@ data class SourceRef(
     val status: String = "",
 )
 
+/** 知识分类：工作区级的三级小树，fullPath 形如「研发 / 部署 / 回滚」。 */
+@Serializable
+data class KnowledgeCategory(
+    val id: String,
+    val name: String = "",
+    @SerialName("parent_id") val parentId: String? = null,
+    val depth: Int = 1,
+    @SerialName("sort_order") val sortOrder: Int = 0,
+    val version: Int = 1,
+    val path: List<String> = emptyList(),
+    @SerialName("full_path") val fullPath: String = "",
+    @SerialName("doc_count") val docCount: Int = 0,
+)
+
+@Serializable
+data class KnowledgeCategoryPage(
+    val items: List<KnowledgeCategory> = emptyList(),
+    @SerialName("max_depth") val maxDepth: Int = 3,
+)
+
 @Serializable
 data class KnowledgeDoc(
     val id: String,
@@ -245,6 +265,7 @@ data class KnowledgeDoc(
     val version: Int = 1,
     val tags: List<Tag> = emptyList(),
     val knowledge: KnowledgeInfo = KnowledgeInfo(),
+    val category: KnowledgeCategory? = null,
     val source: SourceRef? = null,
     val attachments: List<Attachment> = emptyList(),
 )
@@ -325,6 +346,8 @@ private data class KnowledgeCreateRequest(
     val title: String,
     @SerialName("body_md") val bodyMd: String,
     @SerialName("doc_type") val docType: String,
+    @SerialName("tag_names") val tagNames: List<String> = emptyList(),
+    @SerialName("category_id") val categoryId: String? = null,
 )
 
 @Serializable
@@ -351,6 +374,10 @@ private data class KnowledgeUpdateRequest(
     val version: Int,
     val title: String? = null,
     @SerialName("body_md") val bodyMd: String? = null,
+    @SerialName("tag_names") val tagNames: List<String>? = null,
+    @SerialName("category_id") val categoryId: String? = null,
+    // 想把分类清成"未分类"就传 clear_category=true：只传 null 会被服务端当成"不改"
+    @SerialName("clear_category") val clearCategory: Boolean = false,
 )
 
 /**
@@ -666,20 +693,39 @@ class Api(private val tokens: TokenStore) {
         workspaceId: String,
         statuses: List<String> = listOf("draft", "in_review"),
         query: String? = null,
+        categoryId: String? = null,
+        uncategorized: Boolean = false,
     ): KnowledgePage {
         val params = buildString {
             append("?limit=30")
             statuses.forEach { append("&status=").append(it) }
-            if (!query.isNullOrBlank()) append("&q=").append(java.net.URLEncoder.encode(query, "UTF-8"))
+            if (!query.isNullOrBlank()) {
+                append("&q=").append(java.net.URLEncoder.encode(query, "UTF-8"))
+            }
+            if (categoryId != null) append("&category_id=").append(categoryId)
+            if (uncategorized) append("&uncategorized=true")
         }
         return call(path = "/workspaces/$workspaceId/knowledge$params", auth = true)
     }
 
+    /** 工作区三级分类小树（扁平返回，depth 表示层级）。 */
+    suspend fun knowledgeCategories(workspaceId: String): KnowledgeCategoryPage =
+        call(path = "/workspaces/$workspaceId/knowledge/categories", auth = true)
+
     /** 手记：没有来源的知识，得自己写清楚。 */
-    suspend fun createKnowledge(workspaceId: String, title: String, body: String = ""): KnowledgeDoc =
+    suspend fun createKnowledge(
+        workspaceId: String,
+        title: String,
+        body: String = "",
+        docType: String = "note",
+        tags: List<String> = emptyList(),
+        categoryId: String? = null,
+    ): KnowledgeDoc =
         call(
             path = "/workspaces/$workspaceId/knowledge",
-            body = json.encodeToString(KnowledgeCreateRequest(title, body, "note")),
+            body = json.encodeToString(
+                KnowledgeCreateRequest(title, body, docType, tags, categoryId),
+            ),
             auth = true,
         )
 
@@ -709,9 +755,14 @@ class Api(private val tokens: TokenStore) {
         version: Int,
         title: String? = null,
         body: String? = null,
+        tags: List<String>? = null,
+        categoryId: String? = null,
+        clearCategory: Boolean = false,
     ): KnowledgeDoc = call(
         path = "/workspaces/$workspaceId/knowledge/$itemId",
-        body = json.encodeToString(KnowledgeUpdateRequest(version, title, body)),
+        body = json.encodeToString(
+            KnowledgeUpdateRequest(version, title, body, tags, categoryId, clearCategory),
+        ),
         auth = true,
         method = "PATCH",
     )
diff --git a/android/app/src/main/java/com/dadao/task/ui/KnowledgeScreen.kt b/android/app/src/main/java/com/dadao/task/ui/KnowledgeScreen.kt
index 58de4c3..34c9855 100644
--- a/android/app/src/main/java/com/dadao/task/ui/KnowledgeScreen.kt
+++ b/android/app/src/main/java/com/dadao/task/ui/KnowledgeScreen.kt
@@ -1,9 +1,12 @@
 package com.dadao.task.ui
 
+import androidx.compose.foundation.background
+import androidx.compose.foundation.horizontalScroll
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxHeight
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.height
@@ -33,8 +36,11 @@ import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.unit.dp
+import androidx.compose.ui.window.Dialog
+import androidx.compose.ui.window.DialogProperties
 import com.dadao.task.data.Api
 import com.dadao.task.data.ApiException
+import com.dadao.task.data.KnowledgeCategory
 import com.dadao.task.data.KnowledgeDoc
 import com.dadao.task.data.Workspace
 import kotlinx.coroutines.launch
@@ -46,13 +52,26 @@ private val knowledgeTabs = listOf(
     "all" to "全部",
 )
 
-private fun docTypeLabel(type: String): String = when (type) {
-    "howto" -> "怎么做"
-    "faq" -> "问答"
-    "postmortem" -> "复盘"
-    "decision" -> "决策"
-    else -> "笔记"
-}
+private val docTypes = listOf(
+    "note" to "笔记",
+    "howto" to "怎么做",
+    "faq" to "问答",
+    "postmortem" to "复盘",
+    "decision" to "决策",
+)
+
+private fun docTypeLabel(type: String): String =
+    docTypes.firstOrNull { it.first == type }?.second ?: "笔记"
+
+private fun parseTags(raw: String): List<String> =
+    raw.split(' ', '\n', ',', '，', '、')
+        .map { it.trim().removePrefix("#") }
+        .filter { it.isNotBlank() }
+        .distinct()
+
+/** 分类在筛选条里的显示名：用点前缀表达层级，手机上比缩进更稳。 */
+private fun catLabel(cat: KnowledgeCategory): String =
+    "·".repeat((cat.depth - 1).coerceAtLeast(0)) + cat.name
 
 @Composable
 fun KnowledgeScreen(
@@ -66,12 +85,18 @@ fun KnowledgeScreen(
     val scope = rememberCoroutineScope()
     var tab by remember { mutableStateOf("draft") }
     var docs by remember { mutableStateOf<List<KnowledgeDoc>>(emptyList()) }
+    var categories by remember { mutableStateOf<List<KnowledgeCategory>>(emptyList()) }
     var loading by remember { mutableStateOf(true) }
     var message by remember { mutableStateOf<String?>(null) }
     var open by remember { mutableStateOf<KnowledgeDoc?>(null) }
     var adding by remember { mutableStateOf(false) }
-    var newTitle by remember { mutableStateOf("") }
-    var newBody by remember { mutableStateOf("") }
+    // null = 全部；"none" = 未分类；其它是分类 id（服务端含子分类）
+    var catFilter by remember { mutableStateOf<String?>(null) }
+
+    suspend fun loadCategories() {
+        runCatching { api.knowledgeCategories(workspace.id) }
+            .onSuccess { categories = it.items }
+    }
 
     suspend fun reload() {
         loading = true
@@ -81,7 +106,15 @@ fun KnowledgeScreen(
             "all" -> listOf("draft", "in_review", "published", "archived")
             else -> listOf("draft", "in_review")
         }
-        runCatching { api.knowledge(workspace.id, statuses) }
+        val filter = catFilter
+        runCatching {
+            api.knowledge(
+                workspace.id,
+                statuses,
+                categoryId = if (filter != null && filter != "none") filter else null,
+                uncategorized = filter == "none",
+            )
+        }
             .onSuccess {
                 docs = it.items
                 message = null
@@ -90,7 +123,8 @@ fun KnowledgeScreen(
         loading = false
     }
 
-    LaunchedEffect(tab) { reload() }
+    LaunchedEffect(tab, catFilter) { reload() }
+    LaunchedEffect(Unit) { loadCategories() }
 
     // 从编辑器保存回来：本页是新建出来的，刷完列表再把那条详情重新打开。
     LaunchedEffect(reopenItem) {
@@ -125,11 +159,30 @@ fun KnowledgeScreen(
                     }
                 }
                 Spacer(Modifier.height(10.dp))
-                GhostButton("记一条", onClick = {
-                    adding = true
-                    newTitle = ""
-                    newBody = ""
-                })
+                Row(
+                    modifier = Modifier.horizontalScroll(rememberScrollState()),
+                    horizontalArrangement = Arrangement.spacedBy(6.dp),
+                ) {
+                    SurfaceChip(
+                        text = "全部分类",
+                        selected = catFilter == null,
+                        onClick = { catFilter = null },
+                    )
+                    SurfaceChip(
+                        text = "未分类",
+                        selected = catFilter == "none",
+                        onClick = { catFilter = "none" },
+                    )
+                    categories.forEach { cat ->
+                        SurfaceChip(
+                            text = catLabel(cat),
+                            selected = catFilter == cat.id,
+                            onClick = { catFilter = cat.id },
+                        )
+                    }
+                }
+                Spacer(Modifier.height(10.dp))
+                GhostButton("记一条", onClick = { adding = true })
             }
         }
 
@@ -141,7 +194,7 @@ fun KnowledgeScreen(
         if (!loading && docs.isEmpty()) {
             item {
                 EmptyState(
-                    "还没有待核对的知识",
+                    if (catFilter == null) "还没有待核对的知识" else "这个分类下还没有知识",
                     "把工单验收通过，或在任务详情里点「沉淀成知识」",
                 )
             }
@@ -165,6 +218,18 @@ fun KnowledgeScreen(
                     fontWeight = FontWeight.Medium,
                 )
                 Spacer(Modifier.height(6.dp))
+                val meta = buildList {
+                    doc.category?.let { add(it.fullPath.ifBlank { it.name }) }
+                    doc.tags.forEach { add("#${it.name}") }
+                }
+                if (meta.isNotEmpty()) {
+                    Text(
+                        meta.joinToString("  "),
+                        style = MaterialTheme.typography.labelSmall,
+                        color = Primary,
+                    )
+                    Spacer(Modifier.height(4.dp))
+                }
                 Text(
                     sourceLine(doc),
                     style = MaterialTheme.typography.labelSmall,
@@ -182,68 +247,35 @@ fun KnowledgeScreen(
             api = api,
             workspace = workspace,
             doc = target,
+            categories = categories,
             onClose = { open = null },
             onEdit = onEdit,
             onChanged = {
-                scope.launch { reload() }
+                scope.launch {
+                    reload()
+                    loadCategories()
+                }
             },
+            onCategoriesChanged = { scope.launch { loadCategories() } },
             onFail = { fail(it) },
         )
     }
 
     if (adding) {
-        AlertDialog(
-            onDismissRequest = { adding = false },
-            title = { Text("记一条", style = MaterialTheme.typography.titleMedium) },
-            text = {
-                Column {
-                    Text(
-                        "手记没有来源，想沉淀某件具体的事，去那条任务的详情里点「沉淀成知识」。",
-                        style = MaterialTheme.typography.bodySmall,
-                        color = InkMuted,
-                    )
-                    Spacer(Modifier.height(10.dp))
-                    OutlinedTextField(
-                        value = newTitle,
-                        onValueChange = { newTitle = it },
-                        modifier = Modifier.fillMaxWidth(),
-                        placeholder = { Text("一句话说清这条知识是什么", color = InkMuted) },
-                        shape = RoundedCornerShape(10.dp),
-                        colors = TextFieldDefaults.colors(
-                            focusedContainerColor = Color.White,
-                            unfocusedContainerColor = Color.White,
-                            focusedIndicatorColor = Primary,
-                            unfocusedIndicatorColor = Line,
-                        ),
-                    )
-                    Spacer(Modifier.height(8.dp))
-                    OutlinedTextField(
-                        value = newBody,
-                        onValueChange = { newBody = it },
-                        modifier = Modifier.fillMaxWidth().heightIn(min = 90.dp),
-                        placeholder = { Text("正文（可空，之后再补）", color = InkMuted) },
-                        shape = RoundedCornerShape(10.dp),
-                        colors = TextFieldDefaults.colors(
-                            focusedContainerColor = Color.White,
-                            unfocusedContainerColor = Color.White,
-                            focusedIndicatorColor = Primary,
-                            unfocusedIndicatorColor = Line,
-                        ),
-                    )
+        KnowledgeComposerDialog(
+            api = api,
+            workspace = workspace,
+            categories = categories,
+            onDismiss = { adding = false },
+            onCreated = { created ->
+                adding = false
+                scope.launch {
+                    loadCategories()
+                    reload()
+                    open = created
                 }
             },
-            confirmButton = {
-                TextButton(onClick = {
-                    scope.launch {
-                        adding = false
-                        runCatching { api.createKnowledge(workspace.id, newTitle.trim(), newBody) }
-                            .onSuccess { reload() }
-                            .onFailure { fail(it) }
-                    }
-                }) { Text("保存草稿") }
-            },
-            dismissButton = { TextButton(onClick = { adding = false }) { Text("取消") } },
-            containerColor = Paper,
+            onFail = { fail(it) },
         )
     }
 }
@@ -257,18 +289,182 @@ private fun sourceLine(doc: KnowledgeDoc): String {
     }
 }
 
+/**
+ * 新建知识：手机上也要能一次写全（标题/类型/分类/标签/正文）。
+ * 用整屏 94% 宽的 Dialog 而不是 AlertDialog —— AlertDialog 的宽度上限装不下一篇备忘录。
+ */
+@Composable
+private fun KnowledgeComposerDialog(
+    api: Api,
+    workspace: Workspace,
+    categories: List<KnowledgeCategory>,
+    onDismiss: () -> Unit,
+    onCreated: (KnowledgeDoc) -> Unit,
+    onFail: (Throwable) -> Unit,
+) {
+    val scope = rememberCoroutineScope()
+    var title by remember { mutableStateOf("") }
+    var docType by remember { mutableStateOf("note") }
+    var categoryId by remember { mutableStateOf<String?>(null) }
+    var tags by remember { mutableStateOf("") }
+    var body by remember { mutableStateOf("") }
+    var saving by remember { mutableStateOf(false) }
+
+    Dialog(
+        onDismissRequest = onDismiss,
+        properties = DialogProperties(usePlatformDefaultWidth = false),
+    ) {
+        Column(
+            Modifier
+                .fillMaxWidth(0.94f)
+                .fillMaxHeight(0.88f)
+                .background(Paper, RoundedCornerShape(16.dp))
+                .padding(16.dp),
+        ) {
+            Row(verticalAlignment = Alignment.CenterVertically) {
+                Text(
+                    "记一条知识",
+                    style = MaterialTheme.typography.titleMedium,
+                    modifier = Modifier.weight(1f),
+                )
+                GhostButton("取消", onClick = onDismiss)
+                Spacer(Modifier.width(8.dp))
+                PrimaryButton(
+                    "保存",
+                    enabled = !saving && title.isNotBlank(),
+                    onClick = {
+                        scope.launch {
+                            saving = true
+                            runCatching {
+                                api.createKnowledge(
+                                    workspace.id,
+                                    title.trim(),
+                                    body,
+                                    docType,
+                                    parseTags(tags),
+                                    categoryId,
+                                )
+                            }
+                                .onSuccess { onCreated(it) }
+                                .onFailure { onFail(it) }
+                            saving = false
+                        }
+                    },
+                )
+            }
+            Spacer(Modifier.height(12.dp))
+            Column(
+                Modifier.weight(1f).verticalScroll(rememberScrollState()),
+            ) {
+                OutlinedTextField(
+                    value = title,
+                    onValueChange = { title = it },
+                    modifier = Modifier.fillMaxWidth(),
+                    placeholder = { Text("一句话说清这条知识是什么", color = InkMuted) },
+                    shape = RoundedCornerShape(10.dp),
+                    colors = TextFieldDefaults.colors(
+                        focusedContainerColor = Color.White,
+                        unfocusedContainerColor = Color.White,
+                        focusedIndicatorColor = Primary,
+                        unfocusedIndicatorColor = Line,
+                    ),
+                )
+                Spacer(Modifier.height(10.dp))
+                SectionLabel("类型")
+                Row(
+                    modifier = Modifier.horizontalScroll(rememberScrollState()),
+                    horizontalArrangement = Arrangement.spacedBy(6.dp),
+                ) {
+                    docTypes.forEach { (key, label) ->
+                        SurfaceChip(
+                            text = label,
+                            selected = docType == key,
+                            onClick = { docType = key },
+                        )
+                    }
+                }
+                Spacer(Modifier.height(10.dp))
+                SectionLabel("分类")
+                Row(
+                    modifier = Modifier.horizontalScroll(rememberScrollState()),
+                    horizontalArrangement = Arrangement.spacedBy(6.dp),
+                ) {
+                    SurfaceChip(
+                        text = "未分类",
+                        selected = categoryId == null,
+                        onClick = { categoryId = null },
+                    )
+                    categories.forEach { cat ->
+                        SurfaceChip(
+                            text = catLabel(cat),
+                            selected = categoryId == cat.id,
+                            onClick = { categoryId = cat.id },
+                        )
+                    }
+                }
+                if (categories.isEmpty()) {
+                    Text(
+                        "还没有分类，Web 端可以建三级分类",
+                        style = MaterialTheme.typography.labelSmall,
+                        color = InkMuted,
+                        modifier = Modifier.padding(top = 4.dp),
+                    )
+                }
+                Spacer(Modifier.height(10.dp))
+                OutlinedTextField(
+                    value = tags,
+                    onValueChange = { tags = it },
+                    modifier = Modifier.fillMaxWidth(),
+                    singleLine = true,
+                    placeholder = { Text("标签，空格或逗号分隔", color = InkMuted) },
+                    shape = RoundedCornerShape(10.dp),
+                    colors = TextFieldDefaults.colors(
+                        focusedContainerColor = Color.White,
+                        unfocusedContainerColor = Color.White,
+                        focusedIndicatorColor = Primary,
+                        unfocusedIndicatorColor = Line,
+                    ),
+                )
+                Spacer(Modifier.height(10.dp))
+                SectionLabel("正文 · Markdown")
+                OutlinedTextField(
+                    value = body,
+                    onValueChange = { body = it },
+                    modifier = Modifier.fillMaxWidth().heightIn(min = 240.dp),
+                    placeholder = { Text("背景、做法、结论……写清楚以后自己还能看懂", color = InkMuted) },
+                    shape = RoundedCornerShape(10.dp),
+                    colors = TextFieldDefaults.colors(
+                        focusedContainerColor = Color.White,
+                        unfocusedContainerColor = Color.White,
+                        focusedIndicatorColor = Primary,
+                        unfocusedIndicatorColor = Line,
+                    ),
+                )
+                Spacer(Modifier.height(12.dp))
+            }
+        }
+    }
+}
+
 @Composable
 private fun KnowledgeDetailDialog(
     api: Api,
     workspace: Workspace,
     doc: KnowledgeDoc,
+    categories: List<KnowledgeCategory>,
     onClose: () -> Unit,
     onChanged: () -> Unit,
+    onCategoriesChanged: () -> Unit,
     onFail: (Throwable) -> Unit,
     onEdit: (EditRequest) -> Unit,
 ) {
     val scope = rememberCoroutineScope()
     var action by remember { mutableStateOf(doc.status) }
+    var version by remember { mutableStateOf(doc.version) }
+    var categoryId by remember { mutableStateOf(doc.category?.id) }
+    var tags by remember { mutableStateOf(doc.tags.joinToString(" ") { it.name }) }
+    var savingMeta by remember { mutableStateOf(false) }
+    var metaNotice by remember { mutableStateOf<String?>(null) }
     val actions = when (action) {
         "draft" -> listOf("submit_review" to "提交审议", "publish" to "发布", "archive" to "归档")
         "in_review" -> listOf("withdraw" to "撤回审议", "publish" to "发布", "archive" to "归档")
@@ -292,15 +488,61 @@ private fun KnowledgeDetailDialog(
         },
         text = {
             Column(
-                Modifier.heightIn(max = 420.dp).verticalScroll(rememberScrollState()),
+                Modifier.heightIn(max = 460.dp).verticalScroll(rememberScrollState()),
             ) {
                 Text(sourceLine(doc), style = MaterialTheme.typography.labelSmall, color = InkMuted)
                 Spacer(Modifier.height(10.dp))
                 Text(
-                    doc.bodyMd.ifBlank { "（还没有正文，点「补一句」在 Web 端补齐更快）" },
+                    doc.bodyMd.ifBlank { "（还没有正文，点「编辑正文」补齐）" },
                     style = MaterialTheme.typography.bodySmall,
                     color = InkSoft,
                 )
+
+                // 已发布的内容不能直接改，分类/标签也跟着锁住，避免"发布后又悄悄换归属"
+                if (action != "published") {
+                    Spacer(Modifier.height(14.dp))
+                    SectionLabel("分类")
+                    Row(
+                        modifier = Modifier.horizontalScroll(rememberScrollState()),
+                        horizontalArrangement = Arrangement.spacedBy(6.dp),
+                    ) {
+                        SurfaceChip(
+                            text = "未分类",
+                            selected = categoryId == null,
+                            onClick = { categoryId = null },
+                        )
+                        categories.forEach { cat ->
+                            SurfaceChip(
+                                text = catLabel(cat),
+                                selected = categoryId == cat.id,
+                                onClick = { categoryId = cat.id },
+                            )
+                        }
+                    }
+                    Spacer(Modifier.height(10.dp))
+                    OutlinedTextField(
+                        value = tags,
+                        onValueChange = { tags = it },
+                        modifier = Modifier.fillMaxWidth(),
+                        singleLine = true,
+                        placeholder = { Text("标签，空格或逗号分隔", color = InkMuted) },
+                        shape = RoundedCornerShape(10.dp),
+                        colors = TextFieldDefaults.colors(
+                            focusedContainerColor = Color.White,
+                            unfocusedContainerColor = Color.White,
+                            focusedIndicatorColor = Primary,
+                            unfocusedIndicatorColor = Line,
+                        ),
+                    )
+                    if (metaNotice != null) {
+                        Text(
+                            metaNotice.orEmpty(),
+                            style = MaterialTheme.typography.labelSmall,
+                            color = Primary,
+                            modifier = Modifier.padding(top = 6.dp),
+                        )
+                    }
+                }
             }
         },
         confirmButton = {
@@ -312,7 +554,7 @@ private fun KnowledgeDetailDialog(
                                 itemId = doc.id,
                                 title = doc.title,
                                 body = doc.bodyMd,
-                                version = doc.version,
+                                version = version,
                                 titleEnabled = action == "draft",
                                 knowledge = true,
                             ),
@@ -320,6 +562,34 @@ private fun KnowledgeDetailDialog(
                         onClose()
                     },
                 ) { Text("编辑正文") }
+                if (action != "published") {
+                    TextButton(
+                        enabled = !savingMeta,
+                        onClick = {
+                            scope.launch {
+                                savingMeta = true
+                                runCatching {
+                                    api.updateKnowledge(
+                                        workspace.id,
+                                        doc.id,
+                                        version,
+                                        tags = parseTags(tags),
+                                        categoryId = categoryId,
+                                        clearCategory = categoryId == null,
+                                    )
+                                }
+                                    .onSuccess {
+                                        version = it.version
+                                        metaNotice = "分类与标签已保存"
+                                        onChanged()
+                                        onCategoriesChanged()
+                                    }
+                                    .onFailure { onFail(it) }
+                                savingMeta = false
+                            }
+                        },
+                    ) { Text("保存分类标签") }
+                }
                 actions.forEach { (key, label) ->
                     TextButton(onClick = {
                         scope.launch {
diff --git a/backend/alembic/versions/0007_knowledge_categories.py b/backend/alembic/versions/0007_knowledge_categories.py
new file mode 100644
index 0000000..e79a476
--- /dev/null
+++ b/backend/alembic/versions/0007_knowledge_categories.py
@@ -0,0 +1,79 @@
+"""知识分类（M3 补充）
+
+Revision ID: 0007
+Revises: 0006
+Create Date: 2026-10-30
+
+知识库的基本形态是"备忘录"，不是"任务"：一条知识要有标题、正文、标签，
+还要能归类。这里补上分类树（一级大类 / 二级 / 三级，深不过三）。
+
+两个取舍：
+
+1. **分类独立成表，不塞进 item**。分类是工作区级的字典，一条知识挂一个分类；
+   塞进 item 会让"分类"变成每条知识自己的一份副本，改个名字要改几百行。
+2. **删分类不删知识**。外键是 `ON DELETE SET NULL`：知识退回"未分类"，
+   分类只是入口，不是知识的容器。真要连内容一起删，那是删知识，得单独确认。
+"""
+
+from __future__ import annotations
+
+from collections.abc import Sequence
+
+from alembic import op
+
+revision: str = "0007"
+down_revision: str = "0006"
+branch_labels: Sequence[str] | None = None
+depends_on: Sequence[str] | None = None
+
+CREATE_SQL = """
+CREATE TABLE knowledge_category (
+    id uuid PRIMARY KEY DEFAULT gen_random_uuid(),
+    workspace_id uuid NOT NULL REFERENCES workspace(id) ON DELETE CASCADE,
+    parent_id uuid REFERENCES knowledge_category(id) ON DELETE CASCADE,
+    name varchar(40) NOT NULL,
+    depth integer NOT NULL DEFAULT 1,
+    sort_order integer NOT NULL DEFAULT 0,
+    version integer NOT NULL DEFAULT 1,
+    created_at timestamptz NOT NULL DEFAULT now(),
+    updated_at timestamptz NOT NULL DEFAULT now(),
+    CONSTRAINT ck_kcat_depth CHECK (depth BETWEEN 1 AND 3),
+    CONSTRAINT ck_kcat_name CHECK (length(btrim(name)) > 0)
+)
+"""
+
+INDEX_STATEMENTS = (
+    "CREATE INDEX ix_kcat_ws_parent ON knowledge_category (workspace_id, parent_id)",
+    # 同一父级下不许重名。根分类的 parent_id 是 NULL，而 PG 里 NULL 互不相等，
+    # 所以根要单独一条 `WHERE parent_id IS NULL` 的部分索引，否则可以建出两个同名大类。
+    "CREATE UNIQUE INDEX uq_kcat_ws_parent_name ON knowledge_category "
+    "(workspace_id, parent_id, lower(name)) WHERE parent_id IS NOT NULL",
+    "CREATE UNIQUE INDEX uq_kcat_ws_root_name ON knowledge_category "
+    "(workspace_id, lower(name)) WHERE parent_id IS NULL",
+    "COMMENT ON TABLE knowledge_category IS '知识分类树，深不过三'",
+    "ALTER TABLE knowledge_doc ADD COLUMN category_id uuid "
+    "REFERENCES knowledge_category(id) ON DELETE SET NULL",
+    "CREATE INDEX ix_knowledge_ws_category ON knowledge_doc (workspace_id, category_id)",
+)
+
+POLICY_SQL = (
+    "ALTER TABLE knowledge_category ENABLE ROW LEVEL SECURITY",
+    "CREATE POLICY knowledge_category_isolation ON knowledge_category "
+    "USING (workspace_id = app_ws_id()) WITH CHECK (workspace_id = app_ws_id())",
+    "GRANT SELECT, INSERT, UPDATE, DELETE ON knowledge_category TO dadao_app",
+)
+
+
+def upgrade() -> None:
+    op.execute(CREATE_SQL)
+    for statement in INDEX_STATEMENTS:
+        op.execute(statement)
+    for statement in POLICY_SQL:
+        op.execute(statement)
+
+
+def downgrade() -> None:
+    op.execute("DROP INDEX IF EXISTS ix_knowledge_ws_category")
+    op.execute("ALTER TABLE knowledge_doc DROP COLUMN IF EXISTS category_id")
+    op.execute("DROP POLICY IF EXISTS knowledge_category_isolation ON knowledge_category")
+    op.execute("DROP TABLE IF EXISTS knowledge_category")
diff --git a/backend/app/api/knowledge.py b/backend/app/api/knowledge.py
index 04f16f9..e755c26 100644
--- a/backend/app/api/knowledge.py
+++ b/backend/app/api/knowledge.py
@@ -21,15 +21,21 @@ from typing import Annotated, Any
 
 from fastapi import APIRouter, Query
 from pydantic import BaseModel, Field
-from sqlalchemy import Select, and_, or_, select, update
+from sqlalchemy import Select, and_, func, or_, select, update
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from ..audit import record as audit_record
 from ..deps import MemberDep, SessionDep
 from ..domain.knowledge import can_publish_role, sidebar_fields, target_status
 from ..errors import AppError, ErrorCode
-from ..models_knowledge import DOC_TYPES, KNOWLEDGE_STATUSES, KnowledgeDoc
-from ..models_task import Activity, Item
+from ..models_knowledge import (
+    DOC_TYPES,
+    KNOWLEDGE_STATUSES,
+    MAX_CATEGORY_DEPTH,
+    KnowledgeCategory,
+    KnowledgeDoc,
+)
+from ..models_task import Activity, Item, ItemTag, Tag
 from ..schemas import clamp_limit, decode_cursor, encode_cursor, ok
 from ..serializers import item_out, tags_of
 from ..services.knowledge import create_draft_from_source, find_doc_by_source
@@ -47,6 +53,7 @@ class KnowledgeIn(BaseModel):
     doc_type: str = "note"
     source_item_id: uuid.UUID | None = None
     tag_names: list[str] = Field(default_factory=list)
+    category_id: uuid.UUID | None = None
 
 
 class KnowledgePatch(BaseModel):
@@ -55,6 +62,24 @@ class KnowledgePatch(BaseModel):
     summary: str | None = None
     doc_type: str | None = None
     tag_names: list[str] | None = None
+    category_id: uuid.UUID | None = None
+    # 单独一个开关：`category_id=None` 既可能表示"没改"，也可能表示"清空分类"，
+    # 靠 pydantic 的未传/传 null 区分太隐晦，不如显式给一个。
+    clear_category: bool = False
+    version: int
+
+
+class CategoryIn(BaseModel):
+    name: str = Field(min_length=1, max_length=40)
+    parent_id: uuid.UUID | None = None
+    sort_order: int = 0
+
+
+class CategoryPatch(BaseModel):
+    name: str | None = Field(default=None, min_length=1, max_length=40)
+    parent_id: uuid.UUID | None = None
+    move: bool = False
+    sort_order: int | None = None
     version: int
 
 
@@ -112,6 +137,7 @@ def _doc_out(doc: KnowledgeDoc) -> dict[str, Any]:
         "status_hint": doc.status_hint,
         "source_kind": doc.source_kind,
         "source_item_id": str(doc.source_item_id) if doc.source_item_id else None,
+        "category_id": str(doc.category_id) if doc.category_id else None,
         "generated_by": doc.generated_by,
         "published_at": doc.published_at,
         "archived_at": doc.archived_at,
@@ -120,12 +146,96 @@ def _doc_out(doc: KnowledgeDoc) -> dict[str, Any]:
     }
 
 
+# ── 分类 ────────────────────────────────────────────────────────────────
+async def _categories(
+    session: AsyncSession, ws_id: uuid.UUID
+) -> dict[uuid.UUID, KnowledgeCategory]:
+    """一次把分类全捞出来。分类是工作区级的小字典（几十条），比按需查祖先便宜。"""
+    rows = (
+        await session.execute(
+            select(KnowledgeCategory).where(KnowledgeCategory.workspace_id == ws_id)
+        )
+    ).scalars()
+    return {row.id: row for row in rows}
+
+
+def _category_payload(
+    cat: KnowledgeCategory, by_id: dict[uuid.UUID, KnowledgeCategory]
+) -> dict[str, Any]:
+    """分类带上完整路径：`研发 / 部署 / 回滚`。客户端不用自己去拼。"""
+    names: list[str] = []
+    node: KnowledgeCategory | None = cat
+    while node is not None and len(names) < MAX_CATEGORY_DEPTH:
+        names.append(node.name)
+        node = by_id.get(node.parent_id) if node.parent_id else None
+    names.reverse()
+    return {
+        "id": str(cat.id),
+        "parent_id": str(cat.parent_id) if cat.parent_id else None,
+        "name": cat.name,
+        "depth": cat.depth,
+        "sort_order": cat.sort_order,
+        "version": cat.version,
+        "path": names,
+        "full_path": " / ".join(names),
+    }
+
+
+def _subtree_ids(root_id: uuid.UUID, by_id: dict[uuid.UUID, KnowledgeCategory]) -> list[uuid.UUID]:
+    children: dict[uuid.UUID, list[uuid.UUID]] = {}
+    for cat in by_id.values():
+        if cat.parent_id:
+            children.setdefault(cat.parent_id, []).append(cat.id)
+    out = [root_id]
+    stack = [root_id]
+    while stack:
+        for child in children.get(stack.pop(), []):
+            out.append(child)
+            stack.append(child)
+    return out
+
+
+async def _resolve_category(
+    session: AsyncSession, ws_id: uuid.UUID, category_id: uuid.UUID | None
+) -> KnowledgeCategory | None:
+    if category_id is None:
+        return None
+    cat = await session.get(KnowledgeCategory, category_id)
+    if cat is None or cat.workspace_id != ws_id:
+        raise AppError(ErrorCode.KNOWLEDGE_CATEGORY_NOT_FOUND, "这个分类不存在")
+    return cat
+
+
+async def _category_name_taken(
+    session: AsyncSession,
+    ws_id: uuid.UUID,
+    parent_id: uuid.UUID | None,
+    name: str,
+    exclude: uuid.UUID | None = None,
+) -> bool:
+    stmt = select(KnowledgeCategory.id).where(
+        KnowledgeCategory.workspace_id == ws_id,
+        func.lower(KnowledgeCategory.name) == name.strip().lower(),
+    )
+    stmt = (
+        stmt.where(KnowledgeCategory.parent_id.is_(None))
+        if parent_id is None
+        else stmt.where(KnowledgeCategory.parent_id == parent_id)
+    )
+    if exclude is not None:
+        stmt = stmt.where(KnowledgeCategory.id != exclude)
+    return (await session.execute(stmt)).first() is not None
+
+
 async def _knowledge_out(
     session: AsyncSession, ws_id: uuid.UUID, item: Item, doc: KnowledgeDoc
 ) -> dict[str, Any]:
     tags = (await tags_of(session, ws_id, [item.id])).get(item.id, [])
     data = item_out(item, tags)
     data["knowledge"] = _doc_out(doc)
+    by_id = await _categories(session, ws_id)
+    cat = by_id.get(doc.category_id) if doc.category_id else None
+    data["category"] = _category_payload(cat, by_id) if cat else None
     data["source"] = await _source_out(session, ws_id, doc.source_item_id)
     data["attachments"] = await list_for_item(session, ws_id, item.id)
     data["attachment_count"] = len(data["attachments"])
@@ -148,6 +258,9 @@ async def list_knowledge(
     status: Annotated[list[str] | None, Query()] = None,
     doc_type: Annotated[str | None, Query()] = None,
     source_item_id: Annotated[uuid.UUID | None, Query()] = None,
+    category_id: Annotated[uuid.UUID | None, Query(description="含子分类")] = None,
+    uncategorized: Annotated[bool, Query(description="只看未分类")] = False,
+    tag: Annotated[str | None, Query(max_length=32)] = None,
     q: Annotated[str | None, Query(max_length=100)] = None,
     limit: Annotated[int, Query(ge=1, le=100, description="每页条数")] = 30,
     cursor: Annotated[str | None, Query(description="上一页返回的 next_cursor")] = None,
@@ -165,6 +278,21 @@ async def list_knowledge(
         stmt = stmt.where(KnowledgeDoc.doc_type == doc_type)
     if source_item_id:
         stmt = stmt.where(KnowledgeDoc.source_item_id == source_item_id)
+    by_id: dict[uuid.UUID, KnowledgeCategory] = {}
+    if uncategorized:
+        stmt = stmt.where(KnowledgeDoc.category_id.is_(None))
+    elif category_id is not None:
+        by_id = await _categories(session, ws_id)
+        cat = by_id.get(category_id)
+        if cat is None:
+            raise AppError(ErrorCode.KNOWLEDGE_CATEGORY_NOT_FOUND, "这个分类不存在")
+        stmt = stmt.where(KnowledgeDoc.category_id.in_(_subtree_ids(category_id, by_id)))
+    if tag:
+        stmt = (
+            stmt.join(ItemTag, ItemTag.item_id == Item.id)
+            .join(Tag, Tag.id == ItemTag.tag_id)
+            .where(Tag.workspace_id == ws_id, func.lower(Tag.name) == tag.strip().lower())
+        )
     if q:
         like = f"%{q.strip()}%"
         stmt = stmt.where(
@@ -188,12 +316,16 @@ async def list_knowledge(
     has_more = len(rows) > limit
     rows = rows[:limit]
     tag_map = await tags_of(session, ws_id, [it.id for it, _ in rows])
+    if not by_id:
+        by_id = await _categories(session, ws_id)
 
     items = []
     counts = await count_for_items(session, ws_id, [it.id for it, _ in rows])
     for item, doc in rows:
         data = item_out(item, tag_map.get(item.id, []))
         data["knowledge"] = _doc_out(doc)
+        cat = by_id.get(doc.category_id) if doc.category_id else None
+        data["category"] = _category_payload(cat, by_id) if cat else None
         data["source"] = await _source_out(session, ws_id, doc.source_item_id)
         data["attachment_count"] = counts.get(str(item.id), 0)
         items.append(data)
@@ -204,6 +336,207 @@ async def list_knowledge(
     return ok({"items": items, "next_cursor": next_cursor, "has_more": has_more})
 
 
+# ── 分类的增删改查 ──────────────────────────────────────────────────────
+# 路由顺序：`/knowledge/categories` 必须排在 `/knowledge/{item_id}` 之前，
+# 否则 "categories" 会被当成 uuid 解析，直接 422。
+@router.get("/knowledge/categories", summary="知识分类")
+async def list_categories(ctx: MemberDep, session: SessionDep) -> dict:
+    by_id = await _categories(session, ctx.ws_id)
+    counts = dict(
+        (
+            await session.execute(
+                select(KnowledgeDoc.category_id, func.count())
+                .join(Item, Item.id == KnowledgeDoc.item_id)
+                .where(
+                    KnowledgeDoc.workspace_id == ctx.ws_id,
+                    KnowledgeDoc.category_id.is_not(None),
+                    KnowledgeDoc.status_hint != "archived",
+                    Item.deleted_at.is_(None),
+                )
+                .group_by(KnowledgeDoc.category_id)
+            )
+        ).all()
+    )
+    items = []
+    for cat in sorted(by_id.values(), key=lambda c: (c.depth, c.sort_order, c.name)):
+        data = _category_payload(cat, by_id)
+        data["doc_count"] = counts.get(cat.id, 0)
+        items.append(data)
+    return ok({"items": items, "max_depth": MAX_CATEGORY_DEPTH})
+
+
+@router.post("/knowledge/categories", summary="新建分类")
+async def create_category(body: CategoryIn, ctx: MemberDep, session: SessionDep) -> dict:
+    ws_id = ctx.ws_id
+    depth = 1
+    if body.parent_id is not None:
+        parent = await _resolve_category(session, ws_id, body.parent_id)
+        depth = parent.depth + 1
+        if depth > MAX_CATEGORY_DEPTH:
+            raise AppError(
+                ErrorCode.KNOWLEDGE_CATEGORY_DEPTH,
+                f"分类最多 {MAX_CATEGORY_DEPTH} 级，「{parent.name}」下面不能再建了",
+                details={"parent_depth": parent.depth},
+            )
+    name = body.name.strip()
+    if await _category_name_taken(session, ws_id, body.parent_id, name):
+        raise AppError(ErrorCode.KNOWLEDGE_CATEGORY_CONFLICT, "同一层已经有同名的分类")
+    cat = KnowledgeCategory(
+        workspace_id=ws_id,
+        parent_id=body.parent_id,
+        name=name,
+        depth=depth,
+        sort_order=body.sort_order,
+    )
+    session.add(cat)
+    await session.flush()
+    await audit_record(
+        session,
+        workspace_id=ws_id,
+        actor_user_id=ctx.user.id,
+        action="knowledge.category.create",
+        target_type="knowledge_category",
+        target_id=str(cat.id),
+    )
+    by_id = await _categories(session, ws_id)
+    return ok(_category_payload(cat, by_id))
+
+
+@router.patch("/knowledge/categories/{category_id}", summary="改名或移动分类")
+async def patch_category(
+    category_id: uuid.UUID, body: CategoryPatch, ctx: MemberDep, session: SessionDep
+) -> dict:
+    ws_id = ctx.ws_id
+    cat = await session.get(KnowledgeCategory, category_id)
+    if cat is None or cat.workspace_id != ws_id:
+        raise AppError(ErrorCode.KNOWLEDGE_CATEGORY_NOT_FOUND, "这个分类不存在")
+    by_id = await _categories(session, ws_id)
+    now = datetime.now(timezone.utc)
+
+    new_parent_id = cat.parent_id
+    new_depth = cat.depth
+    shift = 0
+    subtree: list[uuid.UUID] = []
+    if body.move:
+        new_parent_id = body.parent_id
+        if new_parent_id is not None and new_parent_id not in by_id:
+            raise AppError(ErrorCode.KNOWLEDGE_CATEGORY_NOT_FOUND, "这个分类不存在")
+        if new_parent_id == category_id:
+            raise AppError(ErrorCode.KNOWLEDGE_CATEGORY_DEPTH, "不能把分类挂到自己下面")
+        subtree = _subtree_ids(category_id, by_id)
+        if new_parent_id is not None and new_parent_id in subtree:
+            raise AppError(ErrorCode.KNOWLEDGE_CATEGORY_DEPTH, "不能把分类移到它自己的子分类下")
+        new_depth = by_id[new_parent_id].depth + 1 if new_parent_id else 1
+        deepest = max(by_id[cid].depth for cid in subtree)
+        shift = new_depth - cat.depth
+        if deepest + shift > MAX_CATEGORY_DEPTH:
+            raise AppError(
+                ErrorCode.KNOWLEDGE_CATEGORY_DEPTH,
+                f"移动后子树最深到第 {deepest + shift} 级，超过 {MAX_CATEGORY_DEPTH} 级",
+                details={"deepest_after_move": deepest + shift},
+            )
+
+    name = body.name.strip() if body.name is not None else cat.name
+    if name != cat.name and await _category_name_taken(
+        session, ws_id, new_parent_id, name, exclude=category_id
+    ):
+        raise AppError(ErrorCode.KNOWLEDGE_CATEGORY_CONFLICT, "同一层已经有同名的分类")
+
+    values: dict[str, Any] = {"name": name, "updated_at": now}
+    if body.move:
+        values.update(parent_id=new_parent_id, depth=new_depth)
+    if body.sort_order is not None:
+        values["sort_order"] = body.sort_order
+
+    result = await session.execute(
+        update(KnowledgeCategory)
+        .where(
+            KnowledgeCategory.id == category_id,
+            KnowledgeCategory.workspace_id == ws_id,
+            KnowledgeCategory.version == body.version,
+        )
+        .values(version=KnowledgeCategory.version + 1, **values)
+    )
+    if result.rowcount == 0:
+        await session.refresh(cat)
+        raise AppError(
+            ErrorCode.VERSION_CONFLICT,
+            "这个分类刚被改过",
+            details={"current_version": cat.version},
+        )
+
+    # 子树跟着整体升降；只改被移动的那棵子树以外的行会留下 depth 不一致
+    if body.move and shift:
+        for cid in subtree:
+            if cid == category_id:
+                continue
+            await session.execute(
+                update(KnowledgeCategory)
+                .where(KnowledgeCategory.id == cid, KnowledgeCategory.workspace_id == ws_id)
+                .values(
+                    depth=KnowledgeCategory.depth + shift,
+                    updated_at=now,
+                    version=KnowledgeCategory.version + 1,
+                )
+            )
+    await session.flush()
+    fresh = await _categories(session, ws_id)
+    return ok(_category_payload(fresh[category_id], fresh))
+
+
+@router.delete("/knowledge/categories/{category_id}", summary="删除分类")
+async def delete_category(
+    category_id: uuid.UUID,
+    ctx: MemberDep,
+    session: SessionDep,
+    force: Annotated[bool, Query(description="真删：里面的知识变成未分类")] = False,
+) -> dict:
+    ws_id = ctx.ws_id
+    cat = await session.get(KnowledgeCategory, category_id)
+    if cat is None or cat.workspace_id != ws_id:
+        raise AppError(ErrorCode.KNOWLEDGE_CATEGORY_NOT_FOUND, "这个分类不存在")
+    children = (
+        await session.execute(
+            select(func.count())
+            .select_from(KnowledgeCategory)
+            .where(
+                KnowledgeCategory.workspace_id == ws_id,
+                KnowledgeCategory.parent_id == category_id,
+            )
+        )
+    ).scalar_one()
+    if children:
+        raise AppError(
+            ErrorCode.KNOWLEDGE_CATEGORY_CONFLICT,
+            f"「{cat.name}」下面还有 {children} 个子分类，先把它们移走或删掉",
+            details={"children": children},
+        )
+    docs = (
+        await session.execute(
+            select(func.count())
+            .select_from(KnowledgeDoc)
+            .where(KnowledgeDoc.workspace_id == ws_id, KnowledgeDoc.category_id == category_id)
+        )
+    ).scalar_one()
+    if docs and not force:
+        raise AppError(
+            ErrorCode.KNOWLEDGE_CATEGORY_CONFLICT,
+            f"「{cat.name}」里还有 {docs} 条知识，先移走，或者带 force 删成未分类",
+            details={"doc_count": docs},
+        )
+    await session.delete(cat)
+    await audit_record(
+        session,
+        workspace_id=ws_id,
+        actor_user_id=ctx.user.id,
+        action="knowledge.category.delete",
+        target_type="knowledge_category",
+        target_id=str(category_id),
+        payload={"orphaned_docs": docs},
+    )
+    return ok({"deleted": str(category_id), "uncategorized_docs": docs})
+
+
 # 注意路由顺序：`/knowledge/search` 必须排在 `/knowledge/{item_id}` 之前，
 # 否则 "search" 会被当成 uuid 解析，返回 422。
 @router.get("/knowledge/search", summary="检索已发布知识")
@@ -257,6 +590,7 @@ async def create_knowledge(body: KnowledgeIn, ctx: MemberDep, session: SessionDe
                 ErrorCode.KNOWLEDGE_SOURCE_REQUIRED,
                 "来源必须是与本知识同一工作区的任务或工单",
             )
+    category = await _resolve_category(session, ws_id, body.category_id)
 
     item = Item(
         workspace_id=ws_id,
@@ -278,6 +612,7 @@ async def create_knowledge(body: KnowledgeIn, ctx: MemberDep, session: SessionDe
         doc_type=body.doc_type,
         status_hint="draft",
         summary=body.summary,
+        category_id=category.id if category else None,
         generated_by="human",
     )
     session.add(doc)
@@ -320,7 +655,10 @@ async def patch_knowledge(
     if body.doc_type is not None:
         values["doc_type"] = body.doc_type
 
-    if values:
+    # 分类/标签也改的是这条知识的"样子"，所以同样要推进 version：
+    # 否则只改了标签的知识，下一次保存还会拿着旧 version 撞 4009。
+    meta_changed = body.clear_category or body.category_id is not None or body.tag_names is not None
+    if values or meta_changed:
         values["updated_at"] = datetime.now(timezone.utc)
         result = await session.execute(
             update(Item)
@@ -344,6 +682,11 @@ async def patch_knowledge(
         doc.doc_type = body.doc_type
     if body.summary is not None:
         doc.summary = body.summary
+    if body.clear_category:
+        doc.category_id = None
+    elif body.category_id is not None:
+        category = await _resolve_category(session, ws_id, body.category_id)
+        doc.category_id = category.id if category else None
     if body.tag_names is not None:
         await _set_tags_for(session, ws_id, item, body.tag_names)
     await session.flush()
diff --git a/backend/app/errors.py b/backend/app/errors.py
index c67a9ec..0f9b2c3 100644
--- a/backend/app/errors.py
+++ b/backend/app/errors.py
@@ -56,6 +56,9 @@ class ErrorCode(IntEnum):
     KNOWLEDGE_STATUS_INVALID = 7003
     KNOWLEDGE_FORBIDDEN = 7004
     KNOWLEDGE_SOURCE_REQUIRED = 7005
+    KNOWLEDGE_CATEGORY_NOT_FOUND = 7006
+    KNOWLEDGE_CATEGORY_DEPTH = 7007
+    KNOWLEDGE_CATEGORY_CONFLICT = 7008
 
     # 8xxx 附件
     ATTACHMENT_NOT_FOUND = 8001
@@ -101,6 +104,9 @@ _HTTP_STATUS: dict[ErrorCode, int] = {
     ErrorCode.KNOWLEDGE_STATUS_INVALID: 409,
     ErrorCode.KNOWLEDGE_FORBIDDEN: 403,
     ErrorCode.KNOWLEDGE_SOURCE_REQUIRED: 409,
+    ErrorCode.KNOWLEDGE_CATEGORY_NOT_FOUND: 404,
+    ErrorCode.KNOWLEDGE_CATEGORY_DEPTH: 422,
+    ErrorCode.KNOWLEDGE_CATEGORY_CONFLICT: 409,
     ErrorCode.ATTACHMENT_NOT_FOUND: 404,
     ErrorCode.ATTACHMENT_TOO_LARGE: 413,
     ErrorCode.ATTACHMENT_FORBIDDEN: 403,
diff --git a/backend/app/models_knowledge.py b/backend/app/models_knowledge.py
index 9b54dda..3771ef9 100644
--- a/backend/app/models_knowledge.py
+++ b/backend/app/models_knowledge.py
@@ -39,6 +39,36 @@ DOC_TYPES: tuple[str, ...] = ("note", "howto", "faq", "postmortem", "decision")
 SOURCE_KINDS: tuple[str, ...] = ("manual", "task", "ticket")
 GENERATED_BY: tuple[str, ...] = ("human", "rule")
 
+# 分类树最多三级。再深就不是"归档"而是"迷宫"了：找东西的人记不住第四层叫什么。
+MAX_CATEGORY_DEPTH = 3
+
+
+class KnowledgeCategory(Base, Timestamps):
+    """知识分类：一级大类 → 二级 → 三级，深不过三。
+
+    `depth` 是冗余列，但值得：每次筛选、移动子树都要判断层级，存下来就不用
+    递归数祖先。写入时由 API 计算，读到不一致的行属于数据事故。
+    """
+
+    __tablename__ = "knowledge_category"
+    __table_args__ = (
+        Index("ix_kcat_ws_parent", "workspace_id", "parent_id"),
+        CheckConstraint("depth BETWEEN 1 AND 3", name="ck_kcat_depth"),
+        CheckConstraint("length(btrim(name)) > 0", name="ck_kcat_name"),
+        {"comment": "知识分类树，深不过三"},
+    )
+
+    id: Mapped[uuid.UUID] = mapped_column(PgUUID(as_uuid=True), primary_key=True, default=new_uuid)
+    workspace_id: Mapped[uuid.UUID] = mapped_column(
+        PgUUID(as_uuid=True), ForeignKey("workspace.id", ondelete="CASCADE"), nullable=False
+    )
+    parent_id: Mapped[uuid.UUID | None] = mapped_column(
+        PgUUID(as_uuid=True), ForeignKey("knowledge_category.id", ondelete="CASCADE")
+    )
+    name: Mapped[str] = mapped_column(String(40), nullable=False)
+    depth: Mapped[int] = mapped_column(nullable=False, default=1)
+    sort_order: Mapped[int] = mapped_column(nullable=False, default=0)
+
 
 class KnowledgeDoc(Base, Timestamps):
     """知识的附加信息，与 item 一比一。"""
@@ -47,6 +77,7 @@ class KnowledgeDoc(Base, Timestamps):
     __table_args__ = (
         Index("ix_knowledge_ws_status", "workspace_id", "status_hint"),
         Index("ix_knowledge_ws_source", "workspace_id", "source_item_id"),
+        Index("ix_knowledge_ws_category", "workspace_id", "category_id"),
         CheckConstraint(
             "source_kind = 'manual' OR source_item_id IS NOT NULL",
             name="ck_knowledge_source_required",
@@ -72,6 +103,10 @@ class KnowledgeDoc(Base, Timestamps):
     doc_type: Mapped[str] = mapped_column(String(16), nullable=False, default="note")
     # 冗余一份状态：列表页要按知识自己的口径筛，不想每次都回 item 表
     status_hint: Mapped[str] = mapped_column(String(16), nullable=False, default="draft")
+    # 分类可以为空（"未分类"）；分类被删时知识不跟着消失，只是回到未分类
+    category_id: Mapped[uuid.UUID | None] = mapped_column(
+        PgUUID(as_uuid=True), ForeignKey("knowledge_category.id", ondelete="SET NULL")
+    )
     summary: Mapped[str] = mapped_column(Text, nullable=False, default="")
     generated_by: Mapped[str] = mapped_column(String(16), nullable=False, default="human")
     published_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True))
@@ -109,4 +144,4 @@ class Chunk(Base):
     embed_model: Mapped[str | None] = mapped_column(String(64))
 
 
-KNOWLEDGE_TENANT_TABLES: tuple[str, ...] = ("knowledge_doc", "chunk")
+KNOWLEDGE_TENANT_TABLES: tuple[str, ...] = ("knowledge_category", "knowledge_doc", "chunk")
diff --git a/backend/tests/test_knowledge_categories.py b/backend/tests/test_knowledge_categories.py
new file mode 100644
index 0000000..c3f0bf8
--- /dev/null
+++ b/backend/tests/test_knowledge_categories.py
@@ -0,0 +1,280 @@
+"""知识库的"备忘录"形态：分类树、正文、标签、筛选。
+
+知识最容易做坏的地方，是把它做成"只填标题的任务"——那样的库三个月后没人会打开。
+所以这里断言的是：一条知识能装下正文和标签、能被归到三级分类里、能按分类和标签找回来。
+
+三条边界单独盯着：
+
+1. **三级到底**。第四级不是"更细"，是"找不到"；越界必须当场拒绝（7007）。
+2. **移动会带着子树一起动**。把一棵三层树挪到第二层下面，结果会是第五层，
+   这种操作要么重算层级、要么拒绝——这里选择拒绝，因为静默改层级同样会让人找不到。
+3. **删分类不删知识**。有内容时必须显式 `force`，否则容易点一下就把别人的整理工作打散。
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+import pytest
+from httpx import AsyncClient
+
+from .conftest import create_workspace, login, unwrap
+
+V1 = "/api/v1"
+
+
+def _code(resp: Any) -> int:
+    return int(resp.json().get("code", 0))
+
+
+async def _ws(client: AsyncClient) -> tuple[dict[str, Any], str]:
+    user = await login(client)
+    ws = await create_workspace(client, user, "知识库")
+    return user, ws["id"]
+
+
+async def _category(
+    client: AsyncClient, user: dict[str, Any], ws_id: str, name: str, parent_id: str | None = None
+) -> dict[str, Any]:
+    return unwrap(
+        await client.post(
+            f"{V1}/workspaces/{ws_id}/knowledge/categories",
+            json={"name": name, "parent_id": parent_id},
+            headers=user["headers"],
+        )
+    )
+
+
+async def _note(
+    client: AsyncClient,
+    user: dict[str, Any],
+    ws_id: str,
+    title: str,
+    *,
+    body: str = "",
+    tags: list[str] | None = None,
+    category_id: str | None = None,
+) -> dict[str, Any]:
+    return unwrap(
+        await client.post(
+            f"{V1}/workspaces/{ws_id}/knowledge",
+            json={
+                "title": title,
+                "body_md": body,
+                "doc_type": "note",
+                "tag_names": tags or [],
+                "category_id": category_id,
+            },
+            headers=user["headers"],
+        )
+    )
+
+
+async def _list(
+    client: AsyncClient, user: dict[str, Any], ws_id: str, **params: Any
+) -> list[dict[str, Any]]:
+    return unwrap(
+        await client.get(
+            f"{V1}/workspaces/{ws_id}/knowledge", params=params, headers=user["headers"]
+        )
+    )["items"]
+
+
+@pytest.mark.asyncio
+async def test_note_keeps_body_tags_and_category_path(client: AsyncClient) -> None:
+    user, ws_id = await _ws(client)
+    root = await _category(client, user, ws_id, "研发")
+    child = await _category(client, user, ws_id, "部署", root["id"])
+    leaf = await _category(client, user, ws_id, "回滚", child["id"])
+    assert leaf["depth"] == 3
+    assert leaf["full_path"] == "研发 / 部署 / 回滚"
+
+    doc = await _note(
+        client,
+        user,
+        ws_id,
+        "回滚前先停掉灰度",
+        body="# 步骤\n\n1. 停灰度\n2. 回滚镜像\n",
+        tags=["发布", "事故"],
+        category_id=leaf["id"],
+    )
+    assert doc["category"]["id"] == leaf["id"]
+    assert doc["category"]["full_path"] == "研发 / 部署 / 回滚"
+    assert {t["name"] for t in doc["tags"]} == {"发布", "事故"}
+
+    detail = unwrap(
+        await client.get(f"{V1}/workspaces/{ws_id}/knowledge/{doc['id']}", headers=user["headers"])
+    )
+    assert "停灰度" in detail["body_md"]
+    assert detail["category"]["full_path"] == "研发 / 部署 / 回滚"
+
+
+@pytest.mark.asyncio
+async def test_category_depth_stops_at_three(client: AsyncClient) -> None:
+    user, ws_id = await _ws(client)
+    l1 = await _category(client, user, ws_id, "一级")
+    l2 = await _category(client, user, ws_id, "二级", l1["id"])
+    l3 = await _category(client, user, ws_id, "三级", l2["id"])
+    resp = await client.post(
+        f"{V1}/workspaces/{ws_id}/knowledge/categories",
+        json={"name": "四级", "parent_id": l3["id"]},
+        headers=user["headers"],
+    )
+    assert resp.status_code == 422, resp.text
+    assert _code(resp) == 7007
+
+
+@pytest.mark.asyncio
+async def test_move_cannot_exceed_depth_or_loop(client: AsyncClient) -> None:
+    user, ws_id = await _ws(client)
+    a = await _category(client, user, ws_id, "A")
+    b = await _category(client, user, ws_id, "B", a["id"])
+    c = await _category(client, user, ws_id, "C", b["id"])
+    other = await _category(client, user, ws_id, "X")
+
+    # 把 A（下面还有 B、C）移到 C 下面：自己是自己的祖先
+    resp = await client.patch(
+        f"{V1}/workspaces/{ws_id}/knowledge/categories/{a['id']}",
+        json={"move": True, "parent_id": c["id"], "version": a["version"]},
+        headers=user["headers"],
+    )
+    assert resp.status_code in (409, 422), resp.text
+    assert _code(resp) == 7007
+
+    # 把 A 移到 X 下面：A 现在是一级，B、C 跟着下沉，C 会到第四级 -> 拒绝
+    resp = await client.patch(
+        f"{V1}/workspaces/{ws_id}/knowledge/categories/{a['id']}",
+        json={"move": True, "parent_id": other["id"], "version": a["version"]},
+        headers=user["headers"],
+    )
+    assert _code(resp) == 7007
+    del c, b
+
+
+@pytest.mark.asyncio
+async def test_rename_conflict_and_move_to_root(client: AsyncClient) -> None:
+    user, ws_id = await _ws(client)
+    a = await _category(client, user, ws_id, "研发")
+    b = await _category(client, user, ws_id, "市场")
+    dup = await client.post(
+        f"{V1}/workspaces/{ws_id}/knowledge/categories",
+        json={"name": "研发"},
+        headers=user["headers"],
+    )
+    assert dup.status_code == 409, dup.text
+    assert _code(dup) == 7008
+
+    child = await _category(client, user, ws_id, "部署", a["id"])
+    moved = unwrap(
+        await client.patch(
+            f"{V1}/workspaces/{ws_id}/knowledge/categories/{child['id']}",
+            json={"move": True, "parent_id": None, "version": child["version"]},
+            headers=user["headers"],
+        )
+    )
+    assert moved["parent_id"] is None
+    assert moved["depth"] == 1
+    assert moved["full_path"] == "部署"
+    del b
+
+
+@pytest.mark.asyncio
+async def test_list_filters_by_category_subtree_tag_and_search(client: AsyncClient) -> None:
+    user, ws_id = await _ws(client)
+    root = await _category(client, user, ws_id, "研发")
+    sub = await _category(client, user, ws_id, "部署", root["id"])
+    other = await _category(client, user, ws_id, "市场")
+
+    deep = await _note(
+        client,
+        user,
+        ws_id,
+        "灰度发布流程",
+        body="先停灰度再回滚",
+        tags=["发布"],
+        category_id=sub["id"],
+    )
+    await _note(
+        client, user, ws_id, "季度预算", body="市场预算表", tags=["财务"], category_id=other["id"]
+    )
+    loose = await _note(client, user, ws_id, "散记", body="还没归类", tags=["草稿"])
+
+    by_category = await _list(client, user, ws_id, category_id=root["id"])
+    assert {d["id"] for d in by_category} == {deep["id"]}
+    by_none = await _list(client, user, ws_id, uncategorized="true")
+    assert {d["id"] for d in by_none} == {loose["id"]}
+    assert {d["id"] for d in await _list(client, user, ws_id, tag="发布")} == {deep["id"]}
+    assert {d["id"] for d in await _list(client, user, ws_id, q="回滚")} == {deep["id"]}
+
+
+@pytest.mark.asyncio
+async def test_delete_category_needs_force_when_docs_exist(client: AsyncClient) -> None:
+    user, ws_id = await _ws(client)
+    cat = await _category(client, user, ws_id, "待清理")
+    doc = await _note(client, user, ws_id, "有主的东西", category_id=cat["id"])
+
+    blocked = await client.delete(
+        f"{V1}/workspaces/{ws_id}/knowledge/categories/{cat['id']}", headers=user["headers"]
+    )
+    assert blocked.status_code == 409, blocked.text
+    assert _code(blocked) == 7008
+
+    forced = unwrap(
+        await client.delete(
+            f"{V1}/workspaces/{ws_id}/knowledge/categories/{cat['id']}?force=true",
+            headers=user["headers"],
+        )
+    )
+    assert forced["uncategorized_docs"] == 1
+    detail = unwrap(
+        await client.get(f"{V1}/workspaces/{ws_id}/knowledge/{doc['id']}", headers=user["headers"])
+    )
+    assert detail["category"] is None
+
+
+@pytest.mark.asyncio
+async def test_category_is_tenant_scoped(client: AsyncClient) -> None:
+    owner, ws_id = await _ws(client)
+    intruder = await login(client)
+    other_ws = await create_workspace(client, intruder, "别人的工作区")
+    foreign = await _category(client, intruder, other_ws["id"], "他们的分类")
+
+    listed = unwrap(
+        await client.get(f"{V1}/workspaces/{ws_id}/knowledge/categories", headers=owner["headers"])
+    )
+    assert listed["items"] == []
+
+    # 用别的工作区的分类 id 建知识：应被当作"不存在"
+    resp = await client.post(
+        f"{V1}/workspaces/{ws_id}/knowledge",
+        json={"title": "越界", "category_id": foreign["id"]},
+        headers=owner["headers"],
+    )
+    assert resp.status_code == 404, resp.text
+    assert _code(resp) == 7006
+
+
+@pytest.mark.asyncio
+async def test_patch_knowledge_moves_and_clears_category(client: AsyncClient) -> None:
+    user, ws_id = await _ws(client)
+    cat = await _category(client, user, ws_id, "研发")
+    doc = await _note(client, user, ws_id, "一篇知识", category_id=cat["id"])
+
+    moved = unwrap(
+        await client.patch(
+            f"{V1}/workspaces/{ws_id}/knowledge/{doc['id']}",
+            json={"category_id": cat["id"], "tag_names": ["运维"], "version": doc["version"]},
+            headers=user["headers"],
+        )
+    )
+    assert moved["category"]["name"] == "研发"
+    assert {t["name"] for t in moved["tags"]} == {"运维"}
+
+    cleared = unwrap(
+        await client.patch(
+            f"{V1}/workspaces/{ws_id}/knowledge/{doc['id']}",
+            json={"clear_category": True, "version": moved["version"]},
+            headers=user["headers"],
+        )
+    )
+    assert cleared["category"] is None
diff --git a/web/e2e/knowledge-notebook.mjs b/web/e2e/knowledge-notebook.mjs
new file mode 100644
index 0000000..769d94d
--- /dev/null
+++ b/web/e2e/knowledge-notebook.mjs
@@ -0,0 +1,201 @@
+/**
+ * 知识备忘录形态 e2e：分类树 + 新建时一次填全（标题/类型/分类/标签/正文）+ 按分类筛。
+ *
+ * 与 knowledge.mjs 的分工：那个脚本验"沉淀 → 发布"闭环，这个只验"知识是最像备忘录的形态"。
+ * 前面造数据走接口，界面部分点真实按钮。
+ */
+import { chromium } from "playwright-core";
+
+const WEB = process.env.WEB ?? "http://127.0.0.1:5180";
+const API = process.env.API ?? "http://127.0.0.1:8100/api/v1";
+const stamp = String(Date.now()).slice(-7);
+const phone = `137${stamp}0`;
+
+let failures = 0;
+function check(name, ok, extra = "") {
+  console.log(`${ok ? "PASS" : "FAIL"} ${name}${extra ? ` — ${extra}` : ""}`);
+  if (!ok) failures += 1;
+}
+
+async function call(method, path, body, token) {
+  const res = await fetch(`${API}${path}`, {
+    method,
+    headers: {
+      "content-type": "application/json",
+      ...(token ? { authorization: `Bearer ${token}` } : {}),
+      ...(method === "GET" ? {} : { "idempotency-key": `e2e-${Math.random()}` }),
+    },
+    body: body ? JSON.stringify(body) : undefined,
+  });
+  const text = await res.text();
+  const json = text ? JSON.parse(text) : {};
+  if (json.code !== 0) throw new Error(`${method} ${path} -> ${json.code} ${json.message}`);
+  return json.data;
+}
+
+const browser = await chromium.launch({
+  executablePath:
+    process.env.CHROME ??
+    `${process.env.LOCALAPPDATA}\\ms-playwright\\chromium-1223\\chrome-win64\\chrome.exe`,
+});
+const consoleErrors = [];
+const context = await browser.newContext({ viewport: { width: 1280, height: 900 } });
+const page = await context.newPage();
+page.on("console", (m) => {
+  if (m.type() === "error") consoleErrors.push(m.text());
+});
+page.on("response", (r) => {
+  if (r.status() >= 400) consoleErrors.push(`${r.status()} ${r.url()}`);
+});
+
+try {
+  await call("POST", "/auth/sms/send", { phone });
+  const login = await call("POST", "/auth/login", { phone, code: "123456" });
+  const token = login.tokens.access_token;
+  const ws = await call("POST", "/workspaces", { name: `知识备忘 ${stamp}` }, token);
+
+  await page.addInitScript(
+    ([access, refresh]) => {
+      localStorage.setItem("dadao.access", access);
+      localStorage.setItem("dadao.refresh", refresh);
+    },
+    [token, login.tokens.refresh_token],
+  );
+  await page.goto(`${WEB}/w/${ws.id}/knowledge`, { waitUntil: "networkidle" });
+  await page.getByRole("heading", { name: "知识" }).waitFor({ timeout: 10_000 });
+
+  // ① 建两级分类：研发 / 部署
+  await page.getByRole("button", { name: "＋ 新建", exact: true }).click();
+  await page.getByLabel("新分类名").fill("研发");
+  await page.getByRole("button", { name: "创建", exact: true }).click();
+  await page.getByRole("button", { name: /^研发/, exact: false }).first().waitFor();
+  await page.getByRole("button", { name: "＋ 新建", exact: true }).click();
+  await page.getByLabel("新分类名").fill("部署");
+  await page.getByLabel("父分类").selectOption({ label: "研发 下" });
+  await page.getByRole("button", { name: "创建", exact: true }).click();
+  await page.getByRole("button", { name: /^部署/, exact: false }).first().waitFor();
+  check("能在侧栏建出「研发 / 部署」两级分类", true);
+
+  // ② 记一条：一个面板里填完标题/类型/分类/标签/正文
+  await page.getByRole("button", { name: "记一条", exact: true }).click();
+  await page.getByLabel("标题").fill("回滚前先停灰度");
+  await page.getByLabel("类型").selectOption("howto");
+  await page.getByLabel("分类", { exact: true }).selectOption({ label: "研发 / 部署" });
+  await page.getByLabel("标签").fill("发布 事故");
+  await page
+    .getByLabel("正文")
+    .fill("## 步骤\n1. 停掉灰度流量\n2. 回滚镜像到上一个 tag\n3. 验证关键接口");
+  await page.getByRole("button", { name: "保存并继续写", exact: true }).click();
+
+  // 保存后直接打开详情：标题、分类路径、标签都在
+  await page.getByText("回滚前先停灰度", { exact: false }).first().waitFor({ timeout: 10_000 });
+  const drawerText = (await page.textContent("body")) ?? "";
+  check(
+    "新建面板能把分类与标签一起存下来",
+    drawerText.includes("研发 / 部署") && drawerText.includes("发布"),
+  );
+  await page.screenshot({ path: "e2e/artifacts/knowledge-composer-saved.png", fullPage: false });
+
+  // ③ 列表卡片上能看到分类路径与标签（不用点开）
+  await page.getByRole("button", { name: "关闭", exact: true }).click();
+  const card = page.locator("li").filter({ hasText: "回滚前先停灰度" }).first();
+  await card.waitFor({ timeout: 10_000 });
+  const cardText = (await card.textContent()) ?? "";
+  check("列表卡片带分类路径与标签", cardText.includes("研发 / 部署") && cardText.includes("#发布"));
+
+  // ④ 侧栏按分类筛：部署里有，未分类里没有
+  await page.getByRole("button", { name: /^部署/, exact: false }).first().click();
+  await page.waitForTimeout(400);
+  check(
+    "点「部署」能看到归属该分类的知识",
+    await page.getByText("回滚前先停灰度", { exact: false }).first().isVisible(),
+  );
+  await page.getByRole("button", { name: "未分类", exact: true }).click();
+  await page.waitForTimeout(400);
+  const uncategorizedHasCard = await page
+    .getByText("回滚前先停灰度", { exact: false })
+    .first()
+    .isVisible()
+    .catch(() => false);
+  check("「未分类」里不出现已归类的知识", !uncategorizedHasCard);
+  await page.screenshot({ path: "e2e/artifacts/knowledge-category-filter.png", fullPage: false });
+
+  // ⑤ 抽屉里能改标签与分类，改完接口里就是新的
+  await page.getByRole("button", { name: "全部知识", exact: true }).click();
+  // 先等抽屉自己把详情拉回来再填：GET 比手快一步的话，刚填的字会被它覆盖掉
+  await Promise.all([
+    page.waitForResponse(
+      (r) =>
+        r.url().includes("/knowledge/") &&
+        r.request().method() === "GET" &&
+        !r.url().endsWith("/knowledge/categories") &&
+        r.status() === 200,
+    ),
+    page.getByRole("button", { name: "打开", exact: true }).first().click(),
+  ]);
+  const tagInput = page.getByLabel("标签", { exact: true }).last();
+  await tagInput.waitFor({ timeout: 10_000 });
+  // 先等抽屉把自己拉回来的旧标签填上——那一刻之后才没有"迟到的响应"来覆盖输入
+  await page
+    .waitForFunction(
+      () => {
+        const el = document.querySelector('input[aria-label="标签"]');
+        return !!el && el.value.includes("事故");
+      },
+      null,
+      { timeout: 10_000 },
+    )
+    .catch(() => {});
+  // 用真实键盘输入而不是 fill：fill 走原生 setter，React 的受控 input 有时收不到这次变更
+  await tagInput.click();
+  await tagInput.press("Control+A");
+  await page.keyboard.type("发布 回滚", { delay: 20 });
+  check("抽屉里的标签输入框拿到新值", (await tagInput.inputValue()) === "发布 回滚");
+  const [patchResp] = await Promise.all([
+    page.waitForResponse(
+      (r) =>
+        r.url().includes("/knowledge/") &&
+        r.request().method() === "PATCH" &&
+        r.status() === 200,
+    ),
+    page.getByRole("button", { name: "保存", exact: true }).last().click(),
+  ]);
+  check("抽屉里保存标签/分类成功", patchResp.ok());
+
+  const list = await call(
+    "GET",
+    `/workspaces/${ws.id}/knowledge?status=draft&status=in_review`,
+    undefined,
+    token,
+  );
+  const doc = list.items.find((d) => d.title === "回滚前先停灰度");
+  check(
+    "接口里标签已更新、分类是「研发 / 部署」",
+    String((doc?.tags ?? []).map((t) => t.name).join(" ")).includes("回滚") &&
+      doc?.category?.full_path === "研发 / 部署",
+    `tags=${JSON.stringify((doc?.tags ?? []).map((t) => t.name))} category=${doc?.category?.full_path}`,
+  );
+  check("正文按 Markdown 存下来了", String(doc?.body_md ?? "").includes("停掉灰度流量"));
+
+  // ⑥ 分类重名与三级上限：接口层面确认约束还在
+  const dup = await fetch(
+    `${API}/workspaces/${ws.id}/knowledge/categories`,
+    {
+      method: "POST",
+      headers: { "content-type": "application/json", authorization: `Bearer ${token}` },
+      body: JSON.stringify({ name: "部署", parent_id: doc.category.parent_id }),
+    },
+  ).then((r) => r.json());
+  check("同层重名被拒（7008）", dup.code === 7008, `code=${dup.code}`);
+
+  check("浏览器控制台与网络无报错", consoleErrors.length === 0, consoleErrors.slice(0, 3).join(" | "));
+} catch (err) {
+  failures += 1;
+  console.log(`FAIL 脚本异常 — ${err.message}`);
+  await page.screenshot({ path: "e2e/artifacts/knowledge-notebook-failure.png" }).catch(() => {});
+  console.log((await page.textContent("body"))?.slice(0, 600));
+} finally {
+  await browser.close();
+  console.log(failures === 0 ? "\nALL PASS" : `\n${failures} FAILED`);
+  process.exit(failures === 0 ? 0 : 1);
+}
diff --git a/web/src/components/TaskDetail.tsx b/web/src/components/TaskDetail.tsx
index 34b181a..21d8f7b 100644
--- a/web/src/components/TaskDetail.tsx
+++ b/web/src/components/TaskDetail.tsx
@@ -353,7 +353,7 @@ export function TaskDetail({
     <Sheet
       open
       onClose={onClose}
-      width="max-w-2xl"
+      size="xl"
       title={item ? item.title : "打开中…"}
       subtitle={meta}
       footer={
diff --git a/web/src/components/icons.tsx b/web/src/components/icons.tsx
index e020199..dba8378 100644
--- a/web/src/components/icons.tsx
+++ b/web/src/components/icons.tsx
@@ -234,6 +234,19 @@ export const Link2 = (p: IconProps) => (
   </svg>
 );
 
+/** 放大到整屏 / 收回原来的宽度：长文和图片需要有地方放 */
+export const Expand = (p: IconProps) => (
+  <svg {...base(p)}>
+    <path d="M9 4H4v5M15 4h5v5M9 20H4v-5M15 20h5v-5" />
+  </svg>
+);
+
+export const Collapse = (p: IconProps) => (
+  <svg {...base(p)}>
+    <path d="M4 9h5V4M20 9h-5V4M4 15h5v5M20 15h-5v5" />
+  </svg>
+);
+
 export const More = (p: IconProps) => (
   <svg {...base(p)}>
     <circle cx="6" cy="12" r="1.2" fill="currentColor" stroke="none" />
diff --git a/web/src/components/ui.tsx b/web/src/components/ui.tsx
index f8a61f2..63347b8 100644
--- a/web/src/components/ui.tsx
+++ b/web/src/components/ui.tsx
@@ -8,7 +8,17 @@ import {
   useState,
   type ReactNode,
 } from "react";
-import { Check, X } from "./icons";
+import { Check, Collapse, Expand, X } from "./icons";
+
+/**
+ * 抽屉宽度档位。以前的抽屉默认 `max-w-xl`（576px），写长文像在门缝里写字；
+ * 知识、工单这类要贴图的内容统一走 xl，上面还有"展开整屏"。
+ */
+const SHEET_SIZE = {
+  md: "max-w-2xl",
+  lg: "max-w-4xl",
+  xl: "max-w-6xl",
+} as const;
 
 /* ——————————————————————————— 按钮 ——————————————————————————— */
 
@@ -267,7 +277,8 @@ export function Sheet({
   subtitle,
   children,
   footer,
-  width = "max-w-xl",
+  size = "lg",
+  width,
 }: {
   open: boolean;
   onClose: () => void;
@@ -275,8 +286,14 @@ export function Sheet({
   subtitle?: ReactNode;
   children: ReactNode;
   footer?: ReactNode;
+  /** 宽度档位；长文/多图用 xl，右上方还能一键放满整屏 */
+  size?: "md" | "lg" | "xl";
+  /** 兜底：直接给 Tailwind 宽度类 */
   width?: string;
 }) {
+  const [expanded, setExpanded] = useState(false);
+  const sizeClass = width ?? SHEET_SIZE[size];
+
   useEffect(() => {
     if (!open) return;
     const onKey = (e: KeyboardEvent) => {
@@ -298,17 +315,31 @@ export function Sheet({
         role="dialog"
         aria-modal="true"
         aria-label={typeof title === "string" ? title : "详情"}
-        className={`relative flex h-full w-full ${width} animate-slide-in-right flex-col border-l border-line-200 bg-white shadow-pop`}
+        className={`relative flex h-full w-full ${
+          expanded ? "max-w-none" : sizeClass
+        } animate-slide-in-right flex-col border-l border-line-200 bg-white shadow-pop`}
       >
         <header className="flex items-start justify-between gap-3 border-b border-line-100 px-6 py-4">
           <div className="min-w-0">
             <div className="text-base font-semibold text-ink-900">{title}</div>
             {subtitle ? <div className="mt-0.5 text-xs text-ink-400">{subtitle}</div> : null}
           </div>
-          <Button variant="subtle" size="sm" onClick={onClose} aria-label="关闭">
-            <X size={15} />
-            关闭
-          </Button>
+          <div className="flex shrink-0 items-center gap-1.5">
+            <Button
+              variant="subtle"
+              size="sm"
+              onClick={() => setExpanded((v) => !v)}
+              aria-label={expanded ? "收起到侧栏" : "展开整屏"}
+              title={expanded ? "收起到侧栏" : "展开整屏"}
+            >
+              {expanded ? <Collapse size={15} /> : <Expand size={15} />}
+              <span className="hidden sm:inline">{expanded ? "收起" : "展开"}</span>
+            </Button>
+            <Button variant="subtle" size="sm" onClick={onClose} aria-label="关闭">
+              <X size={15} />
+              关闭
+            </Button>
+          </div>
         </header>
         <div className="min-h-0 flex-1 overflow-y-auto px-6 py-5">{children}</div>
         {footer ? (
diff --git a/web/src/lib/types.ts b/web/src/lib/types.ts
index 3fc5eca..6ed7e02 100644
--- a/web/src/lib/types.ts
+++ b/web/src/lib/types.ts
@@ -150,8 +150,25 @@ export interface KnowledgeSource {
   status: string;
 }
 
+export interface KnowledgeCategory {
+  id: string;
+  parent_id: string | null;
+  name: string;
+  depth: number;
+  sort_order: number;
+  version: number;
+  /** 从根到自己的名字链，后端拼好了，前端不用自己爬树 */
+  path: string[];
+  full_path: string;
+}
+
+export interface KnowledgeCategoryNode extends KnowledgeCategory {
+  doc_count: number;
+}
+
 export interface Knowledge extends Item {
   knowledge: KnowledgeInfo;
+  category: KnowledgeCategory | null;
   source: KnowledgeSource | null;
   attachments?: Attachment[];
   attachment_count?: number;
diff --git a/web/src/pages/Knowledge.tsx b/web/src/pages/Knowledge.tsx
index 930ce5c..cbf45c1 100644
--- a/web/src/pages/Knowledge.tsx
+++ b/web/src/pages/Knowledge.tsx
@@ -3,7 +3,7 @@ import { useParams } from "react-router-dom";
 import { AppShell } from "../components/AppShell";
 import { AttachmentPanel } from "../components/AttachmentPanel";
 import { RichTextEditor } from "../components/RichTextEditor";
-import { Book, Link2, Plus, Search, Sparkle } from "../components/icons";
+import { Link2, Plus, Search, Sparkle } from "../components/icons";
 import {
   Button,
   EmptyState,
@@ -14,7 +14,13 @@ import {
   StatusPill,
 } from "../components/ui";
 import { ApiError, api } from "../lib/client";
-import type { Attachment, Knowledge, KnowledgeStatus, SearchHit } from "../lib/types";
+import type {
+  Attachment,
+  Knowledge,
+  KnowledgeCategoryNode,
+  KnowledgeStatus,
+  SearchHit,
+} from "../lib/types";
 
 const TABS = [
   { key: "draft", label: "待核对", statuses: ["draft", "in_review"] },
@@ -61,12 +67,48 @@ export function KnowledgePage() {
   const [loading, setLoading] = useState(false);
   const [error, setError] = useState<string | null>(null);
   const [openId, setOpenId] = useState<string | null>(null);
-  const [adding, setAdding] = useState(false);
-  const [draftTitle, setDraftTitle] = useState("");
+  const [composing, setComposing] = useState(false);
   const [hits, setHits] = useState<SearchHit[] | null>(null);
   const [searching, setSearching] = useState(false);
+  /** null = 不按分类筛（全部）；"none" = 未分类；其它是分类 id（含子分类） */
+  const [catFilter, setCatFilter] = useState<string | null>(null);
+  const [categories, setCategories] = useState<KnowledgeCategoryNode[]>([]);
+  const [catBusy, setCatBusy] = useState(false);
   const reqId = useRef(0);
 
+  const loadCategories = useCallback(async () => {
+    try {
+      const page = await api.get<{ items: KnowledgeCategoryNode[] }>(
+        `/workspaces/${wsId}/knowledge/categories`,
+      );
+      setCategories(page.items);
+    } catch (err) {
+      setError(err instanceof ApiError ? err.message : "分类加载失败");
+    }
+  }, [wsId]);
+
+  useEffect(() => {
+    void loadCategories();
+  }, [loadCategories]);
+
+  async function createCategory(name: string, parentId: string | null) {
+    setCatBusy(true);
+    setError(null);
+    try {
+      const created = await api.post<KnowledgeCategoryNode>(
+        `/workspaces/${wsId}/knowledge/categories`,
+        { name, parent_id: parentId },
+      );
+      await loadCategories();
+      return created;
+    } catch (err) {
+      setError(err instanceof ApiError ? err.message : "分类创建失败");
+      return null;
+    } finally {
+      setCatBusy(false);
+    }
+  }
+
   const load = useCallback(
     async (nextCursor: string | null) => {
       // 切 tab / 改搜索会连发请求，慢的回来会盖掉新结果
@@ -78,6 +120,8 @@ export function KnowledgePage() {
         const statuses = TABS.find((t) => t.key === tab)!.statuses;
         for (const s of statuses) qs.append("status", s);
         if (q.trim()) qs.set("q", q.trim());
+        if (catFilter === "none") qs.set("uncategorized", "true");
+        else if (catFilter) qs.set("category_id", catFilter);
         if (nextCursor) qs.set("cursor", nextCursor);
         const page = await api.get<{
           items: Knowledge[];
@@ -94,7 +138,7 @@ export function KnowledgePage() {
         if (mine === reqId.current) setLoading(false);
       }
     },
-    [wsId, tab, q],
+    [wsId, tab, q, catFilter],
   );
 
   useEffect(() => {
@@ -127,22 +171,13 @@ export function KnowledgePage() {
     }
   }
 
-  async function addNote() {
-    const title = draftTitle.trim();
-    if (!title) return;
-    try {
-      const doc = await api.post<Knowledge>(`/workspaces/${wsId}/knowledge`, {
-        title,
-        doc_type: "note",
-      });
-      setDraftTitle("");
-      setAdding(false);
-      setTab("draft");
-      setOpenId(doc.id);
-      void load(null);
-    } catch (err) {
-      setError(err instanceof ApiError ? err.message : "保存失败");
-    }
+  function onCreated(doc: Knowledge) {
+    setComposing(false);
+    setTab("draft");
+    setCatFilter(null);
+    setOpenId(doc.id);
+    void load(null);
+    void loadCategories();
   }
 
   const pendingCount = docs.filter((d) => d.knowledge.status_hint !== "published").length;
@@ -176,7 +211,7 @@ export function KnowledgePage() {
               <Search size={14} />
               {searching ? "检索中…" : "检索"}
             </Button>
-            <Button variant="primary" onClick={() => setAdding((v) => !v)}>
+            <Button variant="primary" onClick={() => setComposing(true)}>
               <Plus size={14} />
               记一条
             </Button>
@@ -184,6 +219,18 @@ export function KnowledgePage() {
         }
       />
 
+      <div className="grid gap-4 lg:grid-cols-[220px_minmax(0,1fr)]">
+        <CategorySidebar
+          categories={categories}
+          selected={catFilter}
+          onSelect={(value) => {
+            setCatFilter(value);
+            setHits(null);
+          }}
+          busy={catBusy}
+          onCreate={(name, parentId) => void createCategory(name, parentId)}
+        />
+        <div className="min-w-0">
       <div className="mb-4 flex flex-wrap items-center gap-1.5">
         {TABS.map((t) => {
           const active = tab === t.key;
@@ -208,34 +255,6 @@ export function KnowledgePage() {
         ) : null}
       </div>
 
-      {adding && (
-        <div className="card mb-4 p-4">
-          <div className="flex items-start gap-2 text-xs text-ink-500">
-            <span className="mt-0.5 text-clay-500">
-              <Book size={14} />
-            </span>
-            <p className="leading-relaxed">
-              手记的知识没有来源，它是你自己的笔记；想沉淀某件事，去那件事的详情里点「沉淀成知识」。
-            </p>
-          </div>
-          <div className="mt-3 flex gap-2">
-            <input
-              className="input flex-1"
-              placeholder="一句话标题，比如「报销单要贴发票原件」"
-              value={draftTitle}
-              autoFocus
-              onChange={(e) => setDraftTitle(e.target.value)}
-              onKeyDown={(e) => {
-                if (e.key === "Enter") void addNote();
-              }}
-            />
-            <Button variant="primary" disabled={!draftTitle.trim()} onClick={() => void addNote()}>
-              保存
-            </Button>
-          </div>
-        </div>
-      )}
-
       {error && (
         <div className="mb-4">
           <InlineAlert>{error}</InlineAlert>
@@ -327,6 +346,11 @@ export function KnowledgePage() {
                       自动整理
                     </span>
                   ) : null}
+                  {d.category ? (
+                    <span className="chip max-w-[16rem] truncate bg-paper-200 text-ink-500">
+                      {d.category.full_path}
+                    </span>
+                  ) : null}
                 </div>
                 <p className="mt-1.5 truncate text-sm font-medium text-ink-900 group-hover:text-primary-700">
                   {d.title}
@@ -339,6 +363,16 @@ export function KnowledgePage() {
                   {d.source ? <span className="max-w-[22rem] truncate">「{d.source.title}」</span> : null}
                   <span>{new Date(d.updated_at).toLocaleString("zh-CN")}</span>
                 </p>
+                {/* 标签是备忘录的检索入口，卡片上就露出来，不用点开才知道归在哪 */}
+                {d.tags.length > 0 ? (
+                  <div className="mt-1.5 flex flex-wrap gap-1">
+                    {d.tags.slice(0, 5).map((t) => (
+                      <span key={t.id} className="chip bg-primary-50 text-primary-700">
+                        #{t.name}
+                      </span>
+                    ))}
+                  </div>
+                ) : null}
               </button>
               <Button variant="ghost" size="sm" className="shrink-0" onClick={() => setOpenId(d.id)}>
                 打开
@@ -355,28 +389,353 @@ export function KnowledgePage() {
           </Button>
         </div>
       )}
+        </div>
+      </div>
+
+      {composing && (
+        <KnowledgeComposer
+          wsId={wsId}
+          categories={categories}
+          catBusy={catBusy}
+          onCreateCategory={createCategory}
+          onClose={() => setComposing(false)}
+          onCreated={onCreated}
+        />
+      )}
 
       {openId && (
         <KnowledgeDrawer
           wsId={wsId}
           itemId={openId}
+          categories={categories}
           onClose={() => setOpenId(null)}
-          onChanged={() => void load(null)}
+          onChanged={() => {
+            void load(null);
+            void loadCategories();
+          }}
         />
       )}
     </AppShell>
   );
 }
 
+/** 左侧分类树：一层一层缩进，点一下就把列表收窄到该分类（含子分类）。 */
+function CategorySidebar({
+  categories,
+  selected,
+  onSelect,
+  busy,
+  onCreate,
+}: {
+  categories: KnowledgeCategoryNode[];
+  selected: string | null;
+  onSelect: (value: string | null) => void;
+  busy: boolean;
+  onCreate: (name: string, parentId: string | null) => void;
+}) {
+  const [adding, setAdding] = useState(false);
+  const [name, setName] = useState("");
+  const [parentId, setParentId] = useState("");
+
+  return (
+    <aside className="card h-fit p-3 lg:sticky lg:top-4">
+      <div className="flex items-center justify-between px-1 py-1">
+        <span className="text-2xs font-medium uppercase tracking-wide text-ink-400">分类</span>
+        <button className="link text-2xs" onClick={() => setAdding((v) => !v)}>
+          {adding ? "取消" : "＋ 新建"}
+        </button>
+      </div>
+
+      {adding && (
+        <form
+          className="mt-2 space-y-1.5 rounded-lg border border-line-200 bg-paper-50 p-2"
+          onSubmit={(e) => {
+            e.preventDefault();
+            const value = name.trim();
+            if (!value) return;
+            onCreate(value, parentId || null);
+            setName("");
+            setAdding(false);
+          }}
+        >
+          <input
+            className="input h-8 text-sm"
+            placeholder="分类名，例如「部署」"
+            value={name}
+            autoFocus
+            onChange={(e) => setName(e.target.value)}
+            aria-label="新分类名"
+          />
+          <select
+            className="input h-8 text-sm"
+            value={parentId}
+            onChange={(e) => setParentId(e.target.value)}
+            aria-label="父分类"
+          >
+            <option value="">放在最外层</option>
+            {categories
+              .filter((c) => c.depth < 3)
+              .map((c) => (
+                <option key={c.id} value={c.id}>
+                  {c.full_path} 下
+                </option>
+              ))}
+          </select>
+          <Button variant="primary" size="sm" type="submit" disabled={busy || !name.trim()}>
+            创建
+          </Button>
+        </form>
+      )}
+
+      <nav className="mt-2 space-y-0.5">
+        <CategoryButton active={selected === null} onClick={() => onSelect(null)}>
+          全部知识
+        </CategoryButton>
+        <CategoryButton active={selected === "none"} onClick={() => onSelect("none")}>
+          未分类
+        </CategoryButton>
+        {categories.map((c) => (
+          <CategoryButton
+            key={c.id}
+            active={selected === c.id}
+            indent={c.depth - 1}
+            onClick={() => onSelect(c.id)}
+          >
+            <span className="truncate">{c.name}</span>
+            {c.doc_count > 0 ? <span className="text-2xs text-ink-400">{c.doc_count}</span> : null}
+          </CategoryButton>
+        ))}
+      </nav>
+
+      {categories.length === 0 ? (
+        <p className="mt-2 px-1 text-2xs leading-relaxed text-ink-400">
+          还没有分类。先建一层「研发 / 部署」这样的目录，知识才有地方落脚。
+        </p>
+      ) : null}
+    </aside>
+  );
+}
+
+function CategoryButton({
+  active,
+  indent = 0,
+  onClick,
+  children,
+}: {
+  active: boolean;
+  indent?: number;
+  onClick: () => void;
+  children: React.ReactNode;
+}) {
+  return (
+    <button
+      onClick={onClick}
+      style={{ paddingLeft: `${8 + indent * 14}px` }}
+      className={`flex w-full items-center justify-between gap-2 rounded-lg py-1.5 pr-2 text-sm transition-colors ${
+        active
+          ? "bg-white text-ink-900 shadow-sm ring-1 ring-line-200"
+          : "text-ink-600 hover:bg-white/60 hover:text-ink-800"
+      }`}
+    >
+      {children}
+    </button>
+  );
+}
+
+/** 新建知识：标题、类型、分类、标签、正文一起填，不再是「输入标题就算完」。 */
+function KnowledgeComposer({
+  wsId,
+  categories,
+  catBusy,
+  onCreateCategory,
+  onClose,
+  onCreated,
+}: {
+  wsId: string;
+  categories: KnowledgeCategoryNode[];
+  catBusy: boolean;
+  onCreateCategory: (name: string, parentId: string | null) => Promise<KnowledgeCategoryNode | null>;
+  onClose: () => void;
+  onCreated: (doc: Knowledge) => void;
+}) {
+  const [title, setTitle] = useState("");
+  const [docType, setDocType] = useState("note");
+  const [body, setBody] = useState("");
+  const [tags, setTags] = useState("");
+  const [categoryId, setCategoryId] = useState("");
+  const [newCat, setNewCat] = useState("");
+  const [busy, setBusy] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+
+  const parentDepth = categories.find((c) => c.id === categoryId)?.depth ?? 0;
+  const canAddCategory = parentDepth < 3 && Boolean(newCat.trim());
+  const canSave = Boolean(title.trim()) && !busy;
+
+  async function addCategory() {
+    const name = newCat.trim();
+    if (!name || !canAddCategory) return;
+    const created = await onCreateCategory(name, categoryId || null);
+    if (created) {
+      setCategoryId(created.id);
+      setNewCat("");
+    }
+  }
+
+  async function save() {
+    if (!canSave) return;
+    setBusy(true);
+    setError(null);
+    try {
+      const doc = await api.post<Knowledge>(`/workspaces/${wsId}/knowledge`, {
+        title: title.trim(),
+        body_md: body,
+        doc_type: docType,
+        tag_names: tags.split(/[\s,，]+/).filter(Boolean),
+        category_id: categoryId || null,
+      });
+      onCreated(doc);
+    } catch (err) {
+      setError(err instanceof ApiError ? err.message : "保存失败");
+    } finally {
+      setBusy(false);
+    }
+  }
+
+  return (
+    <Sheet
+      open
+      onClose={onClose}
+      size="xl"
+      title="记一条知识"
+      subtitle="标题、正文、标签、分类一次填完；保存后可以继续贴图、传附件。"
+      footer={
+        <div className="flex flex-wrap items-center gap-2">
+          <Button variant="primary" disabled={!canSave} onClick={() => void save()}>
+            {busy ? "保存中…" : "保存并继续写"}
+          </Button>
+          <Button variant="ghost" disabled={busy} onClick={onClose}>
+            取消
+          </Button>
+          <span className="ml-auto text-2xs text-ink-400">
+            先存成草稿，核对发布后才进团队检索
+          </span>
+        </div>
+      }
+    >
+      <div className="space-y-4">
+        <label className="block">
+          <span className="label">标题</span>
+          <input
+            className="input text-base font-medium"
+            placeholder="一句话说清这条知识是什么，比如「回滚前先停掉灰度」"
+            value={title}
+            autoFocus
+            onChange={(e) => setTitle(e.target.value)}
+            aria-label="标题"
+          />
+        </label>
+
+        <div className="grid gap-3 sm:grid-cols-2">
+          <label className="block">
+            <span className="label">类型</span>
+            <select
+              className="input"
+              value={docType}
+              onChange={(e) => setDocType(e.target.value)}
+              aria-label="类型"
+            >
+              {Object.entries(DOC_TYPE_LABEL).map(([key, label]) => (
+                <option key={key} value={key}>
+                  {label}
+                </option>
+              ))}
+            </select>
+          </label>
+          <label className="block">
+            <span className="label">分类</span>
+            <select
+              className="input"
+              value={categoryId}
+              onChange={(e) => setCategoryId(e.target.value)}
+              aria-label="分类"
+            >
+              <option value="">未分类</option>
+              {categories.map((c) => (
+                <option key={c.id} value={c.id}>
+                  {c.full_path}
+                </option>
+              ))}
+            </select>
+          </label>
+        </div>
+
+        <div className="rounded-xl border border-line-200 bg-paper-50 p-2.5">
+          <span className="label">在当前分类下新建子分类（最多三级）</span>
+          <div className="flex gap-2">
+            <input
+              className="input h-9 flex-1 text-sm"
+              placeholder={parentDepth >= 3 ? "已经到第三级了" : "子分类名"}
+              value={newCat}
+              disabled={parentDepth >= 3}
+              onChange={(e) => setNewCat(e.target.value)}
+              onKeyDown={(e) => {
+                if (e.key === "Enter") {
+                  e.preventDefault();
+                  void addCategory();
+                }
+              }}
+              aria-label="新建子分类"
+            />
+            <Button
+              variant="ghost"
+              disabled={!canAddCategory || catBusy}
+              onClick={() => void addCategory()}
+            >
+              新建
+            </Button>
+          </div>
+        </div>
+
+        <label className="block">
+          <span className="label">标签（空格或逗号分隔）</span>
+          <input
+            className="input"
+            placeholder="例如：发布 事故"
+            value={tags}
+            onChange={(e) => setTags(e.target.value)}
+            aria-label="标签"
+          />
+        </label>
+
+        <label className="block">
+          <span className="label">正文</span>
+          <textarea
+            className="input min-h-64 resize-y font-mono text-sm leading-relaxed"
+            rows={14}
+            placeholder={"可以直接写 Markdown：\n\n## 步骤\n1. 停灰度\n2. 回滚镜像\n3. 验证关键接口"}
+            value={body}
+            onChange={(e) => setBody(e.target.value)}
+            aria-label="正文"
+          />
+        </label>
+
+        {error && <InlineAlert>{error}</InlineAlert>}
+      </div>
+    </Sheet>
+  );
+}
+
 /** 知识详情抽屉：能改、能提交审议、能发布/归档。 */
 function KnowledgeDrawer({
   wsId,
   itemId,
+  categories,
   onClose,
   onChanged,
 }: {
   wsId: string;
   itemId: string;
+  categories: KnowledgeCategoryNode[];
   onClose: () => void;
   onChanged: () => void;
 }) {
@@ -384,6 +743,8 @@ function KnowledgeDrawer({
   const [error, setError] = useState<string | null>(null);
   const [title, setTitle] = useState("");
   const [body, setBody] = useState("");
+  const [tags, setTags] = useState("");
+  const [categoryId, setCategoryId] = useState("");
   const [attachments, setAttachments] = useState<Attachment[]>([]);
   /** 附件 id → 带签名的直链（见 lib/attachmentUrls.ts） */
   const resources = useMemo(() => {
@@ -394,18 +755,27 @@ function KnowledgeDrawer({
     return map;
   }, [attachments]);
   const [busy, setBusy] = useState(false);
+  /** 已经载入完成的是哪一条知识。重复的 effect / 慢响应不该再覆盖用户正在敲的内容。 */
+  const loadedFor = useRef<string | null>(null);
 
-  const load = useCallback(async () => {
-    try {
-      const data = await api.get<Knowledge>(`/workspaces/${wsId}/knowledge/${itemId}`);
-      setDoc(data);
-      setTitle(data.title);
-      setBody(data.body_md);
-      setAttachments(data.attachments ?? []);
-    } catch (err) {
-      setError(err instanceof ApiError ? err.message : "加载失败");
-    }
-  }, [wsId, itemId]);
+  const load = useCallback(
+    async (force = false) => {
+      if (!force && loadedFor.current === itemId) return;
+      try {
+        const data = await api.get<Knowledge>(`/workspaces/${wsId}/knowledge/${itemId}`);
+        setDoc(data);
+        setTitle(data.title);
+        setBody(data.body_md);
+        setTags(data.tags.map((t) => t.name).join(" "));
+        setCategoryId(data.category?.id ?? "");
+        setAttachments(data.attachments ?? []);
+        loadedFor.current = itemId;
+      } catch (err) {
+        setError(err instanceof ApiError ? err.message : "加载失败");
+      }
+    },
+    [wsId, itemId],
+  );
 
   useEffect(() => {
     void load();
@@ -419,6 +789,8 @@ function KnowledgeDrawer({
       const next = await api.patch<Knowledge>(`/workspaces/${wsId}/knowledge/${itemId}`, {
         title,
         body_md: body,
+        tag_names: tags.split(/[\s,，]+/).filter(Boolean),
+        ...(categoryId ? { category_id: categoryId } : { clear_category: true }),
         version: doc.version,
       });
       setDoc(next);
@@ -426,7 +798,7 @@ function KnowledgeDrawer({
     } catch (err) {
       if (err instanceof ApiError && err.code === 4009) {
         setError("刚被别人改过，已刷新为最新内容");
-        await load();
+        await load(true);
       } else {
         setError(err instanceof ApiError ? err.message : "保存失败");
       }
@@ -448,7 +820,7 @@ function KnowledgeDrawer({
       onChanged();
     } catch (err) {
       setError(err instanceof ApiError ? err.message : "操作失败");
-      await load();
+      await load(true);
     } finally {
       setBusy(false);
     }
@@ -472,13 +844,13 @@ function KnowledgeDrawer({
     <Sheet
       open
       onClose={onClose}
-      width="max-w-2xl"
+      size="xl"
       title={doc ? doc.title : "知识"}
       subtitle={
         doc
-          ? `${DOC_TYPE_LABEL[doc.knowledge.doc_type] ?? doc.knowledge.doc_type} · ${
-              STATUS_LABEL[doc.knowledge.status_hint]
-            } · 版本 ${doc.version}`
+          ? [doc.category?.full_path, DOC_TYPE_LABEL[doc.knowledge.doc_type] ?? doc.knowledge.doc_type]
+              .filter(Boolean)
+              .join(" · ")
           : "加载中…"
       }
       footer={
@@ -543,6 +915,37 @@ function KnowledgeDrawer({
             aria-label="标题"
           />
 
+          <div className="grid gap-3 sm:grid-cols-2">
+            <label className="block">
+              <span className="label">分类</span>
+              <select
+                className="input"
+                value={categoryId}
+                disabled={!canEdit}
+                onChange={(e) => setCategoryId(e.target.value)}
+                aria-label="分类"
+              >
+                <option value="">未分类</option>
+                {categories.map((c) => (
+                  <option key={c.id} value={c.id}>
+                    {c.full_path}
+                  </option>
+                ))}
+              </select>
+            </label>
+            <label className="block">
+              <span className="label">标签（空格或逗号分隔）</span>
+              <input
+                className="input"
+                value={tags}
+                disabled={!canEdit}
+                onChange={(e) => setTags(e.target.value)}
+                placeholder="例如：发布 事故"
+                aria-label="标签"
+              />
+            </label>
+          </div>
+
           <div className="rounded-xl border border-line-200 bg-paper-50 px-3 py-2">
             <RichTextEditor
               ariaLabel="正文"
diff --git a/web/src/pages/Tickets.tsx b/web/src/pages/Tickets.tsx
index 9b0dc70..2bed73a 100644
--- a/web/src/pages/Tickets.tsx
+++ b/web/src/pages/Tickets.tsx
@@ -302,6 +302,7 @@ export function TicketsPage() {
       <Sheet
         open={creating}
         onClose={() => setCreating(false)}
+        size="xl"
         title="新建工单"
         subtitle="不是从任务升级来的也可以——写清楚要办什么，指定一个人。"
         footer={