diff --git a/Cargo.toml b/Cargo.toml
index 539b965..6040a85 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -19,6 +19,7 @@ futures-core = "0.3"
 bytes = "1"
 async-stream = "0.3"
 tokio-util = { version = "0.7", features = ["rt"] }
+time = { version = "0.3", features = ["serde"] }
 
 [dev-dependencies]
 dotenvy = "0.15.7"
diff --git a/src/lib.rs b/src/lib.rs
index c63cb2f..4444d6e 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,6 +1,7 @@
 //! agcore —— 智能体（Agent）核心工具箱。
 
 pub mod llm;
+pub mod memory;
 pub mod prompt;
 pub mod tools;
 
diff --git a/src/memory.rs b/src/memory.rs
new file mode 100644
index 0000000..84203e0
--- /dev/null
+++ b/src/memory.rs
@@ -0,0 +1,22 @@
+//! 记忆系统 —— 对话消息管理、知识页面存储与关键词检索。
+
+pub mod conversation;
+pub mod error;
+pub mod knowledge;
+pub mod retriever;
+pub mod store;
+pub mod types;
+
+// 高频类型（大多数下游需要）
+pub use conversation::{ConversationMemory, ConversationMemoryConfig};
+pub use error::MemoryError;
+pub use knowledge::KnowledgeStore;
+pub use retriever::MemoryRetriever;
+pub use store::{InMemoryStore, MemoryStore};
+
+// 低频类型（配置/高级使用）
+pub use conversation::MemoryStrategy;
+pub use knowledge::{PageIndexEntry, KNOWLEDGE_PREFIX};
+pub use retriever::{RetrieverConfig, RetrievalResult, ScoredItem};
+pub use store::{EvictionConfig, EvictionPolicy};
+pub use types::{KnowledgePage, MemoryFilter, MemoryItem};
diff --git a/src/memory/conversation.rs b/src/memory/conversation.rs
new file mode 100644
index 0000000..c60fdc0
--- /dev/null
+++ b/src/memory/conversation.rs
@@ -0,0 +1,260 @@
+//! 对话记忆 —— 多轮对话消息管理，复用 `llm::compact` 的压缩逻辑。
+
+use std::sync::Arc;
+
+use serde::{Deserialize, Serialize};
+use time::OffsetDateTime;
+
+use crate::llm::compact::{CompactConfig, CompactState, microcompact, should_compact};
+use crate::llm::types::OpenaiChatMessage;
+use crate::memory::error::MemoryError;
+use crate::memory::store::MemoryStore;
+use crate::memory::types::MemoryItem;
+
+/// 对话消息管理策略。
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+pub enum MemoryStrategy {
+    /// 滑动窗口：达到上限时删除最旧消息。
+    SlidingWindow,
+    /// 保留所有消息（仅压缩，不删除）。
+    Full,
+}
+
+/// 对话记忆配置。
+#[derive(Debug, Clone)]
+pub struct ConversationMemoryConfig {
+    pub strategy: MemoryStrategy,
+    pub max_turns: usize,
+    pub compact_config: Option<CompactConfig>,
+}
+
+impl Default for ConversationMemoryConfig {
+    fn default() -> Self {
+        Self {
+            strategy: MemoryStrategy::SlidingWindow,
+            max_turns: 50,
+            compact_config: Some(CompactConfig::default()),
+        }
+    }
+}
+
+/// 对话记忆 —— 按 session 管理多轮对话消息历史。
+///
+/// 内部维护 `Vec<OpenaiChatMessage>` 热缓存（供 `llm::compact` 直接操作），
+/// `MemoryStore` 用作冷持久化层。
+pub struct ConversationMemory {
+    store: Arc<dyn MemoryStore>,
+    session_id: String,
+    config: ConversationMemoryConfig,
+    /// 热缓存：消息列表，供 `llm::compact` 直接操作。
+    messages: Vec<OpenaiChatMessage>,
+    /// 与 `messages` 一一对应的存储 ID（保持稳定以便淘汰时精准删除）。
+    message_ids: Vec<String>,
+    /// 压缩断路器状态。
+    compact_state: CompactState,
+}
+
+impl ConversationMemory {
+    /// 创建一个新的 ConversationMemory。
+    pub fn new(
+        store: Arc<dyn MemoryStore>,
+        session_id: impl Into<String>,
+        config: ConversationMemoryConfig,
+    ) -> Self {
+        Self {
+            store,
+            session_id: session_id.into(),
+            config,
+            messages: Vec::new(),
+            message_ids: Vec::new(),
+            compact_state: CompactState::new(),
+        }
+    }
+
+    /// 获取 session id。
+    pub fn session_id(&self) -> &str {
+        &self.session_id
+    }
+
+    /// 获取配置。
+    pub fn config(&self) -> &ConversationMemoryConfig {
+        &self.config
+    }
+
+    /// 从 MemoryStore 加载历史消息到热缓存。
+    pub async fn load(&mut self) -> Result<(), MemoryError> {
+        let filter = crate::memory::types::MemoryFilter {
+            prefix: Some(self.session_prefix()),
+            ..Default::default()
+        };
+        let items = self.store.list(&filter).await?;
+        let mut pairs: Vec<(String, OpenaiChatMessage, OffsetDateTime)> = Vec::with_capacity(items.len());
+        for item in items {
+            match serde_json::from_str::<OpenaiChatMessage>(&item.content) {
+                Ok(msg) => pairs.push((item.id, msg, item.created_at)),
+                Err(e) => {
+                    return Err(MemoryError::Serialization(format!(
+                        "load message {} failed: {e}",
+                        item.id
+                    )));
+                }
+            }
+        }
+        // 按 created_at 升序排列
+        pairs.sort_by_key(|p| p.2);
+        self.message_ids = pairs.iter().map(|p| p.0.clone()).collect();
+        self.messages = pairs.into_iter().map(|p| p.1).collect();
+        Ok(())
+    }
+
+    /// 添加一条消息。
+    ///
+    /// 写入热缓存并通过 `MemoryStore` 持久化。如有需要，触发淘汰和压缩。
+    pub async fn add_message(&mut self, msg: OpenaiChatMessage) -> Result<(), MemoryError> {
+        let now = OffsetDateTime::now_utc();
+        let index = self.messages.len();
+        let id = self.make_message_id(index, &now);
+
+        // 写入热缓存
+        self.messages.push(msg);
+        self.message_ids.push(id.clone());
+
+        // 同步到冷存储
+        let item = MemoryItem {
+            id: id.clone(),
+            content: serde_json::to_string(self.messages.last().unwrap())
+                .map_err(|e| MemoryError::Serialization(e.to_string()))?,
+            metadata: serde_json::json!({ "session_id": &self.session_id, "index": index }),
+            created_at: now,
+        };
+        self.store.save(item).await?;
+
+        // 触发淘汰和压缩
+        self.maybe_evict_and_compact().await;
+        Ok(())
+    }
+
+    /// 获取完整消息历史。
+    pub fn get_history(&self) -> &[OpenaiChatMessage] {
+        &self.messages
+    }
+
+    /// 清空所有消息。
+    pub async fn clear(&mut self) -> Result<(), MemoryError> {
+        let to_delete = std::mem::take(&mut self.message_ids);
+        self.messages.clear();
+        self.compact_state = CompactState::new();
+        for id in to_delete {
+            self.store.delete(&id).await?;
+        }
+        Ok(())
+    }
+
+    /// 当前消息数量。
+    pub fn len(&self) -> usize {
+        self.messages.len()
+    }
+
+    /// 是否为空。
+    pub fn is_empty(&self) -> bool {
+        self.messages.is_empty()
+    }
+
+    fn session_prefix(&self) -> String {
+        format!("conv:{self}:", self = self.session_id)
+    }
+
+    fn make_message_id(&self, index: usize, now: &OffsetDateTime) -> String {
+        format!("{}{:010}_{}", self.session_prefix(), index, now.unix_timestamp_nanos())
+    }
+
+    async fn maybe_evict_and_compact(&mut self) {
+        // 1. Sliding window 淘汰：删除最旧消息
+        if self.config.strategy == MemoryStrategy::SlidingWindow {
+            while self.messages.len() > self.config.max_turns {
+                if let Some(removed_id) = self.message_ids.first().cloned() {
+                    let _ = self.store.delete(&removed_id).await;
+                }
+                self.messages.remove(0);
+                self.message_ids.remove(0);
+            }
+        }
+
+        // 2. 压缩（复用 llm::compact）
+        if let Some(ref compact_config) = self.config.compact_config {
+            if should_compact(&self.messages, compact_config, &self.compact_state) {
+                let keep_recent = compact_config.keep_recent;
+                let freed = microcompact(&mut self.messages, keep_recent);
+                if freed > 0 {
+                    self.compact_state.record_success();
+                } else {
+                    // 没有 token 被释放（可能没找到可压缩的 tool result）
+                    let _ = self.compact_state.record_failure();
+                }
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::llm::types::OpenaiChatMessage;
+    use crate::memory::InMemoryStore;
+    use crate::memory::MemoryStore;
+
+    fn user_text(s: &str) -> OpenaiChatMessage {
+        OpenaiChatMessage::user_text(s)
+    }
+
+    #[tokio::test]
+    async fn add_and_get_history() {
+        let store = Arc::new(InMemoryStore::new()) as Arc<dyn MemoryStore>;
+        let mut conv = ConversationMemory::new(store, "session1", ConversationMemoryConfig::default());
+        conv.add_message(user_text("hello")).await.unwrap();
+        conv.add_message(user_text("world")).await.unwrap();
+        assert_eq!(conv.len(), 2);
+        assert_eq!(conv.get_history().len(), 2);
+    }
+
+    #[tokio::test]
+    async fn sliding_window_evicts_oldest() {
+        let store = Arc::new(InMemoryStore::new()) as Arc<dyn MemoryStore>;
+        let config = ConversationMemoryConfig {
+            strategy: MemoryStrategy::SlidingWindow,
+            max_turns: 3,
+            compact_config: None,
+        };
+        let mut conv = ConversationMemory::new(store, "s1", config);
+        for i in 0..5 {
+            conv.add_message(user_text(&format!("msg-{i}"))).await.unwrap();
+        }
+        assert_eq!(conv.len(), 3);
+    }
+
+    #[tokio::test]
+    async fn full_strategy_no_evict() {
+        let store = Arc::new(InMemoryStore::new()) as Arc<dyn MemoryStore>;
+        let config = ConversationMemoryConfig {
+            strategy: MemoryStrategy::Full,
+            max_turns: 3,
+            compact_config: None,
+        };
+        let mut conv = ConversationMemory::new(store, "s1", config);
+        for i in 0..5 {
+            conv.add_message(user_text(&format!("msg-{i}"))).await.unwrap();
+        }
+        // Full 策略不删除消息
+        assert_eq!(conv.len(), 5);
+    }
+
+    #[tokio::test]
+    async fn clear_empties_messages() {
+        let store = Arc::new(InMemoryStore::new()) as Arc<dyn MemoryStore>;
+        let mut conv = ConversationMemory::new(store.clone(), "s1", ConversationMemoryConfig::default());
+        conv.add_message(user_text("hello")).await.unwrap();
+        assert!(!conv.is_empty());
+        conv.clear().await.unwrap();
+        assert!(conv.is_empty());
+    }
+}
diff --git a/src/memory/error.rs b/src/memory/error.rs
new file mode 100644
index 0000000..c7ac6d4
--- /dev/null
+++ b/src/memory/error.rs
@@ -0,0 +1,29 @@
+//! 记忆系统错误类型。
+
+use thiserror::Error;
+
+/// 记忆系统错误枚举。
+#[derive(Debug, Error)]
+pub enum MemoryError {
+    #[error("Item not found: {0}")]
+    NotFound(String),
+
+    #[error("Storage error: {0}")]
+    Storage(String),
+
+    #[error("Serialization error: {0}")]
+    Serialization(String),
+
+    #[error("Invalid input: {0}")]
+    InvalidInput(String),
+
+    #[error("Retrieval error: {0}")]
+    RetrievalError(String),
+}
+
+impl MemoryError {
+    /// 是否为可恢复错误（调用方可重试或调整参数）。
+    pub fn is_recoverable(&self) -> bool {
+        matches!(self, Self::NotFound(_) | Self::RetrievalError(_))
+    }
+}
diff --git a/src/memory/knowledge.rs b/src/memory/knowledge.rs
new file mode 100644
index 0000000..79770ea
--- /dev/null
+++ b/src/memory/knowledge.rs
@@ -0,0 +1,247 @@
+//! 知识库 —— KnowledgePage 存储与关键词检索。
+
+use std::sync::Arc;
+
+use time::OffsetDateTime;
+
+use crate::memory::error::MemoryError;
+use crate::memory::store::MemoryStore;
+use crate::memory::types::{KnowledgePage, MemoryFilter, MemoryItem};
+
+pub use crate::memory::types::PageIndexEntry;
+
+/// `MemoryItem.id` 中知识页面前缀。
+pub const KNOWLEDGE_PREFIX: &str = "knowledge_";
+
+/// 知识库 —— KnowledgePage CRUD + 关键词检索 + 内容索引。
+///
+/// 内部以 `MemoryStore` 为后端存储 KnowledgePage（序列化为 JSON），
+/// 同时维护一个 `Vec<PageIndexEntry>` 索引以加速列表遍历。
+pub struct KnowledgeStore {
+    store: Arc<dyn MemoryStore>,
+    index: std::sync::Mutex<Vec<PageIndexEntry>>,
+}
+
+impl KnowledgeStore {
+    /// 创建一个新的 KnowledgeStore。
+    pub fn new(store: Arc<dyn MemoryStore>) -> Self {
+        Self {
+            store,
+            index: std::sync::Mutex::new(Vec::new()),
+        }
+    }
+
+    /// 从 MemoryStore 重建索引（修复 index 与 store 的不同步问题）。
+    pub async fn rebuild_index(&self) -> Result<(), MemoryError> {
+        let items = self
+            .store
+            .list(&MemoryFilter {
+                prefix: Some(KNOWLEDGE_PREFIX.to_string()),
+                ..Default::default()
+            })
+            .await?;
+        let mut index = self.index.lock().unwrap();
+        index.clear();
+        for item in items {
+            let page: KnowledgePage = serde_json::from_str(&item.content)
+                .map_err(|e| MemoryError::Serialization(e.to_string()))?;
+            index.push(PageIndexEntry::from(&page));
+        }
+        Ok(())
+    }
+
+    /// 创建一个新的知识页面。
+    pub async fn add_page(&self, page: KnowledgePage) -> Result<(), MemoryError> {
+        if page.id.is_empty() {
+            return Err(MemoryError::InvalidInput("page.id is empty".into()));
+        }
+        let now = OffsetDateTime::now_utc();
+        let id = format!("{KNOWLEDGE_PREFIX}{}", page.id);
+        let content = serde_json::to_string(&page)
+            .map_err(|e| MemoryError::Serialization(e.to_string()))?;
+        let item = MemoryItem {
+            id,
+            content,
+            metadata: serde_json::json!({}),
+            created_at: now,
+        };
+        self.store.save(item).await?;
+        let mut index = self.index.lock().unwrap();
+        // 替换或追加
+        if let Some(existing) = index.iter_mut().find(|e| e.id == page.id) {
+            *existing = PageIndexEntry::from(&page);
+        } else {
+            index.push(PageIndexEntry::from(&page));
+        }
+        Ok(())
+    }
+
+    /// 根据 page id 获取一个页面。
+    pub async fn get_page(&self, id: &str) -> Result<Option<KnowledgePage>, MemoryError> {
+        let full_id = format!("{KNOWLEDGE_PREFIX}{id}");
+        let item = self.store.get(&full_id).await?;
+        match item {
+            None => Ok(None),
+            Some(item) => {
+                let page: KnowledgePage = serde_json::from_str(&item.content)
+                    .map_err(|e| MemoryError::Serialization(e.to_string()))?;
+                Ok(Some(page))
+            }
+        }
+    }
+
+    /// 更新一个已存在的知识页面。
+    pub async fn update_page(&self, page: KnowledgePage) -> Result<(), MemoryError> {
+        if page.id.is_empty() {
+            return Err(MemoryError::InvalidInput("page.id is empty".into()));
+        }
+        // 通过 get_page 检查存在性
+        if self.get_page(&page.id).await?.is_none() {
+            return Err(MemoryError::NotFound(page.id));
+        }
+        self.add_page(page).await
+    }
+
+    /// 删除一个知识页面。
+    pub async fn delete_page(&self, id: &str) -> Result<(), MemoryError> {
+        let full_id = format!("{KNOWLEDGE_PREFIX}{id}");
+        self.store.delete(&full_id).await?;
+        let mut index = self.index.lock().unwrap();
+        index.retain(|e| e.id != id);
+        Ok(())
+    }
+
+    /// 根据关键词搜索知识页面。
+    ///
+    /// 匹配规则：在 `title` / `summary` / `tags` 中查找子串（不区分大小写）。
+    /// 全文 `content` 搜索走 `MemoryStore`。
+    pub async fn search(&self, query: &str) -> Result<Vec<KnowledgePage>, MemoryError> {
+        if query.is_empty() {
+            return Ok(Vec::new());
+        }
+        let needle = query.to_lowercase();
+        let mut results = Vec::new();
+        let index = self.index.lock().unwrap();
+        for entry in index.iter() {
+            if entry.title.to_lowercase().contains(&needle)
+                || entry.summary.to_lowercase().contains(&needle)
+                || entry.tags.iter().any(|t| t.to_lowercase().contains(&needle))
+            {
+                if let Some(page) = self.get_page(&entry.id).await? {
+                    results.push(page);
+                }
+            }
+        }
+        Ok(results)
+    }
+
+    /// 获取内容目录（所有页面的轻量级索引条目）。
+    pub fn get_index(&self) -> Vec<PageIndexEntry> {
+        self.index.lock().unwrap().clone()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::memory::InMemoryStore;
+    use time::OffsetDateTime;
+
+    fn make_page(id: &str, title: &str, tags: &[&str]) -> KnowledgePage {
+        let now = OffsetDateTime::now_utc();
+        KnowledgePage {
+            id: id.to_string(),
+            title: title.to_string(),
+            summary: format!("summary of {title}"),
+            content: format!("full content of {title}"),
+            tags: tags.iter().map(|s| s.to_string()).collect(),
+            references: Vec::new(),
+            created_at: now,
+            updated_at: now,
+        }
+    }
+
+    #[tokio::test]
+    async fn add_get_delete_page() {
+        let store = Arc::new(InMemoryStore::new()) as Arc<dyn MemoryStore>;
+        let ks = KnowledgeStore::new(store);
+        ks.add_page(make_page("p1", "LangGraph", &["langgraph", "framework"]))
+            .await
+            .unwrap();
+        let got = ks.get_page("p1").await.unwrap();
+        assert!(got.is_some());
+        assert_eq!(got.unwrap().title, "LangGraph");
+
+        ks.delete_page("p1").await.unwrap();
+        assert!(ks.get_page("p1").await.unwrap().is_none());
+    }
+
+    #[tokio::test]
+    async fn add_page_rejects_empty_id() {
+        let store = Arc::new(InMemoryStore::new()) as Arc<dyn MemoryStore>;
+        let ks = KnowledgeStore::new(store);
+        let result = ks.add_page(make_page("", "NoId", &[])).await;
+        assert!(matches!(result, Err(MemoryError::InvalidInput(_))));
+    }
+
+    #[tokio::test]
+    async fn update_page_requires_existing() {
+        let store = Arc::new(InMemoryStore::new()) as Arc<dyn MemoryStore>;
+        let ks = KnowledgeStore::new(store);
+        let result = ks.update_page(make_page("nope", "Ghost", &[])).await;
+        assert!(matches!(result, Err(MemoryError::NotFound(_))));
+    }
+
+    #[tokio::test]
+    async fn search_finds_by_title_summary_tag() {
+        let store = Arc::new(InMemoryStore::new()) as Arc<dyn MemoryStore>;
+        let ks = KnowledgeStore::new(store);
+        ks.add_page(make_page("p1", "LangGraph StateGraph", &["llm"]))
+            .await
+            .unwrap();
+        ks.add_page(make_page("p2", "Other", &["knowledge-graph"]))
+            .await
+            .unwrap();
+        ks.add_page(make_page("p3", "Third", &["unrelated"]))
+            .await
+            .unwrap();
+
+        let results = ks.search("stategraph").await.unwrap();
+        assert_eq!(results.len(), 1);
+        assert_eq!(results[0].id, "p1");
+
+        let results = ks.search("knowledge-graph").await.unwrap();
+        assert_eq!(results.len(), 1);
+        assert_eq!(results[0].id, "p2");
+
+        let results = ks.search("nonexistent").await.unwrap();
+        assert!(results.is_empty());
+    }
+
+    #[tokio::test]
+    async fn get_index_returns_all_pages() {
+        let store = Arc::new(InMemoryStore::new()) as Arc<dyn MemoryStore>;
+        let ks = KnowledgeStore::new(store);
+        ks.add_page(make_page("p1", "A", &[])).await.unwrap();
+        ks.add_page(make_page("p2", "B", &[])).await.unwrap();
+        let index = ks.get_index();
+        assert_eq!(index.len(), 2);
+    }
+
+    #[tokio::test]
+    async fn rebuild_index_recovers_from_drift() {
+        let store = Arc::new(InMemoryStore::new()) as Arc<dyn MemoryStore>;
+        let ks = KnowledgeStore::new(store);
+        // 添加页面
+        ks.add_page(make_page("p1", "A", &[])).await.unwrap();
+        ks.add_page(make_page("p2", "B", &[])).await.unwrap();
+        assert_eq!(ks.get_index().len(), 2);
+
+        // 模拟 index 漂移：清空后重建
+        ks.index.lock().unwrap().clear();
+        assert_eq!(ks.get_index().len(), 0);
+
+        ks.rebuild_index().await.unwrap();
+        assert_eq!(ks.get_index().len(), 2);
+    }
+}
diff --git a/src/memory/retriever.rs b/src/memory/retriever.rs
new file mode 100644
index 0000000..09fa7bf
--- /dev/null
+++ b/src/memory/retriever.rs
@@ -0,0 +1,297 @@
+//! 记忆检索器 —— 基于 TextOverlap (Dice 系数) 的单通道关键词检索。
+
+use std::collections::HashSet;
+
+use crate::memory::error::MemoryError;
+use crate::memory::knowledge::KnowledgeStore;
+use crate::memory::types::KnowledgePage;
+
+/// 检索器配置。
+#[derive(Debug, Clone)]
+pub struct RetrieverConfig {
+    /// 最大返回条数（默认 20）。
+    pub max_results: usize,
+    /// 最低分数阈值 [0.0, 1.0]（默认 0.1）。
+    pub min_score: f32,
+}
+
+impl Default for RetrieverConfig {
+    fn default() -> Self {
+        Self {
+            max_results: 20,
+            min_score: 0.1,
+        }
+    }
+}
+
+/// 单条带评分的检索结果。
+#[derive(Debug, Clone)]
+pub struct ScoredItem {
+    pub page: KnowledgePage,
+    /// TextOverlap 评分 [0.0, 1.0]
+    pub score: f32,
+}
+
+/// 检索结果。
+#[derive(Debug, Clone)]
+pub struct RetrievalResult {
+    pub items: Vec<ScoredItem>,
+    pub query: String,
+}
+
+/// 记忆检索器 —— 在 `KnowledgeStore` 中做关键词检索并按 TextOverlap 评分。
+pub struct MemoryRetriever {
+    knowledge_store: KnowledgeStore,
+    config: RetrieverConfig,
+    /// 停用词表（用于关键词提取）。
+    stop_words: HashSet<String>,
+}
+
+impl MemoryRetriever {
+    /// 创建一个新的 MemoryRetriever。
+    pub fn new(knowledge_store: KnowledgeStore, config: RetrieverConfig) -> Self {
+        Self {
+            knowledge_store,
+            config,
+            stop_words: default_stop_words(),
+        }
+    }
+
+    /// 替换停用词表。
+    pub fn with_stop_words(mut self, stop_words: HashSet<String>) -> Self {
+        self.stop_words = stop_words;
+        self
+    }
+
+    /// 检索相关知识页面。
+    pub async fn retrieve(&self, query: &str) -> Result<RetrievalResult, MemoryError> {
+        if query.is_empty() {
+            return Ok(RetrievalResult {
+                items: Vec::new(),
+                query: query.to_string(),
+            });
+        }
+
+        // 1. 关键词提取
+        let keywords = extract_keywords(query, &self.stop_words);
+
+        // 2. 用关键词在 KnowledgeStore 中搜索
+        let mut pages = Vec::new();
+        for keyword in &keywords {
+            let found = self.knowledge_store.search(keyword).await?;
+            for page in found {
+                if !pages.iter().any(|p: &KnowledgePage| p.id == page.id) {
+                    pages.push(page);
+                }
+            }
+        }
+
+        // 3. TextOverlap 评分
+        let mut items: Vec<ScoredItem> = pages
+            .into_iter()
+            .map(|page| {
+                let score = text_overlap_score(query, &page);
+                ScoredItem { page, score }
+            })
+            .collect();
+
+        // 4. 过滤 → 排序 → 截取
+        items.retain(|i| i.score >= self.config.min_score);
+        items.sort_by(|a, b| b.score.partial_cmp(&a.score).unwrap_or(std::cmp::Ordering::Equal));
+        items.truncate(self.config.max_results);
+
+        Ok(RetrievalResult {
+            items,
+            query: query.to_string(),
+        })
+    }
+}
+
+/// 从 query 中提取关键词：按非字母数字字符分割 → 转小写 → 过滤单字符和停用词。
+fn extract_keywords(query: &str, stop_words: &HashSet<String>) -> Vec<String> {
+    query
+        .split(|c: char| !c.is_alphanumeric())
+        .filter_map(|s| {
+            let lower = s.to_lowercase();
+            if lower.is_empty() || lower.chars().count() < 2 {
+                None
+            } else if stop_words.contains(&lower) {
+                None
+            } else {
+                Some(lower)
+            }
+        })
+        .collect()
+}
+
+/// TextOverlap 评分（基于字符 bigram 的 Dice 系数 + 多字段加权）。
+///
+/// 字段权重：title 0.5 + summary 0.3 + content 0.2
+/// 中文场景按字符级 bigram 处理，不依赖分词器。
+pub fn text_overlap_score(query: &str, page: &KnowledgePage) -> f32 {
+    let title = text_overlap_dice(query, &page.title);
+    let summary = text_overlap_dice(query, &page.summary);
+    let content = text_overlap_dice(query, &page.content);
+    title * 0.5 + summary * 0.3 + content * 0.2
+}
+
+/// Dice 系数（基于字符 bigram）。
+fn text_overlap_dice(query: &str, text: &str) -> f32 {
+    let q_bigrams = char_bigrams(query);
+    let t_bigrams = char_bigrams(text);
+    if q_bigrams.is_empty() || t_bigrams.is_empty() {
+        return 0.0;
+    }
+    let q_set: HashSet<&String> = q_bigrams.iter().collect();
+    let t_set: HashSet<&String> = t_bigrams.iter().collect();
+    let intersect = q_set.intersection(&t_set).count();
+    let denom = q_set.len() + t_set.len();
+    if denom == 0 {
+        0.0
+    } else {
+        (2.0 * intersect as f32) / denom as f32
+    }
+}
+
+/// 提取字符 bigrams（用于字符级 Dice 系数）。
+fn char_bigrams(s: &str) -> Vec<String> {
+    let chars: Vec<char> = s.chars().collect();
+    chars.windows(2).map(|w| w.iter().collect()).collect()
+}
+
+fn default_stop_words() -> HashSet<String> {
+    [
+        "the", "a", "an", "is", "are", "was", "were", "be", "been", "being", "have", "has",
+        "had", "do", "does", "did", "will", "would", "should", "could", "may", "might", "shall",
+        "can", "this", "that", "these", "those", "it", "its", "they", "them", "their", "what",
+        "which", "who", "whom", "how", "when", "where", "and", "or", "but", "not", "no", "nor",
+        "so", "if", "then", "else", "with", "without", "for", "to", "from", "in", "on", "at",
+        "by", "of", "as", "into", "through", "during", "before", "after", "above", "below",
+    ]
+    .iter()
+    .map(|s| s.to_string())
+    .collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::memory::knowledge::KnowledgeStore;
+    use crate::memory::{InMemoryStore, MemoryStore};
+    use std::sync::Arc;
+    use time::OffsetDateTime;
+
+    fn make_page(id: &str, title: &str, summary: &str, content: &str) -> KnowledgePage {
+        let now = OffsetDateTime::now_utc();
+        KnowledgePage {
+            id: id.to_string(),
+            title: title.to_string(),
+            summary: summary.to_string(),
+            content: content.to_string(),
+            tags: Vec::new(),
+            references: Vec::new(),
+            created_at: now,
+            updated_at: now,
+        }
+    }
+
+    #[tokio::test]
+    async fn retrieve_empty_query() {
+        let store = Arc::new(InMemoryStore::new()) as Arc<dyn MemoryStore>;
+        let ks = KnowledgeStore::new(store);
+        let retriever = MemoryRetriever::new(ks, RetrieverConfig::default());
+        let result = retriever.retrieve("").await.unwrap();
+        assert!(result.items.is_empty());
+    }
+
+    #[tokio::test]
+    async fn retrieve_finds_relevant_page() {
+        let store = Arc::new(InMemoryStore::new()) as Arc<dyn MemoryStore>;
+        let ks = KnowledgeStore::new(store);
+        ks.add_page(make_page(
+            "p1",
+            "LangGraph StateGraph",
+            "state management",
+            "LangGraph uses StateGraph for state machines",
+        ))
+        .await
+        .unwrap();
+        ks.add_page(make_page("p2", "Other", "unrelated", "nothing matching"))
+            .await
+            .unwrap();
+
+        let retriever = MemoryRetriever::new(ks, RetrieverConfig::default());
+        let result = retriever.retrieve("LangGraph state").await.unwrap();
+        assert!(!result.items.is_empty());
+        assert_eq!(result.items[0].page.id, "p1");
+        assert!(result.items[0].score > 0.0);
+    }
+
+    #[tokio::test]
+    async fn retrieve_respects_min_score() {
+        let store = Arc::new(InMemoryStore::new()) as Arc<dyn MemoryStore>;
+        let ks = KnowledgeStore::new(store);
+        ks.add_page(make_page("p1", "X", "Y", "Z")).await.unwrap();
+
+        let config = RetrieverConfig {
+            max_results: 10,
+            min_score: 0.99,
+        };
+        let retriever = MemoryRetriever::new(ks, config);
+        let result = retriever.retrieve("totally unrelated content").await.unwrap();
+        assert!(result.items.is_empty());
+    }
+
+    #[tokio::test]
+    async fn retrieve_respects_max_results() {
+        let store = Arc::new(InMemoryStore::new()) as Arc<dyn MemoryStore>;
+        let ks = KnowledgeStore::new(store);
+        for i in 0..5 {
+            ks.add_page(make_page(
+                &format!("p{i}"),
+                "LangGraph",
+                "framework",
+                "agent runtime",
+            ))
+            .await
+            .unwrap();
+        }
+        let config = RetrieverConfig {
+            max_results: 2,
+            min_score: 0.0,
+        };
+        let retriever = MemoryRetriever::new(ks, config);
+        let result = retriever.retrieve("LangGraph").await.unwrap();
+        assert_eq!(result.items.len(), 2);
+    }
+
+    #[test]
+    fn text_overlap_dice_zero_on_empty() {
+        assert_eq!(text_overlap_dice("hello", ""), 0.0);
+        assert_eq!(text_overlap_dice("", "hello"), 0.0);
+    }
+
+    #[test]
+    fn text_overlap_dice_identical() {
+        let s = "hello world";
+        assert!((text_overlap_dice(s, s) - 1.0).abs() < 0.001);
+    }
+
+    #[test]
+    fn extract_keywords_filters_stop_words() {
+        let stop = default_stop_words();
+        let kws = extract_keywords("the quick brown fox is fast", &stop);
+        assert!(!kws.contains(&"the".to_string()));
+        assert!(!kws.contains(&"is".to_string()));
+        assert!(kws.contains(&"quick".to_string()));
+        assert!(kws.contains(&"brown".to_string()));
+    }
+
+    #[test]
+    fn extract_keywords_filters_single_chars() {
+        let stop = default_stop_words();
+        let kws = extract_keywords("a b c dog", &stop);
+        assert!(!kws.contains(&"a".to_string()));
+        assert!(!kws.contains(&"b".to_string()));
+    }
+}
diff --git a/src/memory/store.rs b/src/memory/store.rs
new file mode 100644
index 0000000..1bb65bb
--- /dev/null
+++ b/src/memory/store.rs
@@ -0,0 +1,314 @@
+//! MemoryStore 抽象接口与默认实现。
+
+use std::collections::HashMap;
+use std::sync::Mutex;
+
+use async_trait::async_trait;
+use time::OffsetDateTime;
+
+use crate::memory::error::MemoryError;
+use crate::memory::types::{MemoryFilter, MemoryItem};
+
+/// 底层记忆存储抽象接口。
+///
+/// 下游可实现此 trait 以对接持久化后端（JSON 文件、SQLite、Redis 等）。
+/// 默认实现 [`InMemoryStore`] 基于进程内 HashMap。
+#[async_trait]
+pub trait MemoryStore: Send + Sync {
+    /// 保存/覆盖一个 MemoryItem（upsert 语义）。
+    /// - 如果 id 不存在，则插入新条目
+    /// - 如果 id 已存在，则覆盖旧条目
+    async fn save(&self, item: MemoryItem) -> Result<(), MemoryError>;
+
+    /// 根据 id 获取一个 MemoryItem。
+    async fn get(&self, id: &str) -> Result<Option<MemoryItem>, MemoryError>;
+
+    /// 根据 id 删除一个 MemoryItem。
+    async fn delete(&self, id: &str) -> Result<(), MemoryError>;
+
+    /// 根据 filter 列出 MemoryItem。
+    async fn list(&self, filter: &MemoryFilter) -> Result<Vec<MemoryItem>, MemoryError>;
+}
+
+/// 淘汰策略。
+#[derive(Debug, Clone)]
+pub enum EvictionPolicy {
+    /// 不淘汰（默认）。
+    None,
+    /// 超过存活时间（秒）淘汰。
+    Ttl { ttl_secs: u64 },
+    /// 超过容量上限淘汰最旧（基于 created_at）。
+    Capacity { max_items: usize },
+}
+
+/// 淘汰配置。
+#[derive(Debug, Clone)]
+pub struct EvictionConfig {
+    pub policy: EvictionPolicy,
+    /// 每写入 N 条后检查一次淘汰条件。
+    pub check_interval: usize,
+}
+
+impl Default for EvictionConfig {
+    fn default() -> Self {
+        Self {
+            policy: EvictionPolicy::None,
+            check_interval: 64,
+        }
+    }
+}
+
+/// 进程内默认实现 —— 基于 HashMap + Mutex，纯内存。
+pub struct InMemoryStore {
+    items: Mutex<HashMap<String, MemoryItem>>,
+    eviction: EvictionConfig,
+    /// 自上次淘汰检查以来的写入次数。
+    writes_since_check: Mutex<usize>,
+}
+
+impl InMemoryStore {
+    /// 创建一个无淘汰策略的 InMemoryStore。
+    pub fn new() -> Self {
+        Self {
+            items: Mutex::new(HashMap::new()),
+            eviction: EvictionConfig::default(),
+            writes_since_check: Mutex::new(0),
+        }
+    }
+
+    /// 创建一个带淘汰配置的 InMemoryStore。
+    pub fn with_eviction(eviction: EvictionConfig) -> Self {
+        Self {
+            items: Mutex::new(HashMap::new()),
+            eviction,
+            writes_since_check: Mutex::new(0),
+        }
+    }
+
+    fn maybe_evict(&self) {
+        // 不使用 .lock().await 跨点，先取计数判断是否需要淘汰
+        let should_check = {
+            let mut counter = self.writes_since_check.lock().unwrap();
+            *counter += 1;
+            if *counter >= self.eviction.check_interval {
+                *counter = 0;
+                true
+            } else {
+                false
+            }
+        };
+        if !should_check {
+            return;
+        }
+
+        let policy = self.eviction.policy.clone();
+        match policy {
+            EvictionPolicy::None => {}
+            EvictionPolicy::Ttl { ttl_secs } => {
+                let cutoff = OffsetDateTime::now_utc() - time::Duration::seconds(ttl_secs as i64);
+                let mut items = self.items.lock().unwrap();
+                items.retain(|_, v| v.created_at > cutoff);
+            }
+            EvictionPolicy::Capacity { max_items } => {
+                let mut items = self.items.lock().unwrap();
+                if items.len() > max_items {
+                    let mut vec: Vec<_> = items.drain().collect();
+                    // O(n) 部分排序：保留 created_at 最大的 max_items 个
+                    vec.select_nth_unstable_by(max_items, |a, b| {
+                        b.1.created_at.cmp(&a.1.created_at)
+                    });
+                    vec.truncate(max_items);
+                    *items = vec.into_iter().collect();
+                }
+            }
+        }
+    }
+}
+
+impl Default for InMemoryStore {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[async_trait]
+impl MemoryStore for InMemoryStore {
+    async fn save(&self, item: MemoryItem) -> Result<(), MemoryError> {
+        {
+            let mut items = self.items.lock().unwrap();
+            items.insert(item.id.clone(), item);
+        }
+        self.maybe_evict();
+        Ok(())
+    }
+
+    async fn get(&self, id: &str) -> Result<Option<MemoryItem>, MemoryError> {
+        let items = self.items.lock().unwrap();
+        Ok(items.get(id).cloned())
+    }
+
+    async fn delete(&self, id: &str) -> Result<(), MemoryError> {
+        let mut items = self.items.lock().unwrap();
+        items.remove(id);
+        Ok(())
+    }
+
+    async fn list(&self, filter: &MemoryFilter) -> Result<Vec<MemoryItem>, MemoryError> {
+        let items = self.items.lock().unwrap();
+        let mut result: Vec<MemoryItem> = items
+            .values()
+            .filter(|v| match &filter.prefix {
+                Some(p) => v.id.starts_with(p),
+                None => true,
+            })
+            .filter(|v| match filter.since {
+                Some(t) => v.created_at > t,
+                None => true,
+            })
+            .cloned()
+            .collect();
+        // 按 created_at 升序排列（最旧在前）
+        result.sort_by_key(|v| v.created_at);
+        // 应用 offset
+        if let Some(offset) = filter.offset {
+            if offset < result.len() {
+                result.drain(..offset);
+            } else {
+                result.clear();
+            }
+        }
+        // 应用 limit
+        if let Some(limit) = filter.limit {
+            result.truncate(limit);
+        }
+        Ok(result)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use time::OffsetDateTime;
+
+    fn make_item(id: &str) -> MemoryItem {
+        MemoryItem {
+            id: id.to_string(),
+            content: format!("content-{id}"),
+            metadata: serde_json::json!({}),
+            created_at: OffsetDateTime::now_utc(),
+        }
+    }
+
+    #[tokio::test]
+    async fn save_get_delete_list() {
+        let store = InMemoryStore::new();
+        store.save(make_item("a")).await.unwrap();
+        store.save(make_item("b")).await.unwrap();
+
+        let got = store.get("a").await.unwrap();
+        assert!(got.is_some());
+        assert_eq!(got.unwrap().id, "a");
+
+        let list = store.list(&MemoryFilter::default()).await.unwrap();
+        assert_eq!(list.len(), 2);
+
+        store.delete("a").await.unwrap();
+        assert!(store.get("a").await.unwrap().is_none());
+    }
+
+    #[tokio::test]
+    async fn save_is_upsert() {
+        let store = InMemoryStore::new();
+        store.save(make_item("a")).await.unwrap();
+        let mut item = make_item("a");
+        item.content = "updated".to_string();
+        store.save(item).await.unwrap();
+        let got = store.get("a").await.unwrap().unwrap();
+        assert_eq!(got.content, "updated");
+        let list = store.list(&MemoryFilter::default()).await.unwrap();
+        assert_eq!(list.len(), 1);
+    }
+
+    #[tokio::test]
+    async fn list_with_prefix_and_limit() {
+        let store = InMemoryStore::new();
+        store.save(make_item("foo_a")).await.unwrap();
+        store.save(make_item("foo_b")).await.unwrap();
+        store.save(make_item("bar_a")).await.unwrap();
+
+        let filter = MemoryFilter {
+            prefix: Some("foo_".to_string()),
+            ..Default::default()
+        };
+        let list = store.list(&filter).await.unwrap();
+        assert_eq!(list.len(), 2);
+
+        let filter = MemoryFilter {
+            prefix: Some("foo_".to_string()),
+            limit: Some(1),
+            ..Default::default()
+        };
+        let list = store.list(&filter).await.unwrap();
+        assert_eq!(list.len(), 1);
+    }
+
+    #[tokio::test]
+    async fn capacity_eviction() {
+        // 强制每次写入都检查
+        let eviction = EvictionConfig {
+            policy: EvictionPolicy::Capacity { max_items: 2 },
+            check_interval: 1,
+        };
+        let store = InMemoryStore::with_eviction(eviction);
+        // 第一条和第二条共存
+        store.save(make_item("a")).await.unwrap();
+        store.save(make_item("b")).await.unwrap();
+        // 第三条写入触发淘汰：a 或 b 之一被淘汰
+        store.save(make_item("c")).await.unwrap();
+
+        let list = store.list(&MemoryFilter::default()).await.unwrap();
+        assert_eq!(list.len(), 2);
+        // 留下的应该是 b 和 c（最新的两个）
+        let ids: Vec<&str> = list.iter().map(|v| v.id.as_str()).collect();
+        assert!(ids.contains(&"b"));
+        assert!(ids.contains(&"c"));
+    }
+
+    #[tokio::test]
+    async fn ttl_eviction() {
+        // TTL 设为 0 会立即过期，但我们想保留 "a" 等待 "b" 写入后被淘汰。
+        // 改用小 TTL + 睡眠：先 save a，sleep，save b 时 a 已过期被淘汰。
+        let eviction = EvictionConfig {
+            policy: EvictionPolicy::Ttl { ttl_secs: 1 },
+            check_interval: 1,
+        };
+        let store = InMemoryStore::with_eviction(eviction);
+        store.save(make_item("a")).await.unwrap();
+        // 等待超过 1 秒
+        std::thread::sleep(std::time::Duration::from_millis(1100));
+        // 触发淘汰：a 已超过 ttl_secs=1，应被淘汰
+        store.save(make_item("b")).await.unwrap();
+        let list = store.list(&MemoryFilter::default()).await.unwrap();
+        // 由于 ttl_secs=1，且 b 刚写入，可能刚好处于临界值。
+        // 我们只断言 list 不包含 "a" 即可。
+        let ids: Vec<&str> = list.iter().map(|v| v.id.as_str()).collect();
+        assert!(
+            !ids.contains(&"a"),
+            "expected 'a' to be evicted, but found in {ids:?}"
+        );
+    }
+
+    #[tokio::test]
+    async fn none_policy_no_eviction() {
+        let eviction = EvictionConfig {
+            policy: EvictionPolicy::None,
+            check_interval: 1,
+        };
+        let store = InMemoryStore::with_eviction(eviction);
+        for i in 0..100 {
+            store.save(make_item(&format!("item_{i}"))).await.unwrap();
+        }
+        let list = store.list(&MemoryFilter::default()).await.unwrap();
+        assert_eq!(list.len(), 100);
+    }
+}
diff --git a/src/memory/types.rs b/src/memory/types.rs
new file mode 100644
index 0000000..e7cdf80
--- /dev/null
+++ b/src/memory/types.rs
@@ -0,0 +1,73 @@
+//! 记忆系统核心数据类型。
+
+use serde::{Deserialize, Serialize};
+use time::OffsetDateTime;
+
+/// 记忆条目 —— MemoryStore 存储的基本单元。
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct MemoryItem {
+    /// 唯一标识。
+    pub id: String,
+    /// 内容（通常为 JSON 序列化的具体记忆数据）。
+    pub content: String,
+    /// 任意附加元数据。
+    pub metadata: serde_json::Value,
+    /// 创建时间。
+    pub created_at: OffsetDateTime,
+}
+
+/// MemoryStore 列表查询条件。
+#[derive(Debug, Clone, Default)]
+pub struct MemoryFilter {
+    /// 按 id 前缀过滤。
+    pub prefix: Option<String>,
+    /// 仅返回该时间之后创建的条目。
+    pub since: Option<OffsetDateTime>,
+    /// 跳过前 N 条。
+    pub offset: Option<usize>,
+    /// 最多返回 N 条。
+    pub limit: Option<usize>,
+}
+
+/// 知识页面 —— 描述一段结构化知识。
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct KnowledgePage {
+    /// 唯一标识。
+    pub id: String,
+    /// 标题。
+    pub title: String,
+    /// 一句话摘要。
+    pub summary: String,
+    /// 完整内容。
+    pub content: String,
+    /// 检索标签。
+    pub tags: Vec<String>,
+    /// 交叉引用的其他页面 ID。
+    pub references: Vec<String>,
+    /// 创建时间。
+    pub created_at: OffsetDateTime,
+    /// 最后更新时间。
+    pub updated_at: OffsetDateTime,
+}
+
+/// 知识页面索引条目 —— 用于轻量遍历和内容目录。
+#[derive(Debug, Clone)]
+pub struct PageIndexEntry {
+    pub id: String,
+    pub title: String,
+    pub summary: String,
+    pub tags: Vec<String>,
+    pub updated_at: OffsetDateTime,
+}
+
+impl From<&KnowledgePage> for PageIndexEntry {
+    fn from(p: &KnowledgePage) -> Self {
+        Self {
+            id: p.id.clone(),
+            title: p.title.clone(),
+            summary: p.summary.clone(),
+            tags: p.tags.clone(),
+            updated_at: p.updated_at,
+        }
+    }
+}