diff --git a/backend/app/database/db.py b/backend/app/database/db.py
index 8183929..9df5381 100644
--- a/backend/app/database/db.py
+++ b/backend/app/database/db.py
@@ -26,8 +26,28 @@ def _load_extension(conn: sqlite3.Connection) -> None:
 
 def connect() -> sqlite3.Connection:
     settings = get_settings()
-    settings.db_path.parent.mkdir(parents=True, exist_ok=True)
-    conn = sqlite3.connect(settings.db_path)
+    return _connect_path(settings.db_path)
+
+
+def connect_knowledge() -> sqlite3.Connection:
+    """Desktop projections never share note or vector rows between Vaults."""
+    settings = get_settings()
+    if settings.environment != 'desktop':
+        return connect()
+    from app import host_bridge
+    from app.errors import ApiError
+    from uuid import UUID
+    try:
+        vault = str(UUID(host_bridge.vault_id.get() or ''))
+    except ValueError:
+        raise ApiError(409, 'WORKSPACE_NOT_OPEN', '请先打开授权工作区。') from None
+    # This database also holds durable logical records (tasks); never delete it as a cache.
+    return _connect_path(settings.data_dir / 'vault-state' / vault / 'core.sqlite3')
+
+
+def _connect_path(path) -> sqlite3.Connection:
+    path.parent.mkdir(parents=True, exist_ok=True)
+    conn = sqlite3.connect(path)
     conn.row_factory = sqlite3.Row
     # 关闭 Python sqlite3 的隐式事务，提交时机由 transaction() 或显式 commit 控制。
     conn.isolation_level = None
diff --git a/backend/app/repository.py b/backend/app/repository.py
index bb8213c..fa82787 100644
--- a/backend/app/repository.py
+++ b/backend/app/repository.py
@@ -14,7 +14,7 @@ from dataclasses import dataclass, field
 from datetime import datetime
 
 from app.contracts import NoteBlock
-from app.database.db import connect, transaction
+from app.database.db import connect_knowledge as connect, transaction
 from app.textutils import segment
 
 
diff --git a/backend/app/retrieval/engine.py b/backend/app/retrieval/engine.py
index 82f1008..9ee4eec 100644
--- a/backend/app/retrieval/engine.py
+++ b/backend/app/retrieval/engine.py
@@ -55,6 +55,10 @@ class RetrievalEngine:
 
     @track_search
     async def search(self, request: SearchRequest) -> SearchResponse:
+        from app.config import get_settings
+        if get_settings().environment == 'desktop':
+            from app.services.desktop_projection import refresh
+            await refresh()
         if request.mode == SearchMode.fts:
             return self._search_fts(request)
 
diff --git a/backend/app/retrieval/routed_vectors.py b/backend/app/retrieval/routed_vectors.py
index ab959be..4233e21 100644
--- a/backend/app/retrieval/routed_vectors.py
+++ b/backend/app/retrieval/routed_vectors.py
@@ -17,7 +17,7 @@ import sqlite3
 from dataclasses import dataclass
 from typing import Protocol
 
-from app.database.db import connect, transaction
+from app.database.db import connect_knowledge as connect, transaction
 from app.errors import ApiError
 from app.operation_logs import log_event
 from app.retrieval.vectorstore import VectorHit
diff --git a/backend/app/retrieval/vectorstore.py b/backend/app/retrieval/vectorstore.py
index 58a4a1c..fbfad85 100644
--- a/backend/app/retrieval/vectorstore.py
+++ b/backend/app/retrieval/vectorstore.py
@@ -13,7 +13,7 @@ from typing import Protocol, runtime_checkable
 
 import sqlite_vec
 
-from app.database.db import connect, transaction
+from app.database.db import connect_knowledge as connect, transaction
 
 
 @dataclass
diff --git a/backend/app/services/desktop_projection.py b/backend/app/services/desktop_projection.py
new file mode 100644
index 0000000..8f9a709
--- /dev/null
+++ b/backend/app/services/desktop_projection.py
@@ -0,0 +1,65 @@
+"""Rebuildable per-Vault FTS projection, sourced only through the Host broker."""
+from __future__ import annotations
+import asyncio
+from app import repository
+from app.database.db import connect_knowledge, transaction
+from app.knowledge.parser import parse_note
+from app.services import desktop_notes
+from app.services.coordination import vault_mutation_lock
+
+
+def entries():
+    result, offset = [], 0
+    while True:
+        page = desktop_notes.call('list', offset=offset, limit=1000)
+        result.extend(page['items'])
+        offset += len(page['items'])
+        if offset >= page['total'] or not page['items']: return result
+
+
+def _refresh():
+    current = entries()  # Always validates authorization, including when the cache is current.
+    conn = connect_knowledge()
+    try:
+        conn.execute('CREATE TABLE IF NOT EXISTS host_projection (file_id TEXT PRIMARY KEY, hash TEXT NOT NULL, path TEXT NOT NULL)')
+        old = {row['file_id']: (row['hash'], row['path']) for row in conn.execute('SELECT * FROM host_projection')}
+        changed = []
+        for entry in current:
+            if old.get(entry['file_id']) == (entry['hash'], entry['path']): continue
+            document = desktop_notes.call('read', file_id=entry['file_id'])
+            note = desktop_notes.note_from_document(document)
+            parsed = parse_note(markdown=note.markdown, file_path=note.file_path,
+                                folder=note.file_path.rpartition('/')[0], note_id=note.note_id,
+                                tags=note.tags, created_at=note.created_at, updated_at=note.updated_at)
+            changed.append((document, parsed))
+        removed = set(old) - {entry['file_id'] for entry in current}
+        # Content is verified before starting the projection transaction. No model/network IO inside.
+        with transaction(conn):
+            for file_id in removed:
+                for block_id in repository.delete_note(file_id, conn=conn):
+                    conn.execute('DELETE FROM vec_blocks WHERE block_id=?', [block_id])
+                conn.execute('DELETE FROM host_projection WHERE file_id=?', [file_id])
+            for document, parsed in changed:
+                old_ids = repository.replace_note_metadata(conn=conn, note_id=parsed.note_id, title=parsed.title,
+                    file_path=parsed.file_path, folder=parsed.folder, tags=parsed.tags, created_at=parsed.created_at,
+                    updated_at=parsed.updated_at, blocks=parsed.blocks)
+                for block_id in old_ids:
+                    conn.execute('DELETE FROM vec_blocks WHERE block_id=?', [block_id])
+                conn.execute('UPDATE blocks SET embedding_local_only=? WHERE note_id=?', (int(parsed.embedding_local_only), parsed.note_id))
+                conn.execute('INSERT OR REPLACE INTO host_projection VALUES (?,?,?)', (parsed.note_id, document['hash'], parsed.file_path))
+            if removed or changed:
+                repository.set_index_meta({'workspace_vectors_pending': '1'}, conn=conn)
+    finally:
+        conn.close()
+
+
+async def refresh():
+    async with vault_mutation_lock():
+        work = asyncio.create_task(asyncio.to_thread(_refresh))
+        # Keep the projection gate until the worker has finished even if the request is cancelled.
+        cancelled = False
+        while not work.done():
+            try: await asyncio.shield(work)
+            except asyncio.CancelledError: cancelled = True
+        work.result()
+        if cancelled: raise asyncio.CancelledError
diff --git a/backend/app/services/index_service.py b/backend/app/services/index_service.py
index db80a59..5b38e0b 100644
--- a/backend/app/services/index_service.py
+++ b/backend/app/services/index_service.py
@@ -16,7 +16,7 @@ from app.contracts import IndexJob, IndexRebuildRequest, IndexStatus
 from app.errors import ApiError
 from app.knowledge.parser import parse_note
 from app.services.note_service import index_note, prepare_note_index
-from app.database.db import connect, transaction
+from app.database.db import connect_knowledge as connect, transaction
 from app.services.coordination import vault_mutation_lock
 from app.retrieval.vectorstore import SqliteVecStore
 from app.local_models.runtime import LocalEmbedding
@@ -47,6 +47,14 @@ def _scan_vault() -> list[tuple[str, str, str, datetime, datetime]]:
 
     先读入内存：若文件读取失败，rebuild 尚未清空旧索引，不会造成数据损失。
     """
+    if get_settings().environment == 'desktop':
+        from app.services.desktop_projection import entries
+        from app.services import desktop_notes
+        result = []
+        for entry in entries():
+            note = desktop_notes.note_from_document(desktop_notes.call('read', file_id=entry['file_id']))
+            result.append((note.file_path, note.file_path.rpartition('/')[0], note.markdown, note.created_at, note.updated_at))
+        return result
     vault = get_settings().vault_path.resolve()
     result: list[tuple[str, str, str, datetime, datetime]] = []
     if not vault.exists():
@@ -80,8 +88,12 @@ async def rebuild(request: IndexRebuildRequest) -> IndexJob:
             {"scope": request.scope, "note_ids": request.note_ids},
         )
 
+    if get_settings().environment == 'desktop':
+        from app.services.desktop_projection import refresh
+        await refresh()
     docs = _scan_vault()
-    saved_records = {key: repository.get_note_record(key) for key in _pending_notes()}
+    record_ids = [entry.note_id for entry in repository.list_note_locations()] if get_settings().environment == 'desktop' else _pending_notes()
+    saved_records = {key: repository.get_note_record(key) for key in record_ids}
     saved_paths = {record.file_path: record for record in saved_records.values() if record is not None}
 
     _active_job_id = job_id
@@ -117,7 +129,8 @@ async def rebuild(request: IndexRebuildRequest) -> IndexJob:
         # All network/model awaits precede the transaction. The concrete SQLite
         # methods below complete synchronously despite their async interfaces.
         async with vault_mutation_lock():
-            if _scan_vault() != docs or saved_records != {key: repository.get_note_record(key) for key in _pending_notes()}:
+            current_ids = [entry.note_id for entry in repository.list_note_locations()] if get_settings().environment == 'desktop' else _pending_notes()
+            if _scan_vault() != docs or saved_records != {key: repository.get_note_record(key) for key in current_ids}:
                 raise ApiError(409, "INDEX_SNAPSHOT_CHANGED", "笔记在计算期间发生变化，稍后重新计算。")
             conn = connect()
             try:
diff --git a/backend/app/services/note_service.py b/backend/app/services/note_service.py
index a7a7901..497e38a 100644
--- a/backend/app/services/note_service.py
+++ b/backend/app/services/note_service.py
@@ -14,7 +14,7 @@ from uuid import uuid4
 
 from app import repository
 from app.contracts import Note, NoteBlock, NoteSummary
-from app.database.db import connect, transaction
+from app.database.db import connect_knowledge as connect, transaction
 from app.errors import ApiError
 from app.knowledge.parser import ParsedNote, parse_note
 from app.local_models.runtime import LocalEmbedding, background_embeddings
diff --git a/backend/app/services/task_service.py b/backend/app/services/task_service.py
index 830acb4..c981274 100644
--- a/backend/app/services/task_service.py
+++ b/backend/app/services/task_service.py
@@ -9,7 +9,7 @@ from weakref import WeakKeyDictionary
 
 from app import repository
 from app.contracts import Task, TaskStatus
-from app.database.db import connect, transaction
+from app.database.db import connect_knowledge as connect, transaction
 from app.errors import ApiError
 from app.operation_logs import log_event
 
@@ -39,6 +39,13 @@ def _now() -> datetime:
     return datetime.now(timezone.utc)
 
 
+def _prepare_note_link(note_id: str | None) -> None:
+    from app.config import get_settings
+    if note_id and get_settings().environment == 'desktop':
+        from app.services.desktop_projection import _refresh
+        _refresh()
+
+
 def _task_from_row(row) -> Task:
     return Task(
         task_id=row["task_id"],
@@ -56,6 +63,7 @@ def create_task(
     *, title: str, description: str = "", note_id: str | None = None,
     due_at: datetime | None = None,
 ) -> Task:
+    _prepare_note_link(note_id)
     if note_id and repository.get_note_record(note_id) is None:
         raise ApiError(404, "RESOURCE_NOT_FOUND", "note not found", {"note_id": note_id})
     task_id = f"task_{uuid4().hex}"
@@ -109,6 +117,7 @@ def update_task(task_id: str, values: dict[str, object]) -> Task:
         raise ApiError(404, "RESOURCE_NOT_FOUND", "task not found", {"task_id": task_id})
     if "note_id" in values and values["note_id"]:
         note_id = str(values["note_id"])
+        _prepare_note_link(note_id)
         if repository.get_note_record(note_id) is None:
             raise ApiError(404, "RESOURCE_NOT_FOUND", "note not found", {"note_id": note_id})
     if values.get("title") is None:
diff --git a/backend/tests/test_desktop_projection.py b/backend/tests/test_desktop_projection.py
new file mode 100644
index 0000000..42f1a9f
--- /dev/null
+++ b/backend/tests/test_desktop_projection.py
@@ -0,0 +1,76 @@
+import asyncio
+from dataclasses import replace
+from hashlib import sha256
+from uuid import uuid4
+
+from app import host_bridge, repository
+from app.config import get_settings
+from app.database import db
+from app.contracts import SearchRequest, SearchMode
+from app.retrieval.engine import engine
+from app.services import desktop_notes, desktop_projection, index_service, note_service
+from app.retrieval.embedding import HashEmbeddingProvider
+
+
+def test_projection_isolates_same_path_and_refreshes_changed_deleted_content(tmp_path, monkeypatch):
+    settings = replace(get_settings(), environment='desktop', data_dir=tmp_path, db_path=tmp_path/'global.sqlite3')
+    monkeypatch.setattr(db, 'get_settings', lambda: settings)
+    monkeypatch.setattr('app.config.get_settings', lambda: settings)
+    first, second = str(uuid4()), str(uuid4())
+    documents = {first: {'file_id': 'file-a', 'path': 'same.md', 'content': 'uniquefirsttoken', 'created_at': 0, 'updated_at': 1},
+                 second: {'file_id': 'file-b', 'path': 'same.md', 'content': 'uniquesecondtoken', 'created_at': 0, 'updated_at': 1}}
+    def call(method, **params):
+        doc = documents.get(host_bridge.vault_id.get())
+        if doc: doc['hash'] = sha256(doc['content'].encode()).hexdigest()
+        if method == 'list': return {'items': [doc] if doc else [], 'total': int(doc is not None)}
+        assert method == 'read' and doc['file_id'] == params['file_id']
+        return doc
+    monkeypatch.setattr(desktop_notes, 'call', call)
+    def search(vault, query):
+        token = host_bridge.vault_id.set(vault)
+        try: return asyncio.run(engine.search(SearchRequest(query=query, mode=SearchMode.fts)))
+        finally: host_bridge.vault_id.reset(token)
+    assert 'file-a' in search(first, 'uniquefirsttoken').model_dump_json()
+    assert 'file-a' not in search(second, 'uniquefirsttoken').model_dump_json()
+    assert 'file-b' in search(second, 'uniquesecondtoken').model_dump_json()
+    documents[first]['content'] = 'replacementtoken'
+    assert 'file-a' not in search(first, 'uniquefirsttoken').model_dump_json()
+    assert 'file-a' in search(first, 'replacementtoken').model_dump_json()
+    del documents[first]
+    assert 'file-a' not in search(first, 'replacementtoken').model_dump_json()
+    assert (tmp_path/'vault-state'/first/'core.sqlite3').is_file()
+    assert (tmp_path/'vault-state'/second/'core.sqlite3').is_file()
+    from app.services import task_service
+    token = host_bridge.vault_id.set(second)
+    try:
+        task = task_service.create_task(title='Scoped task', note_id='file-b')
+        assert task.note_id == 'file-b'
+    finally:
+        host_bridge.vault_id.reset(token)
+    token = host_bridge.vault_id.set(first)
+    try:
+        assert task_service.get_task(task.task_id) is None
+    finally:
+        host_bridge.vault_id.reset(token)
+
+
+def test_desktop_semantic_rebuild_preserves_host_file_id(tmp_path, monkeypatch):
+    settings = replace(get_settings(), environment='desktop', data_dir=tmp_path, db_path=tmp_path/'global.sqlite3')
+    monkeypatch.setattr(db, 'get_settings', lambda: settings)
+    monkeypatch.setattr('app.config.get_settings', lambda: settings)
+    monkeypatch.setattr(index_service, 'get_settings', lambda: settings)
+    document = {'file_id': 'stable-host-id', 'path': 'same.md', 'hash': sha256(b'test note').hexdigest(),
+                'content': 'test note', 'created_at': 0, 'updated_at': 1}
+    monkeypatch.setattr(desktop_notes, 'call', lambda method, **params: {'items': [document], 'total': 1} if method == 'list' else document)
+    monkeypatch.setattr(note_service, 'embedding', HashEmbeddingProvider())
+    async def no_remote(*args, **kwargs): return None
+    monkeypatch.setattr('app.retrieval.routed_vectors.embed_remote', no_remote)
+    from app.contracts import IndexRebuildRequest
+    token = host_bridge.vault_id.set(str(uuid4()))
+    try:
+        result = asyncio.run(index_service.rebuild(IndexRebuildRequest()))
+        assert result.status == 'completed'
+        assert repository.get_note_record('stable-host-id') is not None
+        assert [record.note_id for record in repository.list_note_locations()] == ['stable-host-id']
+    finally:
+        host_bridge.vault_id.reset(token)
diff --git a/docs/contracts/Host-v1契约.md b/docs/contracts/Host-v1契约.md
index 231c0ff..6591eb9 100644
--- a/docs/contracts/Host-v1契约.md
+++ b/docs/contracts/Host-v1契约.md
@@ -36,7 +36,9 @@ Windows 使用独立隐藏窗口注册 WTS 会话通知，锁屏、注销及本
 
 Workspace schema 2 新增持久操作回执。`workspace_write` 可选 operation_id（UUID），同 ID、同载荷重放返回原提交条目；不同载荷返回 OPERATION_PAYLOAD_CONFLICT。回执与文件元数据、outbox 在同一 SQLite 事务提交，即使之后再次编辑，查询仍返回对应操作的原始结果。schema 1 升级前用 SQLite VACUUM INTO 保存一致备份；旧 schema 1 Host 拒绝写入 schema 2。
 
-Core 的 `workspace.list/read/write/mutate/operation` RPC 通过受控管道转发，严格拒绝未知字段并校验 Host HTTP 请求捕获的 vault_id。切换或撤销工作区后旧任务返回 VAULT_PERMISSION_CHANGED。普通 HTTP 与 SSE 均由 Rust 添加工作区头，WebView 不能指定。Core 笔记 CRUD 不再写入 unbound-vault，也不从旧 Core 笔记索引回退读取；Markdown 元数据随正文保存，笔记 ID 使用 Rust file_id。当前 Core 笔记 RPC 单篇上限 1 MiB，管道帧上限 8 MiB；大媒体传输与检索投影另行实现，不宣称已满足完整 A-03。
+Core 的 `workspace.list/read/write/mutate/operation` RPC 通过受控管道转发，严格拒绝未知字段并校验 Host HTTP 请求捕获的 vault_id。切换或撤销工作区后旧任务返回 VAULT_PERMISSION_CHANGED。普通 HTTP 与 SSE 均由 Rust 添加工作区头，WebView 不能指定。Core 笔记 CRUD 不再写入 unbound-vault，也不从旧 Core 笔记索引回退读取；Markdown 元数据随正文保存，笔记 ID 使用 Rust file_id。当前 Core 笔记 RPC 单篇上限 1 MiB，管道帧上限 8 MiB；大媒体传输与完整取消提交确认另行实现，不宣称已满足完整 A-03。
+
+桌面检索与任务使用 Core 数据目录中的 `vault-state/<vault_id>/core.sqlite3`，不同 Vault 不共享笔记/向量/任务行。该库含持久任务，不能作为缓存整体删除。搜索前通过 Host 扫描摘要并事务更新全文投影，删除与修改使旧向量失效；向量重建通过 Host 读取正文并保持稳定 file_id。模型配置和凭据仍属设备配置，不随笔记库路由。没有授权 Vault 的知识请求明确失败，不回退全局索引。旧版无归属的 Core 任务不会自动指派给任意 Vault，其迁移入口仍待完成。
 
 OS 文件锁配合 Rust Mutex 维持单实例 Vault 写入。Web `serialized_vault_mutation` 使用同一 OS 文件锁；发现 `.ainote/host.sqlite3` 后拒绝 Web 写入，不自动降级。已有个人 Vault 不会被测试读取或迁移。
 
diff --git a/docs/development/OpenNexus生产化实施进度-2026-09-08.md b/docs/development/OpenNexus生产化实施进度-2026-09-08.md
index a761c0f..dc3045d 100644
--- a/docs/development/OpenNexus生产化实施进度-2026-09-08.md
+++ b/docs/development/OpenNexus生产化实施进度-2026-09-08.md
@@ -6,6 +6,9 @@
 
 ## 持续实施增量
 
+- 桌面全文/向量投影按 Vault 隔离，搜索前经 Host 对账文件摘要；向量重建从 Host 读取正文并保留 file_id。任务和笔记关联使用同一 Vault 的持久库。新增测试覆盖同路径双 Vault 隔离、变更/删除刷新、稳定 ID 和任务跨 Vault 不可见；真实 Core 测试增加全文搜索与删除后的检索验证。
+- 检索隔离增量最终后端全量 899 项通过，真实 Core/Vault 搜索集成和 Rust desktop 全目标 Clippy 通过。语义重建的稳定 ID 测试使用显式测试 Embedding，不作为真实模型质量或性能证据。
+
 - Core 笔记 CRUD 已经由受控管道接入当前授权 Rust Vault，保留稳定 file_id，支持 CAS 和跨 Vault 拒绝。新增 schema 2 操作回执，记录写入/移动/删除提交结果，升级前保存 schema 1 一致备份。同一写入操作重放 100 次不新增 outbox，也不覆盖后续编辑。
 - 真实 Python Core + 临时 Rust Vault 集成测试覆盖创建、列表、修改、并发冲突、移动、删除、跨 Vault 拒绝和提交查询；Rust desktop 全目标 35 项通过。Core 检索投影、后台任务取消的完整提交边界、大媒体和 UI 提交确认仍需继续实现，不能将 CRUD 接通等同整个 AI 工作流验收完成。
 - 此增量后端全量 897 项、前端全量 94 文件/506 项通过；Rust desktop 全目标 Clippy 与文档链接检查通过。旧 Core 打包产物尚未重新构建，不将开发解释器进程测试作为最新安装包证据。
diff --git a/frontend/src-tauri/tests/core_workspace.rs b/frontend/src-tauri/tests/core_workspace.rs
index a94be1a..3466a35 100644
--- a/frontend/src-tauri/tests/core_workspace.rs
+++ b/frontend/src-tauri/tests/core_workspace.rs
@@ -71,6 +71,17 @@ async fn real_core_notes_roundtrip_only_through_bound_host_and_confirm_commits()
     let original = workspace.lock().unwrap().read("Core fixture.md").unwrap();
     assert_eq!(original.entry.file_id, file_id);
     assert!(original.content.contains("original"));
+    let (status, search) = request(
+        &mut core,
+        "POST",
+        "/api/search",
+        &vault,
+        &uuid::Uuid::new_v4().to_string(),
+        Some(json!({"query":"original","mode":"fts"})),
+    )
+    .await;
+    assert_eq!(status, 200, "{search}");
+    assert!(search.to_string().contains(file_id));
     assert_eq!(
         workspace
             .lock()
@@ -146,6 +157,17 @@ async fn real_core_notes_roundtrip_only_through_bound_host_and_confirm_commits()
     .await;
     assert_eq!(status, 200, "{deleted}");
     assert!(!root.join("nested/Core fixture.md").exists());
+    let (status, search) = request(
+        &mut core,
+        "POST",
+        "/api/search",
+        &vault,
+        &uuid::Uuid::new_v4().to_string(),
+        Some(json!({"query":"original","mode":"fts"})),
+    )
+    .await;
+    assert_eq!(status, 200, "{search}");
+    assert!(!search.to_string().contains(file_id));
     assert_eq!(workspace.lock().unwrap().pending_count().unwrap(), 4);
     assert!(!temp
         .path()