Phase 14: multi-host file browser (0.15.0)

The Files page gained a host switcher: when agents are registered, a Host
dropdown switches the whole browser between the local host and any online agent
(switching resets path + clipboard). Every file operation is sandboxed by the
selected agent's own ALLOWED_BROWSE_ROOTS/HOST_ROOT_PREFIX.

- agent_app.py: /agent/files/* (list/read/download/write/mkdir/touch/rename/
  copy/move/delete/upload) reusing file_service + device_service; BrowseError
  -> HTTP 400.
- routers/agents.py: proxy routes at /api/agents/{id}/files/* (audit-logged
  mutations); download streams via download_to_file, upload via upload_file.
  Reuses the WriteBody/NameBody/RenameBody/TransferBody models from routers.files.
- Frontend: filesApi methods take an optional trailing agentId; Files.tsx tracks
  a host and threads it through every call, query key, and the editor/dialogs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/agent_app.py

@@ -39,6 +39,8 @@ from docker_client import DockerError, get_client, safe_call
 from services import (
     backup_service,
     compose_service,
+    device_service,
+    file_service,
     image_service,
     network_service,
     update_service,
@@ -57,7 +59,7 @@ def _map_docker(exc: DockerError):
         raise HTTPException(status_code=code, detail=exc.detail or exc.error)
     raise exc  # falls through to the global 502 DockerError handler
 
-AGENT_VERSION = "0.14.0"
+AGENT_VERSION = "0.15.0"
 
 
 # --------------------------------------------------------------------------- #
@@ -99,6 +101,34 @@ class ContainerRefBody(BaseModel):
     force: bool = False
 
 
+class FileWriteBody(BaseModel):
+    path: str
+    content: str
+
+
+class FileNameBody(BaseModel):
+    path: str
+    name: str
+
+
+class FileRenameBody(BaseModel):
+    path: str
+    new_name: str
+
+
+class FileTransferBody(BaseModel):
+    src: str
+    dest_dir: str
+    overwrite: bool = False
+
+
+def _file_guard(fn, *args, **kwargs):
+    try:
+        return fn(*args, **kwargs)
+    except file_service.BrowseError as exc:
+        raise HTTPException(status_code=400, detail=str(exc)) from exc
+
+
 # --------------------------------------------------------------------------- #
 # Helpers
 # --------------------------------------------------------------------------- #
@@ -406,6 +436,85 @@ async def image_check() -> dict:
     return await update_service.check_all()
 
 
+# --------------------------------------------------------------------------- #
+# File browser (sandboxed by this agent's ALLOWED_BROWSE_ROOTS/HOST_ROOT_PREFIX)
+# --------------------------------------------------------------------------- #
+
+
+@app.get("/agent/files/list", dependencies=[Depends(verify_token)])
+def files_list(path: str = Query("/"), show_hidden: bool = Query(False)) -> dict:
+    return _file_guard(device_service.browse, path, show_hidden)
+
+
+@app.get("/agent/files/read", dependencies=[Depends(verify_token)])
+def files_read(path: str = Query(...)) -> dict:
+    return _file_guard(file_service.read_file, path)
+
+
+@app.get("/agent/files/download", dependencies=[Depends(verify_token)])
+def files_download(path: str = Query(...)):
+    real, filename = _file_guard(file_service.resolve_download, path)
+    return FileResponse(real, filename=filename, media_type="application/octet-stream")
+
+
+@app.put("/agent/files/write", dependencies=[Depends(verify_token)])
+def files_write(body: FileWriteBody) -> dict:
+    return _file_guard(file_service.write_file, body.path, body.content)
+
+
+@app.post("/agent/files/mkdir", dependencies=[Depends(verify_token)])
+def files_mkdir(body: FileNameBody) -> dict:
+    return _file_guard(file_service.create_dir, body.path, body.name)
+
+
+@app.post("/agent/files/touch", dependencies=[Depends(verify_token)])
+def files_touch(body: FileNameBody) -> dict:
+    return _file_guard(file_service.create_file, body.path, body.name)
+
+
+@app.post("/agent/files/rename", dependencies=[Depends(verify_token)])
+def files_rename(body: FileRenameBody) -> dict:
+    return _file_guard(file_service.rename, body.path, body.new_name)
+
+
+@app.post("/agent/files/copy", dependencies=[Depends(verify_token)])
+def files_copy(body: FileTransferBody) -> dict:
+    return _file_guard(file_service.copy, body.src, body.dest_dir, body.overwrite)
+
+
+@app.post("/agent/files/move", dependencies=[Depends(verify_token)])
+def files_move(body: FileTransferBody) -> dict:
+    return _file_guard(file_service.move, body.src, body.dest_dir, body.overwrite)
+
+
+@app.delete("/agent/files", dependencies=[Depends(verify_token)])
+def files_delete(path: str = Query(...), recursive: bool = Query(False)) -> dict:
+    return _file_guard(file_service.delete, path, recursive)
+
+
+@app.post("/agent/files/upload", dependencies=[Depends(verify_token)])
+async def files_upload(
+    path: str = Form(...),
+    overwrite: bool = Form(False),
+    rel_path: str = Form(""),
+    file: UploadFile = File(...),
+) -> dict:
+    real = _file_guard(
+        file_service.upload_target, path, file.filename or "", overwrite, rel_path or None
+    )
+    tmp = tempfile.NamedTemporaryFile(delete=False, dir=os.path.dirname(real))
+    try:
+        while chunk := await file.read(1024 * 1024):
+            tmp.write(chunk)
+        tmp.close()
+        os.replace(tmp.name, real)
+    except OSError as exc:
+        if os.path.exists(tmp.name):
+            os.unlink(tmp.name)
+        raise HTTPException(status_code=400, detail=f"Upload failed: {exc}") from exc
+    return {"ok": True, "name": rel_path or file.filename}
+
+
 @app.websocket("/agent/ws/logs/{stack_id}")
 async def ws_logs(websocket: WebSocket, stack_id: str, token: str | None = Query(default=None)):
     """Stream `docker compose logs -f` to the central app (token via query param)."""