diff --git a/lua/eca/commands.lua b/lua/eca/commands.lua
index 667f228..522c680 100644
--- a/lua/eca/commands.lua
+++ b/lua/eca/commands.lua
@@ -547,6 +547,15 @@ function M.setup()
     desc = "Display ECA server tools (yank preview on confirm)",
   })
 
+  vim.api.nvim_create_user_command("EcaChatClear", function()
+    local sidebar = require("eca").get()
+    if sidebar then
+      sidebar:clear_chat()
+    end
+  end, {
+    desc = "Clear ECA chat buffer",
+  })
+
   Logger.debug("ECA commands registered")
 end
 
diff --git a/lua/eca/config.lua b/lua/eca/config.lua
index 397bccc..60dbe9a 100644
--- a/lua/eca/config.lua
+++ b/lua/eca/config.lua
@@ -17,6 +17,7 @@ M._defaults = {
     auto_start_server = false, -- Automatically start server on setup
     auto_download = true, -- Automatically download server if not found
     show_status_updates = true, -- Show status updates in notifications
+    preserve_chat_history = false, -- When true, chat history is preserved across sidebar open/close cycles
   },
   context = {
     auto_repo_map = true, -- Automatically add repoMap context when starting new chat
diff --git a/lua/eca/sidebar.lua b/lua/eca/sidebar.lua
index c50f112..d6c4e14 100644
--- a/lua/eca/sidebar.lua
+++ b/lua/eca/sidebar.lua
@@ -157,11 +157,19 @@ function M:close()
 end
 
 function M:_close_windows_only()
+  local preserve = Config.behavior and Config.behavior.preserve_chat_history
+
   for name, container in pairs(self.containers) do
     if container and container.winid and vim.api.nvim_win_is_valid(container.winid) then
-      container:unmount()
-      -- Keep the container reference but mark window as invalid
-      container.winid = nil
+      if preserve and name == "chat" then
+        -- Close only the window, keep the buffer alive
+        pcall(vim.api.nvim_win_close, container.winid, true)
+        container.winid = nil
+      else
+        container:unmount()
+        -- Keep the container reference but mark window as invalid
+        container.winid = nil
+      end
     end
   end
   Logger.debug("ECA sidebar windows closed")
@@ -245,6 +253,34 @@ function M:reset()
   end
 end
 
+function M:clear_chat()
+  local chat = self.containers and self.containers.chat
+  if chat and chat.bufnr and vim.api.nvim_buf_is_valid(chat.bufnr) then
+    -- Reset chat content state to prevent stale line numbers / extmark IDs.
+    self._tool_calls = {}
+    self._reasons = {}
+    self._current_tool_call = nil
+    self._is_tool_call_streaming = false
+    self._is_streaming = false
+    self._current_response_buffer = ""
+    self._last_user_message = ""
+    self._stream_visible_buffer = ""
+    if self._stream_queue then
+      self._stream_queue:clear()
+    end
+    -- Reset chat extmark refs (marks are invalidated when the buffer is wiped).
+    if self.extmarks then
+      self.extmarks.assistant = nil
+      self.extmarks.tool_header = nil
+      self.extmarks.tool_diff_label = nil
+    end
+    -- Prevent state/updated events from repopulating the cleared buffer.
+    self._welcome_message_applied = true
+    self._force_welcome = false
+    vim.api.nvim_buf_set_lines(chat.bufnr, 0, -1, false, {})
+  end
+end
+
 function M:new_chat()
   self:reset()
   self._force_welcome = true
@@ -318,6 +354,23 @@ function M:_create_containers()
     winfixwidth = false,
   }
 
+  local preserve = Config.behavior and Config.behavior.preserve_chat_history
+  local existing_chat_bufnr = preserve
+      and self.containers.chat
+      and self.containers.chat.bufnr
+      and vim.api.nvim_buf_is_valid(self.containers.chat.bufnr)
+      and self.containers.chat.bufnr
+    or nil
+
+  -- Always unmount the old Split to clean up its autocmds.
+  local old_chat = self.containers.chat
+  if old_chat then
+    if existing_chat_bufnr then
+      old_chat.bufnr = nil -- detach so unmount() doesn't delete the preserved buffer
+    end
+    pcall(old_chat.unmount, old_chat)
+  end
+
   --  Create and mount main chat container first
   self.containers.chat = Split({
     relative = "editor",
@@ -332,6 +385,13 @@ function M:_create_containers()
     }),
     win_options = base_win_options,
   })
+
+  if existing_chat_bufnr then
+    pcall(vim.api.nvim_buf_delete, self.containers.chat.bufnr, { force = true })
+    self.containers.chat.bufnr = existing_chat_bufnr
+    Logger.debug("Reusing existing chat buffer: " .. existing_chat_bufnr)
+  end
+
   self.containers.chat:mount()
   self:_setup_container_events(self.containers.chat, "chat")
 
diff --git a/tests/test_chat_clear.lua b/tests/test_chat_clear.lua
new file mode 100644
index 0000000..bb3eb9f
--- /dev/null
+++ b/tests/test_chat_clear.lua
@@ -0,0 +1,238 @@
+local MiniTest = require("mini.test")
+local eq = MiniTest.expect.equality
+local child = MiniTest.new_child_neovim()
+
+local function flush(ms)
+  vim.uv.sleep(ms or 120)
+  child.api.nvim_eval("1")
+end
+
+local function setup_helpers()
+  _G.fill_chat = function()
+    local sidebar = require("eca").get()
+    local chat = sidebar.containers.chat
+    vim.api.nvim_buf_set_lines(chat.bufnr, 0, -1, false, { "hello", "world", "foo" })
+  end
+
+  _G.get_chat_lines = function()
+    local sidebar = require("eca").get()
+    if not sidebar then
+      return nil
+    end
+    local chat = sidebar.containers and sidebar.containers.chat
+    if not chat or not vim.api.nvim_buf_is_valid(chat.bufnr) then
+      return nil
+    end
+    return vim.api.nvim_buf_get_lines(chat.bufnr, 0, -1, false)
+  end
+
+  _G.chat_has_old_content = function()
+    for _, line in ipairs(_G.get_chat_lines() or {}) do
+      if line == "hello" or line == "world" or line == "foo" then
+        return true
+      end
+    end
+    return false
+  end
+
+  _G.get_sidebar_flags = function()
+    local sidebar = require("eca").get()
+    if not sidebar then
+      return nil
+    end
+    return {
+      welcome_message_applied = sidebar._welcome_message_applied,
+      force_welcome = sidebar._force_welcome,
+    }
+  end
+end
+
+local function setup_env(preserve_chat_history)
+  child.lua(
+    [[
+    local Eca = require("eca")
+    Eca.setup({
+      behavior = {
+        auto_start_server = false,
+        auto_set_keymaps = false,
+        preserve_chat_history = ...,
+      },
+    })
+    local tab = vim.api.nvim_get_current_tabpage()
+    Eca._init(tab)
+    Eca.open_sidebar({})
+  ]],
+    { preserve_chat_history }
+  )
+  child.lua_func(setup_helpers)
+end
+
+local T = MiniTest.new_set({
+  hooks = {
+    pre_case = function()
+      child.restart({ "-u", "scripts/minimal_init.lua" })
+    end,
+    post_once = child.stop,
+  },
+})
+
+-- EcaChatClear ---------------------------------------------------------------
+
+T["EcaChatClear"] = MiniTest.new_set()
+
+T["EcaChatClear"]["command is registered"] = function()
+  setup_env(false)
+  local commands = child.lua_get("vim.api.nvim_get_commands({})")
+  eq(type(commands.EcaChatClear), "table")
+  eq(commands.EcaChatClear.name, "EcaChatClear")
+end
+
+T["EcaChatClear"]["clears chat buffer when sidebar is open"] = function()
+  setup_env(false)
+  flush(200)
+
+  child.lua("_G.fill_chat()")
+  eq(#child.lua_get("_G.get_chat_lines()"), 3)
+
+  child.cmd("EcaChatClear")
+
+  eq(child.lua_get("_G.get_chat_lines()"), { "" })
+end
+
+T["EcaChatClear"]["works without error when buffer is already empty"] = function()
+  setup_env(false)
+  flush(200)
+
+  child.lua([[
+    local sidebar = require("eca").get()
+    vim.api.nvim_buf_set_lines(sidebar.containers.chat.bufnr, 0, -1, false, {})
+  ]])
+
+  child.cmd("EcaChatClear")
+
+  eq(child.lua_get("_G.get_chat_lines()"), { "" })
+end
+
+T["EcaChatClear"]["clears hidden buffer when sidebar is closed with preserve=true"] = function()
+  setup_env(true)
+  flush(200)
+
+  child.lua("_G.fill_chat()")
+  child.lua([[require("eca").close_sidebar()]])
+  flush(100)
+
+  child.cmd("EcaChatClear")
+
+  eq(child.lua_get("_G.get_chat_lines()"), { "" })
+end
+
+T["EcaChatClear"]["buffer stays cleared on reopen with preserve=true"] = function()
+  setup_env(true)
+  flush(200)
+
+  child.lua("_G.fill_chat()")
+  child.lua([[require("eca").close_sidebar()]])
+  flush(100)
+
+  child.cmd("EcaChatClear")
+
+  eq(child.lua_get("_G.get_chat_lines()"), { "" })
+
+  child.lua([[require("eca").open_sidebar({})]])
+  flush(200)
+
+  eq(child.lua_get("_G.chat_has_old_content()"), false)
+end
+
+T["EcaChatClear"]["is a no-op when sidebar is closed and buffer was destroyed (preserve=false)"] = function()
+  -- With preserve=false, closing the sidebar destroys the buffer, so there is
+  -- nothing for EcaChatClear to clear. The important guarantee is that the
+  -- command does not raise an error in this state.
+  setup_env(false)
+  flush(200)
+
+  child.lua("_G.fill_chat()")
+  child.lua([[require("eca").close_sidebar()]])
+  flush(100)
+
+  local ok = child.lua_get("pcall(vim.cmd, 'EcaChatClear')")
+  eq(ok, true)
+end
+
+T["EcaChatClear"]["marks welcome as applied and clears force_welcome after clear"] = function()
+  setup_env(false)
+  flush(200)
+
+  child.lua("_G.fill_chat()")
+  child.cmd("EcaChatClear")
+
+  local flags = child.lua_get("_G.get_sidebar_flags()")
+  eq(flags.welcome_message_applied, true)
+  eq(flags.force_welcome, false)
+end
+
+T["EcaChatClear"]["is idempotent when called twice"] = function()
+  setup_env(false)
+  flush(200)
+
+  child.lua("_G.fill_chat()")
+  child.cmd("EcaChatClear")
+  child.cmd("EcaChatClear")
+
+  eq(child.lua_get("_G.get_chat_lines()"), { "" })
+end
+
+-- preserve_chat_history toggle cycle -----------------------------------------
+
+T["preserve_chat_history"] = MiniTest.new_set()
+
+T["preserve_chat_history"]["reuses same bufnr and keeps content across close/open"] = function()
+  setup_env(true)
+  flush(200)
+
+  child.lua("_G.fill_chat()")
+  local bufnr_before = child.lua_get("require('eca').get().containers.chat.bufnr")
+
+  child.lua([[require("eca").close_sidebar()]])
+  flush(100)
+  child.lua([[require("eca").open_sidebar({})]])
+  flush(200)
+
+  local bufnr_after = child.lua_get("require('eca').get().containers.chat.bufnr")
+  eq(bufnr_before, bufnr_after)
+  eq(child.lua_get("_G.chat_has_old_content()"), true)
+end
+
+T["preserve_chat_history"]["does not leak buffers across repeated toggles"] = function()
+  setup_env(true)
+  flush(200)
+
+  local buf_count_before = child.lua_get("#vim.api.nvim_list_bufs()")
+
+  for _ = 1, 5 do
+    child.lua([[require("eca").close_sidebar()]])
+    flush(100)
+    child.lua([[require("eca").open_sidebar({})]])
+    flush(200)
+  end
+
+  local buf_count_after = child.lua_get("#vim.api.nvim_list_bufs()")
+  -- Allow at most 1 extra buffer (nui internals), but definitely not 5+
+  eq(buf_count_after - buf_count_before <= 1, true)
+end
+
+T["preserve_chat_history"]["content is lost when preserve is disabled"] = function()
+  setup_env(false)
+  flush(200)
+
+  child.lua("_G.fill_chat()")
+
+  child.lua([[require("eca").close_sidebar()]])
+  flush(100)
+  child.lua([[require("eca").open_sidebar({})]])
+  flush(200)
+
+  eq(child.lua_get("_G.chat_has_old_content()"), false)
+end
+
+return T