diff --git a/lua/agent_term/ui/panel.lua b/lua/agent_term/ui/panel.lua
index 37637f4..d2e46b6 100644
--- a/lua/agent_term/ui/panel.lua
+++ b/lua/agent_term/ui/panel.lua
@@ -24,6 +24,40 @@ local function apply_window_options(win)
 	end
 end
 
+local function apply_panel_size(win)
+	if not (win and vim.api.nvim_win_is_valid(win)) then
+		return
+	end
+
+	if config.options.panel.position == enums.panel_position.BOTTOM then
+		vim.api.nvim_win_set_height(win, size_from(config.options.panel.height, vim.o.lines))
+	else
+		vim.api.nvim_win_set_width(win, size_from(config.options.panel.width, vim.o.columns))
+	end
+end
+
+local function reconcile_layout()
+	state.each_session(function(_, session)
+		if session.panel_win and vim.api.nvim_win_is_valid(session.panel_win) then
+			apply_panel_size(session.panel_win)
+			apply_window_options(session.panel_win)
+		end
+	end)
+end
+
+function M.reconcile_layout()
+	reconcile_layout()
+end
+
+local function schedule_reconcile_layout()
+	vim.schedule(reconcile_layout)
+end
+
+vim.api.nvim_create_autocmd({ "WinResized", "VimResized", "WinNew", "BufWinEnter" }, {
+	group = augroup,
+	callback = schedule_reconcile_layout,
+})
+
 function M.open(buf, agent_name)
 	local session = state.session(agent_name)
 	if state.has_valid_panel_win(agent_name) then
@@ -41,11 +75,7 @@ function M.open(buf, agent_name)
 	end
 
 	local win = vim.api.nvim_get_current_win()
-	if pos == enums.panel_position.BOTTOM then
-		vim.api.nvim_win_set_height(win, size_from(config.options.panel.height, vim.o.lines))
-	else
-		vim.api.nvim_win_set_width(win, size_from(config.options.panel.width, vim.o.columns))
-	end
+	apply_panel_size(win)
 
 	vim.api.nvim_win_set_buf(win, buf)
 	apply_window_options(win)
diff --git a/tests/spec/ui_spec.lua b/tests/spec/ui_spec.lua
index 6e6cf18..63169ee 100644
--- a/tests/spec/ui_spec.lua
+++ b/tests/spec/ui_spec.lua
@@ -93,4 +93,28 @@ describe("Given Agent Term UI views", function()
 		assert.is_nil(state.session("codex").panel_win)
 		assert.is_false(panel.focus("codex"))
 	end)
+
+	it(
+		"When external layout changes resize a side panel Then the configured width is restored",
+		function()
+			config.setup({
+				agents = {
+					codex = { preset = "codex" },
+				},
+				panel = {
+					position = "right",
+					width = 0.35,
+				},
+			})
+
+			local bufnr = track_buf(vim.api.nvim_create_buf(false, true))
+			local win = panel.open(bufnr, "codex")
+			local expected = math.max(1, math.floor(vim.o.columns * 0.35))
+
+			vim.api.nvim_win_set_width(win, math.max(1, expected - 10))
+			panel.reconcile_layout()
+
+			assert.are.equal(expected, vim.api.nvim_win_get_width(win))
+		end
+	)
 end)