fix(renderer/buffer): include first line when slicing extmarks

Author: sudo-tee

lua/opencode/ui/renderer/buffer.lua

@@ -38,7 +38,7 @@ end
 local function slice_extmarks(extmarks, start_line)
   local slice = {}
   for line_idx, marks in pairs(extmarks or {}) do
-    if line_idx >= start_line + 1 then
+    if line_idx >= start_line then
       slice[line_idx - start_line] = vim.deepcopy(marks)
     end
   end

tests/unit/renderer_buffer_spec.lua

@@ -0,0 +1,52 @@
+local buffer = require('opencode.ui.renderer.buffer')
+local ctx = require('opencode.ui.renderer.ctx')
+local output_window = require('opencode.ui.output_window')
+local stub = require('luassert.stub')
+
+describe('renderer.buffer extmarks', function()
+  local set_lines_stub
+  local clear_extmarks_stub
+  local set_extmarks_stub
+  local highlight_changed_lines_stub
+
+  before_each(function()
+    ctx:reset()
+    set_lines_stub = stub(output_window, 'set_lines')
+    clear_extmarks_stub = stub(output_window, 'clear_extmarks')
+    set_extmarks_stub = stub(output_window, 'set_extmarks')
+    highlight_changed_lines_stub = stub(output_window, 'highlight_changed_lines')
+  end)
+
+  after_each(function()
+    set_lines_stub:revert()
+    clear_extmarks_stub:revert()
+    set_extmarks_stub:revert()
+    highlight_changed_lines_stub:revert()
+    ctx:reset()
+  end)
+
+  it('reapplies extmarks on the first changed line when updating a part', function()
+    ctx.render_state:set_part({ id = 'part_1', messageID = 'msg_1', type = 'text' }, 10, 11)
+
+    buffer.upsert_part_now('part_1', 'msg_1', {
+      lines = { 'alpha', 'gamma' },
+      extmarks = {
+        [1] = {
+          { line_hl_group = 'OpencodeReasoningText' },
+        },
+      },
+      actions = {},
+    }, {
+      lines = { 'alpha', 'beta' },
+      extmarks = {},
+      actions = {},
+    })
+
+    assert.stub(clear_extmarks_stub).was_called_with(11, 12)
+    assert.stub(set_extmarks_stub).was_called_with({
+      [0] = {
+        { line_hl_group = 'OpencodeReasoningText' },
+      },
+    }, 11)
+  end)
+end)