fix: drop thinking deltas from background agent loops

Skip thinking-only deltas when accumulating background, scheduled-task, and teacher captured reply text.

src/bg_monitor.py

@@ -55,6 +55,8 @@ async def _drain_agent(sess, messages):
         if "delta" in d:
             delta = d.get("delta")
             if isinstance(delta, str):
+                if d.get("thinking"):
+                    continue
                 full += delta
         elif d.get("type") == "agent_step":
             round_num = d.get("round", round_num)

src/task_scheduler.py

@@ -1649,6 +1649,8 @@ class TaskScheduler:
                     data = json.loads(event_str[6:])
                     # Capture text from all event types, not just delta
                     if "delta" in data:
+                        if data.get("thinking"):
+                            continue
                         full_text += data["delta"]
                     elif data.get("type") == "tool_output":
                         # Tool results — capture summary so we have SOMETHING even

src/teacher_escalation.py

@@ -594,6 +594,8 @@ async def run_teacher_inline(
                         "exit_code": payload.get("exit_code"),
                     })
                 if "delta" in payload and isinstance(payload["delta"], str):
+                    if payload.get("thinking"):
+                        continue
                     captured_text_parts.append(payload["delta"])
                 yield 'data: ' + json.dumps(payload) + '\n\n'
                 continue

tests/test_document_editor_scroll.py

@@ -12,8 +12,8 @@ from pathlib import Path
 
 
 ROOT = Path(__file__).resolve().parents[1]
-DOC_JS = (ROOT / "static/js/document.js").read_text()
-STYLE_CSS = (ROOT / "static/style.css").read_text()
+DOC_JS = (ROOT / "static/js/document.js").read_text(encoding="utf-8")
+STYLE_CSS = (ROOT / "static/style.css").read_text(encoding="utf-8")
 
 
 def test_document_textarea_scrollbar_is_visible():