style: increase ReadoutPanel font sizes and add CSV test fixture for data logging

src/pygui/backend/data/csv_recorder.py

@@ -12,7 +12,7 @@ from pygui.backend.wafer.zwafer_models import Sensor
 class CsvRecorder:
     def __init__(self) -> None:
         self._file_handle: Optional[TextIO] = None
-        self._path: Optional[str] = None
+        self._oath: Optional[str] = None
 
 
     @property
@@ -47,9 +47,15 @@ class CsvRecorder:
         return path
 
     @staticmethod
-    def write_segment(file_path: str, source_path: str, start_frame: int, end_frame: int) ->bool:
+    def write_segment(file_path: str, source_path: str, start_frame: int, end_frame: int) -> bool:
         """Copy a range of frames from source CSV into a new file.
 
+        Preserves the source's header structure so the segment re-imports
+        through FileBrowser unchanged: official CSVs keep their sensor-name
+        row, Z-wafer CSVs keep every metadata line through the "data"
+        sentinel. Frame indices count only valid data rows, matching how
+        the readers in data_records.py number frames.
+
         Args:
             file_path: Output CSV path.
             source_path: Source CSV path with full wafer data
@@ -57,11 +63,53 @@ class CsvRecorder:
             end_frame: Last frame index (inclusive)
 
         Returns:
-            True on success.
+            True on success (at least one frame written).
         """
-        import pandas as pd
-        df = pd.read_csv(source_path)
-        segment = df.iloc[start_frame:end_frame + 1]
-        segment.to_csv(file_path, index=False)
+        from pygui.backend.data.data_records import is_official_csv
+
+        if start_frame < 0 or end_frame < start_frame:
+            return False
+
+        def _is_data_row(stripped: str) -> bool:
+            cols = [c.strip() for c in stripped.split(",") if c.strip()]
+            if not cols:
+                return False
+            try:
+                [float(c) for c in cols]
+            except ValueError:
+                return False
+            return True
+
+        with open(source_path, "r", encoding="utf-8") as f:
+            lines = f.readlines()
+
+        out: list[str] = []
+        written = 0
+        frame_idx = -1
+        in_data = is_official_csv(source_path)
+
+        for i, line in enumerate(lines):
+            stripped = line.rstrip().rstrip(",").strip()
+            if not in_data:
+                out.append(line)
+                if stripped and stripped.split(",")[0].lower() == "data":
+                    in_data = True
+                continue
+            if i == 0:
+                # official format: row 0 is the sensor-name header
+                out.append(line)
+                continue
+            if not stripped or not _is_data_row(stripped):
+                continue
+            frame_idx += 1
+            if start_frame <= frame_idx <= end_frame:
+                out.append(line if line.endswith("\n") else line + "\n")
+                written += 1
+
+        if written == 0:
+            return False
+        Path(file_path).parent.mkdir(parents=True, exist_ok=True)
+        with open(file_path, "w", encoding="utf-8", newline="") as f:
+            f.writelines(out)
         return True