Sync Mark-10 gauge's live unit into ChannelConfig instead of a fixed default

Mark10Layer._parse() already tracked whichever unit suffix the gauge
last reported (lb/kgF/N/ozF — the gauge's physical unit button cycles
these independently of this app). serial_device.py hardcoded the
"force" channel's unit to "N" and never updated it, so switching units
on the gauge itself was invisible here.

Adds Mark10Layer.current_unit and has SerialDevice.read_channels()
keep the "force" ChannelConfig's unit in sync with it on every poll.
This fixes the unit shown in anything that reads ChannelConfig.unit
live — new plots, channel pickers, CSV log headers — but does not
relabel the Y-axis of an already-open plot pane, since plot axis
labels are baked into PlotConfig.y_label once at plot-build time, not
re-read from the channel live. Making an open pane's axis relabel
itself would need new signal plumbing from the device through
AcquisitionEngine to the strip chart — a bigger, separate change.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/api_layers/protocols/mark10.py b/api_layers/protocols/mark10.py
index a209232..48ed927 100644
--- a/api_layers/protocols/mark10.py
+++ b/api_layers/protocols/mark10.py
@@ -44,6 +44,11 @@ class Mark10Layer(BaseProtocol):
         super().__init__(port, baud, poll_interval, simulate)
         self._unit = "N"
 
+    @property
+    def current_unit(self) -> str:
+        """Last unit suffix seen in a gauge reply (e.g. "N", "kgF")."""
+        return self._unit
+
     # ── Protocol ──────────────────────────────────────────────────────────
 
     def _poll(self) -> Dict[str, float]: