sprint-5: True Course + Track Keeping + XTE + PGN 129026/129284

- Python: NmeaNavData (COG/SOG/XTE data models with staleness tracking)
- Python: TrueCoursePilot with TRUE_COURSE and TRACK_KEEPING modes
- Python: 26 new tests (test_nmea_data, test_true_course)
- Modbus: COG/SOG/XTE input registers + TC setpoint/XTE-gain holdings
- Firmware: nmea2000_consumer handles PGN 129026 + 129284
- Firmware: pid_outer_task wired for TC + TK modes with live SOG scheduling
- YAML regenerated; 284 tests pass, firmware compiles clean

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

arautopilot/core/nmea_data.py

@@ -0,0 +1,117 @@
+"""NMEA 2000 navigation data models.
+
+Holds the live data received from PGN 127250/127251 (heading/ROT -- Sprint 3)
+and the new PGN 129026/129284 (COG+SOG / XTE+waypoint -- Sprint 5).
+
+All timestamps are float seconds (time.monotonic()).
+NaN means the value has never been received.
+"""
+
+from __future__ import annotations
+
+import math
+import time
+from dataclasses import dataclass, field
+
+
+@dataclass
+class HeadingData:
+    """PGN 127250 + 127251 -- magnetic heading and rate of turn."""
+
+    heading_deg: float = math.nan
+    rot_dps: float = 0.0
+    timestamp: float = field(default_factory=lambda: 0.0)
+    max_age_s: float = 5.0
+
+    def update(self, heading_deg: float, rot_dps: float) -> None:
+        self.heading_deg = heading_deg
+        self.rot_dps = rot_dps
+        self.timestamp = time.monotonic()
+
+    @property
+    def is_valid(self) -> bool:
+        if math.isnan(self.heading_deg):
+            return False
+        return (time.monotonic() - self.timestamp) < self.max_age_s
+
+    @property
+    def age_ms(self) -> int:
+        return int((time.monotonic() - self.timestamp) * 1000)
+
+
+@dataclass
+class CogSogData:
+    """PGN 129026 -- Course Over Ground (true) and Speed Over Ground.
+
+    COG is in degrees true (0..360).
+    SOG is in knots.
+    """
+
+    cog_deg: float = math.nan
+    sog_kn: float = math.nan
+    timestamp: float = field(default_factory=lambda: 0.0)
+    max_age_s: float = 5.0
+
+    def update(self, cog_deg: float, sog_kn: float) -> None:
+        self.cog_deg = cog_deg % 360.0
+        self.sog_kn = sog_kn
+        self.timestamp = time.monotonic()
+
+    @property
+    def is_valid(self) -> bool:
+        if math.isnan(self.cog_deg) or math.isnan(self.sog_kn):
+            return False
+        return (time.monotonic() - self.timestamp) < self.max_age_s
+
+    @property
+    def age_ms(self) -> int:
+        return int((time.monotonic() - self.timestamp) * 1000)
+
+
+@dataclass
+class XteData:
+    """PGN 129284 -- Cross Track Error and active waypoint.
+
+    xte_m: distance off track in metres.
+      Positive  → vessel is to starboard of the track line (steer port).
+      Negative  → vessel is to port  of the track line (steer starboard).
+
+    waypoint_name: free text from the chart plotter, empty if not available.
+    dtw_m: distance to waypoint in metres (NaN if unknown).
+    """
+
+    xte_m: float = math.nan
+    dtw_m: float = math.nan
+    waypoint_name: str = ""
+    timestamp: float = field(default_factory=lambda: 0.0)
+    max_age_s: float = 5.0
+
+    def update(
+        self,
+        xte_m: float,
+        dtw_m: float = math.nan,
+        waypoint_name: str = "",
+    ) -> None:
+        self.xte_m = xte_m
+        self.dtw_m = dtw_m
+        self.waypoint_name = waypoint_name
+        self.timestamp = time.monotonic()
+
+    @property
+    def is_valid(self) -> bool:
+        if math.isnan(self.xte_m):
+            return False
+        return (time.monotonic() - self.timestamp) < self.max_age_s
+
+    @property
+    def age_ms(self) -> int:
+        return int((time.monotonic() - self.timestamp) * 1000)
+
+
+@dataclass
+class NmeaNavData:
+    """Aggregated live navigation data used by the autopilot control loop."""
+
+    heading: HeadingData = field(default_factory=HeadingData)
+    cog_sog: CogSogData = field(default_factory=CogSogData)
+    xte: XteData = field(default_factory=XteData)