stirrer: decode and report Pololu SMC status errors instead of guessing

Adds StatusError flags for the STATUS register and get_status_errors();
go() now reports if a fail-safe (safe-start violation or other error)
persists after GO instead of failing silently. _on_process uses the
same decoding to log any active error and only auto-recovers on a
safe-start violation, rather than the old narrow status & limit_status
heuristic.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EU3NTwLygh8jkrnqPoHNXF

components/actor/pololu1376.py

@@ -48,6 +48,24 @@ class Varid(enum.Enum):
 	MOTOR_CURRENT_LIMIT_OCCURRENCE_COUNT = 45
 
 
+# Bit flags of the STATUS variable (Varid.STATUS). A non-zero
+# SAFE_START_VIOLATION is the "fail-safe" state: the controller accepted
+# the GO command but still refuses to spin the motor. The other bits are
+# the SMC's other error conditions, which also stop the motor and can
+# make GO fail to bring it back.
+class StatusError(enum.IntFlag):
+	SAFE_START_VIOLATION = 0x0001
+	REQUIRED_CHANNEL_INVALID = 0x0002
+	SERIAL_ERROR = 0x0004
+	COMMAND_TIMEOUT = 0x0008
+	LIMIT_KILL_SWITCH = 0x0010
+	LOW_VIN = 0x0020
+	HIGH_VIN = 0x0040
+	OVER_TEMPERATURE = 0x0080
+	MOTOR_DRIVER_ERROR = 0x0100
+	ERR_LINE_HIGH = 0x0200
+
+
 class Pololu1376:
 	def __init__(self, serial_port):
 		# Deferred-open pyserial idiom: serial_port is constructed with no
@@ -117,8 +135,15 @@ class Pololu1376:
 
 		return rsp[1:]
 
+	def get_status_errors(self):
+		return StatusError(self.get_variable(Varid.STATUS))
+
 	def go(self):
-		return self.cmd("GO")
+		rsp = self.cmd("GO")
+		errors = self.get_status_errors()
+		if errors:
+			print(f"Pololu1376: ERROR - still in fail-safe after GO, active errors: {errors!r}")
+		return rsp
 
 	def stop(self):
 		return self.cmd("X")

components/actor/stirrerpololu1376.py

@@ -75,11 +75,11 @@ class StirrerPololu1376(AStirrer):
 		if not self.connected:
 			return
 		try:
-			status = self.drv.get_variable(Varid.STATUS)
-			limit_status = self.drv.get_variable(Varid.STATUS_LIMIT_STATUS)
-			if status & 0x01 == 0x01:
-				if limit_status & 0x01 == 0x01:
-					print("Recover after motor error!")
+			errors = self.drv.get_status_errors()
+			if errors:
+				print(f"StirrerPololu1376: motor controller reports errors: {errors!r}")
+				if StatusError.SAFE_START_VIOLATION in errors:
+					print("Recover after safe start violation!")
 					self.drv.go()
 		except Exception as e:
 			print(f"StirrerPololu1376: comm error in _on_process: {e}")