Firmware: ignore failed PMIC power-key reads

firmware/main/hal/board/stackchan.cc

@@ -87,7 +87,12 @@ class Pmic : public Axp2101 {
     // (W1C) so subsequent polls only fire on new presses.
     bool ConsumePekLongPress()
     {
-        uint8_t status = ReadReg(0x49);
+        // ReadReg() returns 0xFF on I2C failure, which would look like every
+        // IRQ bit is set and falsely trigger a shutdown. ReadRegs() leaves the
+        // caller-provided buffer untouched on failure, so initialise it to a
+        // safe value and fail closed when the PMIC cannot be read.
+        uint8_t status = 0;
+        ReadRegs(0x49, &status, 1);
         if (status & 0x04) {
             WriteReg(0x49, 0x04);
             return true;

firmware/tests/test_power_key_fail_safe.py

@@ -0,0 +1,23 @@
+"""Host-side source contract for fail-safe PMIC power-key polling."""
+
+from pathlib import Path
+import unittest
+
+
+ROOT = Path(__file__).resolve().parents[1]
+BOARD = (ROOT / "main/hal/board/stackchan.cc").read_text()
+
+
+class TestPowerKeyFailSafe(unittest.TestCase):
+    def test_failed_status_read_cannot_look_like_a_long_press(self):
+        handler = BOARD.split("bool ConsumePekLongPress()", 1)[1].split(
+            "bool IsExternalPowerConnected()", 1
+        )[0]
+
+        self.assertIn("uint8_t status = 0;", handler)
+        self.assertIn("ReadRegs(0x49, &status, 1);", handler)
+        self.assertNotIn("ReadReg(0x49)", handler)
+
+
+if __name__ == "__main__":
+    unittest.main()