checkpoint: working sensor acquisition and axis validation

docs/axis-validation-2026-08-16.md

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+# Enclosure Axis Validation — 2026-08-16
+
+The enclosure was tested with the battery end treated as the bottom of the
+reference orientation. The shared enclosure frame is +X right, +Y toward the
+top, and +Z toward the cover.
+
+## Capture integrity
+
+- 50,001 consecutive samples over 500.000 seconds
+- Effective sample rate: exactly 100 Hz
+- Timestamp interval: 10,000 us for every sample
+- Sequence gaps: 0
+- Axis-mapping mismatches between mapped and native columns: 0
+
+The raw capture is `captures/enclosure_axis_test.csv` and is intentionally
+excluded from source control.
+
+## Accelerometer orientation results
+
+| Position | Mean enclosure counts | Expected dominant axis | Result |
+| --- | ---: | ---: | --- |
+| Flat, cover up | (+4, -5, +258) | +Z | Pass |
+| Left edge down | (+258, -3, +10) | +X | Pass |
+| Right edge down | (-260, -9, +16) | -X | Pass |
+| Battery edge down | (-3, +255, +11) | +Y | Pass |
+| Top edge down | (+5, -264, +15) | -Y | Pass |
+| Cover side down | (-7, -7, -234) | -Z | Pass |
+
+The paired-face results give an initial calibration estimate of:
+
+```text
+offset_counts = (-1.30, -4.45, +12.20)
+counts_per_g  = (258.90, 259.85, 245.70)
+```
+
+These values are recorded as candidates only; calibration is not yet applied
+in firmware.
+
+## Gyroscope rotation results
+
+- The deliberate X rotation was X-dominant in 1,261 dynamic samples, versus
+  44 Y-dominant and 35 Z-dominant samples.
+- The deliberate Z rotation was Z-dominant in all 1,008 dynamic samples. No X
+  or Y sample crossed the same 500-count activity threshold.
+- Earlier side-to-side orientation changes were Y-dominant, confirming the
+  remaining gyro axis.
+
+The mounted sensor axes and the firmware's enclosure-frame mapping are
+consistent.