# Lane K — LED badges & bench kit (M23 firmware+docs, M24 self-test)

You build the wearable side: badge firmware speaking the frozen blink protocol, the hardware
guide, and the bench self-test John runs before a shoot. Spec: `30-phase6.md` M23/M24 +
contract #4. Branch `lane/k-badges`, own worktree.

## M23 — firmware + docs, the parts that bite
- Contract #4 is FROZEN: 133 ms bit, `11100` preamble + 6-bit ID + even parity, continuous
  repeat, ID 63 = sync beacon. Keep the constants in ONE header (`hardware/badge/protocol.h`)
  shared by badge.ino and beacon.ino; document the manual-sync rule with
  `tracker_detect.py`'s decoder constants (can't import across languages — state both
  locations in the header comment and in docs/hardware.md).
- badge.ino: plain Arduino APIs (millis()-paced, no delay()-drift), single bright LED on a
  PWM pin OR a WS2812 (compile-time #define), ID set by #define (document per-badge flashing).
  Hardware is never ideal on paper: expose a `BIT_TRIM_US` calibration knob for clock drift.
- beacon.ino: ID 63, double LED brightness/size guidance.
- docs/hardware.md: parts list with rough prices (ESP32 dev board / ATtiny85, LED + resistor
  or WS2812, LiPo/coin cell, diffuser ping-pong ball), wiring, flashing (`arduino-cli`
  commands), wearing guidance (chest/hat, diffusion, one badge per person, ≥24 fps cameras,
  exposure caveat: blown-out video kills OOK contrast).
- Compile check: `arduino-cli compile --fqbn esp32:esp32:esp32` (and attiny if the core is
  installable). If arduino-cli isn't available in your environment, document the exact
  commands and mark the box unverified — do NOT claim compiled without output.

## M24 — bench self-test, the parts that bite
- `scripts/badge_selftest.py` must run lane H's REAL decoder (`tracker_detect` blink path) —
  import it, don't re-implement; if lane H hasn't merged yet, code against the frozen
  contract #3/#4 shapes and mark the integration box pending (integration3 re-runs it).
- `--synthetic` mode: render a small blinking clip using the fixture's marker-rendering
  helpers (foundation3 exposes them in synthetic.py) and assert the ID round-trips.
- Clear, John-readable failure messages: no blob found / decoded wrong ID / clip too short
  (< 1 word). Exit codes: 0 ok, 1 decode-fail, 2 usage.

## Acceptance (evidence in plan/status/lane-K.md)
- [ ] protocol.h constants byte-identical to contract #4; badge + beacon sketches compile
      (output pasted) or compile commands documented + marked unverified
- [ ] docs/hardware.md complete enough that John can order parts from it
- [ ] `uv run python scripts/badge_selftest.py --synthetic` decodes the rendered ID
      (`test_badge_selftest.py` covers it); failure paths print actionable text
- [ ] Backend suite green; `npm` untouched