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+# Hardware — parts and rationale
+
+Part choices for the bench build, moved here from the README. The display
+medium decision (e-ink over LCD / memory LCD / OLED) is
+[ADR-003](adr.md#adr-003-display-medium--e-ink-gdey0579t93-panel); power is
+[ADR-008](adr.md#adr-008-mvp-power--wall-powered-battery-deferred-to-v08);
+keyboard transport is
+[ADR-009](adr.md#adr-009-keyboard-transport--usb-host-tinyusb).
+
+| Part      | Choice                                                        | Why                                                                                                                                                                                                                                                                                                                                  |
+| --------- | ------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
+| MCU       | **ESP32-S3-N16R8** (16 MB flash, 8 MB octal PSRAM)            | USB OTG host (for the keyboard), Wi-Fi, BLE, dual core @ 240 MHz, plenty of PSRAM for git pack data and screen buffer. Best-supported Rust target in the ESP family.                                                                                                                                                                 |
+| Display   | **GDEY0579T93 + DESPI-C579 breakout** (5.79", 792×272, 1-bit) | Good Display panel matched with its own FPC breakout. Strip aspect (~2.9:1) — Freewrite-coded: ~13 lines, ~79 cols at the editor's 10px font. Tiny framebuffer (~27 KB) leaves PSRAM headroom. The DESPI-C579 is a passive level-shifter / FPC-to-header board, not an active controller — driven over plain SPI like any other epd. |
+| Keyboard  | **Nuphy Air60/Halo65 wired USB-C**                            | ESP32-S3 acts as USB host via TinyUSB. BLE-HID is a fallback but contends with Wi-Fi for radio time during push.                                                                                                                                                                                                                     |
+| Storage   | microSD over SPI                                              | Holds both the git working copy (`/sd/repo/`) **and** the local-only scratch space (`/sd/local/`). Internal flash is for firmware + config only.                                                                                                                                                                                     |
+| Power     | **USB-C wall power for MVP**, 18650 + IP5306 in v0.8          | Measure power profile on real hardware before sizing the battery. E-ink + sleep should give multi-day battery life but battery introduces charging, safety, and BMS complexity we don't need on day one.                                                                                                                             |
+| Enclosure | 3D-printed, hinged lid                                        | v1.0 concern.                                                                                                                                                                                                                                                                                                                        |
+
+## Why the strip aspect
+
+The ~2.9:1 long-narrow shape biases the UX toward "current line + recent
+context" rather than "full page" — the writing posture we want. The renderer
+stays resolution-agnostic so a 10.3" e-ink upgrade (v1.x) is a swap, not a
+rewrite.
+
+## Bench status
+
+The board is on the bench and bring-up is largely done — per-spike results
+live in [`spikes.md`](spikes.md) and
+[`v0.1-mvp-technical.md`](v0.1-mvp-technical.md#hardware-bring-up-order),
+with failure write-ups in [`postmortems/`](postmortems/). Notable: the
+keyboard runs bus-powered on the S3's native USB port, and SD wiring is
+proven on shared SPI2 but blocked on a compatible ≤32 GB card
+([postmortem](postmortems/2026-07-05-spike3-sd-cmd59.md)).