Typoena

A distraction-free, hackable, DIY writing machine. ESP32-S3 + e-ink + a real mechanical keyboard. You write Markdown, you commit, you push. Nothing else runs on it.

Status: pre-MVP, hardware on bench. Display, USB keyboard, live typing with partial refresh, Wi-Fi + TLS, SD storage, and on-device git push are all verified in spikes; SD mount and save are now wired into the app binary. No release has shipped yet — v0.1's remaining gate is the boot splash and wiring git publish (Ctrl-G → push) into the app binary. Live per-item status: docs/roadmap.md · failure write-ups: docs/postmortems/.

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Vision

A single-purpose appliance that boots into a text editor with a Vim keymap, edits Markdown files, and (optionally) pushes them to a git remote (GitHub first) over Wi-Fi. No browser, no notifications, no apps. Open lid → write → push (or don't) → close lid.

Two file scopes coexist on the SD card — formal definitions in CONTEXT.md:

• Tracked — lives in the git working copy, gets Published when the user presses Ctrl-G.
• Local — never leaves the device. Permanently-private: journal entries, scratch, things that aren't anyone else's business. There is no "promote to Tracked" gesture — scope is fixed at file creation.

Same editor, same keymap; the difference is just whether Ctrl-G (publish to the remote) is offered.

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Hardware

ESP32-S3-N16R8 (16 MB flash, 8 MB PSRAM) · GDEY0579T93 5.79″ e-ink strip (792×272, ~2.9:1 — biases the UX toward "current line + recent context", the writing posture we want) · Nuphy wired USB keyboard with the S3 as USB host · microSD over SPI · USB-C wall power for the MVP, battery in v0.8.

Full part table, rationale, and bench status: docs/hardware.md. Enclosure — a parametric, 3D-printable typewriter-body case (OpenSCAD): hardware/case/.

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Software stack

Language: Rust on esp-idf-rs (std). Every stack decision — language, UI strategy, display, git lib, auth, concurrency, storage, power, keyboard transport — has an ADR in docs/adr.md, including the rejected alternatives (Ratatui, Gleam + Shore on AtomVM, C/Arduino — ADR-001/002). How each decision is weighted against the user-facing requirements lives in docs/qfd.md; the ontology those docs use is defined in GLOSSARY.md. Where a default traces to a cost curve rather than a discrete pick — energy, latency, or memory bending against an interval or size — the curve and its knee live in docs/tradeoff-curves/README.md. A memory-safety review of the Rust unsafe/FFI surface (mostly usb_kbd.rs) is in MEMORY_AUDIT.md.

Layer	Choice	Notes
HAL / runtime	esp-idf-svc, esp-idf-hal	std build: heap, threads, VFS, mbedtls, Wi-Fi stack.
Display	Custom SSD1683 driver (src/epd.rs) + embedded-graphics	Dual-controller 792×272 panel; dirty-rect partial refresh (~630 ms measured).
UI layer	Custom thin widget layer	Ratatui's API shape without its char-grid terminal model (ADR-002).
Editor core	Custom, in-tree (src/editor.rs)	Modal (Normal / Insert / View / Command), motions, operators + text objects. Plain-ASCII buffer until the v0.2 UTF-8 work.
USB host	esp-idf TinyUSB bindings	Boot-protocol HID; verified on hardware (Spike 4).
Git	libgit2 via git2, built as an esp-idf component with mbedTLS (firmware/components/libgit2/)	gix was the original pick but can't push over HTTPS — the ADR-004 kill-switch fired (postmortem). On-device add → commit → push verified; ~16 s cold-:sync latency breakdown.
TLS	mbedtls via esp-idf	GitHub HTTPS with the chain checked against embedded roots; ≈35 KB heap measured during handshake (Spike 6).
Auth	HTTPS + GitHub PAT	v0.1 bakes credentials in at build time via TW_* env vars; provisioning + at-rest protection is ADR-011 (open), on-device settings land in v0.9.
Filesystem	FAT on SD (esp_vfs_fat)	Working copy lives here. Internal LittleFS holds config.

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UX boundaries set by the medium

E-ink is a brutal honesty filter on UI choices. Hard constraints we design around, not against:

• No cursor blink. Kills the panel and the battery.
• Typing latency target: ≤ 200 ms from keypress to glyph on screen, using partial refresh on the affected line only.
• Full refresh every ~20 partials to clear ghosting. User-visible flash — schedule it on pauses (>1 s of no input).
• No smooth scrolling. Page-style jumps only.
• No animations. Anywhere.
• Render only changed lines, not the viewport.

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Roadmap

Releases are frequent, and every version is a usable artifact rather than a checkpoint. Per-version scope, current [x]/[~] marks, and the Macroplan source live in docs/roadmap.md.

Version	Theme	One-liner
v0.1	MVP	Boots, edits one file, Ctrl-G pushes.
v0.2	Vim nav	Normal/Insert, motions, line numbers.
v0.2.5	Intl input	US-Intl dead keys: à é ê ç, '+space = '.
v0.3	Vim edit	dd yy p, undo/redo, counts.
v0.4	Visual + ex	v V, :w :q :e command line.
v0.5	Files	Ctrl-P over /repo + /local, buffers.
v0.6	Markdown	Headings, list continuation, soft-wrap.
v0.7	Search + git	/ search, :Gpull.
v0.8	Power	18650 + sleep + lid switch.
v0.9	Robustness	Crash-safe writes, reconnect, settings.
v1.0	Polish	Boot ≤ 3 s, fonts, themes, enclosure, guide.
v1.x	Stretch	10.3″ panel, multi-remote, stats, BLE.

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Repo layout

/firmware                 Rust crate, esp-idf-rs target
                          (SD card mounted at runtime contains /repo and /local)
  /src
    main.rs               app binary — editor + display + USB (SD/git not wired yet)
    editor.rs             modal editor core: buffer, modes, keymap, :commands
    epd.rs                SSD1683 dual-controller e-ink driver
    usb_kbd.rs            TinyUSB host glue, HID → key events
    /bin                  on-device spike binaries (sd_fat, wifi_tls, git_push,
                          git_sync, git_smoke)
  /components/libgit2     libgit2 as an esp-idf CMake component (mbedTLS);
                          source vendored as a git submodule
  build.rs                bakes TW_* env vars (Wi-Fi, PAT, author) — v0.1 config path
/spikes                   desktop spikes (spike7 git push proof, pre-device)
/docs                     ADRs, QFD, hardware, roadmap, per-version specs,
                          spikes.md, postmortems/, notes/
/hardware                 enclosure — parametric OpenSCAD case (case/) + renders
CONTEXT.md                project glossary — Tracked / Local / Save / Publish, and
                          the principles that fall out of them
GLOSSARY.md               methodology glossary — the WHAT / Function /
                          Characteristic / Metric / Target ontology layers
package.json              pnpm + oxfmt — formatting toolchain for docs/JSON

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Open questions / risks (tracked, not yet resolved)

• Heap fragmentation over a long writing session with the PSRAM allocator.
• Real-world e-ink ghosting with the current partial-refresh cadence.
• [~] Use-after-free freeing the in-flight USB transfer on keyboard unplug — fixed in code, pending an on-device hot-plug run to confirm (MEMORY_AUDIT.md finding #1).

Retired risks (gix push, SD CMD59 rejection, TinyUSB HID stability, TLS heap, libgit2-on-xtensa) and how they died: docs/spikes.md and docs/postmortems/.

These get resolved by writing code, not by deciding harder.