# Quality Function Deployment

Translates what the device must _be_ (user-facing requirements) into what it
must _achieve_ (engineering characteristics) and what we must _build_
(components).
Surfaces the few targets that dominate the design and the conflicts between
them. Every decision cell points back to [`adr.md`](adr.md).

Scope: v0.1 MVP — see
[`v0.1-mvp-product.md`](v0.1-mvp-product.md) for user-facing scope and
[`v0.1-mvp-technical.md`](v0.1-mvp-technical.md) for implementation —
with the v0.2–v1.0 trajectory ([README](../README.md),
[roadmap](roadmap.md)) in mind so we don't paint into a corner. Terminology
(e.g. **Tracked**, **Local**, **Save**, **Publish**) follows the project
glossary at [`../CONTEXT.md`](../CONTEXT.md).

Format inspired by the classic House of Quality, kept compact. Strength
weights: **9** strong, **3** medium, **1** weak, blank none. The §3
matrix and §4 roof — plus a guessed competitor perception zone — live
in [`quality-house.md`](quality-house.md); this file owns the WHAT/HOW
catalogues (§1, §2), the narrative reading of the numbers (§3, §4), and
the downstream sections (§5–§8).

---

## 1. Customer requirements (the WHATs)

What a user (= me) values about the device, with importance weights on a
1–10 scale. Source columns point at the doc the requirement comes from.

| ID  | Requirement                                                                        | Weight | Source                                                                                                                         |
| --- | ---------------------------------------------------------------------------------- | :----: | ------------------------------------------------------------------------------------------------------------------------------ |
| W1  | Sub-second visible response to typing                                              |   10   | [product → Write](v0.1-mvp-product.md#user-stories), [README → UX](../README.md#ux-boundaries-set-by-the-medium)               |
| W2  | **Publishing** is one deliberate action away                                       |   9    | [product → Publish](v0.1-mvp-product.md#user-stories), [CONTEXT → Publish](../CONTEXT.md#user-facing-actions)                  |
| W3  | Pulling power never corrupts the file                                              |   10   | [product → Recover](v0.1-mvp-product.md#user-stories), [acceptance](v0.1-mvp-product.md#acceptance-criteria)                   |
| W4  | Provisioning never interrupts a writing session                                    |   7    | [product → Provisioning](v0.1-mvp-product.md#provisioning-build-time-dev-only), [roadmap → v0.9](roadmap.md#v09--robustness--) |
| W5  | Quick boot to a writing cursor                                                     |   6    | [product → acceptance](v0.1-mvp-product.md#acceptance-criteria) (≤ 5 s)                                                        |
| W6  | Long sessions without crash / lag / drift                                          |   9    | [product → acceptance](v0.1-mvp-product.md#acceptance-criteria) (1 h soak)                                                     |
| W7  | Nothing on the device competes with prose                                          |   8    | [README → vision](../README.md#vision)                                                                                         |
| W8  | The UI never moves except when I move it                                           |   7    | [README → UX](../README.md#ux-boundaries-set-by-the-medium)                                                                    |
| W9  | Codebase absorbs the planned roadmap without rewrite                               |   8    | [roadmap](roadmap.md)                                                                                                          |
| W10 | I can repair or fork it with hobbyist tools                                        |   5    | [README → vision](../README.md#vision)                                                                                         |
| W11 | Multi-day battery life (v0.8 onward)                                               |   4    | [roadmap → v0.8](roadmap.md#v08--power-battery--sleep--)                                                                       |
| W12 | Local-only file scope coexists with git scope (v0.5+)                              |   5    | [README → scopes](../README.md#vision), [roadmap → v0.5](roadmap.md#v05--file-palette--multi-file--)                           |
| W13 | Typography sets a writing-tool tone — typewriter or developer editor, never gadget |   7    | [roadmap → v1.0](roadmap.md), [README → UX](../README.md#ux-boundaries-set-by-the-medium)                                      |
| W14 | I can carry the device and write away from a desk                                  |   8    | [roadmap → v0.8](roadmap.md#v08--power-battery--sleep--), [README → hardware](../README.md#hardware)                           |

---

## 2. Engineering characteristics (the HOWs)

Measurable attributes — performance metrics of the device's functions
(below), or properties of its firmware artifact, memory layout, and build
process. See [`../GLOSSARY.md`](../GLOSSARY.md) for the ontology layers
(WHAT / Function / Characteristic / Metric / Target). Targets are v0.1
unless noted. Direction column shows what "better" looks like
(↑ higher, ↓ lower, → fixed).

### Functions

The device performs these. The HOW rows below measure quality attributes
of these functions, or of artifacts they produce.

| Function  | Transformation                                  |
| --------- | ----------------------------------------------- |
| Type      | keypress → glyph rendered + buffer mutated      |
| Save      | dirty buffer → persisted file on SD             |
| Publish   | persisted file → commit on remote               |
| Recover   | degraded file state → readable file             |
| Boot      | power-on → cursor ready                         |
| Provision | uninitialized device → configured device        |

**Provision** is build-time-only in v0.1 ([ADR-005], [ADR-007]); it
joins the runtime five from v0.9 onward. Sub-functions referenced
inside HOW names: **Render** (buffer → e-ink frame, inside Type),
**Reconnect** (network outage → restored, inside Publish).

### Characteristics

| ID  | Characteristic                                     | Dir | v0.1 target              | v1.0 target         |
| --- | -------------------------------------------------- | :-: | ------------------------ | ------------------- |
| H1  | Type latency (keypress → glyph)                    |  ↓  | ≤ 200 ms                 | ≤ 150 ms            |
| H2  | Partial-refresh region area per keystroke          |  ↓  | ≤ 1 text line (~22 px h) | same                |
| H3  | Full-refresh cadence (clears ghosting)             |  →  | 1 per 64 partials        | tuned by panel temp |
| H4  | Boot latency (cold)                                |  ↓  | ≤ 5 s                    | ≤ 3 s †             |
| H5  | Continuous-typing endurance (no drop, no leak)     |  ↑  | ≥ 1 h                    | ≥ 8 h               |
| H6  | Publish reliability (network up)                   |  ↑  | ≥ 95 %                   | ≥ 99 %              |
| H7  | Publish latency (one file)                         |  ↓  | ≤ 30 s                   | ≤ 10 s              |
| H8  | Save durability (post-confirm power loss)          |  →  | 100 %                    | 100 %               |
| H9  | PSRAM heap headroom during Publish                 |  ↑  | ≥ 1 MB free at peak      | same                |
| H10 | Firmware binary size                               |  ↓  | ≤ 2 MB                   | ≤ 1.5 MB            |
| H11 | Stack budget across all tasks                      |  ↓  | ≤ 80 KB (sum)            | same                |
| H12 | Network reconnect time (transient outage)          |  ↓  | ≤ 30 s                   | ≤ 10 s              |
| H13 | Idle / typing / Publish current draw               |  ↓  | measured only            | sized for >2 days   |
| H15 | Build time (clean, release)                        |  ↓  | ≤ 7 min                  | ≤ 5 min             |

† **Boot latency, measured 2026-07-11:** cold boot is **4258 ms**, so the ≤ 5 s
v0.1 target is met. The ≤ 3 s v1.0 target is assessed **marginal-to-unreachable** —
one ~1.9 s full refresh is unavoidable at cold boot (the `0x26` "previous" bank is
garbage until the first full paint), an e-ink floor rather than a tuning knob.
Breakdown + levers: [`notes/boot-time-budget.md`](notes/boot-time-budget.md).

---

## 3. House of Quality — WHATs × HOWs

The matrix (row × column = how strongly characteristic H advances requirement
W) and its Σ row — the weighted vote `Σ(weight × strength)` on which
characteristics deserve the most engineering attention — live in
[`quality-house.md`](quality-house.md). The Σ totals quoted below are
from its basement row.

### Top engineering priorities (from importance)

1. **H9 — PSRAM heap during push** (193). gitoxide pack + rope + TLS all
   share the same arena; [ADR-001] and [ADR-004] trade binary size for ecosystem
   so this becomes the watched metric. The umbrella typography WHAT (W13)
   keeps a fixed-size glyph-cache load on top of that arena pressure.
2. **H2 — partial-refresh region area** (177). Bound how many pixels the
   panel has to flip per keypress; [ADR-003] is the hardware-side answer.
3. **H8 — save durability** (156). Atomic-rename + fsync; FAT's weakness
   is acknowledged in [ADR-007] and mitigated, not designed around. H8's
   voter base spans W3 (power-loss correctness), W6 (long sessions),
   W12 (file scopes), and W14 (carrying = unclean shutdowns) — the
   fourth voter is what lifts H8 into the top three by arithmetic alone.
4. **H12 — network reconnect time** (153). Mobile use is the chief driver
   (W14 + W2 + W4 + W6); [ADR-005] PAT auth and reconnect backoff own
   this. Previously below the top six on a stationary v0.1 reading;
   W14 promotes it.
5. **H1 — Type latency** (148). The single most user-visible number;
   [ADR-002] and [ADR-003] are co-conspirators.
6. **H3 — full-refresh cadence** (144). The ghosting/flash tradeoff; lives
   in the render layer.

H13 (current draw, 137) sits at #7 — close to the top-six cutoff because
W14 promotes the "wall-power for v0.1, measure first" stance from
acknowledged tradeoff to watched metric. The v0.1 "measured only" target
(§2) is still right; what changes is that bench multimeter readings (§6)
gain a second audience — sizing the v0.8 cell against a real portability
target, not just informing ADR-008's deferral.

H6 (Publish reliability, 134) drops out of the top six. Its ADR ownership
([ADR-004] gitoxide + [ADR-005] PAT) and spike 7 kill-switch are unchanged
— the matrix simply reads W14's mobile-use voter as a louder signal for
reconnect (H12) than for the Publish transport itself.

**Why H8 ranks where it does.** Pre-W14, HoQ totals rewarded characteristics
that touch many WHATs over characteristics that absolutely matter for one WHAT.
W3 ("Pulling power never corrupts the file", weight 10) was H8's
strongest single voter, but H8 still sat at #6 because its base was
narrow. W14's "carrying = bumps = unclean shutdowns" widens H8's voter
base and pushes it to #3 by arithmetic. §6's "table-stakes correctness"
override is no longer the load-bearing argument for H8's prominence —
its acceptance-criteria override for H4/H5 still is. See §6.

The bottom three (H7 Publish latency, H15 build time, H10 binary size) are real
costs but ones we knowingly took on ([ADR-001]) and are not in the critical
path of user experience. The tightened H15 v0.1 target (≤ 7 min) reflects
user preference for faster iteration, not matrix-derived priority; if it
pushes back against [ADR-001]'s "+5–10 min" pricing, the target moves
before the runtime decision does.

---

## 4. Roof — HOW-vs-HOW tradeoffs

The roof shows where pushing one characteristic pushes another the wrong way.
ASCII glyphs (with classical QFD equivalents): **`++`** strong
reinforcement (`◎`), **`+`** mild reinforcement (`○`), **`−`** mild
conflict (`×`), **`−−`** strong conflict (`⊗`). The 14×14 roof matrix
lives in [`quality-house.md`](quality-house.md); the cells that
actually shape the design are called out below.

### Conflicts that actually shape the design

- **H1 latency ↔ H3 refresh cadence** (mild). More partial refreshes per
  second pile up ghosting faster, demanding earlier full refreshes —
  visible flashes that hurt H8 perception and H1 burst behaviour. The
  [ADR-003] strip aspect is the structural answer: a small framebuffer makes
  _both_ cheaper, not one at the expense of the other. The runtime answer
  is render §H3: schedule full refreshes on idle ≥ 1 s (v0.1 tech doc). The
  rows-vs-latency cost model behind this tradeoff — full / full-area-partial /
  windowed-Y — is in
  [`tradeoff-curves/epd-refresh-latency.md`](tradeoff-curves/epd-refresh-latency.md).
- **H9 heap ↔ H10 binary size** (strong). std + gitoxide + mbedtls inflate
  both. We chose to spend on these ([ADR-001], [ADR-004]) because 16 MB flash
  and 8 MB PSRAM make them affordable; the kill-switch is spike 7. If
  heap during Publish refuses to come under 1 MB free, [ADR-004] flips to
  libgit2-sys for v0.1.
- **H9 heap ↔ H5 soak** (strong). A long writing session grows the rope
  and the glyph cache; Publishing on top can OOM. Mitigation: 256 KB file
  cap (v0.1 tech doc) + glyph cache eviction before Publish + watching the
  spike in spike 7.
- **H6 Publish reliability ↔ H12 network reconnect** (reinforcing). Both come
  from the same network stack; investing in reconnect backoff helps both.
- **H10 binary ↔ H15 build time** (strong). std builds are slow. Accepted
  in [ADR-001] — refactor leverage is the long-term payoff, not the
  per-build seconds.
- **H4 boot ↔ H10 binary** (mild). Larger binary = slower flash load.
  Affordable at our size class but worth watching as features land.
- **H11 stacks ↔ H13 current draw** (mild, future). Idle threads draw
  little but never zero; a future light-sleep policy (v0.8) wants them
  parked. W14's portability outcome raises the value of that policy
  from "battery hygiene" to "the thing that lets the device leave the
  desk."
- **W13 typography ↔ H9 heap + H10 binary** (mild, future). Achieving a
  writing-tool tone needs room for glyph caches and font assets. Not
  load-bearing in v0.1 (one mono font), but the v1.0 tone goal is why H9
  and H10 keep slack rather than being squeezed to the minimum.
- **Tightened H15 ↔ [ADR-001]** (mild). Pulling v0.1 build time from
  ≤ 10 min to ≤ 7 min eats into [ADR-001]'s accepted "+5–10 min" cost.
  Worth aiming at via cargo profile / vendor LTO / crate-graph trims;
  worth giving up before reversing [ADR-001].

---

## 5. HOW → Component mapping (Phase 2)

Which subsystem owns the delivery of each characteristic. Cells are which ADR
constrains the choice.

Components (with anchoring ADR):

| ID  | Component                            | ADR                   |
| --- | ------------------------------------ | --------------------- |
| C1  | ESP32-S3-N16R8 SoC                   | [ADR-001], [ADR-008]  |
| C2  | `esp-idf-rs` (std) + ESP-IDF         | [ADR-001]             |
| C3  | `std::thread` + `crossbeam-channel`  | [ADR-006]             |
| C4  | PSRAM allocator wrapper              | [ADR-001]             |
| C5  | GDEY0579T93 + DESPI-c579 panel       | [ADR-003]             |
| C6  | `embedded-graphics` + e-paper driver | [ADR-002], [ADR-003]  |
| C7  | Custom widget / dirty-rect layer     | [ADR-002]             |
| C8  | `ropey` rope buffer                  | [ADR-001] (ecosystem) |
| C9  | TinyUSB host (`esp-idf` bindings)    | [ADR-009]             |
| C10 | FAT on microSD                       | [ADR-007]             |
| C11 | LittleFS on internal flash           | [ADR-007]             |
| C12 | `gitoxide` (`gix-*`)                 | [ADR-004]             |
| C13 | mbedtls TLS (via ESP-IDF)            | [ADR-005]             |
| C14 | HTTPS + GitHub PAT auth              | [ADR-005]             |
| C15 | eFuse-derived encryption key         | [ADR-005], [ADR-007]  |
| C16 | USB-C wall PSU                       | [ADR-008]             |

HOW-to-component matrix (9 strong / 3 medium / 1 weak):

|           | C1 SoC | C2 std | C3 thr | C4 PSR | C5 EPD | C6 eg | C7 wid | C8 rope | C9 USB | C10 SD | C11 LFS | C12 gix | C13 TLS | C14 PAT | C15 efs | C16 PSU |
| --------- | :----: | :----: | :----: | :----: | :----: | :---: | :----: | :-----: | :----: | :----: | :-----: | :-----: | :-----: | :-----: | :-----: | :-----: |
| H1 lat    |   3    |   1    |   9    |   3    |   9    |   9   |   9    |    3    |   9    |        |         |         |         |         |         |         |
| H2 area   |        |        |        |        |   9    |   9   |   9    |         |        |        |         |         |         |         |         |         |
| H3 cad    |        |        |        |        |   9    |   3   |   9    |         |        |        |         |         |         |         |         |         |
| H4 boot   |   3    |   9    |   3    |   1    |   3    |       |        |         |        |   9    |    3    |         |         |         |         |         |
| H5 soak   |   3    |   3    |   3    |   9    |   1    |       |        |    9    |   9    |   3    |         |    3    |    3    |         |         |         |
| H6 reli   |        |   3    |        |        |        |       |        |         |        |        |         |    9    |    9    |    9    |         |         |
| H7 lat    |        |        |   3    |   1    |        |       |        |         |        |   3    |         |    9    |    9    |         |         |         |
| H8 dura   |        |   3    |        |        |        |       |        |         |        |   9    |    9    |         |         |         |         |         |
| H9 heap   |   3    |   3    |        |   9    |        |       |        |    3    |        |        |         |    9    |    9    |         |         |         |
| H10 bin   |        |   9    |   1    |        |        |   3   |   3    |    3    |   3    |        |         |    9    |    3    |         |         |         |
| H11 stk   |        |        |   9    |        |        |       |        |         |   3    |        |         |    3    |         |         |         |         |
| H12 recon |   3    |   9    |        |        |        |       |        |         |        |        |         |         |    3    |         |         |         |
| H13 mA    |   9    |        |   1    |        |   9    |       |        |         |   3    |   3    |         |         |         |         |         |    9    |
| H15 build |        |   9    |        |        |        |       |        |         |        |        |         |    9    |    3    |         |         |         |

### Read across, not down

- **C5/C6/C7** (panel + graphics + widget) are the single most leveraged
  cluster — they own H1, H2, H3 (the top of the priority list). [ADR-002]
  and [ADR-003] are the ADRs to keep most honest as v0.x progresses.
- **C12** (`gitoxide`) is overloaded: H6, H7, H9, H10, H11, H15 all
  touch it. That's why [ADR-004] includes a kill-switch (fall back to
  `libgit2-sys` if spike 7 fails). It's also why H9 sits in the top three
  priorities — `gitoxide`'s memory profile is the unknown.
  [ADR-010] pins the _shape_ of the publish sequence (the `gct` flow); C12
  is just the library that implements it. Changing [ADR-010] doesn't change
  C12's column, but changing C12 (the kill-switch) does not change
  [ADR-010]'s user contract.
- **C11** (LittleFS) is unused in v0.1 — config is build-time. Its non-zero
  cells in the matrix describe the v0.9+ shape per [ADR-007], not v0.1
  reality.
- **C2** (std runtime) sits underneath almost everything, but it's the
  _enabler_ (H4 boot, H10 binary, H12 reconnect) rather than the bottleneck.
  Reversing [ADR-001] would force re-deciding [ADR-004], [ADR-005],
  [ADR-006], [ADR-007] all at once — they're a single decision in three
  drawers.

---

## 6. Critical performance budget

A curated rank, drawing from §3 importance and §4 conflicts, with one
deliberate override: acceptance-criteria critical paths (H4 boot,
H5 soak) move up regardless of weighted-vote spread. (Pre-W14 this list
also lifted H8 durability over its narrow voter base; W14 has widened
that base, so H8's #3 spot is now arithmetic — see §3.) These are the
numbers spikes 2–7 must validate before integration starts.

| Rank | Characteristic | Target                                | Watched on        | If we miss it                                                             |
| ---- | -------------- | ------------------------------------- | ----------------- | ------------------------------------------------------------------------- |
| 1    | H2 region area | ≤ 1 line per keypress                 | spike 2 + spike 5 | Increase font size to shrink per-glyph dirty rect ([ADR-003] consequence) |
| 2    | H9 PSRAM heap  | ≥ 1 MB free at push peak              | spike 7           | [ADR-004] kill-switch → `libgit2-sys`; cap rope at 128 KB                 |
| 3    | H8 durability  | 100 % (post-confirm power loss)       | bench HIL         | Re-evaluate [ADR-007] (move config to internal NVS only)                  |
| 4    | H1 Type latency | ≤ 200 ms (keypress → glyph)          | spike 5           | Larger partial-refresh region; render multi-char bursts                   |
| 5    | H6 Publish reliability | ≥ 95 % (network up)           | spike 6 + spike 7 | TLS cipher trim; reconnect backoff tuning                                 |
| 6    | H3 cadence     | full every ~64 partials               | spike 2           | Adjust per panel temperature; defer flash to idle ≥ 1 s                   |
| 7    | H4 Boot latency | ≤ 5 s (cold, to cursor)              | 4258 ms 2026-07-11 ✓ | Editor rides a full-area partial over the splash (done, −1.25 s); PSRAM memtest off (−0.74 s) — [boot-time-budget](notes/boot-time-budget.md) |
| 8    | H5 soak        | 1 h no leak / no drop                 | 1 h bench soak    | Glyph-cache eviction; PSRAM heap-fragmentation review                     |

The two not-in-MVP rows but already-shaped-by-design:

| — | H13 current | Measured only in v0.1 | bench multimeter | Cell sizing for v0.8 is data-driven, not spec-sheet |
| — | H11 stacks | Sum ≤ 80 KB | static analysis | Was off-by-2x in [ADR-006] pre-fix — corrected in §7 |

---

## 7. Tradeoffs and their why, linked to ADRs

Plain-language summary of what we accepted in exchange for what.

| Tradeoff                                        | Got                                                                                                  | Paid                                                                                                                                                  | ADR       |
| ----------------------------------------------- | ---------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------- | --------- |
| std (esp-idf-rs) over no_std (esp-hal)          | Heap, threads, VFS, mbedtls, gitoxide-compatible                                                     | +1 MB binary, +5–10 min builds                                                                                                                        | [ADR-001] |
| Custom widget layer over Ratatui                | Dirty-rects aligned to e-ink regions; 200 KB binary back                                             | 500 LoC we own and maintain                                                                                                                           | [ADR-002] |
| e-ink medium over FSTN / memory LCD / OLED      | Paper aesthetic; 0 W idle persistence; medium enforces writing posture                               | ~200–300 ms typing latency; periodic full-refresh flash (scroll worst-case)                                                                           | [ADR-003] |
| `gitoxide` over `libgit2-sys`                   | Pure Rust, modular, no FFI cross-compile pain                                                        | Smart-HTTP path is newer; PSRAM profile unproven (spike 7)                                                                                            | [ADR-004] |
| HTTPS + PAT over OAuth device-flow or SSH       | Simplest auth that `gitoxide` smart-HTTP already supports                                            | Long-lived secret on device; in v0.1 the PAT is compiled into the binary (dev-only target user makes this acceptable); v0.9 moves it to encrypted NVS | [ADR-005] |
| `std::thread` over `embassy` or `tokio`         | Boring, debuggable, real stack traces; no exec to tune                                               | ~76 KB total stack across 5 tasks                                                                                                                     | [ADR-006] |
| FAT-on-SD + LittleFS-on-flash split             | Desktop can read SD; config survives SD reformat                                                     | Two filesystems to manage; FAT's power-loss weakness mitigated by atomic-rename                                                                       | [ADR-007] |
| Wall power for v0.1, battery deferred           | Measure real draw before sizing the cell                                                             | Tethered MVP; not the final aesthetic                                                                                                                 | [ADR-008] |
| USB host (TinyUSB) over BLE-HID                 | No radio contention with Wi-Fi during push; keyboard powered from the device                         | One more USB connector on enclosure                                                                                                                   | [ADR-009] |
| Atomic `Ctrl-G` + auto-timestamp commit message | One key, one outcome; matches the user's existing `gct` workflow; no modal prompt to slow H1 latency | Commit history is timestamp noise; the device may author merge commits the user never sees; reversal would break muscle memory                        | [ADR-010] |

### Conflicts left explicitly _unresolved_ by v0.1

These are the live tensions we are watching, not deciding harder:

- **[ADR-004] vs H9.** If `gitoxide` cannot keep ≥ 1 MB PSRAM free at push
  peak, we are committed to switching transports for v0.1, not absorbing
  the OOM risk.
- **[ADR-009] vs H6/H13.** If TinyUSB host turns out unstable (spike 4),
  BLE-HID is the documented fallback — at the cost of Wi-Fi radio
  contention during push (re-checking H6).
- **[ADR-007] vs H8.** Power loss between FAT rename and dir flush yields
  the previous saved version. We document this as expected behavior; it
  becomes a real bug only if soak testing shows it triggering on routine
  saves.
- **W13 typography paths.** v0.1 ships one mono font; v1.0's
  writing-tool-tone outcome admits two paths (mono = developer comfort,
  serif = typewriter feel). Not yet decided whether to ship both or one;
  decision deferred to the v1.0 design pass. Cost preview per added font:
  +H9 glyph-cache footprint, +H10 binary for embedded assets.
- **[ADR-008] vs W11+W14.** Wall power in v0.1 is now an explicit
  disappointment of two WHATs, not one (battery W11 + portability W14).
  The disappointment is bounded by [ADR-008]'s commitment to measure
  current draw on real hardware before sizing v0.8's cell — spec the
  cell against measured numbers, not against the spec sheet. The §3
  promotion of H13 (current draw) from #11 to #7 is the matrix
  registering this: bench multimeter readings now serve portability
  sizing as well as power profiling.

---

## 8. Inconsistencies spotted and fixed

- **[ADR-006] stack figure.** [ADR-006] previously said "~40 KB of stack
  space for task stacks" — but the v0.1 technical design's task table
  (`usb 8 + wifi 8 + ui 16 + render 12 + git 32`) sums to **76 KB**.
  Updated [ADR-006]'s Consequences section to reflect the actual budget
  and cross-reference the tech doc. The 76 KB figure still fits
  comfortably in the ESP32-S3's 512 KB internal SRAM, so no design
  change — just documentation accuracy.
- **Commit-message format triple-mismatch.** README said `git commit -m
"wip"`, the v0.1 product doc said `"wip <timestamp>"`, and the user's
  actual shell alias (`gct` / `git-commit-timestamp`) uses a pure ISO-8601
  timestamp with no `wip` prefix. Resolved by aligning all docs on `gct`
  and recording the decision as
  [ADR-010].
  Pulled the v0.7 roadmap item "Commit message prompt instead of hard-coded
  `wip`" — it's now contradicted by [ADR-010] and removed.
- **First-run flow vs. target user.** The v0.1 product doc described a
  captive-portal first-run, but the same doc names the v0.1 target user as
  the dev themselves ("Me. Solo."). Provisioning a solo-dev device through
  a captive portal is ceremony without a user. Resolved by switching v0.1
  to build-time env-var config (no NVS, no LittleFS, no AP mode); on-device
  provisioning is the v0.9 release that introduces non-dev users. Touches
  [ADR-005], [ADR-007], the v0.1 product + technical docs, and the v0.9
  roadmap entry.
- **Vocabulary leak.** Earlier docs used "commit" and "push" as if they
  were distinct user actions; the gct/[ADR-010] model collapses them into a
  single user-facing **Publish**. Resolved by introducing
  [`CONTEXT.md`](../CONTEXT.md) as the canonical glossary; user-facing text
  now uses **Save** and **Publish** only.
- **House of Quality column sums recomputed.** Earlier Σ row drifted from
  the matrix arithmetic — H1 listed 138 but sums to 148; H8 147 vs 132;
  H9 162 vs 172; H13 74 vs 65; smaller deltas elsewhere. Recomputed all
  sums from the cells. H8 dropped from #3 to #6 — a "fewer WHAT voters"
  artifact, not a signal that durability matters less to the design.
- **W13 reframed, W14 removed.** Earlier W13/W14 rows named solutions
  ("beautiful monospace", "beautiful serif") inside the requirements
  column, conflating _what the user values_ with _which asset delivers it_.
  Replaced with one outcome WHAT — typography sets a writing-tool tone —
  and moved the mono+serif option to §7 as a v1.0 unresolved tension.
  Σ shifted (H9 205→193, H2 198→177, H1 155→148) because the prior
  W13/W14 cells were scoring solution-fit rather than outcome-fit.
- **WHATs swept for solution-shape phrasing.** Following the W13 reframe,
  the same drift was found in W2 (named the key `Ctrl-G`), W4 (named the
  process shape "one-shot"), W7 (named the hardware "surface"), W8 (named
  the medium "e-ink"), W10 (named the deliverable "BOM"), and W9 ("nine
  releases" — brittle vs roadmap reshuffles). All rephrased as outcomes;
  the named solutions remain documented in §7 tradeoffs and the relevant
  ADRs where they belong. Matrix cell strengths held — each cell scored
  the characteristic against the underlying outcome, not the surface
  phrasing — so no Σ recompute.
- **§3 vs §6 priority lists clarified.** The two were giving different
  orderings without saying why. §6 now states explicitly that it is a
  curated rank with two named overrides over §3's pure arithmetic:
  acceptance-criteria critical paths (H4, H5) and table-stakes correctness
  (H8) get manual lifts. §3 now names the HoQ structural bias that makes
  the curation necessary — reward for spread, penalty for narrow-but-
  critical characteristics — using H8/W3 as the canonical example.
- **W14 added — portability outcome.** Captures "I can carry the device
  and write away from a desk" as a distinct WHAT from W11 (multi-day
  battery), weight 8. Recomputed basement Σ; H8 lifted from #6 to #3 in
  the §3 priority list as its voter base widened from W3+W6+W12 to also
  include W14, and H12 entered the top six at #4; H6 dropped out. The
  ID "W14" was previously held by a deprecated typography row (see the
  "W13 reframed, W14 removed" bullet above); the slot is now repurposed.
  §6's "(b) narrow voter base" override for H8 no longer applies and
  has been retired in the §6 preamble.
- **H14 retired — outside §2's scope.** §2 covers measurable engineering
  characteristics — performance metrics of the device's functions, or
  properties of its firmware artifact, memory layout, and build process.
  H14 ("Module count / public-API surface (refactor proxy)") is a
  property of source-code organisation, none of those. The refactor-
  leverage idea survives in §5's component structure and the ADRs that
  decide architectural discipline; it does not need a HoQ matrix slot.
  Removed from §2, the §5 matrix row, the C12 overloaded-list mention,
  and the §4 H14↔H15 conflict bullet. W9's matrix vote shrinks from
  `H10 W + H11 W + H14 S + H15 M` to `H10 W + H11 W + H15 M` — an
  honest reading that "codebase absorbs the planned roadmap" is
  delivered by ADRs, not by a measurable characteristic. ID "H14" left
  as a gap (cross-doc HOW references survive without renumbering H15).
  Total basement Σ drops 1674 → 1557, so rel% recomputed in
  [`quality-house.md`](quality-house.md).
- **HOWs renamed "characteristics," not "functions."** A function is a
  transformation (input → output); HOWs like H6 "success rate" and
  H10 "binary size" are *measures* of functions or properties of
  artifacts, not transformations themselves. §2's header, §4's
  ("HOW-vs-HOW tradeoffs"), §5's ("HOW → Component mapping") and
  caption, and §6's column header all cascaded — wherever "function"
  meant HOW. Classical QFD uses "engineering characteristics" (or
  "substitute quality characteristics") for exactly this slot. The
  methodology name in the title (Quality Function Deployment) stays —
  it is the framework's proper noun, not a claim about this doc's
  vocabulary.
- **H6/H7/H8/H12 swept for solution-shape phrasing and measure-vs-
  attribute.** Two drifts in one pass. (a) Solution names inside
  characteristic names: H6 was "`Ctrl-G` push success rate on healthy
  Wi-Fi" — three solutions inside one name (the key, the git verb, the
  transport); H7 was "Push end-to-end (one-file commit)" — git verb and
  its unit; H12 was "Wi-Fi reconnect on transient outage" — transport
  in the name. (b) Measure or behaviour assertion instead of attribute:
  H6's "success rate" is a metric; H8 "Save survives power loss after
  status confirms" is a behaviour assertion. Renamed to pure attributes
  under outcome-shaped conditions: H6 = "Publish reliability (network
  up)", H7 = "Publish latency (one file)", H8 = "Save durability
  (post-confirm power loss)", H12 = "Network reconnect time (transient
  outage)". H7's "latency" pairs with H1's "Type latency".
  Matrix cell strengths held; no Σ recompute.
- **Functions surfaced as their own ontology layer.** Earlier, the
  HOW names packed both a function reference and an attribute
  ("Publish reliability" = Publish [function] + reliability
  [attribute]) without Functions being defined anywhere. §2 now
  opens with a Functions inventory (Type, Save, Publish, Recover,
  Boot, Provision) so the function names HOWs reference have a
  single source of truth. Render and Reconnect remain sub-functions
  referenced inside HOW names; they did not earn top-level slots in
  v0.1. The five-layer ontology stack (WHAT / Function /
  Characteristic / Metric+Unit / Target) is documented in
  [`../GLOSSARY.md`](../GLOSSARY.md), peer to `CONTEXT.md`
  (device vocabulary). With Functions explicit, two arrow-style HOW
  names collapsed for parallelism: H1 "Keypress → glyph latency" →
  "Type latency (keypress → glyph)", H4 "Cold boot → cursor ready" →
  "Boot latency (cold)". The arrow text moved to the parenthetical
  context where it belongs once the function name carries the
  transformation; H4's "to cursor" is implicit in Boot's definition.
  Matrix cell strengths held; no Σ recompute.
- **H4 boot measured; H3 cadence corrected; boot-time docs added
  (2026-07-11).** Cold boot instrumented at **4258 ms** — the ≤ 5 s v0.1 target
  is met; §6's H4 row now carries that measured result and the real mitigation
  (editor rides a full-area partial over the splash, −1.25 s) in place of the
  pre-integration guesses (trim logging / lazy-mount SD). §2's ≤ 3 s v1.0 target
  gained a footnote flagging it **marginal-to-unreachable** — one ~1.9 s full
  refresh is an unavoidable e-ink cold-boot floor. Separately, §2 + §6 H3
  full-refresh cadence corrected from "1 per 20 partials" to **1 per 64**: the
  firmware stretched it (`FULL_REFRESH_EVERY = 64`) once windowed-Y refresh made
  ghosting rare — a drift that predated this pass. New supporting docs:
  [`notes/boot-time-budget.md`](notes/boot-time-budget.md) (waterfall + v1.0
  feasibility) and
  [`tradeoff-curves/epd-refresh-latency.md`](tradeoff-curves/epd-refresh-latency.md)
  (rows-vs-latency model), cross-linked from §4's H1↔H3 bullet.

The earlier variance between README's "~12 lines" and product/[ADR-003]'s
"~11 lines" of "edit area" is now superseded: the side-panel redesign removed
the top header and bottom status bars (metadata moved into the **side panel**),
so the **writing column** spans the full panel height — ~13 lines at the
editor's 20 px font (`FONT_10X20`, `editor.rs` `ROWS = HEIGHT / 20 = 13`).
README, the product/technical docs, and [ADR-003] are all updated to ~13 lines
(writing column).

---

## How to keep this document honest

- When a new ADR lands, add its components to §5 and re-score any
  characteristic-row whose dominant component changed.
- When a spike returns numbers, update §6's "Target" or "Watched on"
  columns — this is the doc that _should_ feel out of date if measured
  reality drifts from estimates.
- The WHATs (§1) change rarely; the HOWs (§2) change with each release.
  When either changes, re-score the matrix and recompute the basement Σ
  in [`quality-house.md`](quality-house.md); then check the §3 priority
  list and §4 conflict list here still match the new picture.

[ADR-001]: adr.md#adr-001-language-and-runtime--rust-on-esp-idf-rs-std
[ADR-002]: adr.md#adr-002-ui-strategy--custom-widgets-on-embedded-graphics-not-ratatui
[ADR-003]: adr.md#adr-003-display-medium--e-ink-gdey0579t93-panel
[ADR-004]: adr.md#adr-004-git-implementation--gitoxide-gix
[ADR-005]: adr.md#adr-005-auth--https--github-personal-access-token
[ADR-006]: adr.md#adr-006-concurrency--stdthread--channels-no-async-runtime
[ADR-007]: adr.md#adr-007-storage-split--fat-on-sd-for-working-copy-littlefs-on-flash-for-config
[ADR-008]: adr.md#adr-008-mvp-power--wall-powered-battery-deferred-to-v08
[ADR-009]: adr.md#adr-009-keyboard-transport--usb-host-tinyusb
[ADR-010]: adr.md#adr-010-publish-ux--atomic-ctrl-g-auto-timestamp-commit-message-no-user-prompt
