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docs(qfd): add font WHATs, tighten H15, fix Σ row arithmetic

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Julien Calixte
2026-05-14 22:08:53 +02:00
parent 76db470da2
commit 88cd08db39
1 changed files with 41 additions and 13 deletions
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docs/qfd.md
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@@ -37,6 +37,8 @@ What a user (= me) values about the device, with importance weights on a
| W10 | Hackable / DIY-shaped BOM and code | 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 | Beautiful monospace font on the writing surface | 7 | [roadmap → v1.0](roadmap.md), [README → UX](../README.md#ux-boundaries-set-by-the-medium) |
| W14 | Beautiful serif font option for reading / published view | 4 | [roadmap → v1.0](roadmap.md) |
---
@@ -61,7 +63,7 @@ shows what "better" looks like (↑ higher, ↓ lower, → fixed).
| H12 | Wi-Fi reconnect on transient outage | ↓ | ≤ 30 s | ≤ 10 s |
| H13 | Idle / typing / push current draw | ↓ | measured only | sized for >2 days |
| H14 | Module count / public-API surface (refactor proxy) | → | ≤ 8 modules | same |
| H15 | Build time (clean, release) | ↓ | ≤ 10 min | ≤ 7 min |
| H15 | Build time (clean, release) | ↓ | ≤ 7 min | ≤ 5 min |
---
@@ -85,27 +87,37 @@ weighted vote on which functions deserve the most engineering attention.
| W10 (5) | | | | | | | | | | 3 | | | 1 | 3 | 1 |
| W11 (4) | | | | | | | | | | | | | **9** | | |
| W12 (5) | | | | | | 1 | | 3 | | | | | | 3 | |
| **Σ** | **138** | **174** | **126** | **54** | **108** | **132** | **27** | **147** | **162** | **38** | **41** | **120** | **74** | **115** | **29** |
| W13 (7) | 1 | 3 | | | | | | | 3 | | | | | | |
| W14 (4) | | | | | | | | | 3 | | | | | | |
| **Σ** | **155** | **198** | **144** | **54** | **111** | **134** | **27** | **132** | **205** | **41** | **45** | **129** | **65** | **117** | **29** |
### Top engineering priorities (from importance)
1. **H2 — partial-refresh region area** (174). Bound how many pixels the
panel has to flip per keypress; [ADR-003] is the hardware-side answer.
2. **H9 — PSRAM heap during push** (162). gitoxide pack + rope + TLS all
1. **H9 — PSRAM heap during push** (205). 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.
3. **H8 — save durability** (147). Atomic-rename + fsync; FAT's weakness is
acknowledged in [ADR-007] and mitigated, not designed around.
4. **H1 — keypress latency** (138). The single most user-visible number;
so this becomes the watched metric. Two embedded fonts (W13, W14) each
keep their own glyph cache, adding to the pressure.
2. **H2 — partial-refresh region area** (198). Bound how many pixels the
panel has to flip per keypress; [ADR-003] is the hardware-side answer.
A mono writing surface (W13) bounds it predictably; a serif option (W14)
widens it.
3. **H1 — keypress latency** (155). The single most user-visible number;
[ADR-002] and [ADR-003] are co-conspirators.
5. **H6 — push success rate** (132). [ADR-004] (gitoxide) and [ADR-005] (PAT
over HTTPS) own this jointly; spike 7 is the kill-switch.
6. **H3 — full-refresh cadence** (126). The ghosting/flash tradeoff; lives
4. **H3 — full-refresh cadence** (144). The ghosting/flash tradeoff; lives
in the render layer.
5. **H6 — push success rate** (134). [ADR-004] (gitoxide) and [ADR-005] (PAT
over HTTPS) own this jointly; spike 7 is the kill-switch.
6. **H8 — save durability** (132). Atomic-rename + fsync; FAT's weakness is
acknowledged in [ADR-007] and mitigated, not designed around. H8 sits
below the latency cluster because only three WHATs touch it (W3, W6,
W12) — fewer voters, not weaker requirement.
The bottom three (H7 push time, 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.
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.
---
@@ -162,6 +174,15 @@ The roof shows where pushing one function pushes another the wrong way.
parked.
- **H14 modularity ↔ H15 build time** (mild). More small crates = more
link work. Boring vs valuable; we lean toward modularity.
- **W13/W14 fonts ↔ H9 heap + H10 binary** (mild, future). Embedding both
a mono and a serif typeface inflates the binary and adds a second glyph
cache. Not load-bearing in v0.1 (one font), but the v1.0 typography goal
is the reason H9 and H10 need 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].
---
@@ -322,6 +343,13 @@ These are the live tensions we are watching, not deciding harder:
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. Folded in W13/W14 at the same pass. The reordering
moved H9 to #1 (205), H2 to #2 (198), H1 to #3 (155); H8 dropped from
#3 to #6 (132). H8's drop is a "fewer WHAT voters" artifact, not a
signal that durability matters less to the design.
The minor variance between README's "~12 lines" and product/[ADR-003]'s
"~11 lines" of edit area is within rounding for a 14 px glyph in a 240 px