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docs: record :sync latency budget from hardware measurement

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New docs/notes/sync-latency.md breaks down the measured ~16 s cold :sync
(Wi-Fi + SNTP + one TLS push), explains the optimistic-retry handshake saving,
the reconcile/last-writer-wins semantics, and why the rest is near the protocol
floor. Linked from the notes index, the docs index, and the Git row of the root
README.
This commit is contained in:
Julien Calixte
2026-07-11 17:04:02 +02:00
parent 92068f1cce
commit a700412773
4 changed files with 91 additions and 2 deletions
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README.md
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@@ -71,7 +71,7 @@ surface (mostly `usb_kbd.rs`) is in [`MEMORY_AUDIT.md`](MEMORY_AUDIT.md).
| UI layer | Custom thin widget layer | Ratatui's API _shape_ without its char-grid terminal model ([ADR-002](docs/adr.md#adr-002-ui-strategy--custom-widgets-on-embedded-graphics-not-ratatui)). |
| 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](docs/adr.md#adr-004-git-implementation--gitoxide-gix) kill-switch fired ([postmortem](docs/postmortems/2026-07-05-spike7-gix-https-push.md)). On-device add → commit → push verified. |
| 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](docs/adr.md#adr-004-git-implementation--gitoxide-gix) kill-switch fired ([postmortem](docs/postmortems/2026-07-05-spike7-gix-https-push.md)). On-device add → commit → push verified; ~16 s cold-`:sync` [latency breakdown](docs/notes/sync-latency.md). |
| 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](docs/adr.md#adr-011-credential-provisioning--how-the-pat-reaches-the-device-and-is-protected-at-rest) (open), on-device settings land in v0.9. |
| Filesystem | FAT on SD (`esp_vfs_fat`) | Working copy lives here. Internal LittleFS holds config. |