Merge main (file sharing, v0.18.0) into the VPN branch

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

docs/milestones/F1.md

@@ -290,3 +290,46 @@ Test pictures were copied to a scratch folder and removed afterwards, with the t
 **A decoder that worked once.** The library's PNG decoder showed the first picture and refused the next five: "no memory". It wants 44 KB in one piece, and after some use the largest piece is 43 to 47 KB. Writing a decoder that needs 32 KB was less work than it sounds, and unlike the library's it has tests.
 
 **Two sentences still said "up to 16 KB"** about editing, in the README and the Storage guide, after issue #47 lifted that. Corrected here.
+
+## Sharing the card with a browser (issue #88)
+
+Files reached the card through the Debug Console's `put` and `get`, or by taking the card out. A phone has neither.
+
+### Decisions (2026-10-07; the recommendation was accepted as it stood, without a round of questions)
+
+- **A web page, not FTP, SFTP or WebDAV.** A browser is the only client every phone has. FTP and WebDAV need an app there; SFTP needs a whole SSH server here. WebDAV can come later on the same server, for computers.
+- **Off unless asked for:** `w` in the Storage App opens a "Share" screen, and the server runs only while that screen is open.
+- **A six-digit code on the screen**, new each time, typed in the page; the address is also a QR code, which carries the code. Five wrong codes close it for a minute (the Debug Console's `AuthGate`). A browser that got it right holds a cookie; starting again puts every browser out.
+- **Not encrypted.** A TLS server costs about 40 KB of memory a connection. The screen says so.
+- **The Storage App's rules** (`whyReadOnly`): the firmware's own folders, and files in use.
+
+### As built
+
+- **`WebShare`** (`src/services/web_share`): ESP-IDF's HTTP server, which is in the framework already. Seven requests: the page, the code, a listing as JSON, a download, an upload, a new folder, a delete.
+- **Every access to the card is handed to the storage task**, 8 KB at a time, from the server's own task: a download and an upload are loops of "one piece from the card, one piece to the network".
+- **An upload is the request's body**, as the browser's `PUT` sends it: no form to take apart. It goes to `<name>.part` and is renamed when the last byte has come; anything less is removed. A file that exists is refused unless the page asked, after asking the user.
+- **The page** (`web_share_page.h`) is one file of 5.4 KB with its style and script in it, served from flash.
+- **`lib/files/src/share_rules.h`** (host-tested, 5 tests): what a request names, which paths a browser may ask for (from the root, no `..`), the JSON, the code and the cookie.
+- **Cost:** 57 KB of flash, most of it the server. 13 KB of memory while sharing (108.4 KB free before, 95.4 with the screen open), given back on leaving.
+
+### Checks on the device (2026-10-07 and 08)
+
+A scratch folder was used and removed.
+
+| Check | Result |
+|---|---|
+| `w` | The QR code, the address and the code; `share: on` on the console |
+| The page, and a listing without the code | 200; 401 |
+| A wrong code, the right one (typed `825 132`) | 403; in |
+| Upload, 2.6 MB | 11 to 17 s (150 to 230 KB/s); downloaded again and compared: the same, byte for byte |
+| The same name again; with "replace" | 409; replaced |
+| `..` in a path; deleting `/notes`; deleting a folder that isn't empty | 400; 403 "The firmware keeps its files in /notes"; 403 |
+| Five wrong codes | The fifth and every one after: 429, the right code too. A browser that was in stays in |
+| In Chromium at a phone's width | The scanned address logs in by itself; two files uploaded, one downloaded and compared, a folder made, a file deleted after asking, a replacement after asking, the refusal shown. No sideways scroll |
+| Back | The server is gone (connection refused), memory is back |
+
+**Found on the way:** the server answers one request at a time. A second request during a slow download waited until it had ended. It is said in the guide, and not changed.
+
+**On a real phone** (the maintainer's, 2026-10-08): the QR code, scanned with the phone's camera, opens the page and logs in; the page lists the card, in the phone's dark theme.
+
+**Not checked:** Safari. A card pulled during a transfer. Sharing with IRC connected, when memory is shorter. Home, and the screen turning off, while sharing (the code stops the server on leaving the App; only Back was tried).