feat: prove the Wi-Fi, LittleFS, and HTTP vertical slice

PLANS.md

@@ -167,7 +167,7 @@ Execution record
 
 ## Milestone 002 — Prove the Wi-Fi, LittleFS, and HTTP vertical slice
 
-**Status:** `READY`  
+**Status:** `DONE`
 **Depends on:** Milestone 001
 
 ### Objective
@@ -203,11 +203,22 @@ Prove the MVP's basic delivery path: home Wi-Fi, LittleFS, and HTTP served direc
 
 If all criteria pass, set this milestone to `DONE`, append its execution record, and change Milestone 003 from `BLOCKED` to `READY`.
 
+### Execution record
+
+- Date: 2026-08-27
+- Board model and revision: ESP32-C6FH4 QFN32, revision v0.2; carrier board remains an unidentified SuperMini-style ESP32-C6 Mini.
+- Toolchain and library versions: PlatformIO Core 6.1.19; `espressif32` 7.0.1; ESP-IDF 6.0.1; pinned `esp_littlefs` 1.20.4 (commit `92ac3c2`).
+- Result: PASS
+- Evidence: Implemented the station-mode Wi-Fi state machine with bounded 2–32 second reconnect backoff, LittleFS mount without auto-formatting, static routes (`/`, `/styles.css`, `/app.js`), and `GET /api/health`. Static files are streamed in 1,024-byte chunks, have explicit MIME/cache headers, and select a matching precompressed `.gz` file when supplied by the LittleFS image. `data/` contains the local Russian diagnostic page, CSS, and JavaScript; `include/wifi_config.h.example` documents the ignored local credential file. `pio run -e esp32-c6-devkitm-1 -t buildfs` successfully created `littlefs.bin` containing all three assets. Firmware and LittleFS were uploaded to the ESP32-C6FH4, and esptool verified every written hash. A serial reset/read confirmed LittleFS mount, HTTP server startup on port 80, Wi-Fi association, and DHCP assignment without a restart. Five consecutive LAN `GET /api/health` requests returned HTTP 200; `GET /styles.css` returned `Content-Type: text/css; charset=utf-8` and `Cache-Control: public, max-age=86400`.
+- Measurements: Final credential-configured firmware build used 37,164 / 327,680 bytes of RAM (11.3%) and 987,644 / 2,097,152 bytes of flash (47.1%). The LittleFS partition is 1,984 KB; the mounted image reported 2,031,616 total bytes and 20,480 used bytes. The health endpoint reported RSSI from -43 to -46 dBm, 324,488 current free heap bytes, and 316,580 minimum free heap bytes after approximately 64 seconds. No new compiler warnings were emitted by the successful builds.
+- Issues or deviations: The first device upload exposed an `Invalid mbox` assertion because the HTTP server started before `esp_netif_init`; this was corrected before the final verified upload. `pio test -e esp32-c6-devkitm-1 --without-uploading` ran but errored because `test/` contains no test suite. On 2026-08-28, the user confirmed completion of the remaining two-device, Wi-Fi interruption/reconnect, gzip-delivery, and LittleFS mount-failure checks; their physical observations are accepted as the required evidence.
+- Next action: Milestone 003 is in progress. Do not begin Milestone 004 as part of this task.
+
 ---
 
 ## Milestone 003 — Prove real-time transport, fallback, and state isolation
 
-**Status:** `BLOCKED`  
+**Status:** `IN PROGRESS`  
 **Depends on:** Milestone 002
 
 ### Objective