Add TODO.md handoff notes for the remaining review items

Records the design-level suggestions from the 2026-08-03 review that were
not part of dd2d428 (UI freeze during fetches, stale-data indication,
debug readout removal, dead utils.c, OTA partitions, small cleanups),
plus the facts already verified and questions already answered so a
future agent does not re-derive or re-ask them.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

TODO.md

@@ -0,0 +1,134 @@
+# TODO — remaining items from the 2026-08-03 code review
+
+Context for whoever (human or AI agent) picks this up. A full review of this
+firmware was done on 2026-08-03. The outright bugs it found were fixed in
+commit `dd2d428` ("Fix WiFi reconnect bugs, negative-temp rounding, and stale
+docs"). This file holds the items that were deliberately **not** done in that
+commit — design-level changes and enhancements — plus the facts the review
+already established so you don't re-derive or re-ask them.
+
+Read `README.md` first. It is accurate as of `dd2d428` and documents the
+hardware constraints that make this board unusual (PSRAM bandwidth, the
+STC8H1K28 board controller, init-order requirements). Do not violate the
+init order in `main.c`: WiFi/NVS before `display_init()`, `backlight_init()`
+before `touch_init()`.
+
+## Already verified — do not re-investigate
+
+- The build compiles clean on ESP-IDF v5.3 (`. ~/esp/esp-idf/export.sh &&
+  idf.py build`). Binary is ~1.1 MB, 74% of the 4 MB factory partition free.
+- `main/app_config.h` exists locally (gitignored, copied from the example
+  with empty credentials, done only to make the build compile). Real WiFi +
+  Ambient Weather credentials still need to be filled in before flashing.
+- `resp_buf` bounds/NUL-termination in `ambient_weather.c` is correct — the
+  guard leaves room for the terminator. Not a bug.
+- GT911 read-then-clear-status ordering in `touch_gt911.c` is correct.
+- Backlight duty inversion in `backlight.c` maps correctly at both endpoints
+  (255→0x00 full, 0→0xF5 off).
+- The `°` glyph exists in LVGL's built-in Montserrat fonts; the `·` separator
+  that does NOT exist in them only appears in log strings, never on screen.
+- The LVGL recursive-mutex locking discipline is consistent across all UI
+  entry points.
+- WiFi reconnect, `wifi_is_connected()` staleness, boot-timeout handling, and
+  negative-temperature rounding were all fixed in `dd2d428`. Don't redo them.
+
+## Tasks, in priority order
+
+### 1. Stop freezing the UI during weather fetches
+
+**Problem:** `weather_update_task` in `main.c` wraps the whole HTTP fetch in
+`lvgl_port_pause()`/`resume()`. Pause stops `lv_timer_handler()` entirely, so
+rendering AND touch input are dead for the whole fetch — worst case
+`WEATHER_TIMEOUT_MS` (30 s), every 60 s. Harmless while the screen is
+passive; a showstopper once thermostat controls (setpoint buttons) exist,
+which is the stated next step in the README.
+
+**Why the pause exists:** the TLS session, the LVGL redraw, and the flush all
+contend with the LCD's own DMA out of PSRAM; overlapping them produces the
+left-edge artefacts documented in the README. Do not simply delete the pause
+— the artefacts will come back. Options, roughly in order of preference:
+
+- Keep the HTTP client alive between polls (`keep_alive_enable` in
+  `esp_http_client_config_t`, don't `cleanup` between calls). The expensive
+  part is the TLS handshake; a reused session makes each poll a short
+  request/response, so the paused window shrinks from seconds to ~100s of ms.
+- After the first successful fetch, drop the timeout from 30 s to ~10 s (the
+  30 s exists only because a *first* handshake on this board is slow).
+- Alternatively pause only around LVGL's flush (the actual PSRAM writes)
+  rather than the whole network transaction — more invasive, only if the
+  above is insufficient.
+
+**Verify on hardware**: watch for the left-edge artefacts after weather
+fetches (they appear near the moment the status line updates). This cannot be
+verified by compiling alone.
+
+### 2. Indicate stale weather data
+
+`weather_data_t.last_update` is set in `ambient_weather.c` but never read.
+After fetch failures the old temperature stays on screen at full styling
+indefinitely. Track the last successful update (the weather task is the
+natural owner); after ~2 missed polls, dim the temperature label
+(e.g. change its text color) or append the age to the status line. Keep it in
+the weather task / `ui_manager` — do not add timekeeping to the API client.
+
+### 3. Remove the debug touch readout from the production UI
+
+`touch_label` + `touch_readout_timer_cb` + the 100 ms `lv_timer` in
+`ui_manager.c` are bring-up diagnostics baked into the shipped screen. Remove
+them or gate behind a compile-time flag (e.g. `#ifdef UI_DEBUG_TOUCH`,
+default off). Keep the explanatory comment about LVGL not bubbling events to
+parents somewhere — it documents a real trap that cost debugging time.
+
+### 4. Delete dead code: `main/utils/utils.c`
+
+`utils_delay_ms`, `utils_get_tick_ms`, `utils_trim` have zero callers;
+nothing outside utils.c includes `utils.h`. Delete `main/utils/` and remove
+its entries from `main/CMakeLists.txt` (SRCS and INCLUDE_DIRS), and drop the
+row from README's Components table and from `project_structure.txt`.
+`touch_get_indev()`, `display_get_panel()`, `lvgl_port_is_paused()` are also
+currently uncalled but were deliberately KEPT as driver API surface — leave
+them.
+
+### 5. Add OTA partitions while the fleet is size zero
+
+16 MB flash, but `partitions.csv` has a single 4 MB factory app and a ~12 MB
+SPIFFS partition nothing mounts. Re-partitioning fielded devices later means
+reflashing over USB, so lay out `otadata` + `ota_0` + `ota_1` now (two 4 MB
+slots fit easily; shrink or drop the unused SPIFFS partition). Note
+`CONFIG_ESP_WIFI_NVS_ENABLED=n` and the flash-write-while-panel-running
+constraint (README "Memory notes"): an OTA *write* happens while the panel is
+scanning, which will fault the bounce-buffer ISR. Any future OTA
+implementation must pause/stop the panel during the download+write, or
+restart into a dedicated updater mode. Adding the partition layout now is
+safe; implementing OTA download is a separate, harder task.
+
+### 6. Small cleanups (batch into one commit)
+
+- `ambient_weather.c` truncation path: the "Response exceeds N bytes" warning
+  logs once per remaining chunk and then JSON parse fails anyway. Log once
+  (set a flag) and consider aborting the transfer.
+- Weather task stack is 6144 bytes with the TLS handshake running in-task.
+  Works (mbedTLS heap goes to PSRAM via `CONFIG_MBEDTLS_EXTERNAL_MEM_ALLOC`)
+  but tight — log `uxTaskGetStackHighWaterMark(NULL)` once after a successful
+  fetch and right-size before more features land in that task.
+- `backlight_set()` is only ever called once with 255. A night-dim schedule
+  or touch-to-wake is a natural small feature; note the STC8H1K28 shares the
+  I2C bus with the GT911, so calls must stay in task context (never ISRs) and
+  brightness writes contend with touch polls on the same bus.
+
+## Questions already asked and answered (don't re-ask the user)
+
+- **"Should the bugs be fixed or just reported?"** — Answered: fix and
+  commit. That happened in `dd2d428`. The items in this file were explicitly
+  left for later; the user has seen this list and asked for it to be recorded
+  here. Proceeding with these tasks does not need re-confirmation, but
+  hardware-verification steps (task 1) need a human with the board.
+- **"Is the bounce buffer supposed to be enabled?"** — Yes. The README
+  previously contradicted the code; fixed in `dd2d428`. It is enabled and
+  load-bearing.
+- **"Is the board N4R8 or N16R8?"** — N16R8 (16 MB flash / 8 MB octal
+  PSRAM). The old sdkconfig header comment saying N4R8 was stale; fixed.
+- **"Why is WiFi brought up before the display?"** — Deliberate and
+  required; see README "Gotchas". Never reorder.
+- **"Why is rendering paused during fetches?"** — Deliberate mitigation for
+  PSRAM bus contention (see task 1). Improve it, don't just remove it.