docs: reflect sender catch-up and local-date CSV/history behavior

Requirements.md

@@ -33,6 +33,7 @@ Function names below are C++ references. Rust naming/layout may differ, but the
 - Sampling/transmit cadence:
   - sender sample cadence 1 Hz.
   - sender batch cadence 30 s.
+  - when sender backlog exists (`batch_count > 1`) and no ACK is pending, sender performs immediate catch-up sends (still stop-and-wait with one inflight batch).
   - sync-request cadence 15 s while unsynced.
   - sender retransmits reuse cached encoded payload bytes for same inflight batch.
   - sender ACK receive window is adaptive from airtime + observed ACK RTT, with expanded second window on miss.
@@ -53,6 +54,8 @@ Function names below are C++ references. Rust naming/layout may differ, but the
   - diagnostics do not change LoRa payload schema or remap payload fields.
 - SD logging:
   - CSV columns include both `ts_utc` and `ts_hms_local`.
+  - per-day CSV file partitioning uses local date (`TIMEZONE_TZ`) under `/dd3/<device_id>/YYYY-MM-DD.csv`.
+  - history day-file resolution prefers local-date filenames and falls back to legacy UTC-date filenames.
   - history parser supports both current (`ts_utc,ts_hms_local,p_w,...`) and legacy (`ts_utc,p_w,...`) layouts.
 
 ## 3. Protocol and Data Contracts
@@ -246,11 +249,11 @@ Function names below are C++ references. Rust naming/layout may differ, but the
 - `void sd_logger_init()`
 - `bool sd_logger_is_ready()`
 - `void sd_logger_log_sample(const MeterData&, bool include_error_text)`
-  - append/create per-day CSV under `/dd3/<device_id>/YYYY-MM-DD.csv`.
+  - append/create per-day CSV under `/dd3/<device_id>/YYYY-MM-DD.csv` using local calendar date from `TIMEZONE_TZ`.
 - Internal behavior-critical helpers:
   - `fault_text`
   - `ensure_dir`
-  - `format_date_utc`
+  - `format_date_local`
   - `format_hms_local`
 
 ## `src/display_ui.cpp`
@@ -309,7 +312,8 @@ Internal route/state functions to preserve behavior:
 - `sanitize_history_device_id`
 - `sanitize_download_filename`
 - `history_reset`
-- `history_date_from_epoch`
+- `history_date_from_epoch_local`
+- `history_date_from_epoch_utc` (legacy fallback mapping)
 - `history_open_next_file`
 - `history_parse_line`
 - `history_tick`
@@ -451,5 +455,7 @@ Suggested Rust primitives:
 - Duplicate batch handling updates counters and suppresses duplicate publish/log.
 - Web UI shows `epoch (HH:MM:SS TZ)` local time.
 - SD CSV header/fields match expected order.
+- SD daily files roll over at local midnight (`TIMEZONE_TZ`), not UTC midnight.
 - History endpoint reads current and legacy CSV layouts successfully.
+- History endpoint can read both local-date and legacy UTC-date day filenames.
 - MQTT state/fault payload fields match existing names and semantics.