diff --git a/README.md b/README.md
index 45086f2..deab2bf 100644
--- a/README.md
+++ b/README.md
@@ -12,6 +12,7 @@ Firmware for LilyGO T3 v1.6.1 (`ESP32 + SX1276 + SSD1306`) that runs in two role
 - Batch payload codec is schema `v3` with a 30-bit `present_mask` over `[t_last-29, t_last]` (`src/payload_codec.cpp`).
 - Sender retries reuse cached encoded payload bytes (no re-encode on retry path).
 - Sender ACK receive windows adapt from observed ACK RTT + miss streak.
+- Sender catch-up mode drains backlog with immediate extra sends when more than one batch is queued (still ACK-gated, single inflight batch).
 - Sender only starts normal metering/transmit flow after valid time bootstrap from receiver ACK.
 - Sender fault counters are reset at first valid time sync and again at each UTC hour boundary.
 - Receiver runs STA mode if stored config is valid and connects, otherwise AP fallback.
@@ -90,6 +91,7 @@ Timestamp derivation:
 - jump checks: rollback, wall-time delta mismatch, anchor drift
 
 Sender builds sparse 30-slot windows and sends every `METER_SEND_INTERVAL_MS` (`30s`).
+When backlog is present (`batch_q > 1`), sender transmits additional queued batches immediately after ACK to reduce lag, while keeping stop-and-wait ACK semantics.
 
 Sender diagnostics (serial debug mode):
 - periodic structured `diag:` line with:
@@ -158,11 +160,13 @@ Web timestamp display:
 SD CSV logging (`src/sd_logger.cpp`):
 - header: `ts_utc,ts_hms_local,p_w,p1_w,p2_w,p3_w,e_kwh,bat_v,bat_pct,rssi,snr,err_m,err_d,err_tx,err_last`
 - `ts_hms_local` is local `HH:MM:SS` derived from `TIMEZONE_TZ`
+- per-day file partition uses local date from `TIMEZONE_TZ`: `/dd3/<device_id>/YYYY-MM-DD.csv`
 
 History parser (`src/web_server.cpp`):
 - accepts both:
   - current layout (`ts_utc,ts_hms_local,p_w,...`)
   - legacy layout (`ts_utc,p_w,...`)
+- daily file lookup prefers local-date filenames and falls back to legacy UTC-date filenames for backward compatibility
 - requires full numeric parse for `ts_utc` and `p_w` (rejects trailing junk)
 
 OLED duplicate display:
diff --git a/Requirements.md b/Requirements.md
index 02f3dfd..a47eeba 100644
--- a/Requirements.md
+++ b/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.