retain telemetry across transport outages

docs/binary-transport-validation-2026-08-17.md

@@ -11,6 +11,8 @@ data.
 - Host compilation of the production C encoder with `-Wall -Wextra -Werror`
 - Fragmented C-encoder-to-Python-parser contract test
 - Deliberately corrupted CRC test with stream resynchronization
+- Full eight-record, timestamp-saturation, invalid-size/count, and truncated-tail
+  encoder/parser contract cases
 - ESP-IDF firmware build and flash on the assembled ESP32-C3 prototype
 - Live USB capture followed by independent offline re-decoding
 
@@ -55,3 +57,26 @@ at priority 5 and receives samples through a 512-entry queue (about 5.12 seconds
 at 100 Hz). The hardware capture's zero timing anomalies and zero loop overruns
 confirm that packet encoding, CRC, float metadata, and USB output did not disturb
 the acquisition cadence.
+
+Output failure is transactional: firmware retains and retries the same encoded
+packet with a scheduler delay instead of discarding it or dequeuing more samples.
+The queue therefore accumulates a disconnected-transport backlog. If an outage
+outlasts the queue, acquisition drops and counts new samples while preserving the
+oldest queued data for ordered delivery after reconnection.
+
+## Forced transport-outage validation
+
+A temporary validation build made the packet writer report transport failure for
+a fixed interval while acquisition continued normally. The failure injection was
+removed before the production build.
+
+With a three-second forced outage, all 2,144 observed samples arrived contiguously
+from sequence 0 through 2,143. Packet gaps, sample gaps, drops, loop overruns, and
+timestamp-saturation flags were all zero.
+
+With a seven-second forced outage, the queue preserved samples 0 through 511 and
+then dropped 138 new samples after reaching capacity. Delivery resumed at sample
+650. The cumulative drop count and observed sequence gap both equaled 138. The
+timestamp difference from sample 511 to 650 was exactly 1,390,000 us, matching
+139 sample intervals, and no saturation flag was emitted. This verifies both the
+oldest-data retention policy and the new exact timestamp re-anchor after overflow.