run 24

captures/rcp-heartbeat-echo-exact-7b5026d0.txt

@@ -0,0 +1,34 @@
+Sequence probe: 5 frames x 2 group(s) on COM5 at 38400 8N1
+FRAME 1: 00 00 A0 00 80 7A
+FRAME 2: 00 00 EC 40 30 C6
+FRAME 3: 07 80 7B 50 26 D0
+FRAME 4: 00 00 00 00 80 DA
+FRAME 5: 00 00 00 00 80 DA
+BASELINE heartbeat-compatible RX: 24 bytes, offset 0, 4 frames + 0 bytes
+BEGIN group 1/2
+19:41:46.849  TX group=1 frame=1 len=006  00 00 A0 00 80 7A
+19:41:46.849  RX group=1 frame=1 heartbeat-compatible RX: 6 bytes, offset 0, 1 frames + 0 bytes
+19:41:47.356  TX group=1 frame=2 len=006  00 00 EC 40 30 C6
+19:41:47.356  RX group=1 frame=2 heartbeat-compatible RX: 6 bytes, offset 0, 1 frames + 0 bytes
+19:41:47.896  TX group=1 frame=3 len=006  07 80 7B 50 26 D0
+19:41:47.896  RX group=1 frame=3 ANOMALY 18 RX bytes; first mismatch at byte 6: got 07, heartbeat offset 0 expected 00
+19:41:47.896  RX group=1 frame=3 raw 00 00 00 00 80 DA 07 C0 2F 95 09 2E 07 C0 2F 95 09 2E
+19:41:48.400  TX group=1 frame=4 len=006  00 00 00 00 80 DA
+19:41:48.400  RX group=1 frame=4 ANOMALY 18 RX bytes; first mismatch at byte 0: got 07, heartbeat offset 0 expected 00
+19:41:48.400  RX group=1 frame=4 raw 07 C0 2F 95 09 2E 00 00 00 00 80 DA 00 00 00 00 80 DA
+19:41:48.936  TX group=1 frame=5 len=006  00 00 00 00 80 DA
+19:41:48.936  RX group=1 frame=5 heartbeat-compatible RX: 18 bytes, offset 0, 3 frames + 0 bytes
+GROUP 1 TAIL heartbeat-compatible RX: 18 bytes, offset 0, 3 frames + 0 bytes
+BEGIN group 2/2
+19:41:50.065  TX group=2 frame=1 len=006  00 00 A0 00 80 7A
+19:41:50.065  RX group=2 frame=1 heartbeat-compatible RX: 12 bytes, offset 0, 2 frames + 0 bytes
+19:41:50.570  TX group=2 frame=2 len=006  00 00 EC 40 30 C6
+19:41:50.570  RX group=2 frame=2 heartbeat-compatible RX: 12 bytes, offset 0, 2 frames + 0 bytes
+19:41:51.107  TX group=2 frame=3 len=006  07 80 7B 50 26 D0
+19:41:51.107  RX group=2 frame=3 heartbeat-compatible RX: 18 bytes, offset 0, 3 frames + 0 bytes
+19:41:51.613  TX group=2 frame=4 len=006  00 00 00 00 80 DA
+19:41:51.613  RX group=2 frame=4 heartbeat-compatible RX: 12 bytes, offset 0, 2 frames + 0 bytes
+19:41:52.118  TX group=2 frame=5 len=006  00 00 00 00 80 DA
+19:41:52.118  RX group=2 frame=5 heartbeat-compatible RX: 12 bytes, offset 0, 2 frames + 0 bytes
+GROUP 2 TAIL heartbeat-compatible RX: 18 bytes, offset 0, 3 frames + 0 bytes
+Anomalies: 2

captures/rcp-heartbeat-echo-host-7b5026.txt

@@ -0,0 +1,34 @@
+Sequence probe: 5 frames x 2 group(s) on COM5 at 38400 8N1
+FRAME 1: 00 00 A0 00 80 7A
+FRAME 2: 00 00 EC 40 30 C6
+FRAME 3: 00 00 7B 50 26 57
+FRAME 4: 00 00 00 00 80 DA
+FRAME 5: 00 00 00 00 80 DA
+BASELINE heartbeat-compatible RX: 24 bytes, offset 0, 4 frames + 0 bytes
+BEGIN group 1/2
+19:42:09.119  TX group=1 frame=1 len=006  00 00 A0 00 80 7A
+19:42:09.119  RX group=1 frame=1 heartbeat-compatible RX: 6 bytes, offset 0, 1 frames + 0 bytes
+19:42:09.655  TX group=1 frame=2 len=006  00 00 EC 40 30 C6
+19:42:09.655  RX group=1 frame=2 ANOMALY 18 RX bytes; first mismatch at byte 6: got 07, heartbeat offset 0 expected 00
+19:42:09.655  RX group=1 frame=2 raw 00 00 00 00 80 DA 07 80 7B 50 26 D0 07 80 7B 50 26 D0
+19:42:10.164  TX group=1 frame=3 len=006  00 00 7B 50 26 57
+19:42:10.164  RX group=1 frame=3 ANOMALY 18 RX bytes; first mismatch at byte 0: got 07, heartbeat offset 0 expected 00
+19:42:10.164  RX group=1 frame=3 raw 07 80 7B 50 26 D0 00 00 00 00 80 DA 00 00 00 00 80 DA
+19:42:10.702  TX group=1 frame=4 len=006  00 00 00 00 80 DA
+19:42:10.702  RX group=1 frame=4 heartbeat-compatible RX: 18 bytes, offset 0, 3 frames + 0 bytes
+19:42:11.208  TX group=1 frame=5 len=006  00 00 00 00 80 DA
+19:42:11.208  RX group=1 frame=5 heartbeat-compatible RX: 12 bytes, offset 0, 2 frames + 0 bytes
+GROUP 1 TAIL heartbeat-compatible RX: 18 bytes, offset 0, 3 frames + 0 bytes
+BEGIN group 2/2
+19:42:12.339  TX group=2 frame=1 len=006  00 00 A0 00 80 7A
+19:42:12.339  RX group=2 frame=1 heartbeat-compatible RX: 12 bytes, offset 0, 2 frames + 0 bytes
+19:42:12.874  TX group=2 frame=2 len=006  00 00 EC 40 30 C6
+19:42:12.874  RX group=2 frame=2 heartbeat-compatible RX: 18 bytes, offset 0, 3 frames + 0 bytes
+19:42:13.380  TX group=2 frame=3 len=006  00 00 7B 50 26 57
+19:42:13.380  RX group=2 frame=3 heartbeat-compatible RX: 12 bytes, offset 0, 2 frames + 0 bytes
+19:42:13.886  TX group=2 frame=4 len=006  00 00 00 00 80 DA
+19:42:13.886  RX group=2 frame=4 heartbeat-compatible RX: 12 bytes, offset 0, 2 frames + 0 bytes
+19:42:14.423  TX group=2 frame=5 len=006  00 00 00 00 80 DA
+19:42:14.423  RX group=2 frame=5 heartbeat-compatible RX: 18 bytes, offset 0, 3 frames + 0 bytes
+GROUP 2 TAIL heartbeat-compatible RX: 18 bytes, offset 0, 3 frames + 0 bytes
+Anomalies: 2

docs/discovery-notes.md

@@ -5294,3 +5294,71 @@ Best current follow-up:
 - treat `EC` as the next strong lead and test exact/host-shaped handling of
   `07 80 7B 50 26 D0`
 - optionally try `ED` next to see whether the `7B` branch continues
+
+### HE16: Exact Echo Of `07 80 7B 50 26 D0`
+
+Recreate the `EC` selector path, then immediately send the exact `7B`-family
+response back to the panel.
+
+```powershell
+python scripts/serial_sequence_probe.py --port COM5 --prompt --frame "00 00 A0 00 80 7A" --frame "00 00 EC 40 30 C6" --frame "07 80 7B 50 26 D0" --frame "00 00 00 00 80 DA" --frame "00 00 00 00 80 DA" --repeat 2 --frame-interval 0.20 --read-after-frame 0.30 --read-after-group 0.8 --log captures/rcp-heartbeat-echo-exact-7b5026d0.txt
+```
+
+### HE17: Host-Shaped Mirror Of `07 80 7B 50 26 D0`
+
+Host-shaped checksum for `00 00 7B 50 26 ??` is `57`.
+
+```powershell
+python scripts/serial_sequence_probe.py --port COM5 --prompt --frame "00 00 A0 00 80 7A" --frame "00 00 EC 40 30 C6" --frame "00 00 7B 50 26 57" --frame "00 00 00 00 80 DA" --frame "00 00 00 00 80 DA" --repeat 2 --frame-interval 0.20 --read-after-frame 0.30 --read-after-group 0.8 --log captures/rcp-heartbeat-echo-host-7b5026.txt
+```
+
+What would count as a hit:
+
+- any non-heartbeat response after the exact or host-shaped `7B 50 26` frame
+- a repeat of `07 80 7B 50 26 D0`
+- crossover into the `7A`-family branches or any new sibling family
+- any sign that `EC` is a second-stage exchange rather than just another
+  selector-produced readable response
+
+### 2026-05-13 `EC` Mirror Result
+
+Captures:
+
+- `captures/rcp-heartbeat-echo-exact-7b5026d0.txt`
+- `captures/rcp-heartbeat-echo-host-7b5026.txt`
+
+Result summary:
+
+- `EC` did not behave exactly like the earlier `E8` / `E9` branches.
+- In the host-shaped mirror run:
+  - `00 00 EC 40 30 C6` reproduced `07 80 7B 50 26 D0` in group 1
+  - host-shaped mirror `00 00 7B 50 26 57` did not advance the exchange; it
+    only drained one more `07 80 7B 50 26 D0` and then returned to heartbeat
+- In the exact-echo run:
+  - the `EC` selector step itself did not expose the `7B` family inside the
+    immediate read window
+  - but exact echo `07 80 7B 50 26 D0` produced a fresh new family:
+    `07 C0 2F 95 09 2E`
+  - that new family appeared twice in group 1, then the run returned to
+    heartbeat
+- Group 2 was heartbeat-only in both runs.
+
+Interpretation:
+
+- `EC` is the first `Ex` selector case so far where the exact downstream echo
+  appears to matter more than the host-shaped mirror.
+- That makes the `7B` branch more interesting than the `7A` branches:
+  - `E8` / `E9` downstream `7A` echoes did not produce a clean second-stage
+    family
+  - exact `7B` echo produced `07 C0 2F 95 09 2E`
+- `07 C0 2F 95 09 2E` is now a strong follow-up target. It may be:
+  - a second-stage response
+  - a different page/family reached through exact `7B` echo
+  - or a context-specific branch member that only appears on the exact-echo
+    path
+
+Best current follow-up:
+
+- test exact and host-shaped handling of `07 C0 2F 95 09 2E`
+- optionally compare whether exact `EC -> 7B` echo is timing-sensitive, since
+  the host-shaped mirror path did not reach the same family

docs/pt2-protocol-summary.md

@@ -242,6 +242,7 @@ confirmed Sony definition.
 | `07 80 7A 50 26 D1` | host-shaped `E8` branch, reproduced across HE8-HE11 group 1 | medium-high | reproducible downstream response family in the `E8` / `FA` / `7A` branch |
 | `07 80 7A 28 D3 5C` | host-shaped `E9` neighbor, group 1 | low-medium | nearby distinct `7A`-family response; suggests an `E8`/`E9` selector neighborhood |
 | `07 80 7B 50 26 D0` | host-shaped `EC` neighbor, group 1 | low-medium | new sibling family suggesting the `Ex` region is a selector-like strip |
+| `07 C0 2F 95 09 2E` | exact echo of `07 80 7B 50 26 D0`, group 1 | low-medium | possible second-stage family on the `EC -> 7B` branch |
 
 Current caution:
 
@@ -272,6 +273,9 @@ Current caution:
 - Extending outward reinforced the selector-strip model:
   `E6` and `EB` fall into the `07 80 40 40 30 ED` transient family, while `EC`
   opens a new `07 80 7B 50 26 D0` sibling response.
+- `EC` is now the first branch where the exact downstream echo looks more
+  meaningful than the host-shaped mirror: exact `07 80 7B 50 26 D0` produced
+  `07 C0 2F 95 09 2E`, while host-shaped `00 00 7B 50 26 57` did not.
 
 ## What We Know
 
@@ -304,6 +308,8 @@ Current caution:
 - The wider `Ex` region now looks like a mixed selector surface:
   some values collapse into heartbeat-family transients, while others open
   related `7A` / `7B` downstream families.
+- The `EC -> 7B` path is currently the strongest sign that some downstream
+  exact echoes may matter, even though most earlier `7A`-family echoes did not.
 
 ## What We Do Not Know