docs: Record V1.2.6 in Script A's history and add the release note

Script A: header to V1.2.6; entries for blanton_fdr.sh, the unused
lanes off in Script A, and the FDR hooks in Script A, B and C, with
notes on the unverified STOp keyword, the lanes never being turned
back on, the both-units-only gating and the exec bits.

CLAUDE.md / ARCHITECTURE.md: status and release to V1.2.6, FDR and the
unused lanes in the overview, the Script A flow, the tree and the
commands.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0131orciRKrejchsuDk6UpXk

docs/release-notes/v1.2.6.md

@@ -0,0 +1,46 @@
+# v1.2.6 — FDR statistics around the traffic run, and unused lanes turned off before the baseline
+
+## ✨ New features
+
+**`blanton_fdr.sh` — FDR statistics through `phydiag fdrstat`**
+* Four sub-commands, each run on unit 0 then unit 1, over ports `'1-259,270-565'`:
+  `start` (`fdrstat STArt bin_group=both Interval=30`), `clear` (`fdrstat clear`), `rdcnt` (`fdrstat Counters`), `stop` (`fdrstat STOp`).
+* Output is printed as is, under a `### [time] unit N: ...` header — no parsing, no PASS/FAIL.
+* `-u 0` / `-u 1` for one switch unit, `-i <sec>` for the interval, `-n` for a dry run. `FDR_PORTS` overrides the port list.
+
+**FDR runs alongside the traffic test in Script A, B and C**
+* **Script A** wraps its traffic baseline: `fdr start` after `init`, `fdr clear` after `clear`, `fdr rdcnt` after the run, `fdr stop` after the traffic stop. The traffic run is now **40 s instead of 15 s**, so the counters are read after the first 30 s interval has been published — the same rule as `prbsstat Ber`.
+* **Script B** starts and clears FDR with the traffic setup, before the soak loop — the counters run for the whole soak.
+* **Script C** reads them (`rdcnt`) before stopping the traffic and stops FDR after it — the closing read of the counters Script B started.
+
+**Script A turns off the unused lanes before the BER baseline**
+* `unused_lanes.sh off` — TX squelch on the unused retimer lanes and TSC31 (`cd112-cd115`) disabled on the TH6, on both switch boards.
+
+## 📦 Downloads
+
+| File | Contents |
+|---|---|
+| `Script_ABC_Blanton_V1.2.6.zip` | The full Tera Term working directory, including `Blanton_Script/` to copy onto the DUT |
+
+```bash
+chmod +x ~/Blanton_Script/*.sh
+grep -rlU $'\r' ~/Blanton_Script    # expect no output
+```
+
+## ⚠️ Before you run
+
+* **`chmod +x` after deploying.** `blanton_fdr.sh`, `unused_lanes.sh` and `retimer_lanes.sh` are all called by path; `unused_lanes.sh` also refuses to start if `retimer_lanes.sh` is not executable.
+* **`blanton_fdr.sh stop` sends `fdrstat STOp` — that keyword is inferred from `prbsstat STOp` and has not been checked on the bench.** `bcmcmd` exits 0 even when the BCM shell rejects a command, so if it is wrong, FDR keeps running and only the log shows it. Check the first run.
+* **FDR only runs when both switch units are enabled** (`SWB_UNIT0 = SWB_UNIT1 = 1`). The single-unit branches have no FDR, and Script A's single-unit traffic run is still 15 s.
+* **Nothing turns the unused lanes back on.** Script C has no `unused_lanes.sh on`; run it by hand when the DUT is needed in its normal state. Whether a reboot clears it has not been checked.
+* **`unused_lanes.sh off` is not gated by `SWB_UNIT0` / `SWB_UNIT1`** — it always acts on both boards.
+* **`blanton_ber.sh` (Script A / C) still uses `p=3` and `sleep 30`**; see v1.2.5.
+* **Script 4 has no teardown**: finish it with `blanton_tr518.sh stop` **and** `systemctl stop mlucas-amm`.
+* **`FAN_SPEED` is 100.**
+
+## 🔗 Links
+
+* [ARCHITECTURE.md](https://etgit.et-wen.com/etwen/Blanton_TTL_Script/src/branch/main/ARCHITECTURE.md) — test flow, data models, constraints
+* [CLAUDE.md](https://etgit.et-wen.com/etwen/Blanton_TTL_Script/src/branch/main/CLAUDE.md) — commands and the bench gotchas
+
+**Full changelog:** [V1.2.5...V1.2.6](https://etgit.et-wen.com/etwen/Blanton_TTL_Script/compare/V1.2.5...V1.2.6)