feat(prbs): Add 100G PRBS monitor; fix the job log path and USB mount

port_prbs_monitor.sh drives PRBS on both 100G uplinks: lpmode off, arm
the pattern, then poll `phy diag <phy> prbs get` in the background until
stopped, counting a poll as PASS only when the output says "PRBS OK!".
prbsstat Ber is captured beside every poll for the record but does not
decide the verdict. `stop` runs prbsstat STOp and prbs clear before
rendering the report, so the test does not leave PRBS armed.

`start a` / `start b` runs one uplink alone, which is how a genuine port
fault is separated from the DUT not coping with two PRBS streams at
once. A port that was not run reports SKIP rather than FAIL -- deciding
on poll count alone would have made a deliberate single-port run look
like half the hardware was broken.

The port status is deliberately not printed at `start`: with PRBS armed
the link reports DOWN, which reads as a failure to anyone glancing at
the console. It appears in the report instead, after prbs clear and
labelled as the recovered state.

The calls in Script A, B and C are committed but commented out -- PRBS
is still under bring-up.

Fix: the job directory was written as /host/hw-eval/current/jobs in some
places and /host/hw-eval/jobs in others, so what Script B wrote was not
what Script C collected. Unified on /host/hw-eval/jobs.

Fix: Script C copied to /mnt/usb assuming it was mounted. It now finds
the device with usb_target.sh and mounts it first, so the logs actually
leave the DUT.

Script C also reorders its results -- stress logs, then the MGMT ping
report, then 100G status -- and cats the bgctl ssd/usb logs.

Script A -> V1.0.9. Docs and docs/release-notes/v1.0.9.md updated.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014RetWKFZFG1ZHcitQAyhwM

docs/release-notes/v1.0.9.md

@@ -0,0 +1,63 @@
+# v1.0.9 — 100G PRBS testing, and the job logs actually reach the USB stick
+
+## ✨ New features
+
+**100G uplink PRBS test**
+* New `port_prbs_monitor.sh` drives a PRBS test on both 100G uplinks: it clears low-power mode, arms the pattern, then polls `phy diag <phy> prbs get` in the background until stopped. A poll counts as PASS only when the output says `PRBS OK!`; `prbsstat Ber` is captured alongside every poll for the record.
+* `stop` runs `prbsstat STOp` and `prbs clear` on each port before rendering the report, so the test does not leave PRBS armed behind it.
+* `report` gives the tally the bench actually wants:
+
+  ```
+  PORT           POLLS    PASS     FAIL     RESULT
+  Ethernet513    42       42       0        PASS
+  Ethernet514    42       40       2        FAIL
+  ```
+* **One port at a time is a first-class mode.** `start a` or `start b` runs a single uplink, which is how you separate a genuine port fault from the DUT not coping with two PRBS streams at once. A port that was not run reports `SKIP`, not `FAIL`.
+* Every command and its full output — setup, each poll, teardown — goes to that port's raw log.
+
+> ⚠️ The script ships in this build and can be run by hand, but **the calls in Script A, B and C are commented out**: PRBS is still under bring-up on this platform.
+
+**USB target detection**
+* `usb_target.sh` reports an inserted USB device's node, mount point or by-id path. It excludes whatever disk backs `/` and `/host` — this platform can boot from a USB DOM, which also reports as USB — refuses to guess when several USB disks are present, and when mounting, verifies the result is writable rather than trusting that `mount` succeeded.
+* Script B builds the USB stress command from the detected node instead of a hard-coded `/dev/sda1`.
+
+## 🐛 Bug fixes
+
+**The job logs were being written to a path nobody collected**
+* Stress output, the monitors' logs and the USB archive disagreed about where the job directory lives. Everything now uses `/host/hw-eval/jobs/`, so what Script B writes is what Script C copies out.
+
+**Script C copied to a USB that was never mounted**
+* The archive step assumed `/mnt/usb` was ready. Script C now finds the device and mounts it first, so a run's logs leave the DUT instead of being written into an empty mount point.
+
+**`show interfaces status` right after starting PRBS reads as a failure**
+* With PRBS armed the link is out of normal operation and reports DOWN. `port_prbs_monitor.sh` deliberately does not print the port status at `start` — it appears in the report instead, after `prbs clear`, labelled as the recovered state.
+
+## 📦 Downloads
+
+| File | Contents |
+|---|---|
+| `Script_ABC_Blanton_V1.0.9.zip` | The full Tera Term working directory, including `Blanton_Script/` to copy onto the DUT |
+
+**After copying to the DUT:**
+
+```bash
+chmod +x ~/Blanton_Script/*.sh      # see below
+grep -rlU $'\r' ~/Blanton_Script    # expect no output
+```
+
+`mgmt_ping_monitor.sh` and `port_prbs_monitor.sh` launch their workers through `bash`, so those two run without the execute bit. `bmc_monitor.sh` and `usb_target.sh` still need it, and neither git (mode 100644) nor a Windows/USB copy carries it. Without the `chmod`, `start` fails with `Permission denied` and the later `cat` finds nothing: **the section ends up empty and nothing reports an error.**
+
+## ⚠️ Before you run
+
+* **Declare the switch population.** `SWB_UNIT0` / `SWB_UNIT1` in `config.ttl` say which switch units this DUT has; traffic and the readiness gate both follow them.
+* **Set `FAN_SPEED`.** It is applied at the start of every run.
+* **Management connectivity is in use, not preserved.** Both management NICs are up and pinging — drive the run from the serial console.
+* **PRBS is not wired into the macros yet.** Run `port_prbs_monitor.sh` by hand if you want it; uncommenting the calls in A/B/C is not supported in this build.
+* **Two settings persist to `config_db.json`** and survive a reboot: LLDP is left disabled and the 100G uplinks are left configured. Restore them before the DUT moves on.
+
+## 🔗 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:** [V1.0.8...V1.0.9](https://etgit.et-wen.com/etwen/Blanton_TTL_Script/compare/V1.0.8...V1.0.9)