fix(legacy-mcu1): preserve Bluetooth patches for product 0x8820

Keep the product-specific syscfg writes and restore all patch uploads, including patch configuration. Derive the syscfg condition from the current product readback without retaining a loader flag.

Update regression checks for full patch uploads on both products and syscfg write failures, and document the reported hardware results and remaining validation.

tests/issue119-8820/README.md

@@ -3,14 +3,26 @@
 Run `python3 tests/issue119-8820/test_loader.py` with a C compiler available.
 The test extracts the actual system configuration, normal-mode upload branch,
 and busy-connect guard and runs them against mocked USB requests. It checks
-that alternating/reprobing M80 and regular D80 devices preserves each loader
-sequence, retains the MCU1 cache fix, propagates configuration errors, and
-rejects a new connect without overwriting an operation already in progress.
+that both product `0x8820` and regular D80 devices upload the complete
+adid/patch/extended-patch/patch-table/patch-config layer before starting FMAC.
+Alternating and reprobed devices receive the extra syscfg writes only when
+their current product readback is `0x8820`. The checks also retain the MCU1
+cache fix, propagate read/cache/syscfg write errors, and reject a new connect
+without overwriting an operation already in progress.
 
-These checks do not establish hardware or Bluetooth compatibility. Issue #118
-reports working Wi-Fi on one UGREEN `a69c:5723`, chip revision 7, MCU1 unit
-with product `0x8820` and the branch's 327,037-byte V3 FMAC. Bluetooth pairing
-and audio remain unverified. Product `0x8820` is not a rule to skip patches
-on every MCU1 device, and the report does not establish that every device in
-issue #79 works with this firmware.
+The [hardware follow-up in PR #119](https://github.com/shenmintao/aic8800d80/pull/119#issuecomment-6468608942)
+corrects the initial FMAC-only hypothesis from #118. On one UGREEN
+`a69c:5723`, chip revision 7, MCU1, product `0x8820` unit running Ubuntu 26.04
+and kernel `7.0.0-14-generic`, the two syscfg writes alone resolve the
+`MM_START` timeout. Skipping the patch layer causes Bluetooth HCI Reset
+(`0x0c03`) to time out; restoring all patch uploads, including patch config,
+preserves Wi-Fi and restores controller initialization and LE discovery.
+The firmware remains the branch's matched V3 set, including its 327,037-byte
+FMAC.
+
+The contributor tested the restored-patch variant, rather than this exact
+follow-up commit. The cold-start sequence was replayed through USB
+re-enumeration; physical unplug/replug, reboot of that variant, Bluetooth
+pairing/audio, and other units remain unverified. These mocked checks do not
+establish hardware compatibility or support for every device in issue #79.