docs(heidenhain): honest provenance for alarm class/group codes (#853)

No public source exists for DNC_ERROR_CLASS / DNC_ERROR_GROUP or their numbers
(the table was written from memory). The iTNC 530 Technical Manual's PLC error
table documents the same class and group NAMES without codes; three real
iTNC 530 records corroborate 7/4, 7/3 and 1/3. DNC and LSV2 numberings are
known to differ (ProgramStatus vs R_RI 26), so the numbers stay unproven.
Docs/comments only; no behaviour change.

Claude-Session: https://claude.ai/code/session_01GT67AD99zQQqpLCVm3p7xk

docs/drivers/Heidenhain.md

@@ -311,12 +311,25 @@ are 0–65535 (wire uint16), NUMBER is int32. Selectors always filter on the **r
 `Alarms/Groups` or a condition message, then filter. One parser (`HeidenhainAlarmSelector`) backs the editor, the deploy
 inspector and the driver.
 
-**Class / group names and the Part 9 condition class (Gitea #839).** LSV2 documents neither field (pyLSV2 and the Java
-port keep them raw). `HeidenhainAlarmClasses` carries HEIDENHAIN's own names from the **DNC interface** (RemoTools SDK
-`DNC_ERROR_CLASS` / `DNC_ERROR_GROUP`), which describe the same control error list. That the LSV2 codes share that
-numbering is corroborated by the one real record we hold — the captured iTNC 530 "Run test of cutout channels" is class 7
-`INFO`, group 4 `GENERAL`, a power-up self-test notice — and is otherwise **hardware-unproven** (the commissioning gate
-should confirm it on a live control).
+**Class / group names and the Part 9 condition class (Gitea #839, #853).** LSV2 documents neither field (pyLSV2 and the
+Java port keep them raw — pyLSV2's `decode_error_message` is class/group/number/text only). The names in
+`HeidenhainAlarmClasses` were originally written as the DNC interface's `DNC_ERROR_CLASS` / `DNC_ERROR_GROUP` enums
+**from memory**; a 2026-11-13 search found **no public source for those enums or their numeric values**. What the
+public sources do establish:
+
+- **Names (vendor-documented, numbers not).** The iTNC 530 HSCI Technical Manual's PLC error table (`.PET`) has a
+  **Class** column — ERROR (collective), FEED HOLD, PGM HOLD, PGM ABORT, EMERG. STOP, RESET — and a **Group** column —
+  GENERAL, OPERATING, PROGRAMMING, PLC — plus a separate E/W/I message-type column. That is the same class set as our
+  2–6 (and in the same order) and the same group set as our 1–4; WARNING/INFO/NOTE look like the message type folded
+  into the LSV2 class code, which is unconfirmed.
+- **Observed records (real iTNC 530, read-only).** class 7 / group 4 "Run test of cutout channels" (power-up self-test);
+  class 7 / group 3 "701550 Cabin unlocked! B301" (Hermle70, Hermle29); class 1 / group 3 "700520 Tool life exceeded"
+  (Hermle49). Both 7xxxxx records are machine-builder PET messages and both report group 3 — consistent with 3 = PLC.
+- ⚠️ **"LSV2 shares the DNC numbering" is not a safe general assumption.** The DNC COM interface's `ExecutionMode`
+  (0 MANUAL, 1 MDI, 2 RPF, 3 SINGLESTEP, 4 AUTOMATIC) matches LSV2 `R_RI 23`, but its `ProgramStatus` (0 IDLE,
+  1 RUNNING, …) does **not** match LSV2 `R_RI 26` (0 Started … 7 Idle, which real controls confirm). So the class/group
+  numbers stay **hardware-unproven** except where a record above shows them; the Safety branch (class 5) has never
+  been observed.
 
 | Class | 1 Warning · 2 FeedHold · 3 ProgramHold · 4 ProgramAbort · **5 EmergencyStop** · 6 Reset · 7 Info · 8 Error · 9 Note |
 |---|---|