Auto: ablegacy-11 — RSLogix 500/PLC-5 CSV symbol import

Closes #254

docs/drivers/AbLegacy-Test-Fixture.md

@@ -59,6 +59,28 @@ supplies a `FakeAbLegacyTag`.
   `_Diagnostics/<host>/<name>` short-circuit returns the live snapshot through
   `ReadAsync` without bumping `RequestCount`; two devices keep counters
   independent.
+- `RsLogixSymbolImportTests` — ablegacy-11 / #254 RSLogix CSV symbol-import parser:
+  canonical 8-row CSV (one row per N/F/B/L/ST/T/C/R) → 8 typed
+  `AbLegacyTagDefinition`s with the right `DataType`; header + comment-line
+  (`;` / `#`) skipping; malformed-row → log warning + skip (`IgnoreInvalid=true`
+  default) vs. `InvalidDataException` (`IgnoreInvalid=false`); empty stream →
+  empty result; UTF-8 BOM survival; embedded comma in quoted Description;
+  doubled-quote escape; `--scope` filter (Global vs. Local:N); `MaxRowsToImport`
+  cap; missing required header column → `InvalidDataException` regardless of
+  `IgnoreInvalid`; `TryResolveDataType` rejects garbage + bit-suffix overrides
+  the file letter (`N7:0/3` → Bit).
+- `RsLogixSymbolImportGoldenTests` — golden-snapshot integration: loads
+  `Fixtures/rslogix-canonical.csv` (8-row canonical export covering every v1
+  file letter), serialises the resulting tag list, and compares to
+  `Fixtures/rslogix-canonical-expected.json`. On mismatch the actual JSON is
+  dumped to `%TEMP%/rslogix-canonical-actual.json` and the path printed in the
+  failure message so the dev can `cp` the golden after reviewing the diff.
+- `AbLegacyDriverFactoryAddRsLogixImportTests` — covers the
+  `AbLegacyDriverFactoryExtensions.AddRsLogixImport` extension method:
+  appends imported tags onto an existing options object without dropping the
+  hand-rolled tags or the device list; mutates by-copy (immutability
+  guarantee); `AddRsLogixImportWithResult` tuple overload returns both the
+  modified options and the import counters.
 - `AbLegacyDeadbandTests` — PR 8 per-tag deadband / change filter:
   absolute-only suppression sequence `[10.0, 10.5, 11.5, 11.6] -> [10.0, 11.5]`,
   percent-only suppression with a zero-prev short-circuit, both-set logical-OR
@@ -173,5 +195,10 @@ falsely marked Stopped just because the driver-wide probe timeout is tight.
   — known-limitations write-up + resolution paths
 - `tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/FakeAbLegacyTag.cs` —
   in-process fake + factory
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/Fixtures/rslogix-canonical.csv`
+  — ablegacy-11 / #254 8-row canonical RSLogix CSV symbol export, one row per
+  v1 file letter (N/F/B/L/ST/T/C/R)
+- `tests/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.Tests/Fixtures/rslogix-canonical-expected.json`
+  — golden snapshot the import tests compare against
 - `src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyDriver.cs` — scope remarks
   at the top of the file