did2: daqmetadatareader migrator preserves tab_separated_file_parameter

src/did/+did2/+convert/+migrators/daqmetadatareader.m

@@ -3,10 +3,14 @@
 %
 %   Renames the v1 `ndi_daqmetadatareader_class` field on the
 %   daqmetadatareader property block to the V_delta-required
-%   `reader_class` field. The v1 `tab_separated_file_parameter` field
-%   has no V_delta counterpart and is dropped (per
-%   docs/v2/RFC-step6d-ci-pipeline.md decision-default Q1: drop v1
-%   fields that V_delta does not declare).
+%   `reader_class` field. Preserves the optional v1
+%   `tab_separated_file_parameter` field as a V_delta pass-through:
+%   it is the "lazy hook" for TSV-per-epoch metadata sources and
+%   real v1 corpora populate it. See
+%   `did-schema/schemas/V_delta/conversions/from_did_v1/daqmetadatareader.md`
+%   and `did-schema#50` for the V_delta-side decision to keep the
+%   field rather than force per-doc synthesis of a
+%   `daqmetadatareader_tsv` subclass.
 
 arguments
     preBody (1,1) struct
@@ -31,5 +35,9 @@
 if isfield(block, 'metadata_names')
     newBlock.metadata_names = char(block.metadata_names);
 end
+if isfield(block, 'tab_separated_file_parameter')
+    newBlock.tab_separated_file_parameter = ...
+        char(block.tab_separated_file_parameter);
+end
 v2Body.daqmetadatareader = newBlock;
 end

tests/+did2/+unittest/testMigrators.m

@@ -151,10 +151,45 @@ function testDaqmetadatareaderRenamesReaderClass(testCase)
     'ndi.daq.metadatareader.RayoLabStims');
 verifyFalse(testCase, isfield(out.daqmetadatareader, ...
     'ndi_daqmetadatareader_class'));
+% tab_separated_file_parameter is the optional V_delta "lazy hook"
+% field for TSV-per-epoch metadata sources. Real v1 corpora populate
+% it; the migrator preserves the value rather than dropping (see
+% did-schema#50).
+verifyTrue(testCase, isfield(out.daqmetadatareader, ...
+    'tab_separated_file_parameter'));
+verifyEqual(testCase, ...
+    out.daqmetadatareader.tab_separated_file_parameter, 'something');
+end
+
+function testDaqmetadatareaderTabSeparatedHookAbsentStaysAbsent(testCase)
+% A v1 body without the optional TSV hook should not gain an empty
+% one after migration.
+v1 = wrap('daqmetadatareader', 'daqmetadatareader', struct( ...
+    'ndi_daqmetadatareader_class', 'ndi.daq.metadatareader'));
+out = did2.convert.migrators.daqmetadatareader( ...
+    did2.convert.universalRenames(v1));
+verifyEqual(testCase, out.daqmetadatareader.reader_class, ...
+    'ndi.daq.metadatareader');
 verifyFalse(testCase, isfield(out.daqmetadatareader, ...
     'tab_separated_file_parameter'));
 end
 
+function testDaqmetadatareaderTabSeparatedHookRoundtripsAlreadyVDelta(testCase)
+% A body already in V_delta shape (reader_class +
+% tab_separated_file_parameter) should pass through the migrator
+% unchanged.
+v1 = wrap('daqmetadatareader', 'daqmetadatareader', struct( ...
+    'reader_class',                 'ndi.daq.metadatareader', ...
+    'tab_separated_file_parameter', 'epoch_metadata.tsv'));
+out = did2.convert.migrators.daqmetadatareader( ...
+    did2.convert.universalRenames(v1));
+verifyEqual(testCase, out.daqmetadatareader.reader_class, ...
+    'ndi.daq.metadatareader');
+verifyEqual(testCase, ...
+    out.daqmetadatareader.tab_separated_file_parameter, ...
+    'epoch_metadata.tsv');
+end
+
 function testElementRenamesAndCoerces(testCase)
 v1 = wrap('element', 'element', struct( ...
     'ndi_element_class', 'ndi.probe.timeseries.mfdaq', ...