Exclude Migrations namespace from dotnet code coverage

EF migrations are generated scaffolding with no meaningful logic to
test; counting them against the coverage target only dilutes the
signal.

scripts/ci/test.sh

@@ -8,9 +8,17 @@ cd "$CI_ROOT"
 
 ensure_dotnet
 
+# --results-directory doesn't clear prior runs - it adds a new GUID folder
+# alongside old ones every time. On a runner that reuses its workspace
+# (self-hosted, unlike GitHub's ephemeral ones), stale coverage from past
+# runs would otherwise get merged in by coverage.sh and silently skew the
+# combined percentage.
+rm -rf "$CI_ROOT/coverage/dotnet"
+
 log "Running MicCheck.Api.Tests.Unit"
 dotnet test tests/api/MicCheck.Api.Tests.Unit/MicCheck.Api.Tests.Unit.csproj -c Release --logger trx \
-  --collect:"XPlat Code Coverage" --results-directory "$CI_ROOT/coverage/dotnet"
+  --collect:"XPlat Code Coverage" --results-directory "$CI_ROOT/coverage/dotnet" \
+  --settings tests/api/MicCheck.Api.Tests.Unit/coverlet.runsettings
 
 log "Running admin Jest tests"
 npm --prefix src/admin test -- --coverage --coverageReporters=lcov --coverageReporters=text-summary

tests/api/MicCheck.Api.Tests.Unit/coverlet.runsettings

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<RunSettings>
+  <DataCollectionRunSettings>
+    <DataCollectors>
+      <DataCollector friendlyName="XPlat code coverage">
+        <Configuration>
+          <Exclude>[MicCheck.Api]MicCheck.Api.Migrations.*</Exclude>
+        </Configuration>
+      </DataCollector>
+    </DataCollectors>
+  </DataCollectionRunSettings>
+</RunSettings>