test: raise Orleans code coverage above 90%

[ReubenBond]

Goal

Raise canonical Orleans repository line coverage from 78.54% to above 90% while improving branch coverage and reducing high-risk uncovered code.

Current baseline from the complete CI matrix:

• 99,056 / 126,115 lines covered (78.54%)
• Approximately 14,448 additional lines must be covered or removed to exceed 90% at the current denominator.
• Method-level analysis found 458 methods with CRAP >30 and **7,197 method entries below 90% line / 80% branch thresholds.
• Branch coverage is approximately 65.5% in raw Cobertura and needs canonical de-duplication before enforcement.

Reports:

• GitHub coverage check: https://github.com/dotnet/orleans/runs/98679059570
• Azure Pipelines coverage view: https://dev.azure.com/dnceng/internal/_build/results?buildId=3058646&view=codecoverage-tab

Workstreams

• test(analyzers): raise compiler tooling coverage above 90% #10857 — Compiler tooling and analyzer/codegen coverage (first slice merged: test(analyzers): raise compiler tooling coverage #10894)
• test(runtime): raise core runtime coverage above 90% #10858 — Core runtime, directory, activation, networking, and compatibility coverage (first slice: test(runtime): cover ring range collection invariants #10879)
• test(serialization): raise serialization coverage above 90% #10859 — Serialization, copying, reader, and segmented-buffer coverage (first slice: test(serialization): cover multidimensional array copying #10880)
• test(adonet): raise relational provider coverage above 90% #10860 — ADO.NET and shared relational storage coverage (first slice merged: test(adonet): raise relational provider coverage above 90% #10892)
• test(providers): raise cloud provider coverage above 90% #10861 — AWS, Azure, Google, Redis, and Cassandra provider coverage (first slice: test(azure): cover queue JSON validation #10876)
• test(streaming): raise streaming and broadcast coverage above 90% #10862 — Streaming and broadcast-channel coverage (first slice: test(streaming): cover JSON converter read contracts #10884)
• test(state): raise journaling and transaction coverage above 90% #10863 — Journaling, event sourcing, durable jobs, and transaction coverage (first slice: test(transactions): verify consistency histories #10875)
• test(testing): raise TestingHost and test-kit coverage above 90% #10864 — TestingHost and shipped TestKit coverage (first slice: test(testing): cover TestingHost failure diagnostics #10883)
• test(hosting): close long-tail package coverage gaps #10865 — Dashboard, connection security, hosting, diagnostics, and long-tail packages (first slice merged: test(dashboard): cover hosting and routing behavior #10885)
• refactor: audit zero-coverage and unreachable code #10866 — Zero-coverage reachability, unsupported paths, and dead-code cleanup (first slice merged: refactor(codegen): remove unused method signature comparer #10874)
• ci: add trustworthy coverage ratcheting toward 90% #10867 — Canonical coverage reporting and non-regression ratcheting (first slice merged: ci: add trusted coverage report validation #10882)

Strategy

1. Land deterministic unit and integration coverage for high-complexity, critical-path behavior first.
2. Correct coverage-lane omissions where substantial existing tests are not selected.
3. Audit zero-coverage code and remove confirmed dead/obsolete implementation.
4. Treat generated, linked, platform-specific, and shipped TestKit source consistently without broad exclusions.
5. Introduce a report-only main-vs-PR ratchet, then enforce non-regression and raise the floor as workstreams land.

Program acceptance criteria

• Canonical repository line coverage exceeds 90% on the complete CI matrix.
• Canonical branch coverage is published and materially improved, with no critical package below its agreed threshold.
• Every maintained package is at least 90% line coverage or has an evidence-backed, reviewed scope decision.
• No high-risk uncovered method remains without tests, simplification, removal, or an explicit follow-up.
• Coverage changes report newly covered lines, removed dead code, and approved scope corrections separately.
• CI detects missing matrix artifacts, missing maintained source, coverage regressions, and unauthorized filter/exclusion changes.
• Tests assert behavior and invariants; the initiative does not optimize the metric through shallow execution-only tests.