Vendor a neutral SuspendCodeCoverage in PlatformServices (Phase 6e-4c3)

[Evangelink]

Phase 6e-4c3 — vendor a neutral SuspendCodeCoverage

Part of the initiative to make Microsoft.VisualStudio.TestPlatform.MSTestAdapter.PlatformServices platform-agnostic by removing its dependency on Microsoft.TestPlatform.ObjectModel. Strict byte-for-byte, no behavior change.

What this changes

TestDeployment (netfx) wraps the deployment file-copy in using (new SuspendCodeCoverage()) to pause dynamic code-coverage instrumentation of modules loaded while files are copied. That type came from Microsoft.VisualStudio.TestPlatform.ObjectModel.Utilities.

This vendors an internal neutral copy at Utilities/SuspendCodeCoverage.cs (namespace ...PlatformServices.Utilities), reproducing the VSTest behavior exactly:

• On construction: capture the current value of the process environment variable __VANGUARD_SUSPEND_INSTRUMENT__, then set it to TRUE.
• On dispose: restore the captured previous value (idempotent).

The environment-variable name and value are the collector IPC contract the dynamic code-coverage (Vanguard) engine reads, so they are preserved byte-identical. The wrapper is internal sealed with a straightforward idempotent Dispose — the original's Dispose(bool) / GC.SuppressFinalize plumbing has no finalizer to suppress and is behavior-equivalent to the direct restore.

TestDeployment now resolves SuspendCodeCoverage through its already-present using ...PlatformServices.Utilities;; the VSTest ObjectModel.Utilities using (and its deferral comment) is removed.

Fidelity proof and test-net limitation

The mechanism is a process environment variable (__VANGUARD_SUSPEND_INSTRUMENT__), not a named event / mutex / EventWaitHandle. There is no signal/listener model — the dynamic code-coverage (Vanguard) collector reads this variable from the process environment when deciding whether to instrument a module being loaded. The fidelity of the vendored copy therefore rests entirely on replicating that wire contract byte-identically against the OSS source (vstest v18.4.0 SuspendCodeCoverage.cs).

Source-diff (fidelity proof of record) — OSS original vs vendored copy:

Contract element	OSS (Microsoft.TestPlatform.ObjectModel)	Vendored copy
env var name	"__VANGUARD_SUSPEND_INSTRUMENT__"	"__VANGUARD_SUSPEND_INSTRUMENT__"
set value	"TRUE"	"TRUE"
target (all 3 accesses)	EnvironmentVariableTarget.Process	EnvironmentVariableTarget.Process
ctor	GetEnvironmentVariable(name, Process) → capture; SetEnvironmentVariable(name, "TRUE", Process)	identical
dispose	SetEnvironmentVariable(name, prev, Process), guarded by _isDisposed	identical

The only intentional difference is the collapse of the OSS Dispose() / protected virtual Dispose(bool) / GC.SuppressFinalize into a single idempotent Dispose() — behavior-equivalent because the OSS type declares no finalizer (so GC.SuppressFinalize is a no-op and disposing is always true on the public path). The name/value/target/sequence — the entire wire contract the collector keys off — are verbatim.

Note on the test net: PlatformServices.Desktop.IntegrationTests runs with no coverage collector attached, so its green result proves the vendored code does not crash / the deploy path still works — it does not exercise a real collector reading the variable. That is acceptable here precisely because there is no signaling to get wrong: correctness is fully determined by the (source-identical) variable name/value/target above. There is no clean seam to assert the variable mid-deploy without contorting the copy loop, so no brittle probe was added.

Result: PlatformServices is ObjectModel-type-free

After this change, PlatformServices has zero using/type references to the Microsoft.TestPlatform.ObjectModel package — only string-literal assembly names (used for by-name runtime assembly lookup in the AppDomain/source-host wiring) remain. This clears the way to drop the package reference in the capstone (Phase 7).

Verification

• Builds 0-warning (net462 and all real TFMs; netfx-guarded change).
• MSTestAdapter.PlatformServices.UnitTests: 935/935 (net462), 897/897 (net8.0).
• PlatformServices.Desktop.IntegrationTests: 15/15 (net462) — exercises the deployment path that runs inside the SuspendCodeCoverage scope.
• Expert-reviewer pass.

Stacking

Stacks on #9631 (Phase 6e-4c2); base branch dev/amauryleve/vstest-decoupling-sourcehandler. Review/merge after the earlier PRs in the chain reach the base. Do not squash-rebase the base.