fix(handlers): stop flaky coverage CI from global-logger race in parallel tests

[AbirAbbas]

Summary

The coverage (control-plane) CI job (and the cascading coverage-summary job) flake because two tests mutate the process-global logger.Logger while running with t.Parallel():

• TestDiscoveryLoggingIncludesOptionalRequestID
• TestExecutionCleanupService_StartStopBranches

Both call setupExecutionCleanupTestLogger, which swaps logger.Logger and restores it via t.Cleanup. Run in parallel, a sibling test reassigns the global logger mid-run, so the discovery test's captured buffer comes back empty and its assertions fail:

coverage_handlers_92_target_test.go:380: "" does not contain "\"request_id\":\"req-123\""

coverage-summary then fails with missing input: control-plane.total.txt because the control-plane coverage step exited non-zero. The non-test build is unaffected, which is why this slipped past the required gates and only surfaced in the coverage job's full parallel run.

Fix

Drop t.Parallel() from both tests so they run in the serial phase, where nothing else mutates the global logger concurrently. This matches the existing convention — the logger-swapping tests in execution_cleanup_test.go are already non-parallel for the same reason.

Verification

• go test ./internal/handlers/ -count=20 -run 'TestDiscoveryLoggingIncludesOptionalRequestID|StartStopBranches|TestExecution' — passes (this exact command reproduced the failure before the fix)
• full go test ./internal/handlers/ — passes
• go vet clean; no new gofmt drift introduced (the file has pre-existing struct-alignment drift on main, left untouched to keep this PR scoped)

Out of scope (flagged, not fixed here)

Running the package under -race surfaces several separate, pre-existing data races in the heartbeat coverage tests (processHeartbeatAsync async goroutines writing to test stubs in TestHeartbeatHandler_AdditionalCoverage / TestDiscoveryAndNodeHandlers_AdditionalCoverage). The coverage CI job does not run with -race, so those are not what breaks it — worth a separate follow-up.

🤖 Generated with Claude Code

[github-actions]

📊 Coverage gate

Thresholds from .coverage-gate.toml: per-surface ≥ 86%, aggregate ≥ 88%, max per-surface regression ≤ 1.0 pp, max aggregate regression ≤ 0.50 pp.

Surface	Current	Baseline	Δ
control-plane	87.50%	87.30%	↑ +0.20 pp	🟡
sdk-go	92.00%	90.70%	↑ +1.30 pp	🟢
sdk-python	93.73%	93.63%	↑ +0.10 pp	🟢
sdk-typescript	92.80%	92.56%	↑ +0.24 pp	🟢
web-ui	89.93%	90.01%	↓ -0.08 pp	🟡
aggregate	89.03%	89.01%	↑ +0.02 pp	🟡

✅ Gate passed

No surface regressed past the allowed threshold and the aggregate stayed above the floor.

[github-actions]

📐 Patch coverage gate

Threshold: 80% on lines this PR touches vs origin/main (from .coverage-gate.toml:thresholds.min_patch).

Surface	Touched lines	Patch coverage	Status
control-plane	0	—	➖ no changes
sdk-go	0	—	➖ no changes
sdk-python	0	—	➖ no changes
sdk-typescript	0	—	➖ no changes
web-ui	0	—	➖ no changes

✅ Patch gate passed

Every surface whose lines were touched by this PR has patch coverage at or above the threshold.

[AbirAbbas]

Folded into #602 — keeping it to a single PR. The coverage flake fix (drop t.Parallel() from the two global-logger-swapping tests) is now the first commit on that branch.