Fix plan-delegate timeout completion

[asim]

Summary:

• Treat a post-side-effect client 408 in the plan-delegate harness as completed work when all required task and delegated notify side effects are present.
• Keep failing early when timeout happens before those side effects, and include counts for triage.
• Add deterministic coverage for completed-side-effect and incomplete-side-effect timeout paths.

Testing:

• go build ./...
• go test ./... (fails in this environment: loopback targets forbidden in client/grpc and transport/grpc)
• go test ./internal/harness/plan-delegate -run 'TestPlanDelegateExecution' -count=1\n- golangci-lint run ./...\n\nCloses Fix atlascloud plan-delegate flow completion timeout after delegated notify #3766\nCloses Loop: build increment #34 #3773