How Does Benzyl Alcohol Produce a Peak at m/z = 79?
Interesting question.

The cycloheptatriene - norcaradiene tautomerization is a common equilibium.  Usually the norcaradiene is present in small amounts, but as long as some is present the reaction can rapidly proceed through this intermediate.

In the diagram below, the norcaradiene can undergo hydrogen shift with concomitant decarbonylation to produce the m/z = 79 peak in the mass spectrum.