PM- thanks for your kind compliment and again, MAZEL TOV on your new family addition!
i reviewed the tosefos again and , with great respect to your interpretation, I take a slightly different view. Clearly, tosefos calls gram kibbui if you reduce the amount of fuel ,as in a long candle that is cut to shorter the time of burning that tosefos explicitly calls gram kibbui. In the case of taking oil from a lamp ,tosefos say that, in the moment of taking the oil, it reduces the flame and this tosefos considers kibbui. This must be conclusively understood from the story upon which this tosefos is based ( the gabbai of ulloh tiltied the lamp to draw the oil away from the canlde,see rashi)
so, tosefos view -“lefi anyas daati”- is that, when, in the actual act, the fuel to the light is diminished on the spot and the light dimmed, this should be considered kibbui. cutting off the supply-and at that moment disturbing the light, is still gram kibbui. The qestion before us is what is the shutting off of a gas line. And I must say that-if you accept this view- reducing the gas by reducing the pressure of the gas may very well be considered kibbui according to these views.
However, I did mention the rambam and the lechem mishneh and if yo uwould cut off the gasl ine at another source (say, at the entrance into the house),which has no immediate influence on the gas fire, this would be considered gram kibbui.
I saw the Mogen Avroho you mention and I will gracefully acknoweldge that it seems that the Mogen Avrohom would consider kibbui if the light gets starved from oxygen and this actually dovetails with your understanding of the gas supply cutoff.
I accept your view of gram by R”Shlomo Zalman zz’l but it gets on shaky ground when you start dealing in seconds or the like. Gram is gram regardless of the time lapse, but who am I to argue with R’Shlomo Zalman?