I think it was a double cross the whole time. I think the deal that was set up and struck with tony through the contact in the third family (who I think was a representative of the lucchese family) for phil was real, but albie planned to double cross tony and kill him anyway (think luciano-masseria-maranzano) because tony and phil were creating a problem for everybody. Also tony had really been on borrowed time since usurping his uncle in season 1 and number of other ridiculous stunts, most of which are outlined in the "tony worst mob boss" thread.

I always reason it out that at the meeting between albie and tony, paulie joins tony. I think later on they reach out to paulie (who's been on the outs with tony since the pine barrens episode in season 3) and while he's very loyal, he's also a prototype wiseguy who's not afraid to change his tune to suit his needs. After silivio got shot, I don't think paulie was going to dig his grave with tony.
Patsy is in paulie's crew after he was brought over from junior's crew in season 2, and paulie would be one of the few who would know that patsy's son is dating meadow, so albie reaches out to paulie and they reach a deal; paulie talks to patsy who talked to his son and they see an opportunity, they send a guy on short notice to the dinner and there you go.

Tony could have been tailed, I don't remember where he was before going to the dinner so I can't really have an opinion on that theory.