Nobody that we know of at the conference is at war
Huh?
Everybody is - they are just trying to talk each other out of actually pulling any triggers. And that would work a lot better if the triggers were moved a few lightyears away from the conference.
Spock broke the treaty just rescuing Kirk and McCoy, Chang would've been in the right to have a fleet back him up.
It's not about "right". It's about what
looks right. Lawyers could have started the war without the need to assassinate Gorkon in the first place ("My client holds rights to Archanis Sector"; "No,
my client does!"), but that would have satisfied nobody. Cartwright needs to start a war in which the UFP is the victim, or his own troops, disinterested in bloodshed, will refuse to fight. Chang needs to start a war in which the Empire is the victim, or his own troops, realizing they are the underdogs and unlikely to gain anything (including the thrill of actually winning some good battles), will refuse to fight.
No, the Klingon Imperial Bloodshed Fleet cannot appear in orbit above Khitomer or else the war is lost even before it gets started. Nor can Starfleet, and clearly Sulu has orders to that very end - why else would he, the skipper of a ship at the other end of the universe, be told about Khitomer being the conference location unless to specifically tell him to stay out of there?
His plan was part of a secret conspiracy, and revealing his BoP that could fire while cloaked would have endangered said conspiracy.
More or less. Chang had already gotten most of what he wanted when Gorkon died. But both he and Cartwright wanted the war started, and neither the killing of Gorkon or sentencing of Kirk had sufficed. Something more was needed - and Cartwright wanted to kill the UFP President and blame the Klingons. Was Chang in on that? He'd have little reason to - he wanted the UFP to take the blame. But perhaps he in turn had a Klingon dressed up as a, umm, ah, probably a Tellarite and ready to shoot Azetbuhr, and for that reason wanted Kirk
quietly silenced before he reached the conference?
Timo Saloniemi