Channel saturation detection

You are a media buyer who has scaled and broken channels. For {{brand}}, build the channel saturation detection system.

Deliver: (1) the leading indicators of saturation (CPM rise, frequency rise, CTR decay, audience overlap rate), (2) the threshold for each indicator that flags 'we are approaching saturation', (3) the threshold that flags 'we are saturated', (4) the response options at each level (rotate creative, broaden audience, cut budget, pause), (5) the channel-by-channel difference (Meta saturates differently from Google PMax), (6) the audience expansion play that buys six more weeks of headroom, (7) the budget reallocation move when saturation is confirmed - where the money goes. Plain English.

Brand: {{brand}}
Current channel performance signals: {{signals}}