Detect Meta creative fatigue

Compares the first days of a window with the last days, per ad, and flags creative fatigue: click-through rate falling while frequency and CPM rise. Use when: performance has drifted down without an obvious change, the user asks whether to refresh creative, or before scaling an ad that has been running a while. Do not use it on an ad that has barely delivered — the tool says "insufficient data" rather than reading noise, and that answer is the truth, not a failure. Do not read a single flagged signal as proof: one signal earns "watch", agreeing signals earn "fatigued". Report which signals fired. Returns per-ad baseline and recent numbers (CTR, CPM, frequency, cost per result), the signals that fired and a plain-language verdict. The default window is 14 days, which is the shortest span where a three-day baseline and a three-day recent period are both meaningful.