If your AppKit window looks fine in Interface Builder but detonates when you drag a corner, it’s usually not a design issue—it’s a constraint system picking the wrong winner. The fix starts by seeing what the solver sees, not by guessing.

• Use Debug View Hierarchy to inspect active NSLayoutConstraints, hugging/compression priorities, and intrinsicContentSize. Capture screenshots of the failing state.
• Order priorities; don’t tie them. Keep .required for truly non‑negotiable edges and ladder the rest with .defaultHigh/.defaultLow.
• Treat intrinsic sizes as signals. After changing text, symbols, or accessibility, call invalidateIntrinsicContentSize() and re-evaluate layout.
• Flatten hierarchies where you can. NSGridView helps with cross‑axis alignment; deep nested NSStackViews can create churn.
• Validate under runtime conditions: add layout XCTests, profile resize loops