The action bar leaves the scroller: a flex footer, not a sticky trick

[AllTerrainDeveloper]

Follow-up to #26, from live inspection of the window chrome after Daniel reported the window "can be scrolled a bit, and it shouldn't."

Diagnosis (measured, not guessed)

The sticky bar was part of the scroll math — that single fact produced every symptom:

• A window a few pixels shorter than its content scrolled by exactly those pixels, with nothing meaningful hidden. It felt broken because it was: you could see everything, yet it still nudged.
• A window taller than the content left the bar floating at the end of the text rather than on the window's bottom edge.
• And earlier, the negative sticky offset had parked half the bar past the scrollport where overflow: hidden clipped it.

Fix

The window host is now a flex column of exactly two things:

.atfb-valwin--window          → position: absolute; inset: 0; flex column; overflow hidden
├── .atfb-valwin__scroll      → flex: 1; min-block-size: 0; overflow-y: auto   (the editor)
└── .atfb-modal__actions      → flex: 0 0 auto; border-top                     (Save / Cancel)

The bar is chrome, not content: buildEditor() still emits it, and the window host lifts it out of the scroller into the footer slot. The overlay fallback is untouched.

Verified against the live chrome

Geometry	scrollable px	bar on window edge	bar fully visible
Long content (Easy blocks, 700px window)	363 (real overflow)	✓	✓
Short content (Expression tab)	0	✓	✓

🤖 Generated with Claude Code

https://claude.ai/code/session_0119U4sRRWGcTQdwYreTwpAp