Keep a Main loop's children under it in the sidebar

[scgopi]

The bug

Create child loops from a Main loop and they list as top-level rows beside their parent, not under it — and collapsing the parent leaves them on screen. Only Main-parented loops are affected; every other loop type nests correctly.

Why

LoopGraph.startAnchors picks entry points from non-sketch nodes (a Main loop is .sketch on disk), then walks out from them; anything the walk never reaches is treated as a headless component and promoted to an anchor of its own.

A Main loop is never an entry, so the walk never started at one — its children came back unreached and each got promoted. sidebarRoots is startAnchors plus untargeted sketches, so the children landed at depth 0 as siblings, and flattenedNodeRows' collapse only hides rows that are actually nested.

The fix

Seed the walk with the sketches sidebarRoots actually rows. A targeted sketch stays out of it deliberately: it has no row of its own, so it cannot be the beginning its subtree is reached through — covering it would strand that subtree with no row at all (the handoff-ring case, pinned by the second test).

startAnchors has no other production caller — canvas entry ports come from entryPoints/cycleOnlyNodeIDs — so the canvas is unaffected.

Verification

Check	Result
xcodebuild test	✅ 1508 tests in 156 suites passed (+2 new)
make check	✅ 0 serious violations, format clean

🤖 Generated with Claude Code

https://claude.ai/code/session_01AoiYAyXWLj4b8xMumkDCNT