# UC1 tree event parity

Source evidence is the read-only original
`C:\Users\MD\source\repos\MBN_STOCK_N\MBN_STOCK_N\Control\UC1.cs`:

- `UC1_Load` checks `Expand`, selects the first rendered root, and calls
  `EnsureVisible`.
- `treeView_MouseDown`, `treeView_BeforeExpand`, and
  `treeView_BeforeCollapse` prevent a double-click from also changing a
  root's expanded state.
- `treeView_DoubleClick` activates either the selected leaf or every direct
  child of the selected root.
- `chE_CheckedChanged` expands or collapses every root. Collapsing does not
  clear `SelectedNode`.

The WebView tree therefore owns only presentation state (open roots, selected
node, focused node, and scroll position). C# remains the authority for every
leaf/root action. A root label click selects without expanding; only its
disclosure glyph changes `open`. A root or leaf double-click emits one closed
native intent and does not invoke the browser's whole-`summary` toggle.

On each real tab activation/re-entry the presentation state is recreated like
the original `UC1`: `Expand` is checked, all sections are open, and the first
root is selected, focused, and scrolled into view. State-only renders within
the same activation preserve per-section open state, selection, focus, and
scroll position. Busy and fixed-section-batch states reject both actions and
local expand/collapse changes.

## Intentional defect exclusion

The original `treeView_DoubleClick` reads `uc_3.FpSpread` in the parent-node
path before checking which UC1 file is active. For UC1 instances constructed
with `uc_3 == null`, that can throw `NullReferenceException`; the surrounding
empty `catch` silently drops the operator action. This is an original defect,
not observable intended behavior, so the migration does **not** reproduce it.
The WebView sends only the selected root identity and C# validates/materializes
the corresponding section without dereferencing an unrelated comparison
control.