New clipboard serialiser for the flowchart editor. Pure module —
no DOM, no globals — so it's unit-testable in isolation.
- Captures the selected node + its connected edges to a JSON envelope
that survives a paste-into-new-graph round trip. Edge-only selection
is also supported.
- Paste creates a new node offset from the original (default 24px)
and re-attaches every connected edge to the new id. Only edges
whose other endpoint still exists in the graph are recreated, so
deleting a neighbour before pasting doesn't try to reconnect to a
ghost.
- Preserves node color on paste.
Wire-up into the renderer controller (Cmd+C / Cmd+V / Cmd+D handlers
+ canvas-owned selection reading) is the next commit; this one just
lands the testable math.
9 new tests cover selection capture, edge-only selection, paste with
offset, edge re-attachment, dangling-edge handling, color preservation,
and the null-payload no-op.
Amit Haridas
