[endrix]

Selecting a node draws every path through it: what leads to it in green, what it leads to in blue, and the rest fades. It is mlir-viewer's trace highlighter (packages/client/src/trace-highlighter.ts) ported onto Dialogram's model, opt-in with clientBehavior.selectionTrace.

How it walks

• Port to port, both ways, as far as the edges go.
• A boundary port on a group's frame (port:group-boundary, where splitEdgesAtGroups cuts an edge) is passed through, so the group never counts as a node on the path. A path follows a cut edge out of one group and into another at any depth, and every piece and boundary port of it is drawn.
• On a cycle, where reachability would light the whole diagram, the trace is cut to the node's direct neighbours, as mlir-viewer does.
• A selected edge draws all its pieces and its two ends.
• A selected container draws what feeds it and what it feeds across its frame, and leaves its members as they are.
• A container is never faded, because its opacity would fade every member.

How it draws

• The classes go on as GLSP feedback, like published node states (execution-states.ts), so the dispatcher re-applies them to every model and a relayout or an edit keeps the trace.
• The listener and command are bound in the base module, so every container has them, the headless one included.
• An edge is recoloured through color: its line and arrowhead use currentColor, so a product's dash pattern per edge type stays.

Tooling. scripts/render-svg --select <id> selects an element as a click would, by the diagram's id or the producer's (wf:graphNodeId), so a trace can be rendered and looked at.

Tests. selection-trace.test.ts has 13 tests. The nested cases build their models with the server's own splitEdgesAtGroups, so the pieces and boundary ports are the ones the client receives. The parity baseline gains exactly the three new registrations.

Checked visually with the renderer

• picorv32 20-behavior/trap.md, grouped by layer, with TRAP-CAUSE-001 selected: its whole upstream cone across the L2 to L1 frames is green and TRAP-001 → PIPE-FSM-001 is blue. VER-TRAP-001, trap_halt and PRM-CATCH-001, which touch the path only at TRAP-001, fade.
• hdl-sidecar's glue golden with input a selected: the path through a & b, u_buf and the mux to lo and y; the rest fades.

Gates. npm run build and check:neutrality pass. Every test passes except the two known load-flaky ones (session-manager, and the variant wizard's 5 s timeout), which pass when run alone.

https://claude.ai/code/session_01E8WfqKknDNN6xpNVcJL5K8