graph::language::build_graph discards Routing::Conditional targets

[senamakel]

Problem

In crates/tinyagents-graph/src/language.rs, build_graph handles a node whose blueprint declares Routing::Conditional { .. } by calling mark_command_routing only. The declared (label, target) pairs are dropped: they are never passed to add_conditional_edges and never exposed through with_command_destinations.

Consequences:

• The routing table written in a .rag blueprint is not structurally validated at compile time; an unknown target only fails at runtime when the handler emits Command::goto.
• graph::export (topology / Mermaid / JSON) cannot see the conditional edges, so exported diagrams of blueprint-built graphs are missing them.
• The materialised node handler must independently resolve the same labels the blueprint already declared.

Question

This may be intentional (factory-owned routing logic), but if so the blueprint's target list is dead data. If not, build_graph should at least forward the targets via with_command_destinations so validation and export see them.

An inline comment describing the current behaviour was added in #162; this issue tracks deciding which way it should go.

[tinysweeper]

build_graph discards Routing::Conditional targets, preventing validation and export of conditional edges.

Labelled priority: p2.