Extend actor YAML schema to support hierarchical graphs with explicit
node types (agent, tool, conditional, subgraph), per-node LSP bindings
(lsp_binding with server, languages, auto, capabilities), and tool-source
references (skills, mcp_servers, agent_skills).
Add schema validation for namespaced actor references, duplicate node IDs,
edge target existence, and graph reachability — all nodes must be reachable
from entry_node via explicit edges or conditional node routing targets.
Update loader to report YAML parse errors with precise line/column positions
and schema validation errors with dotted field paths and remediation hints
pointing to docs/reference/actor_config.md.
Add docs/reference/actor_config.md as the practical configuration reference
covering hierarchical graph examples, node type table, topology rules, and
common error cases with fix guidance.
Refresh examples/actors/graph_workflow.yaml to replace deprecated actor_path
with actor_ref. Add benchmarks/actor_yaml_bench.py for schema load overhead.
Tests: 95 Behave scenarios, 10 Robot smoke tests (including hierarchical
loader smoke test), security scan clean, coverage 99% (threshold 97%).
ISSUES CLOSED: #157
