Function resolve_step 

pub fn resolve_step(
    step: &ProcedureStep,
    requirements: &[McpRequirement],
    inventory: &McpInventory,
) -> Resolution

Resolve a single procedure step against the agent’s MCP inventory.

Decision tree:

1. tool set + intent unset → Literal(tool) (pre-M6b behaviour).
2. tool_hint set + inventory match → Hint(tool).
3. intent set + mcp_requirements glob matches an inventory tool → IntentMatch(shortest tool, capability).
4. intent set + no glob match but fallback in inventory → Fallback(fallback).
5. Otherwise → Unresolved { reason }.