Why a delegation was refused before any worker was built. How many
workers may run (and exist unreconciled) is the delegation policy’s job
(subagent.max_concurrent / subagent.max_total); the tree only adds
what the policy cannot see: how deep workers nest.
Canonicalize a runtime foreground model string into its exact qualified
identity. Legacy configs persist bare Anthropic IDs (e.g. claude-fable-5)
which the runtime router still deliberately routes to anthropic; the
canonical identity is derived from that single routing entry point — never
from substring heuristics. Unroutable values fail closed.
Validate an exact identity against source-controlled runtime routing/catalog
descriptors before allowing a model-driven session grant. This operation is
credential- and network-blind: availability is checked later by normal
provider execution, while invented identities fail before policy mutation.