Summary

Fixes #28023

Portal free-tier recommendations (e.g. nemotron-free, llama70b-free) and short aliases (e.g. sonnet, opus) are convenient for display but are NOT valid model IDs for upstream API calls. When such an alias lands in delegation.model (or is resolved from a runtime provider default), the delegation call fails with a 400 Bad Request from the upstream API.

Root Cause

_resolve_delegation_credentials() passes the configured model string through verbatim to the child agent. When the model is a Portal alias like nemotron-free, OpenRouter rejects it with:

{"error":{"message":"nemotron-free is not a valid model ID","code":400}}

Changes

Added _resolve_model_alias() in tools/delegate_tool.py which:

1. Pass-through for fully-qualified model IDs (containing /) — no resolution needed
2. Static catalog resolution via detect_static_provider_for_model() — reuses the same alias logic as /model switching
3. Suffix stripping — removes -free/_free suffixes and retries (handles Portal aliases like nemotron-free → nemotron → nvidia/nemotron-3-super-120b-a12b)
4. Graceful fallback — returns the original string with a warning log if resolution fails

Applied at all three return points in _resolve_delegation_credentials():

• delegation.base_url path
• No-provider path (child inherits from parent)
• Provider-resolved path (via resolve_runtime_provider)

Testing

• Syntax validation: ast.parse() passes
• The resolution logic reuses existing detect_static_provider_for_model() which has its own test coverage

Files Changed

• tools/delegate_tool.py — +71 lines (_resolve_model_alias + 3 call sites)