[cmpadden]

Summary

• Add pi-delegate.model in settings and make the tool model argument optional.
• Resolve models in order: explicit call override, delegation setting, then the parent session model (including its provider).
• Configure the gateway-qualified default to avoid accidental direct-OpenAI authentication failures, and encourage agents to omit unnecessary model overrides.
• Display the resolved model in parent tool rows; reject invalid defaults before queueing without silent fallback.
• Simplify the delegate README into settings, examples, an argument table, and concise behavior/safety bullets.

Validation

• All 44 delegate tests pass, including default/override precedence, provider IDs containing slashes, invalid configuration, resolved-model rendering, and real tmux tests.
• make format
• git diff --cached --check and staged diff audit for credentials/runtime state
• make lint: all available checks pass; both ShellCheck hooks are blocked because shellcheck is not installed.

Only four delegate/config files are included. Unrelated local changes, including the changelog-version update, are excluded.