Summary

Add model, provider, and base_url parameters to delegate_task, allowing per-call overrides for subagents — both at the top level and per-task in batch mode. api_key is kept in the code path (works via delegation.api_key config) but excluded from the schema for security.

Changes

tools/delegate_tool.py:

• Extended delegate_task() function signature with model, provider, base_url params
• Added fields to DELEGATE_TASK_SCHEMA at top-level and per-task — api_key excluded from schema to prevent LLM secret leakage
• Credential resolution happens per-child: per-task > top-level per-call > delegation config > parent inherit
• All pre-existing code preserved (cost rollup, ACP transport safety, ACP override clearing)

tests/tools/test_delegate.py:

• Updated test_schema_valid to assert new fields
• Added test_per_call_model_override

Security

api_key is NOT exposed to the model via the schema. The code path still supports it internally — set via delegation.api_key in config.yaml — but the LLM cannot inject or read it through tool calls.

Example

# Single task with model override
delegate_task(goal="Do X", model="gemini-flash-latest", provider="google")

# Batch with per-task overrides
delegate_task(tasks=[
    {"goal": "Research", "model": "fast-model"},
    {"goal": "Analyze", "model": "reasoning-model", "provider": "openrouter"},
])

Verification

• All 121 delegate tests pass