What does this PR do?

Fixes a bug in delegate_task where delegation.base_url is ignored when the child agent's provider matches the parent's provider ("custom"). The child's explicit base_url is silently overwritten at runtime by _swap_credential() from a shared credential pool entry that points to the parent's endpoint.

Related Issue

Fixes #13678

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)

Changes Made

• tools/delegate_tool.py: Added if not override_base_url: guard before _resolve_child_credential_pool() call in _build_child_agent(). When override_base_url is set, the child is not bound to the parent's credential pool, preventing _swap_credential() from overwriting the child's explicit endpoint with the parent's URL on first API call.

How to Test

1. Configure parent agent with provider="custom" and base_url="http://localhost:8000"
2. Spawn subagent via delegate_task with delegation.base_url="http://localhost:8001" and delegation.provider="custom" (same provider as parent)
3. The subagent should call http://localhost:8001/v1
4. Before fix: first API call silently redirects to port 8000 (404 or wrong model)
5. After fix: subagent correctly calls port 8001

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits
• I've searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix (no unrelated commits)
• I've run pytest tests/ -q — tests not added for this fix (would require mocking two vLLM endpoints)
• I've added tests for my changes — same as above
• I've tested on my platform: Debian 13

Documentation & Housekeeping

• I've considered cross-platform impact — no OS-specific code in this change
• I've updated tool descriptions/schemas if I changed tool behavior — N/A (only logic change)

For New Skills

N/A — not a skill