[BUG][P2] validate CLI falsely warns Missing tool: set_output / ask_user

[mishrapravin114]

Summary

./engine validate reports Missing tool implementations: set_output (and sometimes ask_user) for many templates, even though these are built-in EventLoopNode tools and work at runtime.

Evidence

./engine validate examples/templates/support_triage
# WARNING: Missing tool implementations: set_output

Affected templates include: support_triage, invoice_review, hourly_tracking, deep_research, meeting_scheduler, all supervisors/*, supervised_agreement_analysis.

Built-in registration lives in core/engine/graph/event_loop/node.py — not in per-agent tools.py.

Validator logic: core/engine/runner/runner.py → validate() checks self._tool_registry.has_tool(tool_name) only.

Expected behavior

• set_output and ask_user should not appear in missing-tool warnings
• Validate should still catch genuinely missing custom tools (e.g. fetch_broker_transactions without tools.py)

Proposed fix

File: core/engine/runner/runner.py (or shared constant)

BUILTIN_NODE_TOOLS = frozenset({"set_output", "ask_user"})
# skip these when building missing_tools list

Add/update test in core/tests/ for validate on an agent that only uses set_output.

Acceptance criteria

• ./engine validate examples/templates/support_triage — no missing-tool warning for set_output
• Agents with actually missing custom tools still warn/error correctly
• Unit test added

Effort

~1 hour