Add Phase 5.5: verify mismatches via agent discussion

[hua7450]

Summary

• Adds Phase 5.5 to the audit-state-tax command that verifies reported mismatches via agent-to-agent discussion before including them in the final report

Motivation

During a full audit of Iowa's 2025 income tax PR (#7389 in policyengine-us), an audit agent reported a false positive: it flagged the QBI fraction parameter as wrong for 2023+ (0.75 instead of 1.0). However, tracing the code revealed that ia_qbi_deduction (which uses the fraction) is only called in the pre-2023 indiv/joint path — the 2023+ consolidated path starts from federal taxable income directly, where the QBI deduction is already included. The parameter was correct; the agent just didn't trace the code path.

What Phase 5.5 Does

For each MISMATCH reported by an audit agent:

1. Creates a verification team (TeamCreate)
2. Spawns a verifier agent that greps for parameter usages and traces the call chain from the top-level tax variable down to the flagged parameter
3. Resumes the original audit agent as a teammate so it can explain its reasoning
4. Lets them discuss (up to 3-4 round-trips via SendMessage)
5. Collects a verdict: CONFIRMED, REJECTED, or INCONCLUSIVE
   • CONFIRMED → proceeds to Phase 6 (600 DPI visual verification)
   • REJECTED → excluded from final report (noted as "investigated and cleared")
   • INCONCLUSIVE → proceeds to Phase 6 for manual verification

Other Changes

• Updated Key Rules to require both code-path verification AND visual confirmation
• Added Rule 8: "Trace code paths" — a parameter mismatch is only real if the parameter is reachable in the target tax year
• Updated Pre-Flight Checklist

Test plan

• Verified the edit applies cleanly on top of add-audit-state-tax-command
• Run an actual audit with mismatches to test the team discussion flow

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