When LLM agents exchange messages in a pipeline, abstractive compression discards task constraints. Routing tags get absorbed into prose, privacy fields get paraphrased, hard instructions get softened. Even exhaustive reminder-based prompting retains only 53% of required routing markers, as measured by RTD: constraint tokens are low-salience relative to task content and are dropped at generation step boundaries even when restated in full. We propose C2-FAIC (Contract-Claim Failure-Aware Inter-agent Compliance), which guards the handoff moment directly: it maintains task requirements in a contract ledger outside agent context and checks each candidate message before it enters the shared trace. On 916 task-metric slices across AgentCollabBench, C2-FAIC is strongest on tracer retention and cross-context leakage control, while also reducing instruction decay and claim propagation relative to no intervention. Critic agents remain stronger on pure IDR and CPR process scores, showing that contract enforcement and generic critique address different failure structures. Multi-agent reliability requires controlling what crosses communication boundaries, not only evaluating what the pipeline ultimately produces.

Multi-strategy question-answering agents often produce several plausible responses to one query, but must ultimately show the user only one. Voting treats answer agreement as trust, yet strategies can disagree for different reasons, and identical answers can rest on evidence of unequal quality. We cast this final choice as diagnosis-first evidence-risk arbitration and introduce the Evidence-Risk-Aware Strategy Reranker (ERSR), which canonicalizes a pool of six responses, classifies their agreement type, and applies a type-specific evidence rule while returning one unchanged response. Calibration uses only development data; for each evaluation item, trusted reference answers, trusted reference evidence, and utility stay hidden, and the selector never abstains. On a 900-item development split drawn from FEVER, HotpotQA, and SciFact, ERSR improves evidence-aware utility over a development-selected fixed strategy by +0.052, with the largest gains on label conflicts and unanimous answers with uneven evidence. These results suggest that response-set structure, not agreement alone, is a useful signal for choosing trustworthy answers.