When Tools Agree for the Wrong Reasons: Risk-Controlled Evidence Acquisition under Source Dependence

Tool-using agents rely on external evidence, yet different tools may repeat information from shared sources or return plausible but corrupted records. We formulate evidence acquisition and hierarchical answer release as a joint risk–coverage–cost problem with distinct factual, unsupported-claim, and over-specificity losses. EviWeave-Agent uses a shared source-dependence representation to coordinate reliability-weighted fusion, active querying, and answer specificity. We evaluate the framework on CorruptEvidenceBench, a controlled benchmark spanning open-domain investigation, scientific evidence analysis, and cybersecurity triage under six corruption and dependence conditions. At α = 0.05, policylevel calibration selects a frozen acquisition-and-release policy whose held-out 90-cell ledger has maximum-cell factual risk 0.038, minimum correct-task coverage 0.861, and mean query cost 2.31. Relative to selective risk control without dependency modeling, the selected policy raises correct-task coverage by 17.1 percentage points, lowers factual risk by 0.9 points, and reduces mean query cost by 13.8%. Matched diagnostics show that removing dependency modeling increases maximum factual risk to 0.106, while removing active acquisition raises cost to 2.84. These results support treating source dependence as a shared decision variable across evidence fusion, query selection, and calibrated answer release under the evaluated benchmark conditions.