factcheck-subagent-needs-complete-sources

Fact-check subagents need complete primary sources

Problem

You dispatch a subagent to independently fact-check a document against its sources. To save context or tokens, you pass the agent a summary or partial dump of one source instead of the full original. The agent then reports a false positive: "Claim X is unsupported — the term appears in no source." The claim was actually fine; the supporting text was in the part of the source you abridged away.

The failure is asymmetric and dangerous: a missing source region does not make the agent say "I can't tell." It makes the agent confidently say "unsupported" or "fabricated" — because absence-of-evidence reads as evidence-of-absence when the agent believes it holds the complete source.

Context / Trigger Conditions

• About to launch an Agent/Task subagent to "fact-check", "verify", "independently check", "stress-test", or "review the claims in" a document.
• Assembling the source bundle / writing the prompt for that agent.
• A verification subagent returns "claim X unsupported / appears nowhere / fabricated / not in any source" — especially for one specific claim while everything else verifies cleanly.

Solution

Prevention — when assembling the agent's sources:

1. Pass the agent the COMPLETE primary source (full file, full document dump, full repo clone), not a hand-written summary of it. If a source is large, give it the real artifact and let the agent read what it needs — do not pre-digest.
2. If you genuinely must abridge, say so explicitly in the prompt: name which sources are partial and which sections were cut, and instruct the agent to mark any verdict touching those sections UNVERIFIABLE rather than INACCURATE.
3. Prefer pointing the agent at retrievable originals (a cloned repo, a file path, a document ID it can fetch itself) over your transcription of them.

Response — when the agent flags a claim as unsupported:

1. Before accepting an "unsupported / fabricated" verdict, read the agent's own report for hedges — a good agent will say "the dump I was given is partial" or "this section was not in my sources." That hedge is the tell.
2. Reconcile the flagged claim against the COMPLETE source yourself. If the supporting text is in a region you abridged, the verdict is a false positive — keep the original claim; do not "correct" the document.
3. Treat genuine errors and source-gap false positives separately: apply the real corrections, reject the false positive, and state plainly why each.