[P2] Confirm and document the evidence-sourcing policy

[Sanjan-Prabu]

Context. The evidence-sourcing policy (which sources are admissible — e.g., source-agnostic "any source that proves the claim" vs a primary/secondary distinction) should be confirmed and written down so curation and the critic enforce one rule.
Goal. A recorded sourcing policy.
What to do. Confirm the policy with maintainers and document it; ensure the prompt/critic reflect it.
Done when. The policy is documented and enforced consistently.

[Sanjan-Prabu]

Update (2026-07-23): sourcing remains source-agnostic, with DrugBank removed from the sanctioned-source set (see #60 — ToS/CC0 incompatibility). Current sanctioned sources: PubMed, ChEMBL, ClinicalTrials.gov, bioRxiv/medRxiv, plus reviews / well-sourced references, verified verbatim by QC Layer 4. Leaving open pending your final documented sign-off on the policy.

[andrewsu]

Agree on removing DrugBank. The list of current sanctioned sources looks good. In general, most sources are fine to use as long as we are limited in how much of their content we cite verbatim as evidence. But yes, let's at least review any sources that don't have a CC license in this issue.