Require exhaustive file:line-cited research before design or code changes

Before architecture, cross-cutting, migration, compatibility, unfamiliar-implementation, or release-readiness decisions, perform a non-mutating, evidence-based investigation. Preserve the worktree; inspect repository state, relevant source, tests, docs, schemas, workflows, complete diffs, and upstream/PR context. Produce a file:line- and commit-cited map of current behavior, contracts, touchpoints, dependencies, risks, compatibility/security concerns, test coverage/gaps, precedents, and open questions. Verify claims against source, track work with a todo list, ask explicit design questions, record decisions durably, and obtain user sign-off before implementation when required. Isolate risky shared-infrastructure changes into small reviewable PRs.