Detect outdated documentation by comparing docs against actual code state — broken references, version mismatches, stale code examples, and missing CHANGELOG entries. Documentation drifts from code silently: a function gets renamed, an import path changes, a version bumps, but the README and CHANGELOG still reference the old state. `/sync-docs` compares documentation files against the current codebase, finds the gaps, and auto-applies safe fixes (version updates, CHANGELOG entries) while flagging ambiguous cases (removed exports referenced in docs, code examples needing context) for manual review. Plug into /next-task and /prepare-delivery as the pre-ship docs gate.