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Why: the user asked for a reviewable plan covering (a) previews for office/image/markdown/code files and web links, docked in the right rail or the system overlay, (b) keeping artifact deletion as a capability with no UI entry, and (c) implementing fs tools without enabling them. Evidence: the proposal assesses each idea against current architecture, defines the FilePreview capability component with a format matrix and lazy-loaded office parsers, the SSRF-guarded url-preview endpoint, the gated sandboxed fs tool family, four delivery phases with acceptance criteria, and decision points D1-D5 for the user. Impact: documentation only; implementation follows in a separate task after D1-D5 are settled. Refs: task feature/file-preview-proposal; extends 2026-09-30 ui-redesign-and-auth.md section 9.