v0.20.0

New

• cadagent.mechanical.inserts.printed_hole: the insert's hole for the filament and the nozzle (#323). It takes
  SPIROL's larger hole for filled plastics, a coupon's undersize (which governs; CNC Kitchen's published 0.1 to
  0.25 mm otherwise), the RepRap arc balance as a floor for the line width, and the mesh's facets. hole_design and
  check_joint take line_mm, filler_pct, undersize_mm and facets. A fibre-filled filament adds a printed hole
  row, and line_mm adds a boss perimeters row.
• cadagent.formulas: facet_diameter, polyhole (Nophead), arc_path_radius and arc_printed_diameter (RepRap
  wiki), with golden vectors from the sources' own numbers.
• The first reference promotion sweep (#323 phase 7), on threaded inserts. It read 41 insert guides at the source:
  22 snippet-only records were promoted to read or above, and 4 read records went up to verified-at-source or encoded.
  Two new sources were added (Nophead's Polyholes, the RepRap wiki's Arc Compensation). The sweep's checklist is
  in research/references/README.md.
• research/process-profiles.yaml: four rules, the filled-plastic hole (SPIROL), the 2019 undersize (CNC Kitchen) and
  the perimeters round an insert (LulzBot, PADT), each with the source that governs where they differ.
• python3 tools/resource_audit.py references: the reference registry's link health, with no AI. It sends conditional requests (ETag, Last-Modified), hashes each page's normalised visible text, finds soft-404s by rule, reads GitHub repository metadata (gone, renamed, archived, last push, licence, default-branch head), sends at most one request a second to any host, leaves a host that answers 401 or 403 alone for 30 days, and rotates through the records (400 a run, the longest unchecked first) (#323).
• The weekly supply-chain workflow runs it on dev, with lychee for every link in the published Markdown (anchors and files included). It keeps one issue, "Reference health: open findings", and opens one bot PR into dev with the evidence changes its rules allow (tools/references_health_apply.py) (#323).
• Link health stays out of git (#323, Q5). It lives in the workflow's references-health artifact. A site build given that file (CAD_AGENT_REFERENCES_HEALTH) adds each record's health to catalog/references/*.json (#323).

Changed

• tools/import_refmap.py reconciles instead of overwriting. A re-import keeps every record someone has read,
  verified or lowered, and every record the map does not make, byte for byte. It still applies the map's changes
  to the rest, so --check passes after a promotion sweep.
• research/process-profiles.yaml rules may name what applies them (applied_by, checked by the tests), and
  expressions may use sqrt() and cos(). The insert hole's arc floor, facets and SPIROL perimeter rules are
  profile lines that printed_hole and perimeter_counts evaluate.
• check_joint on a fibre-filled filament (PETG-CF, PA6-CF20) now warns until you give filler_pct or print the
  hole coupon, because neither data sheet states the fibre content. Its hole band widens by SPIROL's 0 to 0.15 mm.
• Registry records may carry evidence.lowered (from, date, why). The weekly bot PR writes it when a record's link stays dead for two checks and its evidence class falls one rung. --check validates it (#323).
• The README hero holds its finished frame (wordmark and every check) for about 4 s before it fades and the loop
  restarts, up from 1.4 s; its cycle is 13.2 s (#339).
• cadagent.publish.anim.svg.problems refuses an animation that plays once and stops: every animated figure must
  loop, so a reader who scrolls to it late still sees it play (svg.timed lists the ones that do not) (#339).