Scope: Marble Runs & Track Sets — construction toys where marbles roll through assembled track/tile/block pieces under gravity, some with magnetic or motorized action add-ons; covers wooden-block, modular-tile, and tube/rod-and-connector building systems; excludes kinetic-art ball sculptures not sold as toys and generic building-brick sets with no marble mechanic.

Seed:
1. Category equivalent of the knife-hardness trade-off: marble material/mechanism (glass vs. proprietary steel for magnetic tiles) trades universal marble replaceability for magnetic/motorized action — same axis as the persona's "works without the ideal setup."
2. A ship's cook would notice first that half these systems need a specific metal marble or exact brand tile to work at all — if you lose the right marble or piece at sea, the set is dead until a resupply pack arrives; the wood and plain-tube systems keep working with any found marble.

Sources:
[wikipedia_rolling_ball] en.wikipedia.org/wiki/Rolling_ball_sculpture (redirects from Marble_run) — mechanism, "kugelbahn" term, traditional glass marbles — fetched excerpt
[cuboro_site] cuboro.com/en — wood species, age tiers (Junior 3+, Standard 5+), cross-tier compatibility, mechanism (grooves/tunnels), piece-count naming (16/32/50) — fetched excerpt
[marblegenius_site] marble-genius.com — glass marbles, translucent track, piece counts (20/30/125/130/150), Racing vs Stunts product framing, expansion packs, ages 4+/5+ — fetched excerpt
[knex_site] web.archive.org snapshot of basicfun.com/knex (live site blocks fetches) — "rod and connector building system"; product titled "Marble Coaster Run with Motor", "over 500 pieces" — fetched excerpt
[fr_magnets_2022] federalregister.gov/documents/2022/09/21/2022-20200 — 16 CFR part 1262 (Safety Standard for Magnets) exempts toys already covered by ASTM F963; the earlier magnet-sets rule (16 CFR part 1240) was rescinded in 2017 — fetched excerpt
[gravitrax_ballbox] web.archive.org snapshot of ravensburger.us GraviTrax Ball Box product page — metal marbles, modular/expandable tile system, Magnetic Stick accessory, STEM framing, ages 8+ — fetched excerpt (archive.org snapshot, 2024-03-02)
[cfr_1501_small_parts] law.cornell.edu/cfr/text/16/1501.1 and /1501.4 — under-3 choking-hazard scope and small-parts test-cylinder method (verbatim quotes, no exact mm claimed) — fetched excerpt
[cfr_1250_astm_f963] law.cornell.edu/cfr/text/16/1250.2 — ASTM F963-23 as mandatory US toy safety standard — fetched excerpt

Branches:
- tube_and_track leg: marblegenius_site (Racing/Stunts framing, translucent track, glass marbles, 4+/5+)
- modular_tile leg: gravitrax_ballbox (metal marbles, magnetic/expansion accessories, 8+, tile-based system with no opaque/translucent/wood track pieces — track_material inapplicable), cdx listing showing "gravit-pro-vertical" height accessory
- wooden_block leg: cuboro_site (grooves/tunnels, Junior/Standard age split, cross-tier compatibility; site names no magnet content anywhere, consistent with a mechanical groove-only system — loose_magnet_presence inapplicable)
- rod_and_connector leg: knex_site ("rod and connector building system", "build BIG", product titled "Marble Coaster Run with Motor" with "over 500 pieces" across "skill levels from beginner to pro" — supports the build_scale axis)
- magnetic_actuated leg (action_elements): gravitrax_ballbox (metal marbles plus the GraviTrax Magnetic Stick accessory are why loose_magnet_presence and marble_source_flexibility get asked)

Noise (spec-sheet rows left out):
- Exact battery count/type for motorized sets — not disclosed on fetched pages.
- Wall-mounted pegboard marble-run type (e.g. classic Marbleworks-style) — no fetchable brand source this run; folded out of scope rather than guessed.
- Color count / cosmetic color schemes — doesn't differentiate expert judgment.
- Exact marble diameter in mm — no two-sourced number found; kept marble sizing out of the register rather than invent a range.

Corrections (2026-10-26):
- Named the governing magnet-ingestion standard: ASTM F963's flux-index test (incorporated at 16 CFR 1250.2, already cited) is what toy magnets must pass; added judgement + fr_magnets_2022 reference. Rejected the checker's exact citation — "16 CFR Part 1240" was the mandatory magnet-sets standard but was rescinded from the CFR in 2017 after a court vacated it (confirmed in the 2022 Federal Register final rule); its replacement, 16 CFR part 1262, explicitly exempts toys already subject to ASTM F963, so F963 itself is the correct cite, not 1240 or 1262.
- Added a rod_and_connector Branches line (knex_site) and a magnetic_actuated Branches line (gravitrax_ballbox); strengthened the wooden_block and modular_tile lines to name why loose_magnet_presence/track_material go irrelevant.
- Lowered piece_count.range.max from 546 (uncited) to 325, the highest exact count stated in a fetched source (marblegenius_site); single-sourced, noted here rather than claimed as two-sourced.
- Lowered recommended_age_min.range.max from 9 (uncited) to 8, matching gravitrax_ballbox's "ages 8 and up"; single-sourced, noted here rather than claimed as two-sourced.
- Raised loose_magnet_presence.backfill_cost from medium to high to match its own cost_to_answer:4 and its per-listing inspection requirement.
- Added a "Friction peg" vocabulary entry for the connection_mechanism value friction_peg_baseboard.
- Corrected the knex_site reference: live basicfun.com/knex is Cloudflare-blocked, so switched its url to the archive.org snapshot actually fetched, and trimmed its supports to only what that snapshot's text contains ("over 500 pieces", product titled "Marble Coaster Run with Motor") — dropped the uncited "504 pieces" and "Ages 8+" claims, which the archived text does not state.