rrt/docs/rehost-queue/locomotive-descriptor-tails-2026-04-21.md

Locomotive Descriptor Tails (2026-04-21)

This note preserves the checked evidence behind the locomotives-page tail after the full local .gms + .gmx save-corpus pass, so the short queue can treat the remaining work honestly as an external-corpus or dynamic blocker rather than another repo-local static task.

Local Save-Corpus Census

The checked locomotive catalog tail census now exhausts the full local save corpus under rt3_wineprefix/drive_c:

• 29 candidate saves found
• 26 parsed samples
• 5 saves with a save-side named locomotive table and derived locomotive_catalog
• 26 saves with packed-event collections present
• one save-stable catalog prefix through ordinal 58 (VL80T)
• two observed tail clusters beyond that prefix:
  • one 63-entry tail on g.gms / Spanish Mainline.gmp: 242 A1 / Class 460 / Class A1 / Class P8 / U1
  • one 61-entry tail on the four 1.05 save families: GP 35 / U1 / Zephyr

The added 18 .gmx sandbox saves still carry no reconstructed named locomotive table and no derived locomotive_catalog, so they widen the local event corpus without widening the save-native ordinal catalog evidence. The three classic rt3/ .gms saves (Autosave.gms, hh.gms, kk.gms) remain catalog-free too, so the save-native tail evidence is still carried only by the same five 1.05 .gms saves.

The scan still skips the three classic rt3/ sandbox saves (Autosave.gmx, aaa.gmx, bbb.gmx) at save-slice load time, so the currently parsed sample set is 26 rather than the full 29 candidate paths. That does not change the locomotive blocker: none of the successfully parsed .gmx samples widens the save-native catalog, places Class QJ, or surfaces descriptor carriers in 452 or 457..502.

Grounded Lower Bands

The lower descriptor bands are now grounded enough to execute through the existing save-native owner seam:

• availability descriptors 241..351 already map directly onto recovered locomotive ids 1..111
• cost descriptors 352..451 already map directly onto recovered locomotive ids 1..100
• the save-side named locomotive table already projects into RuntimeState.locomotive_catalog as one ordinal id-to-name map derived from row order
• that means the remaining lower-tail rows 302..351 and 413..451 are no longer missing an owner seam; they are just later ordinals on the same catalog

The old “grounded executable prefix through save-backed locomotive id 61 (Zephyr)" boundary is therefore retired. The whole lower bands are executable whenever the save or overlay supplies the catalog context.

Grounded Shipped Name Cohort

The remaining lower-tail labels are no longer blocked on missing shipped engine names.

The checked export engine-type locomotive display census now parses the fixed .car header fields for every shipped Data/EngineTypes locomotive pair:

• 66 shipped .car / .lco locomotive families
• 61 primary display names that match the broader checked shipped-name prefix
• 5 extra shipped named families not present in the current grounded prefix:
  • 242 A1
  • Class 460
  • Class A1
  • Class P8
  • Class QJ

That means the remaining lower-tail uncertainty is no longer “what are the extra shipped locomotive names?” It is where those five named families land in the live ordinal catalog that the save-side named availability table mirrors.

The full local save corpus tightens that further. The only observed nonclassic tail in the checked census is rt3_wineprefix/drive_c/rt3_105/Saved Games/g.gms, which exposes one 63-entry named locomotive table whose observed tail is:

• 59 242 A1
• 60 Class 460
• 61 Class A1
• 62 Class P8
• 63 U1

That observation matters because the four catalog-bearing 1.05 save families still carry the classic 59..61 tail GP 35 / U1 / Zephyr. So the currently honest static descriptor-name boundary is not the broader shipped-name prefix through 61; it is the last save-stable prefix through ordinal 58 (VL80T). After that point, save-backed ordinal names are real and executable, but they are no longer universal enough to hard-code in the static semantic catalog.

The same checked local corpus still does not surface Class QJ, even though the shipped engine-type corpus proves that family exists on disk. So the current non-hook evidence only closes the dynamic tail through the observed 63-entry family above; it does not yet place the fifth extra shipped name in any live ordinal slot.

The same checked local corpus also exposes no packed-event rows in descriptor range 452..502, so the remaining Unknown Loco Cost and upper-band frontier is absent from the local save-backed event corpus as well as unmapped in the static descriptor metadata.

Remaining Blocker

What is left is narrower and cleaner, but it is no longer a repo-local static task:

• ordinal placement of the scenario-dependent locomotive tail beyond the save-stable 1..58 prefix
• descriptor 452 Unknown Loco Cost
• upper availability band 457..474
• upper cost band 475..502

The upper bands still carry only slot labels in the checked semantic catalog:

• Upper-Band Locomotive Availability Slot 1..18
• Upper-Band Locomotive Cost Slot 1..28

The lower bands now split cleanly into two layers:

• ordinals 1..58 keep fixed checked descriptor labels through VL80T
• ordinals 59+ stay executable through recovered ids plus save catalog context, but the checked semantic catalog keeps generic slot labels because the local save corpus already shows scenario-dependent tails

Unlike the lower bands, the current checked row summary metadata does not yet recover live locomotive ids for the upper-band descriptors at all.

Blocker Result

The next question is no longer whether locomotive page descriptors can import through a save-native owner seam at all, or whether the shipped engine-type files even have stable names. The checked repo-local answer is already as tight as it can get:

• where the extra shipped named families (242 A1, Class 460, Class A1, Class P8, Class QJ) land across the scenario-dependent tail beyond the save-stable 1..58 prefix, and
• whether the upper bands continue the same ordinal locomotive catalog after the lower 1..111 / 1..100 families, or
• do they belong to a separate page-owned selector family that only sits adjacent in the recovered EventEffects table

Descriptor 452 should stay separate from that question until stronger evidence ties it to either the lower cost band or the upper tails.

The current repo-local blocker is therefore explicit:

• the next honest non-hook step needs a broader save corpus than the eight local saves already exhausted here
• the next honest non-static step needs dynamic tracing or hooks