map/archive/generated-history/FIX_SEAM_CONTINUITY_NOTES.md

Additional-generation seam continuity fix

Date: 2026-08-07

Scope

This revision addresses the remaining defect from the previous geography-integrity package: visible terrain discontinuities along the established-map / newly-generated-map frontier.

The previously reported disconnected prefecture component is not treated as an error merely because it is small. A sea-separated component can be a legitimate island. Existing component cleanup already preserves sea-isolated administrative components when there is no adjacent land region to merge into, and this revision does not add an island-erasing cleanup pass.

Changes

1. Literal old/new frontier constraint

   • The final terrain pass now measures the actual generated-coverage transition rather than relying only on the selection rectangle or alpha feather.
   • Newly generated land cells directly touching established land are constrained to the established elevation neighborhood.
   • The established side remains unchanged.

2. Outward gradient propagation

   • The solved contact edge is propagated up to 12 cells into the new side using coverage distance.
   • This avoids simply moving the visible seam one or two cells inward.

3. Dedicated hard seam metric

   • maxEstablishedFrontierElevationJump measures only land/land edges where generated coverage changes from established to new.
   • Hard limit: 0.075.
   • A candidate above this limit fails with established-frontier-elevation-jump.

4. Best-available policy split

   • Interactive preview may still show a candidate that only misses a soft terrain/human-geography quality floor.
   • A hard seam failure is never accepted as best available; it is rolled back.

5. Diagnostic warning semantics

   • Natural cliffs inside the newly generated region no longer make the whole seam status warning merely because one cliff exists.
   • Cliff density and literal frontier continuity are evaluated separately.
   • Advanced diagnostics now show Established frontier elevation and the hard limit.

Validation

Reported-bug regression

node VALIDATE_REPORTED_PATCH_BUGS.mjs

• river path points on sea: 0
• duplicate prefectural-capital prefectures: 0
• tiny generated prefectures: 0
• municipal breaks on established frontier: 0
• prefecture breaks on established frontier: 0
• maximum established-frontier elevation jump: 0.0268
• seam status: clean
• seam gate reasons: none

Direction / seed stress validation

VALIDATE_SEAM_STRESS.mjs was run in four separate two-case processes (to avoid cumulative process runtime limits): 2 base seeds × right/left/down/up.

• cases: 8
• hard limit: 0.075
• maximum independently measured frontier jump: 0.0364
• all cases: seam hard gate PASS

See SEAM_STRESS_RESULT.json for per-case values.

Existing regression suites

STEP15_VALIDATION.mjs: PASS

• expansion seam status: clean
• generated-footprint escaped cells: 0
• unresolved road portals: 0
• unresolved rail portals: 0

STEP17_VALIDATION.mjs: PASS

• Alternative variants differ
• explicit render revision retained
• single-patch Worker lifetime retained

FIX_ADDITIONAL_GENERATION_VALIDATION.mjs: PASS

• strict quality caller still rolls back on quality failure
• interactive preview still accepts a soft-quality best-available candidate when seam continuity passes