Port seeded Age completion and Accelerated pages to 26.3 beta

docs/MINECRAFT_26_3_PORT.md

@@ -10,6 +10,17 @@ tracks issues #97–#103 under parent #96.
 
 ## Version boundary
 
+Local slice `1.0.1.98-beta.1` ports the 1.21.1 Accelerated environment page:
+stacking extra random block ticks in already-loaded player-nearby chunks,
+eight-chunk/16,384-attempt default budgets, fair rotating section allocation,
+and an Age-local saved page count. The 26.3 LOCAL config holds these limits.
+Entities, machines and scheduled ticks are unaffected. Existing Ages remain
+unaccelerated; random Age inclusion and instability scoring are not added.
+The suspected host-seed biome zoom mismatch was checked against NeoForge's
+patched ServerLevel constructor: seedOverride already replaces it correctly,
+so the backend seed path was left unchanged. Native Cave policy issue #111
+remains separate future work for both Minecraft tracks.
+
 Minecraft 26.3/NeoForge uses Java 25, while Rivencraft 1.21.1 uses Java 21.
 Build and publish separate artifacts; do not widen the Minecraft dependency
 range of the 1.21.1 JAR. The official [26.3 release notes](https://www.minecraft.net/en-us/article/minecraft-java-edition-26-3),
@@ -1801,6 +1812,144 @@ fresh chunks after full restart again used Nylium/End Stone. No full feature
 or entity chunk scans were run. The server was stopped and temporary world
 deleted. Nothing was committed, pushed or published.
 
+## Structure-aware biome completion
+
+`1.0.1.94-beta.1` adapts root `AgeBiomeSelection.completeStructureBiomes` for
+explicit non-Native biome controllers. It reads compatible biome IDs from
+the active registered structure sets and shares this lookup with random
+structure eligibility, avoiding two different compatibility definitions.
+Repeated structure pages produce one requirement; Dungeons are excluded.
+Single with no supplied biome chooses from the intersection of all structure
+requirements and terrain-eligible biomes. No intersection leaves ordinary
+seeded filling intact. An explicit Single biome is never rewritten.
+
+Multi-biome completion adds one seeded compatible biome for each unmet
+requirement where a terrain-eligible candidate exists, before ordinary minimum
+filling. Root's salts, requirement order and shuffled candidate selection are
+preserved. Existing biome order and duplicate weights remain, but a structure
+can intentionally extend a pool beyond the usual minimum. Native and the
+port's no-controller fallback remain unchanged. Impossible requirements do
+not become new writing rejections: authored structure overrides still apply.
+No saved format, network protocol or generated chunks are changed.
+
+The completed-biome fixture accepts an optional structure page and checks
+32 seeds for compatible Single/Cave Fortress choices, common Village/Stronghold
+requirements, explicit End Single precedence, Native behavior, multi-biome
+prefix preservation and avoiding unnecessary additions for already-compatible
+or repeated structure pages. Existing biome plan codec checks remain in place.
+
+The .94 build and disposable server checks passed. Village Single and Tiny
+fixtures included compatible Plains; Cave Fortress Single selected Crimson
+Forest. The 32-seed authoring assertions and the preexisting no-structure
+completion checks passed. Saved generator pools survived unload/reload,
+terrain reseed and full restart. The server was stopped and its temporary
+world deleted. No structure-placement chunk scan was needed. Client book
+authoring remains a manual check; no commit, push or publication occurred.
+
+## Omitted biome-controller completion
+
+`1.0.1.95-beta.1` ports the no-controller branch of root `AgeBiomeSelection`
+and the first `AgeTraits.select` draw. The rank table and seed stream are
+shared with `PortRandomAgeSelection` rather than duplicated. The production
+seeded biome compiler uses that default when there is no explicit controller;
+the registry-only diagnostic overload retains its exact older defaults.
+Explicit controllers are unchanged. Native rolls with authored biomes, or
+Single rolls with more than one biome page, fall back by authored count to
+Single/Tiled/Medium. Other multi-biome rolls retain their distribution and
+ordinary minimum-only filling, plus .94's structure requirements.
+
+Void's omitted controller remains Single for empty pools and count-based
+for supplied biome pages. Cave's omitted Native roll follows the port's
+existing page-free seeded Single workaround; a native multi-cave source is
+still not implemented. Explicit Native is not silently converted. No other
+terrain, weather, lighting, color or body seed stream changes. Saved plans
+remain frozen through restart and terrain reseed; old Ages are not rewritten.
+
+The completed-biome diagnostic accepts `auto` and checks 128 seeds for all
+nine distribution results, independence from unrelated weather pages,
+authored prefix preservation, one/two-biome fallbacks, Void behavior and
+structure-aware completion. Existing explicit-controller checks still run.
+
+The .95 build and disposable-server checks passed. The expanded 128-seed
+matrix covered all distributions, authored one/two-biome rules and Cave pools.
+Created automatic Standard, Cave, Void and Cave Fortress fixtures, plus the
+unchanged full-random command and explicit Single/Native Cave controls.
+Generator pools survived unload/reload, reseed and full restart. A second seed
+produced Small regions with three biomes, while explicit Native Cave retained
+its Lush Caves source. No chunk-generation scan was needed. The server was
+stopped and its temporary world deleted. Client authoring remains a manual
+check; nothing was committed, pushed or published.
+
+## Omitted terrain completion
+
+`1.0.1.96-beta.1` adapts root `AgeRuntimeProfiles.selectForWriting`. A partly
+authored book without terrain starts with the shared ranked terrain draw;
+if unsupported, compatible profiles in stable ID order are indexed using
+`floorMod(Long.hashCode(seed), count)`. Explicit terrain is never substituted.
+Unlike root's feature-only candidate test, the port additionally preflights
+registry-backed biome restrictions to avoid selecting an unloadable Cave
+combination for supplied surface biomes. This is a deliberate compatibility
+guard while the broader writing/instability recovery remains unported.
+
+Binder availability checks now consider whether any supported terrain can
+host an omitted-terrain book instead of assuming Standard. The server resolves
+the actual terrain and biome plan once, then passes the resolved internal page
+view to material/feature compilers. The inferred terrain is appended internally,
+not inserted before original pages or written back to the book. Original
+indices and ordered modifiers remain intact. Environment controllers use the
+selected terrain, while sky colors and celestials still compile from original
+pages. Page-free random books retain their original path and seed streams.
+The chosen terrain and generator plans use existing saved fields, so no
+network protocol change or retroactive terrain reroll is introduced.
+
+The fixture checks 64 seeds for terrain coverage, deterministic selection,
+original page prefixes, Cave-only Fortress support, implied-fluid constraints,
+surface-biome compatibility, explicit terrain precedence and Binder
+availability. Generator placement still uses the previously ported routines.
+
+The .96 build and disposable server checks passed. The 64-seed assertions
+covered all six terrains, deterministic fallback, page-prefix preservation,
+explicit Flat, surface-biome protection and Cave-only Fortress availability.
+Created Sky-only, Fortress-only, Water-only, Plains-only, explicit Flat and
+full-random fixtures. A Water page retained Water as its implied lake fluid;
+Fortress-only selected Cave with eligible biomes. Plans survived unload/reload,
+reseed and full restart. The server was stopped and its temporary world
+deleted. No chunk scan was needed; client Binder checks remain manual.
+Nothing was committed, pushed or published.
+
+## Native Cave regions
+
+`1.0.1.97-beta.1` ports root `AgeBiomeSelection`'s full Native Cave pool and
+`AgeDimensionService.createBiomeSource`'s Native-to-Tiny mapping. New Native
+Cave plans retain distribution NATIVE with a saved recognized Cave/Nether
+list, and the backend uses `PortScaledBiomeSource` at scale 0 (or Fixed for
+a one-biome pool). Explicit Native biome pages remain prohibited. Both authored
+and page-free/omitted-controller paths use the same eligibility query; the
+temporary Native-to-Single Cave conversions are removed.
+
+Native pool data is permitted only for Cave terrain at backend validation.
+Other Native terrain sources are unchanged. Empty older Native Cave records
+still load the old Lush source; old Single choices also remain frozen. New
+Native pools are saved through the existing biome-plan codec without a new
+network protocol, but earlier betas cannot decode populated Native pools, so
+downgrading those saves is not supported. The current pool is passed to random
+structure eligibility rather than incorrectly assuming Lush Caves.
+
+The fixture verifies registry-derived pool ordering, old empty Native codec
+defaults, the actual generator source, deterministic Tiny-region equivalence,
+horizontal region variation and sampled pool membership without loading
+chunks. The omitted-controller matrix now expects Native Cave to remain
+Native with its full pool. This does not implement modded surface rules.
+
+The .97 build and disposable-server checks passed: explicit and omitted
+Native Cave, the full-random Native Cave path (seed 114), Native + Fortresses,
+explicit Single and the legacy Lush-only control. The vanilla registry pool
+contained nine biomes, including Sulfur Caves and all five Nether biomes;
+the actual Native source passed Tiny-equivalence and sample-membership checks.
+Pools survived unload/reload, reseed and full restart. The server was stopped
+and its temporary world deleted. No chunk scan was needed. Client exploration
+remains a manual check; nothing was committed, pushed or published.
+
 ## Verification of this first slice
 
 The 1.21.1 `compileJava` and `build` tasks passed offline after the backend