Visual: remove purple ground clutter and unify the lush Lowlands

[ael-dev3]

Summary

Presentation-only Lowlands unification based on the reviewed PR5 head.

Exact review base

• Base branch: review/pr5-head-fc95959 (preserves the deleted PR5 source ref)
• Base commit: fc95959d3c2128c267e535a6e6cffec5aaa692ff
• Head branch: visual/lush-lowlands-unification
• Head commit: 52c997c7caaf848b183bbefe0d591b0e8d701522
• This is a draft PR. Do not merge, activate, deploy, tag, or retarget it.

Diagnosis

PR5 made the grass layer readable, but the remaining Lowlands presentation still had a purple semantic heath tint, a purple-gray Ancient Stone treatment, and one ordinary heath-bloom per High/Balanced heath cell. Heath grass was also the sparsest of the usable green biomes, leaving isolated color blobs.

Changes

• Removed ordinary heath-bloom generation and filtered the historical type from the live feature layer. The feature kind remains in the compatibility union and telemetry is explicitly zero.
• Replaced the broad heath purple tint with a restrained moss/olive tint.
• Reworked Ancient Stone semantic color and monolith fallback material to neutral slate/moss with no violet emissive read.
• Increased Meadow/Lowland/Forest/Heath candidate and retention policy for more continuous grass, while retaining slope thinning, deterministic hashes, structure/resource exclusions, active-window packing, and quality caps.
• Kept Ridge and Ancient Stone grass modest so height, outcrops, and monoliths remain legible.
• Added bounded telemetry for feature counts, candidate/active cells by terrain, retained instances and average density by terrain, bare/rejection counts, grass luminance/green ranges, draw calls, triangles, cache state, and overview-hidden state.
• Added the visual policy note in docs/plans/2026-07-21-lush-lowlands-unification.md.

Authority boundary

No terrain schema, terrain membership, passability, resource/core/reserve metadata, castles, routes, economy, SpacetimeDB, auth, Pages, production, or release files changed. No new runtime binary or texture was added. The shared ambient scheduler, selection/interaction uniforms, no-op grass raycast, lifecycle cleanup, camera-local cache, and quality budgets remain intact.

Budgets and overview

The existing High/Balanced/Reduced grass instance, triangle, variant, draw-call, active-window, and overview-hidden policies remain enforced. Grass remains hidden in overview mode and uses the same shared demand-driven wind scheduler.

Verification

• Focused visual/scene contracts: 47 tests passing.
• TypeScript project build: tsc -b passing.
• Production client bundle: vite build passing.
• Runtime asset verifier: 40 exact runtime assets and 4 provenance masters verified.
• Full Vitest run reached 1,622 passing tests; remaining failures were existing sandbox-only loopback/tsx socket restrictions in Hermes/browser-probe lanes. The canonical grass digest was updated for the intentional density-policy change and the focused Genesis bounds test passes.
• Rendered WebGL QA was attempted with elevated loopback permission but stopped before rendering because the repository's reviewed local castle-source archive is unavailable. No screenshot is claimed from that run; identical-camera screenshot QA remains blocked on that pre-existing local archive prerequisite.

Risk and review notes

Main review risks are visual calibration on real mobile GPUs, grass density/thermal behavior, and the unavailable local rendered-QA archive. The changes are deterministic and bounded; no gameplay or authority behavior is inferred from the new diagnostics.