# Linux78 report

## Passage cost and world identity

The expensive path is `ApplyResolvedStratePassageCarves`: negative density samples enter the passage loop and query the segment index even when their tile has little passage overlap. The route relief calls `VF_FieldPassageWallRelief`, three 3D value-noise octaves at 43/29/19 voxel wavelengths; mouth relief uses the three-octave surface relief. A representative W8 tunnel LOD0 composer census recorded 6.0M composer queries, 18.1M passage iterations, 45.1M segment visits, and 40.8M relief calls.

The retained exact changes are a conservative tile-level upper-mouth candidate list and early return, segment-index min/max rejection before `lower_bound`, and a 64-entry thread-local cache of value-noise lattice corners. The cache preserves the existing interpolation operations and values. The passage share remains high: FI/TN near-LOD passage phase averages 63.0%/63.7% after the change, versus 64.6%/65.9% before; support is 13.8%/13.5% versus 14.1%/13.2%.

The world is exact. The L75 full-grid owner hash and all 24 Clang/GCC × W1/W8/W12 × four-strate density, mesh, payload, and topology comparisons match. No version bump or new captures were needed. Fast-tier passage audits passed.

## Readiness, W8, three interleaved pairs, median seconds

| Strate | LOD0–2 before | LOD0–2 after | Whole view before | Whole view after |
|---|---:|---:|---:|---:|
| SurfaceWorld | 4.36 | 1.76 | 4.36 | 3.43 |
| FloatingIslands | 6.89 | 5.26 | 6.89 | 6.93 |
| TunnelNetwork | 4.88 | 3.22 | 4.88 | 4.55 |
| VerticalShafts | 2.71 | 1.56 | 2.71 | 2.84 |

The headless and Unreal schedulers now submit the collision-critical walkable ring first, then LOD0, LOD1, and LOD2. Far LOD work waits until the requested near LODs are ready and runs at lower priority. The ~1 s near-LOD target is not met for FI/TN; their medians are 5.26 s and 3.22 s. Whole-view times are reported separately above.

## L77 sampler closure and phase census

Values are mean sampled grid-fill/direct grid-fill closure; passage and support are their sampled CPU shares. Near is LOD0–2.

| Strate | Near closure B/A | Whole closure B/A | Passage share near B/A | Support share near B/A |
|---|---:|---:|---:|---:|
| SurfaceWorld | 99.1% / 99.9% | 100.1% / 99.6% | 45.1% / 47.6% | 15.0% / 12.8% |
| FloatingIslands | 99.9% / 99.5% | 99.8% / 99.8% | 64.6% / 63.0% | 14.1% / 13.8% |
| TunnelNetwork | 99.9% / 100.1% | 99.8% / 100.2% | 65.9% / 63.7% | 13.2% / 13.5% |
| VerticalShafts | 100.0% / 100.2% | 99.9% / 100.9% | 45.9% / 42.9% | 5.9% / 6.6% |

Sampler handler cost stayed below 0.05% of profiled thread CPU. Detailed samples and route counts are in `Saved/Linux/l78/sampler-census.csv`, `closure-census.csv`, and `route-census.csv`.

## Builds and checks

- Fast tier: PASS, 366.8 s.
- Hash matrix: PASS, 24/24; the pinned L75 full-grid owner hash also matches.
- Linux VFHostEditor: PASS after timing, `-MaxParallelActions=4`, no address-space limit; UBT reported 70.35 s in its parallel executor.
- No installs, commit, push, or stash.

## Failed runs and rejected experiment

- The first fast-tier launch pointed at an output directory without its expected verifier binaries; corrected, then the final fast tier passed.
- L76's broad per-tile passage-loop experiment caused 612 density mismatches and changed mesh, payload, and topology hashes on 24 tiles; L76 rejected it. It is not part of the accepted L76 reference. In L78, per-brick and direct per-sample feature-bound filters also failed the pinned L75 owner hash, so both were removed. The retained path matches the accepted L76 matrix and pinned L75 owner hash.
- The first direct UBT call could not find `dotnet` in PATH; rerunning through the engine `Build.sh` wrapper succeeded.