# L168 — Default the incremental desired set

**Result:** `voxel.StreamingIncrementalDesiredSet` now defaults to `1`. In five interleaved 30 m/s UE pairs against `assembler/world` `c6357b5`, candidate tick p99 fell from **10.07 to 7.01 ms** and median worst tick from **13.24 to 11.63 ms**. P99 was lower in all five pairs; worst tick was lower in four, with one +0.06 ms pair.

## Defaults and trace

The main switch gates the Core clipmap delta, overlay membership updates, priority-order merge/reuse, and the incremental path's same-center Core-key cache. Overlay and priority updates have no separate switches. Defaults after the change:

| CVar | Default | Meaning |
|---|---:|---|
| `StreamingIncrementalDesiredSet` | 1 | Core, overlay, and priority updates are incremental. |
| `StreamingCoreDesiredCacheByCenter` | 0 | Separate L160 cache stays off; the incremental path has its own cache. |
| `StreamingRebuildOnCoreRegionCompletion` | 1 | L160 same-center rebuild suppression stays off. |
| `StreamingFastTravelForwardFirst` | 0 | L160 ahead-first stays off. |
| `StreamingFastTravelWaitForAllCriticalTiles` | 1 | L157 early admission stays off. |
| `StreamingFastTravelApplyBudgetMilliseconds` | 0 | L157 fast-travel apply cap stays off. |
| `StreamingIncrementalDesiredAuditEvery` | 0 | Set/order audit stays off. |
| `StreamingIncrementalDesiredMaterializationAuditEvery` | 0 | Materialization audit stays off. |
| `StreamingIncrementalDesiredAuditInjectMismatch` | 0 | Negative-control injection stays off. |

The candidate warm-up was a default 30 m/s run with no streaming-configuration CVar overrides. Readback showed `incremental_desired_set=1`; its 12-second movement trace recorded 40 Core deltas, 313 incremental materialization updates, 168 priority-order updates, and 105 priority-order reuses. Baseline readback was `incremental_desired_set=0`. Every timing run also read back the L157/L160 and audit defaults in the table; only the VFHost movement and trace harness arguments were supplied.

## Measurement and checks

Five interleaved W8 pairs used the four-strata owner plan, a 12-second move plus 5-second dwell, and eight effective streaming slots. Tick metrics below are medians of per-run values over the 12-second movement window. One warm-up per binary was excluded. I discarded an initial provisional matrix because the longer load averages exceeded the quiet gate; the reported matrix began at **0.45 / 0.69 / 1.47** (1/5/15-minute averages), with no build running.

| Metric | `c6357b5` | Default-on | Paired result |
|---|---:|---:|---|
| Tick p99 | 10.07 ms | 7.01 ms | Lower in all 5 pairs |
| Worst tick | 13.24 ms | 11.63 ms | Lower in 4/5; one +0.06 ms pair |
| Near LOD0–2 readiness | 42.33% | 43.73% | +1.40 pp median |
| Moving far holes | 2.04% | 1.85% | −0.19 pp median |
| First settled LOD0–2 | 1.677 s | 1.672 s | 5 ms earlier median |

The separate audit run enabled both audit intervals at 1: **307** desired-set/collision-only comparisons, **307** priority-order comparisons, and **302** materialization comparisons passed; there were zero mismatches. Audit-run metrics are excluded from timing.

`verify.py fast` passed in **301.7 s** (268 pass, 0 fail, 5 diagnostics; 84 binary runs). VFHost Linux Development builds succeeded for the baseline and candidate with `-NoUBA -MaxParallelActions=4`. Runner `py_compile` and `git diff --check` passed. Fast-tier determinism covers W1/W8/W12. UE W12 movement was not run because the same 12-core VFHost affinity exposes eight TaskGraph background workers/effective streaming slots; movement used W8.

Changed Unreal `Source/` files:

- `Source/VoxelForge/Private/VoxelWorld.cpp`