beezm
537bd3e048
Diagnostic first (SouthernStretchTool, ISLA_DIAG_ONLY; scratch/southern_diagnosis.md). Along the central south profile the mask blend climbs 0.018 per 0.01 N, edge noise adds 0.03-0.06, and the southern sinker is zero until 0.75 N then adds 0.024 per 0.01 N before the 2.5 power; the coast sits at 0.76-0.82 N, ~0.06 N north of where the blend alone would end. The stretch compresses the southward distance the mask sees inside a fixed feathered latitude band, y' = yB + (y - yB)/(1 + s*ramp), texture (base noise, edge noise, latitude) untouched, so the extended mass keeps the elevation of the rows it came from. With the sinker reading the REAL y it cancels the stretch outright: median coast saturates at 0.83-0.84 from s = 1 to 16 and the south stays 1-10 tiny nubs on both seeds. The lever is therefore two things - extend reach AND hold the sinker back - and this pass couples them 1:1 (StretchSinker = true; the real-y mode is kept as the config's other setting). Ladder chosen from the sweep, non-linear: 0.5, 1, 2, 3, 5 (peninsula / onset / few big pieces / big pieces consolidating / over-stretched sheet); 8 and 16 are indistinguishable from 5. Topography: cells above the band take the untouched code path (fy == y), so the classify field north of the band is bit-identical by construction. SouthernStretch.cs holds the band constants (start 0.70 N, feather 0.05 N - fixed for the batch) and the ramp. TerrainGenConfig: SouthStretch (the swept axis, 0 = off), SouthBandStartFrac, SouthBandFeatherFrac, StretchSinker. Oracle, all passing: a1/a3 stretch OFF bit-identical; a3b stretch 5 north of the band bit-identical to the task-03 dump (2.93 M cells), a4b the same at 8192 against the terrain-curve-v1 gallery dump (46.97 M cells north of the band, 20.1 M differ below - the relaxation); per field north bit-locked classify and render vs stretch 0 (p, p2), northern island set invariant (q), centre is land, tag/coastline, classify == raw; ids and heights deterministic. Batch: BatchRoot(8, "southern_stretch_explore") - 5 levels x 2 seeds (1063685222, 999999937 - the two 07 seeds with the most mainland south of the band), lean render (regions overlay + relief + .f32), the hemisphere-split count/size table. Region labeling on, offshore / shelf / speck revert off: the pure fragmentation signal. The read at 4096: s 0.5 peninsula (coast +0.04 N); s 1 onset (999999937 6 -> 12 southern islands, 11 substantial); s 2 few big pieces (35k / 86k-cell fragments); s 3-5 a solid sheet to the trench whose southern edge is the trench wall - a ruler-straight coast - and whose island count falls as pieces re-merge. Gravel never dominates. Graduation held, per the task. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_013EY3ZTF6NwzF8ukBHQXSK7
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