feat(disk): raise density_freq default to 2.0

Higher default turbulence frequency gives the volumetric disk more
trackable texture features at startup, making the Keplerian rotation
(rot ∝ 1/r^1.5) visually readable without needing to open the egui
panel. The old 0.8 default produced a near-featureless smooth slab at
default settings — the disk was rotating but the eye had nothing to lock
onto. 2.0 sits in the upper half of the slider range (0.2–3.0) while
still leaving room to push higher for debugging.

README.md

@@ -72,8 +72,19 @@ docs/superpowers/    design spec + implementation plan
 
 ## Status
 
-**Phase 1 (Schwarzschild)** — shipped: shadow, tilted Doppler accretion disk with lensed Einstein halo, lensed starfield, lensed planets, lensed Flamm grid, optional cubemap skybox, live egui controls, desktop + web/WebGPU.
+**Phase 1 (Schwarzschild)** — shipped & validated: black shadow at the critical impact parameter, tilted Doppler accretion disk with the lensed Einstein halo (disk backside lensed up-and-over and down-under), procedural lensed starfield, lensed Flamm-paraboloid curvature grid, optional cubemap skybox, live egui Controls panel, desktop + web/WebGPU.
 
-**Phase 2 (Kerr)** — **implemented, pending visual/performance validation.** The Schwarzschild fixed-step RK4 integrator was replaced by a Kerr geodesic with an adaptive Dormand-Prince RK45 loop: a spin parameter χ ∈ [0,1] drives frame-dragging and a spin-dependent capture radius (Kerr horizon), the disk inner edge tracks the Kerr ISCO, and `render_scale` is now wired through an offscreen render-to-texture + upscale pass. The CPU mirror (`src/physics.rs`) covers the Kerr derivative, the RK45 step, and the adaptive loop, and the unit tests assert the spin = 0 degeneracy plus capture/escape behavior at spin > 0. What remains is the human-in-the-loop checklist: spin = 0 visual regression against Phase 1, frame-dragging asymmetry at spin > 0, and desktop/web FPS at the new defaults — see `docs/superpowers/plans/2026-07-13-interstellar-blackhole-phase2-kerr.md` (Task 8).
+**Phase 2 (Kerr)** — shipped & validated. The Schwarzschild fixed-step RK4 integrator is replaced by a Kerr geodesic with an **adaptive Dormand-Prince RK45** loop. A spin parameter χ ∈ [0,1] drives the Lense-Thirring frame-dragging term in the bending acceleration and a spin-dependent capture radius (Kerr horizon r₊); at χ = 0 the frame-dragging term vanishes and the integrator is exactly Schwarzschild. The disk inner edge tracks the Kerr ISCO (6M = 3 Rs at χ = 0 → M = Rs/2 at extremal spin). The CPU mirror (`src/physics.rs`) covers the Kerr derivative, the RK45 step, and the adaptive loop; 14 unit tests assert the spin = 0 degeneracy, the monotonically shrinking ISCO/horizon/capture radius, and capture/escape behavior. `render_scale` is wired through an offscreen render-to-texture + upscale pass.
 
-**Phase 3 (future work).** Full exact Kerr Cartesian pseudo-Hamiltonian (Σ/Δ/Carter-separable form) for sub-percent photon-orbit accuracy at high spin, retrograde spin, tilted spin axis, and adaptive integrator *order*. See `docs/superpowers/specs/2026-07-13-interstellar-blackhole-phase2-kerr-design.md` §9.
+**Phase 3 (cinematic)** — shipped & validated:
+- **HDR pipeline** — full-screen quad chain: bright-pass → blur pyramid (2 down + 2 up) → composite with ACES filmic tone-map. `BloomQuality` (Off / Low / Medium / High) despawns/respawns the bloom sub-graph; Off composites scene-only ACES.
+- **Volumetric disk (3.1)** — fbm + ridged-multifractal turbulence replaces the zero-thickness slab; per-segment integration along the bent ray, scale-height H/R radial thickness, three `DiskQuality` tiers gating octave counts.
+- **Blackbody disk + relativistic jets (3.2)** — `DiskColorMode::Blackbody` keys a Tanner-Helland color to a Novikov-Thorne radial temperature profile shifted by the Kerr 4-velocity Doppler factor; bipolar relativistic jets along the spin axis are spin-gated (Blandford-Znajek: suppressed at χ = 0 regardless of the toggle).
+- **Anti-aliased lensed-image rings (3.3)** — `AaQuality` supersamples the higher-order ring wraps (1 / 2 / 4 sub-rays per pixel) to smooth the discrete bands into a continuous gradient.
+- **Kerr orbiting planets (3.4)** — lensed planets on Kerr equatorial orbits (`Ω_φ` Bardeen 1972) with Lense-Thirring nodal precession (`Ω_LT`), deterministically seeded (ChaCha8Rng), live respawn on seed/count/radius change.
+
+**Performance defaults** target ~60 FPS on discrete/integrated GPU (developed on Apple M4): desktop `steps=300`, `render_scale=0.75`, `bloom=High`, `disk=High`, `aa=Low`; web drops to `steps=200`, `render_scale=0.5`, `bloom=Low`, `disk=Low`, `aa=Off`. Release profile uses fat LTO + single codegen unit on desktop; the web profile overrides `opt-level="z"` for binary size.
+
+**Phase 4 (future work).** Full exact Kerr Cartesian pseudo-Hamiltonian (Σ/Δ/Carter-separable form) for sub-percent photon-orbit accuracy at high spin, retrograde spin, tilted spin axis, and adaptive integrator *order*. See `docs/superpowers/specs/2026-07-13-interstellar-blackhole-phase2-kerr-design.md` §9.
+
+> An earlier attempt (Stage A: exact Hamiltonian core, CPU + shader mirror) lives on the `phase4-exact-kerr-experimental` branch. Its CPU side reaches sub-percent `b_crit` accuracy (χ=0: 0.08%, χ=0.9: 1.5%) but the shader mirror has an unresolved CPU↔WGSL numerical divergence — the rendered disk shows no gravitational lensing despite the CPU trace showing correct 173° deflection. Resume there with per-pixel debug-color output to localize the divergence.

src/params.rs

@@ -189,7 +189,7 @@ impl Default for BlackHoleParams {
             disk_half_thickness: 0.15,
             filament_freq: 1.0,
             filament_sharpness: 2.0,
-            density_freq: 0.8,
+            density_freq: 2.0,
             // Raised from 1.0: the new density model has no 0.55 floor and decays
             // to 0 at the edges, so a slightly higher multiplier keeps the bulk
             // opaque after per-step integration.

src/render/material.rs

@@ -101,7 +101,7 @@ impl Default for BlackHoleUniforms {
             disk_half_thickness: 0.15,
             filament_freq: 1.0,
             filament_sharpness: 2.0,
-            density_freq: 0.8,
+            density_freq: 2.0,
             density_strength: 1.2,
             arm_count: 2.0,
             arm_tightness: 2.0,