[Rendering] Unify temporal history and eliminate TSR, SSR, GI, and PT instability

[proggeramlug]

Parent: #126
Includes engine ticket EN-061 from docs/tickets.md
Related: #56

Problem

Temporal effects multiply both quality and failure modes. Bloom uses temporal reconstruction/history in TAA/TSR, SSR, screen-probe GI, denoising, exposure, and realtime path tracing, but these systems do not yet share one authoritative motion/history contract. Observed symptoms include SSR fireflies in dark interiors, specular trails, disocclusion smearing, widened block artifacts after upscale, and soft defaults.

Outcome

A common temporal contract plus a qualification/fix pass that makes still and moving output stable across camera motion, object motion, disocclusion, lighting changes, resolution changes, and feature toggles.

Common temporal contract

Define and document once:

• motion-vector convention (current-to-previous or previous-to-current), units, jitter inclusion, clip/NDC Y convention, and validity;
• current/previous transforms for static, rigid, skinned, particle, and procedural content;
• camera-cut/teleport detection and explicit reset API;
• history allocation, resize/render-scale change, exposure domain, and reset rules;
• disocclusion/depth/normal/material rejection thresholds;
• reactive/composition masks for transparency, particles, emissive changes, and refraction;
• per-pixel history confidence/length semantics.

Create debug views for motion, reprojected UV, rejection reason, history length, reactive mask, variance, and clamped history.

Required work

TSR/TAA

• Validate jitter sequence and projection integration.
• Use neighborhood statistics/variance clipping in a stable color space.
• Handle subpixel detail, alpha-test coverage, responsive content, render-scale changes, and sharpening without excessive softness/ringing.
• Integrate quality presets so Ultra is not silently half-resolution/soft; coordinate with Default render_scale=0.5 + TAA + no sharpening makes output blurry #56.

SSR

• Implement roughness/BRDF-aware ray eligibility and mip choice.
• Validate hit thickness against the actual Hi-Z level/footprint used.
• Clamp or reject firefly radiance using local exposure/luminance statistics without crushing valid bright reflections.
• Weight SSR against probe/planar/ray-query/environment fallback and confidence.
• Reproduce EN-061's dim-interior/bright-window case.

GI and PT denoisers

• Share motion/disocclusion rules where representations match.
• Bound radiance outliers before they poison temporal/spatial history.
• Preserve fast lighting changes without persistent lag.
• Reset/reseed correctly on mode toggles and camera cuts.

Motion corpus

Automate at least:

• slow pan, subpixel crawl, fast rotation, camera cut, and FOV change;
• translating/rotating rigid object;
• skinned animation;
• alpha-tested foliage/card motion;
• emissive light turning on/off;
• dark interior looking at bright exterior;
• transparent/refractive object motion;
• dynamic-resolution step and window resize.

Compare sequences, not only final frames. Report temporal SSIM/FLIP, flicker/variance, ghost trail duration, rejection ratio, and stable-frame convergence.

Acceptance criteria

• The shared convention is documented and unit-tested with known matrices/points, including jitter and Y orientation.
• All motion-producing paths either write valid motion/reactive data or explicitly opt out with correct history rejection.
• EN-061 interior SSR case contains no isolated high-luminance fireflies above an approved local threshold and retains valid smooth-metal reflections.
• Camera cuts, mode toggles, resize, and render-scale changes leave no prior-frame image after the documented reset window.
• Moving geometry has no persistent (> approved frame count) ghost trail in the corpus.
• Quality presets define render scale, temporal mode, sharpening, and per-effect history behavior together; default output is not unintentionally soft.
• PT motion goldens and full quality corpus pass on supported backends.
• Before/after pass timings and memory for every added history/mask are reported.

Likely files

• native/shared/src/renderer/postfx_chain.rs, ssr_pass.rs, ssgi_pass.rs, pt_pass.rs, hiz.rs, drs.rs
• shaders under native/shared/src/renderer/shaders/
• transform/motion ownership in scene/model/animation code
• quality APIs in src/core/
• native/shared/tests/golden_render.rs

Non-goals

• Adding frame generation.
• Replacing all temporal systems with one shader.
• Hiding instability by disabling SSR/TAA globally.

Dependencies

• [Quality][P0] Add deterministic reference-scene visual and GPU performance qualification #128 and [Rendering][P0] Restore deterministic path-tracing goldens and oracle correctness #127 for final acceptance.
• Individual convention/debug work can begin immediately.