docs: initialize project

.planning/PROJECT.md

@@ -0,0 +1,77 @@
+# Yazi Image Preview Quality Improvement
+
+## What This Is
+
+An improvement to yazi's image preview downscaling so that thumbnails displayed in the terminal preview pane are visibly sharper. The current pipeline uses the `image` crate's built-in `resize()` with configurable filter types, but the results appear noticeably less sharp than native image viewers like macOS Preview.
+
+## Core Value
+
+Image previews in yazi should look as sharp as the terminal's pixel resolution allows — downscaling artifacts should not be the bottleneck.
+
+## Requirements
+
+### Validated
+
+(None yet — ship to validate)
+
+### Active
+
+- [ ] Improve the downscaling/resizing algorithm in `yazi-adapter` so preview thumbnails are visibly sharper
+- [ ] Maintain existing configurability (users can still select filter types)
+- [ ] No regression in preview latency perceptible during normal navigation
+
+### Out of Scope
+
+- Full image pipeline audit (ICC, encoding, protocol drivers) — focus is the resize step only
+- Color accuracy improvements — not the reported issue
+- Sixel/Chafa-specific quality — user's workflow is iTerm2/WezTerm (IIP protocol)
+- Adding new image protocol support
+
+## Context
+
+**Current implementation:** `yazi-adapter/src/image.rs` — `Image::downscale()` and `Image::precache()` both call `img.resize(w, h, Self::filter())` using the `image` crate's `DynamicImage::resize()`. The default filter is `lanczos3` (configured in `yazi-config/preset/yazi-default.toml`).
+
+**Why it's blurry:** The `image` crate's resize implementation, while functional, uses a simpler convolution approach compared to dedicated image processing libraries (e.g., `fast_image_resize`, `resize`). For downscaling large images to small preview sizes, the quality difference is noticeable — especially for fine detail and text in images.
+
+**Key files:**
+- `yazi-adapter/src/image.rs` — resize logic, filter selection, decode pipeline
+- `yazi-config/src/preview/preview.rs` — `image_filter` and `image_quality` config
+- `yazi-config/preset/yazi-default.toml` — default settings (`image_filter = "lanczos3"`, `image_quality = 90`)
+- `yazi-adapter/src/drivers/iip.rs` — iTerm2 Inline Protocol driver (user's protocol)
+
+**Brownfield context:** This is an existing, mature Rust project (1,363 commits, 15 workspace crates). The `yazi-adapter` crate has zero tests currently (noted in codebase concerns). The project uses Rust edition 2024 with MSRV 1.92.0.
+
+## Constraints
+
+- **Rust edition**: 2024, MSRV 1.92.0
+- **Dependencies**: Must be compatible with existing workspace dependency versions
+- **Performance**: Preview generation must not add perceptible latency
+- **Backward compatibility**: Existing `image_filter` config option must continue to work
+- **No tests exist**: `yazi-adapter` has zero tests — any changes are validated at runtime only
+
+## Key Decisions
+
+| Decision | Rationale | Outcome |
+|----------|-----------|---------|
+| Focus on resize algorithm only | User reports sharpness, not color; current pipeline is otherwise functional | — Pending |
+| Target iTerm2/WezTerm (IIP) | User's primary terminal; IIP driver calls `Image::downscale()` directly | — Pending |
+
+## Evolution
+
+This document evolves at phase transitions and milestone boundaries.
+
+**After each phase transition** (via `/gsd:transition`):
+1. Requirements invalidated? → Move to Out of Scope with reason
+2. Requirements validated? → Move to Validated with phase reference
+3. New requirements emerged? → Add to Active
+4. Decisions to log? → Add to Key Decisions
+5. "What This Is" still accurate? → Update if drifted
+
+**After each milestone** (via `/gsd:complete-milestone`):
+1. Full review of all sections
+2. Core Value check — still the right priority?
+3. Audit Out of Scope — reasons still valid?
+4. Update Context with current state
+
+---
+*Last updated: 2026-03-21 after initialization*