Channel properties editor, per-channel scaling, and dependency/toolchain updates

AGENTS.md

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+# AGENTS.md
+
+## Project Overview
+
+i3rs is an open-source cross-platform alternative to MoTeC i2 Pro for motorsport telemetry analysis. It parses MoTeC `.ld` binary log files and `.ldx` XML sidecar files. The full roadmap is in `docs/PLAN.md`.
+
+## Build & Test
+
+```bash
+cargo build --release          # Build all crates
+cargo test                     # Run tests (5 unit tests in i3rs-core)
+cargo run --release -p i3rs-app -- test_data/VIR_LAP.ld   # Run GUI with test file
+cargo run --release -p i3rs-cli -- test_data/VIR_LAP.ld   # Run CLI inspector
+```
+
+Rust 2024 edition — requires rustc 1.85+.
+
+## Workspace Structure
+
+Three crates in `crates/`:
+
+- **i3rs-core** — Pure library. Parsing, data model, lap detection, downsampling. No GUI dependencies.
+- **i3rs-app** — egui desktop GUI. Depends on i3rs-core.
+- **i3rs-cli** — Simple CLI that prints session info and channel stats. Depends on i3rs-core.
+
+## Key Source Files
+
+### i3rs-core (`crates/i3rs-core/src/`)
+- `lib.rs` — Public API re-exports: `LdFile`, `Session`, `ChannelMeta`, `Event`, `DataType`, `LdxFile`, `LdxLap`, `Lap`, `detect_laps`, `downsample_minmax`, `DownsampledPoint`, `format_state_value`, `is_state_channel`
+- `ld_parser.rs` — Binary .ld format parser using memmap2. Key types: `LdFile` (entry point), `Session` (metadata), `ChannelMeta` (channel info + lazy data access + `enum_labels`). Methods: `read_channel_data()`, `read_channel_range()`, `format_channel_value()`. Internal: `parse_enum_tables()` scans for embedded enum/state label definitions
+- `state_labels.rs` — Hardcoded fallback text labels for known MoTeC M1 ECU state channels (Gear, Brake State, etc.). Used when file-parsed enum tables are unavailable
+- `ldx_parser.rs` — XML sidecar parser for lap timing. `find_ldx_for_ld()` locates the .ldx next to a .ld file
+- `lap_detect.rs` — Detects lap boundaries from "Lap Number" channel data
+- `downsample.rs` — Min-max decimation for efficient chart rendering
+- `math_expr.rs` — Recursive descent expression parser (AST: `Expr`, `BinOp`)
+- `math_engine.rs` — Expression evaluator with built-in functions, channel resampling, `evaluate_expression()` entry point
+- `export.rs` — CSV export with multi-frequency resampling
+- `track.rs` — GPS track extraction, normalization, color mapping, sector timing. Key types: `TrackData`, `Sector`, `SectorTime`. Functions: `extract_gps_track()`, `find_nearest_sample()`, `compute_color_map()`, `compute_sector_times()`
+
+### i3rs-app (`crates/i3rs-app/src/`)
+- `app.rs` — Top-level `App` struct, egui-dock layout, file open logic, menu bar
+- `state.rs` — `SharedState`: cursor position, zoom range, selected lap, channel data cache, `ChannelId` (Physical/Math), `MathChannelDef`
+- `workspace.rs` — Save/load workspace layouts + math channels as JSON
+- `panels/graph.rs` — Main graph panel: multi-channel time-series, overlay/tiled modes, dual Y-axes, zoom/pan. Uses `ChannelId` for both physical and math channels
+- `panels/channel_browser.rs` — Searchable channel list with drag-and-drop, includes math channels section
+- `panels/cursor_readout.rs` — Shows all plotted channel values at cursor time (uses file-parsed enum labels with hardcoded fallback)
+- `default_layouts.rs` — Default i2-style worksheet templates (Driver, Braking, Engine, Fuel/Ign, Spare) auto-populated on file open
+- `panels/timeline.rs` — Overview bar with draggable zoom window
+- `panels/math_editor.rs` — Math channel definition UI: add/edit/delete/evaluate expressions, predefined calculation templates, channel alias management
+- `panels/report.rs` — Statistics report panel: min/max/avg/stddev per channel per lap
+- `panels/track_map.rs` — GPS track map panel: rainbow coloring by channel value, sector editor, sector time report, cursor sync, reference lap selection
+- `panels/histogram.rs` — Distribution histogram with configurable bins, per-lap breakdown, cursor value lines
+- `panels/scatter.rs` — XY scatter plot (channel vs channel), cursor highlight point
+- `panels/fft.rs` — FFT frequency spectrum analysis with Hann window, log scale option, cached computation
+- `panels/gauge.rs` — Gauges panel: analog arc, bar, digital, and steering wheel angle widgets at cursor time
+- `panels/mixture_map.rs` — 2D heatmap (e.g., AFR vs RPM vs TPS), binned with heat color scale
+
+## Architecture Notes
+
+- Files are opened via `memmap2` — no full file read, OS pages data on demand
+- Channel sample data is decoded lazily when requested (not at file open time)
+- All panels share state through `SharedState` for cursor/zoom synchronization
+- GUI uses immediate-mode rendering (egui) — redraws every frame during interaction
+- egui-dock provides the dockable/tabbable panel layout system
+
+## Binary Format
+
+The .ld format is little-endian throughout. Key constants in `ld_parser.rs`:
+- Header size: `0x6E2` (1762 bytes)
+- Channel metadata entry size: 212 bytes (120 base + 92 extended)
+- Magic byte: `0x40`
+- Channel metadata is a linked list (each entry has `next_chan_meta_ptr`)
+- Extended metadata contains enum table reference at offset +0xD0 (type u16) and +0xD2 (id u16)
+- Enum/state tables are embedded in the ECU config section (latter portion of file), parsed by scanning
+- Data types: u8/u16/u32/i8/i16/i32/f16/f32 (see `DataType` enum)
+
+Full format docs: `docs/ld-file-format.md`
+
+## Test Data
+
+- `test_data/VIR_LAP.ld` (~4.8MB) — single lap at Virginia International Raceway
+- `test_data/VIR_LAP.ldx` — accompanying lap metadata XML
+- `examples/` (gitignored) — larger files up to 100MB for manual testing
+
+## Current Status
+
+Milestones 1–6 complete. Next up: Milestone 7 (overlays — compare laps across sessions).