sfx-maker: sfxc - sfxr-style .sfx text presets -> 16-bit WAV synthesis

- waves: square (duty), saw, sine, triangle, pitched noise (seeded, deterministic)
- envelope attack/sustain/decay, freq slide, vibrato, arpeggio jump,
  one-pole low/high-pass filters, clamped output
- presets blip/coin/explosion/hurt/jump/laser/powerup with seeded variants;
  preset writes editable .sfx or renders .wav directly
- go tests: parse/validate, determinism, per-preset RMS, WAV header roundtrip

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmdG9GqfSWCzts7AkDwRDh

sfx-maker/README.md

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+# sfx-maker (`sfxc`)
+
+Synthesizes **retro game sound effects** (sfxr-style) from `.sfx` text
+files and writes 16-bit mono **WAV**. Sound design becomes text an agent
+can read, tweak and reason about — no DAW needed. Go, zero
+dependencies, single static binary.
+
+## Build
+
+```bash
+# Arch/Garuda: sudo pacman -S go
+cd sfx-maker
+go build -o build/sfxc .        # or the VS Code task "build sfx-maker"
+go test ./...
+```
+
+## Quick start
+
+```bash
+sfxc preset jump -o jump.sfx      # editable text preset
+sfxc build jump.sfx               # -> jump.wav
+mpv jump.wav                      # listen (or aplay/ffplay)
+
+sfxc preset coin -o coin.wav      # straight to WAV
+sfxc preset coin --seed 3 -o coin3.wav    # deterministic variant
+sfxc info laser.sfx               # validate + summary
+```
+
+Presets: `blip, coin, explosion, hurt, jump, laser, powerup`.
+`--seed 0` is the canonical sound; any other seed nudges pitch/length
+deterministically — ask for three seeds, keep the one that sounds best.
+
+## The `.sfx` format
+
+```
+# comment
+sfx: jump            name
+wave: square         square | saw | sine | triangle | noise
+volume: 0.7          0..1
+attack: 0.01         seconds: fade in
+sustain: 0.08        hold at full volume
+decay: 0.18          fade out (total length = a+s+d, max 10 s)
+freq: 330            start pitch, Hz
+freq-slide: 900      Hz/second (positive = rising, negative = falling)
+duty: 0.5            square pulse width 0.05..0.95 (thinner = buzzier)
+vibrato-depth: 25    pitch wobble, Hz
+vibrato-rate: 9      wobbles per second
+arpeggio: 1.335      multiply pitch by this...
+arpeggio-time: 0.06  ...after this many seconds (classic coin blip)
+lowpass: 2200        cutoff Hz (muffle: explosions, thuds)
+highpass: 300        cutoff Hz (thin out: lasers, clicks)
+sample-rate: 44100   8000-96000
+seed: 1              noise randomness — same seed = same sound
+```
+
+Unknown keys are **errors**, so typos surface immediately. Everything is
+deterministic: same file → byte-identical WAV.
+
+## Recipe intuition for agents
+
+- **Jump**: square wave + rising `freq-slide`.
+- **Coin/pickup**: square + `arpeggio` > 1 shortly after the start.
+- **Laser**: saw + steep negative `freq-slide` + `highpass`.
+- **Explosion**: noise + `lowpass` ~2 kHz + long `decay`.
+- **Hurt**: saw, low pitch, quick fall.
+- **Power-up**: rising slide + `vibrato`.
+
+[`examples/`](examples/) contains all presets as `.sfx` + rendered `.wav`.