feat: loader formatter architecture

.claude/settings.local.json

@@ -0,0 +1,16 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(git checkout:*)",
+      "Bash(cargo test:*)",
+      "Bash(git add:*)",
+      "Bash(git commit:*)",
+      "Bash(cargo check:*)",
+      "Bash(cargo llvm-cov:*)",
+      "Bash(cargo tarpaulin:*)",
+      "Bash(grcov:*)",
+      "Bash(git status:*)",
+      "Bash(git push:*)"
+    ]
+  }
+}

prefer/Cargo.toml

@@ -29,6 +29,9 @@ notify = { version = "6.1", optional = true }
 # Platform-specific path handling (std only)
 dirs = { version = "5.0", optional = true }
 
+# Plugin registration (std only)
+inventory = { version = "0.3", optional = true }
+
 # Optional format support (std only, no serde)
 roxmltree = { version = "0.20", optional = true }
 rust-ini = { version = "0.20", optional = true }
@@ -48,6 +51,7 @@ std = [
     "dep:toml_edit",
     "dep:notify",
     "dep:dirs",
+    "dep:inventory",
 ]
 json5 = ["std"]  # JSON5 features handled by jzon fallback
 xml = ["std", "dep:roxmltree"]

prefer/src/builder.rs

@@ -3,6 +3,8 @@
 //! The `ConfigBuilder` provides a fluent API for creating configurations
 //! from multiple sources with layered overrides.
 
+#![allow(deprecated)] // Builder still uses Source/FileSource internally during transition
+
 use crate::config::Config;
 use crate::error::Result;
 use crate::source::{EnvSource, FileSource, LayeredSource, MemorySource, Source};