# sim-config
`sim-config` is the Table and Dir substrate for layered SIM configuration. It
keeps configuration as kernel `Expr::Map` data, merges layers with provenance,
binds shape-checked defaults, offers typed read views, and builds safe
per-library config paths.
It does not introduce a private config value model. Decoders, bootloaders,
probes, and explicit overrides all produce the same `ConfigDir` shape, then
callers merge those Dirs from built-in defaults through the highest-precedence
process override.
## What it provides
- `ConfigTable` for one library's map-valued table.
- `ConfigDir` for a library-id-to-table Dir.
- `ConfigLayer`, `EffectiveConfig`, `MergeTrace`, and `merge_layers`.
- Merge rules for scalar replacement, nested table overlays, id-keyed repeated
table replacement, and absent-field preservation.
- `ConfigShape` and `LibConfigDefaults` for shape-backed defaults, unknown-field
reports, and secret-field metadata.
- `ConfigView` typed accessors over table fields.
- `ConfigRoots` and `lib_config_path` for root selection and safe
`libs/<lib-id>.toml` paths.
## Example
```rust
use sim_config::{ConfigDir, ConfigLayer, ConfigSource, merge_layers};
use sim_kernel::Symbol;
use sim_value::build::{map, text};
let lib = Symbol::qualified("model", "defaults");
let built_in = ConfigDir::one(lib.clone(), map(vec![("provider", text("modeled"))]))?;
let work = ConfigDir::one(lib.clone(), map(vec![("provider", text("openai"))]))?;
let effective = merge_layers(&[
ConfigLayer::new(ConfigSource::BuiltIn { lib: lib.clone() }, built_in),
ConfigLayer::new(ConfigSource::Explicit { label: "cli".into() }, work),
]);
assert!(effective.dir.table(&lib).is_some());
# Ok::<(), Box<dyn std::error::Error>>(())
```
## Examples, Docs, And Validation
Rustdoc examples cover layered merge and typed reads. The crate has no recipe
directory because it stays at the configuration-substrate layer.
- API docs: <https://docs.rs/sim-config>
- Repository guide: <https://github.com/sim-nest/sim-foundation>
From the `sim-foundation` checkout:
```bash
cargo test -p sim-config
RUSTDOCFLAGS="-D warnings" cargo doc -p sim-config --no-deps
cargo run -p xtask -- check-recipes
cargo run -p xtask -- check-package-floors
cargo run -p xtask -- simdoc --check
```