firma-config: minimize indirection, duplication and risk of TOCTOU bugs

Cargo.toml

@@ -53,6 +53,7 @@ firma-protobuf = "0.1.1"
 firma-run = { path = "crates/firma-run" }
 firma-sidecar = { path = "crates/firma-sidecar" }
 firma-stack = { path = "crates/firma-stack" }
+fs-err = "3"
 governor = "0.10"
 hex = "0.4"
 http-body = "1"

crates/firma-config/Cargo.toml

@@ -13,8 +13,10 @@ workspace = true
 clap = ["dep:clap"]
 
 [dependencies]
+anyhow = { workspace = true }
 clap = { workspace = true, optional = true, features = ["derive"] }
 dirs = { workspace = true }
+fs-err = { workspace = true }
 serde = { workspace = true }
 thiserror = { workspace = true }
 toml = { workspace = true }

crates/firma-config/src/lib.rs

@@ -5,16 +5,12 @@
 //! paths. Fail-closed: no silent fallback to an empty config.
 
 mod profile;
-mod provider;
 mod resolver;
 mod schema;
 
 /// Canonical config file name shared by every binary.
 pub const CONFIG_FILE_NAME: &str = "firma.toml";
-/// Application subdir under a platform config root (e.g. `~/.config/firma`).
-pub const CONFIG_SUBDIR: &str = "firma";
 
 pub use profile::AgentProfile;
-pub use provider::{DirProvider, SystemDirs};
-pub use resolver::{ConfigResolveError, ConfigSource, ResolvedConfig, resolve_config};
+pub use resolver::{ConfigResolveError, ConfigSource, ResolvedConfig, SystemDirs};
 pub use schema::{FirmaConfig, load_section};