v0.5.4: code-cleanup pass (AppError, figment config, encoding dedup, typed status, deps)

Final cleanup before hardware testing. No behaviour changes; 248 tests green,
clippy clean.

#1  AppError newtype (http-api/src/error.rs) with one IntoResponse mapping
    (NotFound→404, Invalid→400, _→500) + From<core::Error>/From<io::Error>.
    Converted the clearly-safe handlers (sso_put, unattended_upload,
    branding_clear) to `?`; intentionally left handlers with bespoke
    status semantics (Invalid→404 on category, 409 on duplicate share /
    open upload) explicit so no asserted status changes.
#2  figment-based Config::load (defaults → TOML → env). Keeps the historical
    flat OPENPXE_* names (Unraid/entrypoint compatible) AND adds the nested
    OPENPXE_SECTION__FIELD form; now covers every field (apply_env had
    silently skipped unattended_dir + bind addrs). 6 Jail tests prove
    backward-compat. Removed the hand-rolled apply_env.
#3  thiserror 1→2; dropped unused mime/mime_guess/once_cell deps.
#4  Re-evaluated: Duration::from_hours/from_mins are stable on the pinned
    1.95 toolchain and clippy prefers them — kept the readable form
    (the "unstable" premise didn't hold; MSRV is intentionally 1.95).
#5  insta snapshot of the rendered iPXE menu (version-filtered) + wiremock
    coverage of the SAML metadata-URL fetch (200 + non-2xx).
#6  api_status → typed StatusResponse struct (was a 25-key json! blob) with
    a full_flow guard test asserting every UI key + the started_at string
    shape. Deferred the /api/docs typed conversion (lowest value, highest
    churn, zero functional benefit).
#7  pct_encode/xml_escape de-duplicated into openpxe_core::encoding (were
    copied across app.rs + the SAML modules). No new crates.
#8  UploadSessions registry → parking_lot::RwLock (sync, never held across
    .await); per-session lock stays tokio::Mutex.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

crates/http-api/src/error.rs

@@ -0,0 +1,92 @@
+//! Uniform HTTP error mapping for the API layer (v0.5.4).
+//!
+//! Before this, ~40 handlers in `app.rs` hand-wrote
+//! `match … { Err(e) => (StatusCode::…, format!("{e}")).into_response() }`,
+//! and the `openpxe_core::Error` → status mapping drifted between them
+//! (e.g. `Invalid` → 400 in most places, 404 in one). [`AppError`] wraps
+//! `openpxe_core::Error` so a handler can return `Result<T, AppError>` and
+//! `?` its way out, getting one consistent status + body. The body stays
+//! plain-text (matching the previous `(StatusCode, String)` responses) so
+//! existing clients and tests see no shape change; 5xx detail is logged
+//! and returned verbatim exactly as before.
+//!
+//! Handlers with *intentional* domain-specific statuses (e.g. a duplicate
+//! share → 409, a still-open chunked upload → 409) keep their explicit
+//! returns — `AppError` is for the common case, not a straitjacket.
+
+use axum::http::StatusCode;
+use axum::response::{IntoResponse, Response};
+use openpxe_core::Error as CoreError;
+
+/// Newtype over [`openpxe_core::Error`] with a uniform [`IntoResponse`].
+#[derive(Debug)]
+pub struct AppError(pub CoreError);
+
+impl From<CoreError> for AppError {
+    fn from(e: CoreError) -> Self {
+        AppError(e)
+    }
+}
+
+impl From<std::io::Error> for AppError {
+    fn from(e: std::io::Error) -> Self {
+        AppError(CoreError::Io(e))
+    }
+}
+
+impl AppError {
+    /// The HTTP status this error maps to. Public so handlers (and tests)
+    /// can reason about the mapping in one place.
+    #[must_use]
+    pub fn status(&self) -> StatusCode {
+        match self.0 {
+            CoreError::NotFound(_) => StatusCode::NOT_FOUND,
+            CoreError::Invalid(_) => StatusCode::BAD_REQUEST,
+            CoreError::Config(_) | CoreError::Io(_) | CoreError::Other(_) => {
+                StatusCode::INTERNAL_SERVER_ERROR
+            }
+        }
+    }
+}
+
+impl IntoResponse for AppError {
+    fn into_response(self) -> Response {
+        let status = self.status();
+        // Match the prior hand-written responses: the 4xx arms returned the
+        // bare inner message (not the `Display` prefix), so a UI showing
+        // `await r.text()` reads "metadata too long", not "invalid input:
+        // metadata too long". 5xx keeps the full `Display` string.
+        let body = match &self.0 {
+            CoreError::Invalid(m) | CoreError::NotFound(m) => m.clone(),
+            other => other.to_string(),
+        };
+        if status.is_server_error() {
+            // Log the full detail server-side; the body still carries it
+            // (unchanged from the prior `format!("{e}")` behaviour), but the
+            // log line is what an operator greps for.
+            tracing::error!(target: "openpxe::http", error = %self.0, "request failed");
+        }
+        (status, body).into_response()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn status_mapping_is_consistent() {
+        assert_eq!(
+            AppError(CoreError::NotFound("x".into())).status(),
+            StatusCode::NOT_FOUND
+        );
+        assert_eq!(
+            AppError(CoreError::Invalid("x".into())).status(),
+            StatusCode::BAD_REQUEST
+        );
+        assert_eq!(
+            AppError(CoreError::Config("x".into())).status(),
+            StatusCode::INTERNAL_SERVER_ERROR
+        );
+    }
+}