store: Rust: reqwest response.json() yields reqwest::Error, not serde_json::Error

graph/fixes/rust-reqwest-responsejson-yields-reqwesterror-not-serde-json-27a1f7.md

@@ -0,0 +1,44 @@
+---
+id: 27a1f728-ec90-469c-a6ab-5644d333322f
+type: fix
+title: "Rust: reqwest response.json() yields reqwest::Error, not serde_json::Error"
+tags: [rust, reqwest, serde, error-handling, serde_json, api]
+importance: 0.5
+confidence: 0.8
+created: "2026-02-28T04:58:15.771467+00:00"
+updated: "2026-02-28T04:58:15.771467+00:00"
+---
+
+# Fix: reqwest JSON Error Type Mismatch
+
+## Problem
+
+When using `response.json::<T>().await`, JSON decode failures produce a `reqwest::Error` — not a `serde_json::Error`. This means a custom error variant like:
+
+```rust
+#[derive(Debug, thiserror::Error)]
+enum ApiError {
+    #[error("Parse error: {0}")]
+    Parse(#[from] serde_json::Error),
+    // ...
+}
+```
+
+...is **unreachable** if you only call `response.json()`. The `#[from]` impl exists but can never fire.
+
+## Fix
+
+Decode manually in two steps so the `serde_json::Error` is produced directly:
+
+```rust
+let body = response.text().await.map_err(ApiError::Request)?;
+let data = serde_json::from_str::<T>(&body).map_err(ApiError::Parse)?;
+```
+
+## Why It Matters
+
+This lets callers distinguish **network errors** (connection dropped, timeout) from **JSON parse errors** (malformed response, schema mismatch). With `response.json()`, both collapse into `reqwest::Error` and you lose that distinction.
+
+## Context
+
+Caught during code review of `api/client.rs` in SBA Scout Rust rewrite Phase 2.