Catch stack unwinds in /answer endpoint (BloopAI#545)

* Catch unwind in answer API

Due to the design of the `EventStream` web API, browsers will attempt to
reconnect when a connection is closed. The bloop client has special logic
to prevent this, but only when an error occurs in the stream, signalled
by a serialized error, or when the `[DONE]` message is encountered.
Previously, when the HTTP handler panicked, this would result in a
logged message and a closed stream, as an error would fail to be
transmitted.

Now, we catch stack unwinds, and return an error to the client, so that
we can ensure its error handling logic is triggered in order to display
a proper error message, and to stop automatically reconnecting to the
event stream endpoint.

* remove tauri test

---------

Co-authored-by: Gabriel Gordon-Hall <[email protected]>

server/bleep/src/webserver/answer.rs

@@ -2,6 +2,7 @@ use std::{
     borrow::Cow,
     collections::{HashMap, HashSet},
     mem,
+    panic::AssertUnwindSafe,
     path::{Component, PathBuf},
     str::FromStr,
     time::Duration,
@@ -179,11 +180,15 @@ pub(super) async fn _handle(
         Ok(sse::Event::default().data(params.thread_id.to_string()))
     });
 
-    let answer_stream = stream.map(|upd: Result<Exchange>| {
-        sse::Event::default()
-            .json_data(upd.map_err(|e| e.to_string()))
-            .map_err(anyhow::Error::new)
-    });
+    // We know the stream is unwind safe as it doesn't use synchronization primitives like locks.
+    let answer_stream = AssertUnwindSafe(stream)
+        .catch_unwind()
+        .map(|res| res.unwrap_or_else(|_| Err(anyhow!("stream panicked"))))
+        .map(|upd: Result<Exchange>| {
+            sse::Event::default()
+                .json_data(upd.map_err(|e| e.to_string()))
+                .map_err(anyhow::Error::new)
+        });
 
     let done_stream = futures::stream::once(async { Ok(sse::Event::default().data("[DONE]")) });