1 files changed, 65 insertions, 2 deletions

diff --git a/libpanto/src/provider_anthropic_messages.zig b/libpanto/src/provider_anthropic_messages.zig
index 9740c0e..be4268e 100644
--- a/libpanto/src/provider_anthropic_messages.zig
+++ b/libpanto/src/provider_anthropic_messages.zig
@@ -187,6 +187,7 @@ pub const ResumableResponse = struct {
     const vtable: provider_mod.ProviderStream.VTable = .{
         .produce = produceVT,
         .deinit = deinitVT,
+        .last_error = lastErrorVT,
     };
 
     fn produceVT(ptr: *anyopaque, out: *EventQueue) anyerror!ProduceStatus {
@@ -194,6 +195,11 @@ pub const ResumableResponse = struct {
         return self.produce(out);
     }
 
+    fn lastErrorVT(ptr: *anyopaque) ?[]const u8 {
+        const self: *ResumableResponse = @ptrCast(@alignCast(ptr));
+        return self.state.stream_error_message;
+    }
+
     fn deinitVT(ptr: *anyopaque) void {
         const self: *ResumableResponse = @ptrCast(@alignCast(ptr));
         self.deinit();
@@ -274,6 +280,10 @@ const StreamState = struct {
     usage: provider_mod.Usage = .{},
     usage_seen: bool = false,
     stop_reason: ?[]u8 = null,
+    /// Owned, human-readable description of a mid-stream `error` event
+    /// (e.g. `"overloaded_error: Overloaded"`), surfaced to the agent via
+    /// `ProviderStream.lastError` so the retry notice can show *why*.
+    stream_error_message: ?[]u8 = null,
 
     const ActiveBlock = struct {
         /// Index reported on the wire (Anthropic's content-array index).
@@ -304,6 +314,7 @@ const StreamState = struct {
         for (self.blocks.items) |*b| b.deinit(self.allocator);
         self.blocks.deinit(self.allocator);
         if (self.stop_reason) |s| self.allocator.free(s);
+        if (self.stream_error_message) |s| self.allocator.free(s);
     }
 
     fn ensureStarted(self: *StreamState, out: *EventQueue) !void {
@@ -435,6 +446,22 @@ const StreamState = struct {
         self.stop_reason = if (reason) |r| try self.allocator.dupe(u8, r) else null;
     }
 
+    /// Record a readable description of a mid-stream `error` event, combining
+    /// the error `kind` and `message` into one owned string (either may be
+    /// absent). Replaces any previous value.
+    fn setStreamErrorMessage(self: *StreamState, kind: ?[]const u8, message: ?[]const u8) !void {
+        if (self.stream_error_message) |old| self.allocator.free(old);
+        self.stream_error_message = null;
+        self.stream_error_message = if (kind != null and message != null)
+            try std.fmt.allocPrint(self.allocator, "{s}: {s}", .{ kind.?, message.? })
+        else if (kind) |k|
+            try self.allocator.dupe(u8, k)
+        else if (message) |m|
+            try self.allocator.dupe(u8, m)
+        else
+            null;
+    }
+
     /// Close the active block: append it to `blocks` and emit block_complete.
     fn closeBlock(
         self: *StreamState,
@@ -576,8 +603,17 @@ fn handleEvent(
             if (!@import("builtin").is_test) {
                 std.log.err("anthropic stream error: {?s}: {?s}", .{ e.kind, e.message });
             }
-            // Mid-stream error event (e.g. `overloaded_error`) before the
-            // message was committed: retryable malformed-stream failure.
+            // Stash a readable description so the agent's retry notice can
+            // explain *why* the stream failed instead of only showing the
+            // bare error name. Owned by `state`; freed in `deinit`.
+            state.setStreamErrorMessage(e.kind, e.message) catch {};
+            // Mid-stream error event before the message was committed. Map
+            // the common overload case to a dedicated retryable error so the
+            // UI can say "overloaded" rather than "malformed stream"; other
+            // kinds stay as the generic retryable malformed-stream error.
+            if (e.kind) |k| {
+                if (std.mem.eql(u8, k, "overloaded_error")) return error.ProviderOverloaded;
+            }
             return error.ProviderStreamMalformed;
         },
         .unknown => {
@@ -1073,7 +1109,34 @@ test "error event propagates as Zig error" {
         &state,
         &queue,
     );
+    // `overloaded_error` maps to the dedicated retryable error, and the
+    // provider's diagnostic is stashed for the agent's retry notice.
+    try testing.expectError(error.ProviderOverloaded, result);
+    try testing.expectEqualStrings("overloaded_error: too busy", state.stream_error_message.?);
+}
+
+test "non-overloaded error event stays malformed and stashes message" {
+    const allocator = testing.allocator;
+
+    var conv = conversation.Conversation.init(allocator);
+    defer conv.deinit();
+    try addUserText(&conv, "hi");
+
+    var queue = EventQueue.init(allocator);
+    defer queue.deinit();
+
+    var state: StreamState = .init(allocator);
+    defer state.deinit();
+
+    const result = handleEvent(
+        allocator,
+        \\{"type":"error","error":{"type":"api_error","message":"boom"}}
+    ,
+        &state,
+        &queue,
+    );
     try testing.expectError(error.ProviderStreamMalformed, result);
+    try testing.expectEqualStrings("api_error: boom", state.stream_error_message.?);
 }
 
 test "two streamed turns persist assistant replies in the conversation" {