1 files changed, 14 insertions, 40 deletions

diff --git a/libpanto/src/provider_anthropic_messages.zig b/libpanto/src/provider_anthropic_messages.zig
index 5c24b8f..e77d6a5 100644
--- a/libpanto/src/provider_anthropic_messages.zig
+++ b/libpanto/src/provider_anthropic_messages.zig
@@ -110,6 +110,12 @@ pub const AnthropicMessagesRequest = struct {
                 @intFromEnum(response.head.status),
                 err_buf.items,
             });
+            // Anthropic rejects oversized requests with HTTP 400 and a
+            // "prompt is too long" message; surface as ContextOverflow so
+            // the caller can compact and retry.
+            if (@intFromEnum(response.head.status) == 400 and provider_mod.isContextOverflowBody(err_buf.items)) {
+                return error.ContextOverflow;
+            }
             return error.HttpError;
         }
 
@@ -329,35 +335,6 @@ const StreamState = struct {
         self.stop_reason = if (reason) |r| try self.allocator.dupe(u8, r) else null;
     }
 
-    fn isJSONObject(input: []const u8) bool {
-        if (input.len == 0) return true;
-        var parsed = std.json.parseFromSlice(std.json.Value, std.heap.page_allocator, input, .{}) catch return false;
-        defer parsed.deinit();
-        return parsed.value == .object;
-    }
-
-    fn appendAnthropicFailureResult(
-        allocator: Allocator,
-        blocks: *std.ArrayList(conversation.ContentBlock),
-        tool_use_id: []const u8,
-        input: []const u8,
-        stop_reason: ?[]const u8,
-    ) !void {
-        const id_copy = try allocator.dupe(u8, tool_use_id);
-        errdefer allocator.free(id_copy);
-        const msg = try std.fmt.allocPrint(
-            allocator,
-            "Tool call was not executed: Anthropic stopped before completing valid tool input JSON (stop_reason={s}). Partial input: {s}",
-            .{ stop_reason orelse "unknown", input },
-        );
-        errdefer allocator.free(msg);
-        var content: conversation.TextualBlock = .empty;
-        errdefer content.deinit(allocator);
-        try content.appendSlice(allocator, msg);
-        allocator.free(msg);
-        try blocks.append(allocator, .{ .ToolResult = .{ .tool_use_id = id_copy, .content = content } });
-    }
-
     /// Close the active block: append it to `blocks` and emit onBlockComplete.
     fn closeBlock(
         self: *StreamState,
@@ -391,16 +368,13 @@ const StreamState = struct {
                 .text = a.text_buf,
                 .signature = a.signature,
             } },
+            // An interrupted/malformed tool_use (incomplete or non-object
+            // input JSON) is preserved as-is. The agent's dispatch path
+            // detects invalid input and answers it with a synthetic error
+            // ToolResult in the *following user message* — emitting a
+            // ToolResult here would wrongly place it in this assistant
+            // message, which Anthropic rejects.
             .tool_use => blk: {
-                if (!isJSONObject(a.text_buf.items)) {
-                    try appendAnthropicFailureResult(
-                        self.allocator,
-                        &self.blocks,
-                        a.tool_id.?,
-                        a.text_buf.items,
-                        self.stop_reason,
-                    );
-                }
                 break :blk .{ .ToolUse = .{
                     .id = a.tool_id.?,
                     .name = a.tool_name.?,
@@ -444,10 +418,10 @@ const StreamState = struct {
         const moved_blocks = try self.blocks.toOwnedSlice(self.allocator);
         defer self.allocator.free(moved_blocks);
 
-        try conv.addAssistantMessage(moved_blocks);
+        const usage: ?provider_mod.Usage = if (self.usage_seen) self.usage else null;
+        try conv.addAssistantMessageWithUsage(moved_blocks, usage);
 
         const msg = conv.messages.items[conv.messages.items.len - 1];
-        const usage: ?provider_mod.Usage = if (self.usage_seen) self.usage else null;
         try receiver.onMessageComplete(msg, usage);
     }
 };