1 files changed, 23 insertions, 4 deletions
diff --git a/libpanto/src/conversation.zig b/libpanto/src/conversation.zig
index 0e9a4e9..6776412 100644
--- a/libpanto/src/conversation.zig
+++ b/libpanto/src/conversation.zig
@@ -13,6 +13,22 @@ pub fn textualBlockFromSlice(alloc: Allocator, slice: []const u8) !TextualBlock
     return buf;
 }
 
+/// A reasoning/thinking block from the assistant.
+///
+/// `text` is the streamed reasoning content. `signature` is the opaque
+/// integrity token Anthropic emits with extended-thinking responses and
+/// requires echoed back verbatim on follow-up turns. It is optional because
+/// other providers (OpenAI-compatible APIs) do not produce it.
+pub const ThinkingBlock = struct {
+    text: TextualBlock = .empty,
+    signature: ?[]const u8 = null,
+
+    pub fn deinit(self: *ThinkingBlock, alloc: Allocator) void {
+        self.text.deinit(alloc);
+        if (self.signature) |sig| alloc.free(sig);
+    }
+};
+
 pub const ToolUseBlock = struct {
     id: []const u8,
     name: []const u8,
@@ -37,13 +53,16 @@ pub const ToolResultBlock = struct {
 
 pub const ContentBlock = union(enum) {
     Text: TextualBlock,
-    Thinking: TextualBlock,
+    Thinking: ThinkingBlock,
     ToolUse: ToolUseBlock,
     ToolResult: ToolResultBlock,
 
     pub fn deinit(self: *ContentBlock, alloc: Allocator) void {
         switch (self.*) {
-            inline else => |*b| b.deinit(alloc),
+            .Text => |*b| b.deinit(alloc),
+            .Thinking => |*b| b.deinit(alloc),
+            .ToolUse => |*b| b.deinit(alloc),
+            .ToolResult => |*b| b.deinit(alloc),
         }
     }
 };
@@ -175,11 +194,11 @@ test "ContentBlock - Thinking variant" {
     defer conv.deinit();
 
     try conv.addAssistantMessage(&.{
-        .{ .Thinking = try textualBlockFromSlice(allocator, "hmm...") },
+        .{ .Thinking = .{ .text = try textualBlockFromSlice(allocator, "hmm...") } },
         .{ .Text = try textualBlockFromSlice(allocator, "answer") },
     });
 
     try std.testing.expectEqual(@as(usize, 2), conv.messages.items[0].content.items.len);
-    try std.testing.expectEqualStrings("hmm...", conv.messages.items[0].content.items[0].Thinking.items);
+    try std.testing.expectEqualStrings("hmm...", conv.messages.items[0].content.items[0].Thinking.text.items);
     try std.testing.expectEqualStrings("answer", conv.messages.items[0].content.items[1].Text.items);
 }