1 files changed, 21 insertions, 0 deletions
diff --git a/libpanto/src/provider_anthropic_messages.zig b/libpanto/src/provider_anthropic_messages.zig
index 03c1d90..96649b6 100644
--- a/libpanto/src/provider_anthropic_messages.zig
+++ b/libpanto/src/provider_anthropic_messages.zig
@@ -283,6 +283,15 @@ const StreamState = struct {
         };
         if (block_type) |bt| {
             try receiver.onBlockStart(bt, wire_index);
+            // Anthropic delivers tool id+name whole on content_block_start,
+            // so we can fire onToolDetails immediately — before any arg
+            // deltas. If the wire was malformed and either field is
+            // missing, skip: closeBlock will drop the block defensively.
+            if (kind == .tool_use) {
+                if (ab.tool_id != null and ab.tool_name != null) {
+                    try receiver.onToolDetails(wire_index, ab.tool_id.?, ab.tool_name.?);
+                }
+            }
         }
     }
 
@@ -506,6 +515,7 @@ const RecordingReceiver = struct {
     const vt: provider_mod.ReceiverVTable = .{
         .onMessageStart = onMessageStart,
         .onBlockStart = onBlockStart,
+        .onToolDetails = onToolDetails,
         .onContentDelta = onContentDelta,
         .onBlockComplete = onBlockComplete,
         .onMessageComplete = onMessageComplete,
@@ -524,6 +534,17 @@ const RecordingReceiver = struct {
         const self: *RecordingReceiver = @ptrCast(@alignCast(ptr));
         try self.events.append(self.allocator, .{ .block_start = .{ .kind = bt, .index = idx } });
     }
+    fn onToolDetails(
+        _: *anyopaque,
+        _: usize,
+        _: []const u8,
+        _: []const u8,
+    ) anyerror!void {
+        // Anthropic delivers identity at block_start time; the existing
+        // tests assert tool-use blocks via the ContentBlock in conv after
+        // finalize, not via the event stream. We accept and drop these
+        // here to keep the test recorder schema stable.
+    }
     fn onContentDelta(ptr: *anyopaque, idx: usize, delta: []const u8) anyerror!void {
         const self: *RecordingReceiver = @ptrCast(@alignCast(ptr));
         const copy = try self.allocator.dupe(u8, delta);