1 files changed, 31 insertions, 2 deletions

diff --git a/libpanto/src/agent.zig b/libpanto/src/agent.zig
index 08cc91c..a42c16c 100644
--- a/libpanto/src/agent.zig
+++ b/libpanto/src/agent.zig
@@ -43,6 +43,23 @@ const Entry = tool_registry_mod.Entry;
 
 pub const Config = config_mod.Config;
 
+fn isValidToolInput(input: []const u8) bool {
+    if (input.len == 0) return true;
+    if (input[0] != '{') return true; // legacy tests/tools may use opaque bytes
+    var parsed = std.json.parseFromSlice(std.json.Value, std.heap.page_allocator, input, .{}) catch return false;
+    defer parsed.deinit();
+    return parsed.value == .object;
+}
+
+fn invalidInputResult(allocator: Allocator, input: []const u8) ![]u8 {
+    return std.fmt.allocPrint(
+        allocator,
+        "Tool call was not executed: tool input was incomplete or invalid JSON. Partial input: {s}",
+        .{input},
+    );
+}
+
+
 pub const Agent = struct {
     allocator: Allocator,
     io: Io,
@@ -132,6 +149,17 @@ pub const Agent = struct {
         for (assistant_msg.content.items) |block| {
             if (block != .ToolUse) continue;
             const tu = block.ToolUse;
+            if (!isValidToolInput(tu.input.items)) {
+                try calls.append(.{
+                    .tool_use_id = tu.id,
+                    .tool_name = tu.name,
+                    .input = tu.input.items,
+                    .entry = null,
+                    .result = try invalidInputResult(self.allocator, tu.input.items),
+                    .err = null,
+                });
+                continue;
+            }
             const entry = self.config.registry.lookup(tu.name) orelse {
                 // Unknown tool: abort the turn with a clear error.
                 return error.UnknownTool;
@@ -236,7 +264,7 @@ const FlatCall = struct {
     tool_use_id: []const u8, // borrowed from assistant_msg
     tool_name: []const u8, // borrowed from assistant_msg
     input: []const u8, // borrowed from assistant_msg
-    entry: Entry,
+    entry: ?Entry,
 
     /// Owned result bytes from `Tool.invoke` or `ToolSource.invoke_batch`.
     /// Allocated with the agent's allocator. Transferred into a
@@ -292,7 +320,8 @@ fn buildGroups(
     }
 
     for (calls, 0..) |c, i| {
-        switch (c.entry) {
+        const ent = c.entry orelse continue;
+        switch (ent) {
             .single => |t| try out.append(.{ .single = .{ .tool = t, .call_index = i } }),
             .source => |sr| {
                 const gop = try pending.getOrPut(sr.source);