Merge pull request #3073 from lightpanda-io/agent-tool-cap

agent: reduce tool output cap to 64KB except for extract

src/agent/Agent.zig

@@ -1535,7 +1535,7 @@ fn recordSlashToolCall(
 
     // capToolOutput returns its input unchanged under the cap; dupe so content
     // doesn't alias the caller's per-iteration arena.
-    const capped = capToolOutput(ma, result.text);
+    const capped = capToolOutput(ma, tool_name, result.text);
     const content = if (capped.ptr == result.text.ptr) try ma.dupe(u8, capped) else capped;
 
     const tool_results = try ma.alloc(zenai.provider.ToolResult, 1);
@@ -1807,15 +1807,23 @@ fn buildUserMessageParts(
     return parts.toOwnedSlice(ma);
 }
 
-// Cap per-call tool output so heavy pages don't balloon the message arena (and
-// the next request body) without bound.
-const tool_output_max_bytes: usize = 1 * 1024 * 1024;
+// Tool results are re-sent with every subsequent turn, so an unscoped read of
+// a huge page is paid once per remaining turn — the cap bounds that growth.
+// `extract` is exempt up to the loose backstop: its output is schema-shaped
+// JSON the model explicitly asked for, and truncation would corrupt it.
+const tool_output_max_bytes: usize = 64 * 1024;
+const extract_output_max_bytes: usize = 1024 * 1024;
 
-fn capToolOutput(allocator: std.mem.Allocator, output: []const u8) []const u8 {
-    if (output.len <= tool_output_max_bytes) return output;
-    const prefix = string.truncateUtf8(output, tool_output_max_bytes);
-    var suffix_buf: [64]u8 = undefined;
-    const suffix = std.fmt.bufPrint(&suffix_buf, "\n...[truncated, original {d} bytes]", .{output.len}) catch return prefix;
+fn toolOutputCap(tool_name: []const u8) usize {
+    return if (std.mem.eql(u8, tool_name, "extract")) extract_output_max_bytes else tool_output_max_bytes;
+}
+
+fn capToolOutput(allocator: std.mem.Allocator, tool_name: []const u8, output: []const u8) []const u8 {
+    const cap = toolOutputCap(tool_name);
+    if (output.len <= cap) return output;
+    const prefix = string.truncateUtf8(output, cap);
+    var suffix_buf: [128]u8 = undefined;
+    const suffix = std.fmt.bufPrint(&suffix_buf, "\n...[truncated, original {d} bytes — re-read scoped (selector/backendNodeId)]", .{output.len}) catch return prefix;
     return std.mem.concat(allocator, u8, &.{ prefix, suffix }) catch prefix;
 }
 
@@ -1836,7 +1844,7 @@ fn handleToolCall(ctx: *anyopaque, allocator: std.mem.Allocator, tool_name: []co
     defer self.terminal.spinner.setThinking();
 
     const outcome: zenai.provider.Client.ToolHandler.Result = if (browser_tools.call(allocator, self.session, &self.node_registry, tool_name, arguments)) |result|
-        .{ .content = capToolOutput(allocator, result.text), .is_error = result.is_error }
+        .{ .content = capToolOutput(allocator, tool_name, result.text), .is_error = result.is_error }
     else |err|
         .{ .content = std.fmt.allocPrint(allocator, "Error: {s}", .{@errorName(err)}) catch "Error: tool execution failed", .is_error = true };
 
@@ -1952,7 +1960,7 @@ test "savePrompt: save instructions followed by the rendered script skill" {
 
 test "capToolOutput: passes through when under cap" {
     const ta = std.testing.allocator;
-    const out = capToolOutput(ta, "short");
+    const out = capToolOutput(ta, "markdown", "short");
     try std.testing.expectEqualStrings("short", out);
 }
 
@@ -1972,9 +1980,23 @@ test "capToolOutput: appends a marker when truncating" {
     buf[cap + 1] = 0x9C;
     @memset(buf[cap + 2 ..], 'b');
 
-    const out = capToolOutput(ta, buf);
+    const out = capToolOutput(ta, "markdown", buf);
     defer if (out.ptr != buf.ptr) ta.free(out);
 
     try std.testing.expect(std.unicode.utf8ValidateSlice(out));
     try std.testing.expect(std.mem.indexOf(u8, out, "truncated") != null);
 }
+
+test "capToolOutput: extract is exempt from the default cap" {
+    const ta = std.testing.allocator;
+
+    const buf = try ta.alloc(u8, tool_output_max_bytes + 8);
+    defer ta.free(buf);
+    @memset(buf, 'a');
+
+    const out = capToolOutput(ta, "extract", buf);
+    try std.testing.expect(out.ptr == buf.ptr);
+
+    try std.testing.expectEqual(extract_output_max_bytes, toolOutputCap("extract"));
+    try std.testing.expectEqual(tool_output_max_bytes, toolOutputCap("html"));
+}