From 9c64a7d4462a11674e2dea481b037b5f5d9c62fc Mon Sep 17 00:00:00 2001
From: t <t@tjp.lol>
Date: Tue, 2 Jun 2026 09:02:49 -0600
Subject: system prompt building and logging

---
 libpanto/src/openai_chat_json.zig | 79 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)

(limited to 'libpanto/src/openai_chat_json.zig')

diff --git a/libpanto/src/openai_chat_json.zig b/libpanto/src/openai_chat_json.zig
index 6991559..3b81c41 100644
--- a/libpanto/src/openai_chat_json.zig
+++ b/libpanto/src/openai_chat_json.zig
@@ -140,7 +140,24 @@ pub fn serializeRequest(
 
     try s.objectField("messages");
     try s.beginArray();
+    // Hoist the effective system prompt to the front as separate,
+    // individually-positioned `system` messages (one per surviving block,
+    // in derivation order). Keeping them distinct preserves block-level
+    // addressability for `/tree`-style truncation — we deliberately do NOT
+    // concatenate them the way Anthropic's single-string format forces.
+    var sys_blocks = try conversation.effectiveSystemBlocks(allocator, conv.messages.items);
+    defer sys_blocks.deinit(allocator);
+    for (sys_blocks.items) |text| {
+        try s.beginObject();
+        try s.objectField("role");
+        try s.write("system");
+        try s.objectField("content");
+        try s.write(text);
+        try s.endObject();
+    }
+    // Then every non-system message, in its original order.
     for (conv.messages.items) |msg| {
+        if (msg.role == .system) continue;
         try writeMessage(&s, msg, allocator);
     }
     try s.endArray();
@@ -497,6 +514,68 @@ test "serializeRequest - system + user" {
     try testing.expectEqualStrings("Hello!", msgs[1].object.get("content").?.string);
 }
 
+test "serializeRequest - multiple system blocks hoisted as separate leading messages" {
+    const allocator = testing.allocator;
+
+    var conv = conversation.Conversation.init(allocator);
+    defer conv.deinit();
+
+    try conv.addSystemMessage("seed");
+    try conv.addUserMessage("Hello!");
+    try conv.addSystemMessage("mid-conversation append");
+    try conv.addUserMessage("again");
+
+    const cfg = testConfig("gpt-4o");
+    var tools = emptyTools();
+    defer tools.deinit();
+    const body = try serializeRequest(allocator, &cfg, &conv, &tools);
+    defer allocator.free(body);
+
+    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
+    defer parsed.deinit();
+
+    const msgs = parsed.value.object.get("messages").?.array.items;
+    // Two system messages first (in derivation order), then the two users.
+    try testing.expectEqual(@as(usize, 4), msgs.len);
+    try testing.expectEqualStrings("system", msgs[0].object.get("role").?.string);
+    try testing.expectEqualStrings("seed", msgs[0].object.get("content").?.string);
+    try testing.expectEqualStrings("system", msgs[1].object.get("role").?.string);
+    try testing.expectEqualStrings("mid-conversation append", msgs[1].object.get("content").?.string);
+    try testing.expectEqualStrings("user", msgs[2].object.get("role").?.string);
+    try testing.expectEqualStrings("Hello!", msgs[2].object.get("content").?.string);
+    try testing.expectEqualStrings("user", msgs[3].object.get("role").?.string);
+    try testing.expectEqualStrings("again", msgs[3].object.get("content").?.string);
+}
+
+test "serializeRequest - replace-mode system block wipes prior system messages" {
+    const allocator = testing.allocator;
+
+    var conv = conversation.Conversation.init(allocator);
+    defer conv.deinit();
+
+    try conv.addSystemMessage("original");
+    try conv.replaceSystemMessage("fresh seed");
+    try conv.addSystemMessage("fresh append");
+    try conv.addUserMessage("Hi");
+
+    const cfg = testConfig("gpt-4o");
+    var tools = emptyTools();
+    defer tools.deinit();
+    const body = try serializeRequest(allocator, &cfg, &conv, &tools);
+    defer allocator.free(body);
+
+    var parsed = try std.json.parseFromSlice(std.json.Value, allocator, body, .{});
+    defer parsed.deinit();
+
+    const msgs = parsed.value.object.get("messages").?.array.items;
+    try testing.expectEqual(@as(usize, 3), msgs.len);
+    try testing.expectEqualStrings("system", msgs[0].object.get("role").?.string);
+    try testing.expectEqualStrings("fresh seed", msgs[0].object.get("content").?.string);
+    try testing.expectEqualStrings("system", msgs[1].object.get("role").?.string);
+    try testing.expectEqualStrings("fresh append", msgs[1].object.get("content").?.string);
+    try testing.expectEqualStrings("user", msgs[2].object.get("role").?.string);
+}
+
 test "serializeRequest - assistant Thinking blocks are stripped from outbound history" {
     const allocator = testing.allocator;
 
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