Alias Conversation instead of facading it; merge addAssistantMessage

A facade that forwards every method 1:1 is worse than paring the real type
down to the intended surface and aliasing it. conversation.Conversation's
interface is already the public surface we want (init/deinit, the
add*/replace* builders, and messages/allocator as plain data fields), so
public.zig now aliases it straight through and Agent.conversation() returns
a borrowed *Conversation for in-place surgery. Drops the ConversationData
alias and the pointer-wrapper.

Merged addAssistantMessageWithUsage into addAssistantMessage(blocks, ?usage)
on the real type (separate method deleted), so the alias has the intended
one-method shape; all call sites updated.

Only Agent and Stream remain true facades -- they have genuinely-internal
fields plus API-shaping renames (Stream.phase->state, Phase->State) an alias
can't express.

1 files changed, 11 insertions, 11 deletions

diff --git a/libpanto/src/agent.zig b/libpanto/src/agent.zig
index 6d62b8a..45347ea 100644
--- a/libpanto/src/agent.zig
+++ b/libpanto/src/agent.zig
@@ -1552,7 +1552,7 @@ const StubResponse = struct {
         }
         const moved = try blocks.toOwnedSlice(self.allocator);
         defer self.allocator.free(moved);
-        try self.conv.addAssistantMessageWithUsage(moved, self.turn.usage);
+        try self.conv.addAssistantMessage(moved, self.turn.usage);
 
         const msg = self.conv.messages.items[self.conv.messages.items.len - 1];
         try out.push(.{ .message_complete = .{ .message = msg, .usage = self.turn.usage } });
@@ -2651,11 +2651,11 @@ test "compact: summarizes prefix, keeps suffix, system survives" {
     try conv.addUserMessage("first question here with several words");
     try conv.addAssistantMessage(&.{
         .{ .Text = try conversation.textualBlockFromSlice(allocator, "first answer with several words") },
-    });
+    }, null);
     try conv.addUserMessage("second recent question");
     try conv.addAssistantMessage(&.{
         .{ .Text = try conversation.textualBlockFromSlice(allocator, "second recent answer") },
-    });
+    }, null);
 
     const res = try agent.compact("Summarize the conversation.", null);
     try testing.expect(res.compacted);
@@ -2714,21 +2714,21 @@ test "compact: restated suffix usage reconstructs a fresh cumulative chain" {
     // = 600. Its real usage (with cache buckets) is irrelevant
     // post-compaction.
     try conv.addUserMessage("first question here with several words");
-    try conv.addAssistantMessageWithUsage(
+    try conv.addAssistantMessage(
         &.{.{ .Text = try conversation.textualBlockFromSlice(allocator, "first answer with words") }},
         .{ .input = 500, .output = 50, .cache_read = 40, .cache_write = 10 },
     );
     // Kept turn 1: cumulative 608 (delta 8 over prefix). Reasoning is a
     // subset of output.
     try conv.addUserMessage("kept question"); // 2 words => ceil(2*1.3)=3 tokens
-    try conv.addAssistantMessageWithUsage(
+    try conv.addAssistantMessage(
         &.{.{ .Text = try conversation.textualBlockFromSlice(allocator, "kept answer") }},
         .{ .input = 600, .output = 8, .reasoning = 5 },
     );
     // Kept turn 2: cumulative 614 (delta 6). Cache buckets present to prove
     // they collapse into `input` on restatement.
     try conv.addUserMessage("two more words here"); // 4 words => ceil(4*1.3)=6
-    try conv.addAssistantMessageWithUsage(
+    try conv.addAssistantMessage(
         &.{.{ .Text = try conversation.textualBlockFromSlice(allocator, "final answer") }},
         .{ .input = 600, .output = 4, .cache_read = 8, .cache_write = 2 },
     );
@@ -2788,7 +2788,7 @@ test "compact: no-op when conversation already fits the budget" {
     try conv.addUserMessage("hi");
     try conv.addAssistantMessage(&.{
         .{ .Text = try conversation.textualBlockFromSlice(allocator, "hello") },
-    });
+    }, null);
 
     const res = try agent.compact("Summarize.", null);
     try testing.expect(!res.compacted);
@@ -2825,11 +2825,11 @@ test "compact: extra instructions are appended to the system prompt" {
     try conv.addUserMessage("question one two three");
     try conv.addAssistantMessage(&.{
         .{ .Text = try conversation.textualBlockFromSlice(allocator, "answer one two three") },
-    });
+    }, null);
     try conv.addUserMessage("question two");
     try conv.addAssistantMessage(&.{
         .{ .Text = try conversation.textualBlockFromSlice(allocator, "answer two") },
-    });
+    }, null);
 
     const res = try agent.compact("Base prompt.", "keep bug #3 details");
     try testing.expect(res.compacted);
@@ -2867,7 +2867,7 @@ test "runStep: auto-compacts on context overflow and retries once" {
     try conv.addUserMessage("first question with several words here");
     try conv.addAssistantMessage(&.{
         .{ .Text = try conversation.textualBlockFromSlice(allocator, "first answer with several words") },
-    });
+    }, null);
 
     try drainTurn(&agent, "second recent question");
 
@@ -3247,7 +3247,7 @@ test "runStep: context-overflow compaction fires a compaction retry notification
     try conv.addUserMessage("first question with several words here");
     try conv.addAssistantMessage(&.{
         .{ .Text = try conversation.textualBlockFromSlice(allocator, "first answer with several words") },
-    });
+    }, null);
 
     var rr = RetryRecorder{ .allocator = allocator };
     defer rr.deinit();