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.

2 files changed, 10 insertions, 10 deletions

diff --git a/src/main.zig b/src/main.zig
index 61a88bd..2887730 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -358,7 +358,7 @@ pub fn main(init: std.process.Init) !void {
     // On resume, reconstruct the conversation from the store. (The
     // dangling-prompt recovery feature was dropped in R2.) On a fresh
     // session, the agent starts with an empty conversation.
-    var adopted_conversation: ?panto.ConversationData = null;
+    var adopted_conversation: ?panto.Conversation = null;
     if (is_resume) {
         adopted_conversation = try session.load();
         const sid = session.info.id;
diff --git a/src/system_prompt.zig b/src/system_prompt.zig
index 39c3ea8..eea0b97 100644
--- a/src/system_prompt.zig
+++ b/src/system_prompt.zig
@@ -193,7 +193,7 @@ pub fn reconcileResumeLayers(
     const resolved = try resolveLayers(arena, io, base_dir, user_dir, project_dir);
     const config_blocks = try resolved.blocks(arena);
 
-    const window = try effectiveConfigWindow(arena, agent.conversation().messages());
+    const window = try effectiveConfigWindow(arena, agent.conversation().messages.items);
 
     if (blocksEqual(config_blocks, window)) return;
 
@@ -339,7 +339,7 @@ test "blocksEqual - length and content" {
 
 test "effectiveConfigWindow - no replace anchors to leading system blocks" {
     const alloc = testing.allocator;
-    var conv = panto.ConversationData.init(alloc);
+    var conv = panto.Conversation.init(alloc);
     defer conv.deinit();
 
     try conv.addSystemMessage("seed");
@@ -357,7 +357,7 @@ test "effectiveConfigWindow - no replace anchors to leading system blocks" {
 
 test "effectiveConfigWindow - anchors to last replace block" {
     const alloc = testing.allocator;
-    var conv = panto.ConversationData.init(alloc);
+    var conv = panto.Conversation.init(alloc);
     defer conv.deinit();
 
     try conv.addSystemMessage("old seed");
@@ -483,7 +483,7 @@ const SPAgentHarness = struct {
     fn init(
         self: *SPAgentHarness,
         session: panto.Session,
-        adopted: ?panto.ConversationData,
+        adopted: ?panto.Conversation,
     ) !void {
         self.config = .{
             .provider = .{ .openai_chat = .{ .api_key = "k", .base_url = "u", .model = "m" } },
@@ -502,9 +502,9 @@ const SPAgentHarness = struct {
     /// memory until the first assistant message; a realistic resume only
     /// sees what a completed turn persisted.)
     fn forceFlush(self: *SPAgentHarness) !void {
-        var conv = panto.ConversationData.init(testing.allocator);
+        var conv = panto.Conversation.init(testing.allocator);
         defer conv.deinit();
-        try conv.addAssistantMessage(&.{});
+        try conv.addAssistantMessage(&.{}, null);
         const id: panto.WireIdentity = .{ .api_style = .openai_chat, .base_url = "u", .model = "m" };
         var batch = [_]panto.PersistentMessage{
             .{ .message = conv.messages.items[0], .identity = id },
@@ -557,7 +557,7 @@ test "seedFresh then no-config-change resume is a no-op" {
     try h2.init(sess2, conv2);
     defer h2.deinit();
     try reconcileResumeLayers(arena, testing.io, null, null, project_dir, h2.agent);
-    const eff_after = try panto.effectiveSystemBlocks(arena, h2.agent.conversation().messages());
+    const eff_after = try panto.effectiveSystemBlocks(arena, h2.agent.conversation().messages.items);
     try testing.expectEqual(seeded_count, eff_after.items.len);
 }
 
@@ -600,7 +600,7 @@ test "resume after config change appends replace + append sequence" {
     try reconcileResumeLayers(arena, testing.io, null, null, project_dir, h2.agent);
 
     // The effective prompt now reflects only the new config blocks.
-    const eff = try panto.effectiveSystemBlocks(arena, h2.agent.conversation().messages());
+    const eff = try panto.effectiveSystemBlocks(arena, h2.agent.conversation().messages.items);
     try testing.expectEqual(@as(usize, 2), eff.items.len);
     try testing.expectEqualStrings("new seed", eff.items[0]);
     try testing.expectEqualStrings("new append", eff.items[1]);
@@ -608,7 +608,7 @@ test "resume after config change appends replace + append sequence" {
     // A second no-op resume must not change the effective prompt (anchors
     // to the new `replace` window, not the stale original seed).
     try reconcileResumeLayers(arena, testing.io, null, null, project_dir, h2.agent);
-    const eff2 = try panto.effectiveSystemBlocks(arena, h2.agent.conversation().messages());
+    const eff2 = try panto.effectiveSystemBlocks(arena, h2.agent.conversation().messages.items);
     try testing.expectEqual(@as(usize, 2), eff2.items.len);
 }