Plug the deep-embedder holes; remove public.zig escape hatch

Close the gap that forced the CLI to import internal libpanto namespaces,
then delete the transitional re-exports. The CLI now uses only the curated
public surface.

Additions to the public Agent facade:
- init/deinit (heap-pin the inner; the handle is a copyable value).
- addSystemMessage (.append) and setSystemPrompt (.replace).
- compact(override_system_prompt, extra) falling back to the config prompt.
- sessionId() accessor.

CompactionConfig gains compaction_prompt, which owns the compaction system
prompt for both auto-compaction and the explicit compact() default; the
Agent.compaction_system_prompt field is deleted. ConversationData is the
public name for the owned conversation value type (Session.load returns it,
Agent.init adopts it), distinct from the borrowed Conversation handle.

Agent.addSystemMessage/setSystemPrompt are kept on Agent (they persist with
the SystemMode) rather than dropped as the plan first proposed.

1 files changed, 11 insertions, 9 deletions

diff --git a/src/main.zig b/src/main.zig
index 995735f..61a88bd 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -144,7 +144,7 @@ const CLIRenderer = struct {
 /// it terminates (`turn_complete` → `next()` returns null). A failure
 /// surfaces as the error from `next()`; the caller renders it. The stream is
 /// always `deinit`ed (persisting the turn tail) on every exit path.
-fn driveTurn(agent: *panto.agent.Agent, message: panto.agent.Agent.UserMessage, renderer: *CLIRenderer) !void {
+fn driveTurn(agent: panto.Agent, message: panto.UserMessage, renderer: *CLIRenderer) !void {
     var stream = try agent.run(message);
     defer stream.deinit();
     while (try stream.next()) |ev| try renderer.render(ev);
@@ -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.conversation.Conversation = null;
+    var adopted_conversation: ?panto.ConversationData = null;
     if (is_resume) {
         adopted_conversation = try session.load();
         const sid = session.info.id;
@@ -376,11 +376,11 @@ pub fn main(init: std.process.Init) !void {
     // built but before the first turn, so in-place registration is visible.
     // System-prompt seeding/reconciliation below runs *through* the agent
     // so those entries persist.
-    const active_config: panto.Config = .{
+    var active_config: panto.Config = .{
         .provider = provider_config,
         .compaction = compaction_cfg,
     };
-    var agent = panto.agent.Agent.init(
+    const agent = try panto.Agent.init(
         alloc,
         io,
         &active_config,
@@ -424,7 +424,7 @@ pub fn main(init: std.process.Init) !void {
             io,
             init.environ_map,
             luarocks_rt.layout.agent_dir,
-            &agent,
+            agent,
         );
     } else {
         // Fresh session — source and install the system prompt.
@@ -433,7 +433,7 @@ pub fn main(init: std.process.Init) !void {
             io,
             init.environ_map,
             luarocks_rt.layout.agent_dir,
-            &agent,
+            agent,
         );
     }
 
@@ -476,7 +476,9 @@ pub fn main(init: std.process.Init) !void {
         init.environ_map,
         luarocks_rt.layout.agent_dir,
     );
-    agent.compaction_system_prompt = compaction_prompt;
+    // The compaction prompt is resolved after extension load; set it on the
+    // config the agent re-reads each turn (visible before the first turn).
+    active_config.compaction.compaction_prompt = compaction_prompt;
 
     const banner_base: []const u8 = switch (provider_config) {
         inline else => |c| c.base_url,
@@ -521,7 +523,7 @@ pub fn main(init: std.process.Init) !void {
 
     var cmd_ctx: command.Context = .{
         .allocator = alloc,
-        .agent = &agent,
+        .agent = agent,
         .stdout = stdout,
         .stdout_file = &stdout_file,
         .compaction_prompt = compaction_prompt,
@@ -570,7 +572,7 @@ pub fn main(init: std.process.Init) !void {
         // auto-compaction) through its session store — the CLI no longer
         // touches persistence.
         cli_renderer.beginTurn();
-        driveTurn(&agent, .{ .text = line }, &cli_renderer) catch |err| {
+        driveTurn(agent, .{ .text = line }, &cli_renderer) catch |err| {
             cli_renderer.renderError(err);
             try stdout.print("\n[error: {s}]\n", .{@errorName(err)});
         };