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, 1 insertions, 1 deletions

diff --git a/src/compaction.zig b/src/compaction.zig
index 4ec5732..5d64f98 100644
--- a/src/compaction.zig
+++ b/src/compaction.zig
@@ -22,7 +22,7 @@ pub fn register(registry: *command.Registry) !void {
 fn run(args: []const u8, ctx: *command.Context) anyerror!void {
     const extra: ?[]const u8 = if (args.len > 0) args else null;
 
-    const res = ctx.agent.compactAndPersist(ctx.compaction_prompt, extra) catch |err| {
+    const res = ctx.agent.compact(ctx.compaction_prompt, extra) catch |err| {
         try ctx.stdout.print("\n[compaction failed: {s}]\n> ", .{@errorName(err)});
         try ctx.stdout_file.flush();
         return;