Sync Agent/Stream internals to public names; alias Stream

Push the API-shaping we'd done in the public facade down into the internal
types, collapsing the wrappers:

- Stream: rename phase->state, Phase->State; underscore-prefix the internal
  fields (_agent/_queue/_response/_start/_persisted/_pending_error). state
  is the one intended-public field. public.zig now aliases Stream; run
  returns *Stream.
- Agent compaction: pure transform compact()->private _compactInPlace;
  compactAndPersist()->compact() (the public name, persists).
- Agent system prompt: addSystemMessage(text,mode) split into
  addSystemMessage(text) + setSystemPrompt(text) over a private
  _persistSystemMessage.
- UserMessage moved off Agent to module scope.
- Underscore-prefix pure-internal Agent fields: _open_stream_fn,
  _auto_compacted, _retry_prng.

The Agent facade is now pure 1:1 forwarders; it stays a wrapper only because
init heap-pins the inner (copyable, move-safe handle) and conversation()/
sessionId() are accessors. Conversation and Stream are plain aliases.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/main.zig b/src/main.zig
index 2887730..a4d524b 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -99,7 +99,7 @@ const CLIRenderer = struct {
                 switch (b.block) {
                     .Thinking => try self.stdout.writeAll("\x1b[0m\n"),
                     // Append the tool name now that we know it for certain.
-                    .ToolUse => |tu| try self.stdout.print("\x1b[36m : ({s})\x1b[0m\n", .{tu.name}),
+                    .ToolUse => |tu| try self.stdout.print("\x1b[36m : ({s})\x1b[0m", .{tu.name}),
                     else => {},
                 }
                 try self.file.flush();