repl + renderer: streaming assistant output (Phase 1)

repl.ask_ai now drives broker.chat_stream and pumps each delta into
renderer.assistant_delta(delta) as it arrives. renderer.assistant_flush
is called when the stream ends to add a trailing newline if missing.
The full reassembled response is then handed to executor.extract_cmd_lines
for the CMD: confirm-and-execute path (unchanged from Phase 0).

renderer.assistant() is kept for non-streaming callers (none in tree
right now, but cheap to keep around). assistant_delta/flush share no
state with assistant(); they use a module-local stream_buf that tracks
the in-progress streamed block.

Q12 deferred: incremental CMD: highlighting (cursor-positioning re-
render on flush) is not implemented in Phase 1 — deltas emit raw. The
§6 CMD: marker is still extractable on the reassembled string post-
stream, which is what executor cares about. Renderer's bold+cyan
treatment for CMD: lines stays available via M.assistant().

Broker error / SSE-framed api-error path still pops the user turn and
restores ctx.pending_exec_output. Order: assistant_flush always runs
(even on error) so the cursor lands on a fresh line before the broker-
error status renders.

Live verification: `Count one to ten` against hossenfelder fast streams
deltas through to stdout incrementally; CMD: extraction works on the
reassembled string; confirm gate intact.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

renderer.lua

@@ -1,7 +1,10 @@
 -- renderer.lua — output formatting and ANSI sequences.
 -- Phase 0: assistant text plain-printed with `CMD: ` lines highlighted;
--- exec output framed with the exit code on the closing rule. Syntax
--- highlighting hooks land in Phase 6 (was Phase 5 pre-MCP renumber).
+-- exec output framed with the exit code on the closing rule.
+-- Phase 1: assistant_delta + assistant_flush for streaming render. CMD:
+-- highlighting in streaming mode is deferred (Q12); deltas print raw, the
+-- §6 substrate `CMD: ` line is still extractable by executor afterwards.
+-- Syntax highlighting hooks land in Phase 6 (was Phase 5 pre-MCP renumber).
 
 local M = {}
 
@@ -48,4 +51,26 @@ function M.status(line)
     emit(A.dim, "[aish] ", tostring(line), A.reset, "\n")
 end
 
+-- Streaming assistant output. Phase 1: deltas are written raw — the §6 CMD:
+-- highlighting from M.assistant() is not applied incrementally because
+-- mid-line cursor manipulation isn't worth the complexity for Phase 1.
+-- Q12 (PHASE1.md §10) tracks the upgrade. The full assistant text is still
+-- captured by repl.lua and CMD: extraction works against the reassembled
+-- string after the stream ends.
+
+local stream_buf = nil   -- non-nil while a stream is in progress
+
+function M.assistant_delta(chunk)
+    if not chunk or chunk == "" then return end
+    if stream_buf == nil then stream_buf = "" end
+    stream_buf = stream_buf .. chunk
+    emit(chunk)
+end
+
+function M.assistant_flush()
+    if stream_buf == nil then return end
+    if not stream_buf:match("\n$") then emit("\n") end
+    stream_buf = nil
+end
+
 return M