fix(prompter): keep a watched intake chat alive (idle-reap counted reading as idle) (#379)

* fix(prompter): keep a watched intake chat alive (idle-reap counted reading as idle)

Intake chats "dropped after a while" — the panel showed "Live connection lost".
The idle reaper retires an interactive session whose last_activity is older than
interactive_idle_reap_seconds (30m default), but last_activity was bumped only by
an agent event or a human turn. An open SSE stream — the human reading a proposed
draft / MegaTask spec without typing — bumped nothing, so a chat under active
review was reaped mid-read, closing the stream (the SSE transport error the panel
reports as "Live connection lost").

stream() now runs a keepalive task that refreshes last_activity every 60s while
the stream is connected, so an open, actively-watched chat counts as alive; when
the tab closes the generator ends, the keepalive is cancelled, and a genuinely
abandoned chat still reaps after the threshold. The keepalive runs beside an
un-cancelled queue.get() so no live token or the close sentinel can be dropped.

* fix(tests): conventions PR integration test honors the #375 workspace-scope guard

#375 added a containment guard to open_conventions_pr (workspace_path must sit
under {workspaces_root}/{slug}); the unit test was updated but this integration
test still seeded a bare tmp_path/repo, so open_conventions_pr returned None and
test_open_conventions_pr_commits_locally_without_remote failed on master. Anchor
workspaces_root at the test dir and place the repo under the project's slug.

---------

Co-authored-by: Renn F <rennf93@users.noreply.github.com>

tests/unit/services/test_prompter_live.py

@@ -8,6 +8,7 @@ import time
 
 import httpx
 import pytest
+import roboco.services.prompter_live as pl
 from roboco.services.prompter_live import (
     PrompterLiveRegistry,
     get_live_registry,
@@ -151,6 +152,35 @@ async def test_stream_yields_queued_events_then_ends_on_close() -> None:
     ]
 
 
+@pytest.mark.asyncio
+async def test_stream_keepalive_keeps_watched_chat_alive(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """An open SSE stream refreshes last_activity even with no events, so a
+    human reading a proposal (tab open, not typing) is not idle-reaped. Without
+    this the chat "drops after a while" mid-review."""
+    monkeypatch.setattr(pl, "_STREAM_KEEPALIVE_SECONDS", 0.01)
+    reg = PrompterLiveRegistry()
+    session = reg.open("s1", "intake-1")
+    session.last_activity = time.monotonic() - 4000  # silent for >1h
+
+    # Before anyone connects, the abandoned-looking chat IS idle-reapable.
+    assert ("s1", "intake-1") in reg.idle_session_ids(1800)
+
+    async def watch() -> None:
+        async for _ in reg.stream("s1"):
+            pass
+
+    task = asyncio.create_task(watch())
+    try:
+        await asyncio.sleep(0.05)  # let a keepalive tick fire on the open stream
+        # The connected stream refreshed activity → no longer idle.
+        assert reg.idle_session_ids(1800) == []
+    finally:
+        reg.close("s1")
+        await asyncio.wait_for(task, timeout=1.0)
+
+
 @pytest.mark.asyncio
 async def test_stream_unknown_session_is_empty() -> None:
     reg = PrompterLiveRegistry()