fix(agent): prevent panic from closing events channel while readLoop may still send

In 6 agent session implementations (codex, opencode, qoder, iflow, cursor,
gemini), Close() unconditionally calls close(events) after an 8-second
timeout, even when the readLoop goroutine may still be running and
sending events to the channel. Due to Go's select non-determinism, the
readLoop goroutine can choose the send case over the ctx.Done() case,
causing a "send on closed channel" panic.

Move close(events) into the case where wg.Wait() succeeds (readLoop has
fully exited), and skip closing on timeout to prevent the race. This
follows the same safe pattern already used by claudeSession, where the
events channel is only closed after the readLoop goroutine has finished.

agent/codex/session.go

@@ -497,10 +497,10 @@ func (cs *codexSession) Close() error {
 	}()
 	select {
 	case <-done:
+		close(cs.events)
 	case <-time.After(8 * time.Second):
 		slog.Warn("codexSession: close timed out, abandoning wg.Wait")
 	}
-	close(cs.events)
 	return nil
 }
 

agent/cursor/session.go

@@ -464,10 +464,10 @@ func (cs *cursorSession) Close() error {
 	}()
 	select {
 	case <-done:
+		close(cs.events)
 	case <-time.After(8 * time.Second):
 		slog.Warn("cursorSession: close timed out, abandoning wg.Wait")
 	}
-	close(cs.events)
 	return nil
 }
 

agent/gemini/session.go

@@ -469,10 +469,10 @@ func (gs *geminiSession) Close() error {
 	}()
 	select {
 	case <-done:
+		close(gs.events)
 	case <-time.After(8 * time.Second):
 		slog.Warn("geminiSession: close timed out, abandoning wg.Wait")
 	}
-	close(gs.events)
 	return nil
 }
 

agent/iflow/session.go

@@ -897,9 +897,9 @@ func (s *iflowSession) Close() error {
 	}()
 	select {
 	case <-done:
+		close(s.events)
 	case <-time.After(8 * time.Second):
 		slog.Warn("iflowSession: close timed out, abandoning wg.Wait")
 	}
-	close(s.events)
 	return nil
 }

agent/opencode/session.go

@@ -393,10 +393,10 @@ func (s *opencodeSession) Close() error {
 	}()
 	select {
 	case <-done:
+		close(s.events)
 	case <-time.After(8 * time.Second):
 		slog.Warn("opencodeSession: close timed out, abandoning wg.Wait")
 	}
-	close(s.events)
 	return nil
 }
 

agent/qoder/session.go

@@ -288,10 +288,10 @@ func (qs *qoderSession) Close() error {
 	}()
 	select {
 	case <-done:
+		close(qs.events)
 	case <-time.After(8 * time.Second):
 		slog.Warn("qoderSession: close timed out, abandoning wg.Wait")
 	}
-	close(qs.events)
 	return nil
 }