fix(ui): persist session queue to sessionStorage across page refresh (#768)

Queued follow-up messages now survive page refresh. Persisted atomically in queueSessionMessage/shiftQueuedSessionMessage. On reload: if agent still active, queue is silently hydrated (done handler drains it); if idle, first entry is restored as a composer draft with a toast. Stale entries discarded.

Fixes #660

tests/test_issue660.py

@@ -0,0 +1,76 @@
+"""
+Tests for #660: session queue persistence across page refresh.
+
+The queue is stored to sessionStorage when entries are added/removed,
+and restored from sessionStorage on session load when the agent is idle.
+"""
+import pathlib
+
+UI_JS = pathlib.Path(__file__).parent.parent / 'static' / 'ui.js'
+SESSIONS_JS = pathlib.Path(__file__).parent.parent / 'static' / 'sessions.js'
+
+ui_src = UI_JS.read_text(encoding='utf-8')
+sess_src = SESSIONS_JS.read_text(encoding='utf-8')
+
+
+class TestQueuePersistence:
+    """queueSessionMessage persists to sessionStorage."""
+
+    def test_queue_writes_to_session_storage(self):
+        """queueSessionMessage must write to sessionStorage after enqueueing."""
+        assert "sessionStorage.setItem('hermes-queue-'+sid" in ui_src
+
+    def test_queue_stamps_queued_at_timestamp(self):
+        """Each queue entry must have a _queued_at timestamp for stale-entry detection."""
+        assert '_queued_at' in ui_src
+
+    def test_shift_removes_from_session_storage(self):
+        """shiftQueuedSessionMessage must remove/update sessionStorage on dequeue."""
+        assert "sessionStorage.removeItem('hermes-queue-'+sid)" in ui_src
+
+    def test_shift_updates_session_storage_when_items_remain(self):
+        """When queue still has items after shift, sessionStorage is updated (not removed)."""
+        # After shift: if queue still has items, update storage with remaining
+        assert "sessionStorage.setItem('hermes-queue-'+sid, JSON.stringify(q))" in ui_src
+        # Counts: should appear in both add and update paths (2 occurrences minimum)
+        count = ui_src.count("sessionStorage.setItem('hermes-queue-'+sid")
+        assert count >= 2, f"Expected >=2 sessionStorage.setItem calls, found {count}"
+
+
+class TestQueueRestore:
+    """Queue is restored from sessionStorage on session load when agent is idle."""
+
+    def test_restore_reads_session_storage(self):
+        """sessions.js must read from sessionStorage in the idle-session load path."""
+        assert "sessionStorage.getItem('hermes-queue-'+sid)" in sess_src
+
+    def test_restore_uses_timestamp_guard(self):
+        """Stale entries (created before last assistant response) must be dropped."""
+        assert '_queued_at' in sess_src
+        assert '_lastAsst' in sess_src
+
+    def test_restore_shows_toast(self):
+        """User must see a toast notification when a queue is restored."""
+        assert 'queued message' in sess_src.lower() and 'restored' in sess_src.lower()
+
+    def test_restore_puts_text_in_composer(self):
+        """First queued message goes into the composer input, not auto-sent."""
+        assert "_msg.value=_first.text" in sess_src
+
+    def test_restore_clears_stale_storage(self):
+        """On timestamp mismatch, stale sessionStorage entry is removed."""
+        assert "sessionStorage.removeItem('hermes-queue-'+sid)" in sess_src
+
+    def test_restore_wrapped_in_try_catch(self):
+        """sessionStorage access must be wrapped in try/catch (private browsing may block it)."""
+        # The restore block must have a catch that clears the bad key
+        assert "catch(_){sessionStorage.removeItem" in sess_src
+
+    def test_active_session_not_restored_as_draft(self):
+        """When agent is active (INFLIGHT), queue restore must NOT run."""
+        # The restore block must be inside the else branch (idle path), not the INFLIGHT branch
+        inflight_pos = sess_src.find("if(INFLIGHT[sid]){")
+        restore_pos = sess_src.find("sessionStorage.getItem('hermes-queue-'")
+        else_pos = sess_src.find("}else{", inflight_pos)
+        assert restore_pos > else_pos, \
+            "Queue restore must be inside the else (idle) branch, not the INFLIGHT branch"