fix: surface auto-compression handoff

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Surface automatic-compression handoff metadata through the `compressed` SSE event so the active browser stream keeps the completion card even after the backend rotates to a compressed continuation session. The event now carries both the origin session id and continuation id, and the automatic-compression detail line names the compressed session instead of silently dropping the done state.
+
 ## [v0.51.91] — 2026-05-18 — Release BO (stage-384 — 5-PR full sweep batch — reasoning-replay history fix + archive-extract per-session inbox + fallback streaming warnings + sanitized custom-provider env hints + Slice 3c queue/goal adapter routing)
 
 ### Fixed

api/streaming.py

@@ -4345,11 +4345,15 @@ def _run_agent_streaming(
                 # reference stays alive even after the dict entry is removed.
                 # Concurrent readers that already looked up the old ID will still
                 # see the same Lock object until they release it.
+                _compression_origin_session_id = session_id
+                _compression_continuation_session_id = None
                 _agent_sid = getattr(agent, 'session_id', None)
                 _compressed = False
                 if _agent_sid and _agent_sid != session_id:
                     old_sid = session_id
                     new_sid = _agent_sid
+                    _compression_origin_session_id = old_sid
+                    _compression_continuation_session_id = new_sid
                     s.session_id = new_sid
                     # Carry profile identity across the compression boundary.
                     # Without this, s.profile stays None on the continuation
@@ -4426,8 +4430,13 @@ def _run_agent_streaming(
                         _compression_summary_from_messages(s.messages)
                         or _compression_summary_from_messages(s.context_messages)
                     )
+                    if _compression_continuation_session_id is None:
+                        _compression_continuation_session_id = s.session_id
                     put('compressed', {
-                        'session_id': s.session_id,
+                        'session_id': _compression_origin_session_id,
+                        'old_session_id': _compression_origin_session_id,
+                        'new_session_id': _compression_continuation_session_id,
+                        'continuation_session_id': _compression_continuation_session_id,
                         'message': 'Context auto-compressed to continue the conversation',
                         'usage': _live_usage_snapshot(),
                     })

static/messages.js

@@ -1809,7 +1809,9 @@ function attachLiveStream(activeSid, streamId, uploaded=[], options={}){
       if(!S.session||S.session.session_id!==activeSid) return;
       let d={};
       try{ d=JSON.parse(e.data||'{}')||{}; }catch(_){ d={}; }
-      if(d.session_id&&d.session_id!==activeSid) return;
+      const eventSid=d.old_session_id||d.session_id||activeSid;
+      if(eventSid!==activeSid) return;
+      const continuationSid=d.new_session_id||d.continuation_session_id||'';
       const message=String(d.message||'Context auto-compressed to continue the conversation').trim();
       if(d.usage&&typeof _syncCtxIndicator==='function'){
         S.lastUsage={...(S.lastUsage||{}),...d.usage};
@@ -1822,6 +1824,7 @@ function attachLiveStream(activeSid, streamId, uploaded=[], options={}){
           automatic:true,
           message,
           summary:{headline:message},
+          continuationSessionId:continuationSid,
         };
         setCompressionUi(state);
         const appended=typeof appendLiveCompressionCard==='function'&&appendLiveCompressionCard(state);

static/ui.js

@@ -5015,7 +5015,10 @@ function _autoCompressionDetailText(state){
   const running=state&&state.phase==='running';
   const base=_autoCompressionBaseDetail(state);
   const elapsedLabel=running?_compressionElapsedLabel(state):'';
-  return elapsedLabel?`Elapsed: ${elapsedLabel}`:base;
+  if(running)return elapsedLabel?`Elapsed: ${elapsedLabel}`:base;
+  const continuation=String(state&&state.continuationSessionId||'').trim();
+  const handoff=continuation?`Continued in compressed session: ${continuation}`:'';
+  return [base,handoff].filter(Boolean).join('\n');
 }
 function _autoCompressionCardsHtml(state){
   const running=state&&state.phase==='running';

tests/test_auto_compression_card.py

@@ -160,6 +160,19 @@ def test_auto_compression_running_detail_avoids_duplicate_message_text():
     assert "${base}\\nElapsed:" not in helper
 
 
+def test_auto_compression_done_detail_surfaces_continuation_handoff():
+    src = _read("static/ui.js")
+    start = src.find("function _autoCompressionDetailText")
+    assert start != -1, "auto compression detail helper not found"
+    end = src.find("function _autoCompressionCardsHtml", start)
+    assert end != -1, "auto compression card helper not found after detail helper"
+    helper = src[start:end]
+
+    assert "continuationSessionId" in helper
+    assert "Continued in compressed session" in helper
+    assert "return [base,handoff].filter(Boolean).join('\\n');" in helper
+
+
 def test_auto_compression_live_card_keeps_elapsed_state_for_timer_refresh():
     src = _read("static/ui.js")
     start = src.find("function appendLiveCompressionCard")
@@ -208,7 +221,22 @@ def test_auto_compression_sse_keeps_inactive_and_malformed_paths_safe():
     assert guard in block
     assert block.index(guard) < block.index("setCompressionUi")
     assert "try{ d=JSON.parse(e.data||'{}')||{}; }catch(_){ d={}; }" in block
-    assert "if(d.session_id&&d.session_id!==activeSid) return;" in block
+    assert "const eventSid=d.old_session_id||d.session_id||activeSid;" in block
+    assert "if(eventSid!==activeSid) return;" in block
+
+
+def test_auto_compression_done_accepts_rotated_continuation_session_event():
+    block = _compressed_listener_block()
+
+    # Auto-compression can rotate the backend session id before the 'compressed'
+    # event is emitted. The browser stream still belongs to the pre-compression
+    # activeSid, so the listener must correlate on old_session_id and keep the
+    # continuation id as display metadata instead of dropping the event.
+    assert "const eventSid=d.old_session_id||d.session_id||activeSid;" in block
+    assert "const continuationSid=d.new_session_id||d.continuation_session_id||'';" in block
+    assert "if(eventSid!==activeSid) return;" in block
+    assert block.index("const eventSid=") < block.index("if(eventSid!==activeSid) return;")
+    assert "continuationSessionId:continuationSid" in block
 
 
 def test_auto_compression_done_sse_refreshes_context_indicator_usage():
@@ -228,10 +256,28 @@ def test_auto_compression_done_payload_includes_live_usage_snapshot():
     assert end != -1, "compressed SSE payload end not found"
     block = src[start:end]
 
-    assert "'session_id': s.session_id" in block
+    assert "'session_id': _compression_origin_session_id" in block
+    assert "'old_session_id': _compression_origin_session_id" in block
+    assert "'new_session_id': _compression_continuation_session_id" in block
+    assert "'continuation_session_id': _compression_continuation_session_id" in block
     assert "'usage': _live_usage_snapshot()" in block
 
 
+def test_auto_compression_rotation_tracks_origin_and_continuation_ids_for_sse():
+    src = _read("api/streaming.py")
+    rotate_start = src.find("# ── Handle context compression side effects ──")
+    assert rotate_start != -1, "compression side-effect block not found"
+    rotate_end = src.find("# Stamp 'timestamp'", rotate_start)
+    assert rotate_end != -1, "compression side-effect block end not found"
+    block = src[rotate_start:rotate_end]
+
+    assert "_compression_origin_session_id = session_id" in block
+    assert "_compression_continuation_session_id = None" in block
+    assert "_compression_origin_session_id = old_sid" in block
+    assert "_compression_continuation_session_id = new_sid" in block
+    assert "'new_session_id': _compression_continuation_session_id" in block
+
+
 def test_auto_compression_card_reuses_compression_card_renderer():
     src = _read("static/ui.js")
     start = src.find("function _autoCompressionCardsHtml")