fix: refresh project move cache

static/sessions.js

@@ -3569,7 +3569,12 @@ function _showProjectPicker(session, anchorEl){
     picker.remove();
     document.removeEventListener('click',close);
     await api('/api/session/move',{method:'POST',body:JSON.stringify({session_id:session.session_id,project_id:null})});
-    session.project_id=null;
+    // Sidebar rows are shallow copies of _allSessions entries (see
+    // _attachChildSessionsToSidebarRows), so mutating `session` only updates
+    // the discarded copy. Write into the authoritative cache so the next
+    // renderSessionListFromCache() reflects the move. (#2551)
+    const idx=_allSessions.findIndex(s=>s&&s.session_id===session.session_id);
+    if(idx>=0) _allSessions[idx].project_id=null;
     renderSessionListFromCache();
     showToast('Removed from project');
   };
@@ -3591,7 +3596,9 @@ function _showProjectPicker(session, anchorEl){
       picker.remove();
       document.removeEventListener('click',close);
       await api('/api/session/move',{method:'POST',body:JSON.stringify({session_id:session.session_id,project_id:p.project_id})});
-      session.project_id=p.project_id;
+      // See #2551 — write to _allSessions, not the shallow sidebar copy.
+      const idx=_allSessions.findIndex(s=>s&&s.session_id===session.session_id);
+      if(idx>=0) _allSessions[idx].project_id=p.project_id;
       renderSessionListFromCache();
       showToast('Moved to '+p.name);
     };

tests/test_issue2551_project_picker_cache_refresh.py

@@ -0,0 +1,144 @@
+"""Regression coverage for #2551 stale sidebar after Move-to-Project.
+
+The single-session project picker (`_showProjectPicker` in `static/sessions.js`)
+used to mutate the sidebar's shallow row copy and then call
+`renderSessionListFromCache()`, which re-reads the unmodified `_allSessions`
+cache and renders the old `project_id`. The server-side move was correct, so
+the next `/api/sessions` poll healed the UI — but until then the sidebar was
+visually stale.
+
+The fix writes the new `project_id` into the authoritative `_allSessions`
+entry before re-rendering, so the optimistic update reflects the move
+immediately without a wasted `/api/sessions` round trip.
+"""
+
+from pathlib import Path
+import json
+import subprocess
+
+REPO = Path(__file__).resolve().parents[1]
+SESSIONS_SRC = (REPO / "static" / "sessions.js").read_text(encoding="utf-8")
+
+
+def _show_project_picker_body() -> str:
+    start = SESSIONS_SRC.find("function _showProjectPicker(")
+    assert start != -1, "_showProjectPicker not found in sessions.js"
+    # Pick a stable downstream sentinel that lives after the function ends.
+    end = SESSIONS_SRC.find("function _resizeProjectInput(", start)
+    assert end != -1, "_resizeProjectInput sentinel not found after picker"
+    return SESSIONS_SRC[start:end]
+
+
+PICKER_BODY = _show_project_picker_body()
+
+
+def test_no_project_branch_writes_to_allSessions_cache():
+    """The 'No project' callback must update `_allSessions[idx].project_id`
+    after the /api/session/move call so the re-render reflects the move."""
+    none_idx = PICKER_BODY.find("'Removed from project'")
+    assert none_idx != -1, "'Removed from project' branch not located"
+    # Look back over the callback body
+    window = PICKER_BODY[max(0, none_idx - 600): none_idx]
+    assert "_allSessions.findIndex" in window, (
+        "No-project branch must locate the session in _allSessions so the "
+        "cache reflects the move (issue #2551)."
+    )
+    assert "_allSessions[idx].project_id=null" in window, (
+        "No-project branch must write project_id=null into _allSessions, "
+        "not just the shallow sidebar copy (issue #2551)."
+    )
+
+
+def test_existing_project_branch_writes_to_allSessions_cache():
+    """The existing-project callback must update `_allSessions[idx].project_id`
+    after the /api/session/move call so the re-render reflects the move."""
+    moved_idx = PICKER_BODY.find("'Moved to '+p.name")
+    assert moved_idx != -1, "'Moved to '+p.name branch not located"
+    window = PICKER_BODY[max(0, moved_idx - 600): moved_idx]
+    assert "_allSessions.findIndex" in window, (
+        "Existing-project branch must locate the session in _allSessions so "
+        "the cache reflects the move (issue #2551)."
+    )
+    assert "_allSessions[idx].project_id=p.project_id" in window, (
+        "Existing-project branch must write project_id=p.project_id into "
+        "_allSessions, not just the shallow sidebar copy (issue #2551)."
+    )
+
+
+def test_picker_callbacks_do_not_rely_on_shallow_copy_mutation():
+    """Pinning the failure mode: the picker callbacks must not return without
+    updating the authoritative cache. The previous bug looked like
+    `session.project_id=null; renderSessionListFromCache();` with no cache
+    write between, which is what produced the stale render."""
+    # Both branches end with renderSessionListFromCache(). Count how many
+    # times the buggy bare mutation precedes a cache render with no
+    # _allSessions write in between.
+    buggy_no_project = "session.project_id=null;\n    renderSessionListFromCache();"
+    buggy_existing = "session.project_id=p.project_id;\n      renderSessionListFromCache();"
+    assert buggy_no_project not in PICKER_BODY, (
+        "No-project branch still mutates only the shallow copy before "
+        "re-render — restore the _allSessions write (issue #2551)."
+    )
+    assert buggy_existing not in PICKER_BODY, (
+        "Existing-project branch still mutates only the shallow copy before "
+        "re-render — restore the _allSessions write (issue #2551)."
+    )
+
+
+def test_cache_write_makes_render_observe_new_project_id():
+    """End-to-end behavioural check: simulate the cache-write step from each
+    picker branch and confirm `_allSessions` reflects the new project_id,
+    which is what `renderSessionListFromCache` reads to repaint the sidebar.
+    """
+    script = """
+let _allSessions = [
+  {session_id: 'sa', project_id: 'proj-old', title: 'A'},
+  {session_id: 'sb', project_id: null, title: 'B'},
+];
+
+// Sidebar copy, the way _attachChildSessionsToSidebarRows produces it:
+const sidebarCopy = {..._allSessions[0]};
+
+// Simulate the 'No project' branch cache write:
+{
+  const session = sidebarCopy;
+  const idx = _allSessions.findIndex(s => s && s.session_id === session.session_id);
+  if (idx >= 0) _allSessions[idx].project_id = null;
+}
+
+// Then the 'Moved to <project>' branch on session B going to proj-new:
+{
+  const session = {..._allSessions[1]};
+  const p = {project_id: 'proj-new', name: 'New Project'};
+  const idx = _allSessions.findIndex(s => s && s.session_id === session.session_id);
+  if (idx >= 0) _allSessions[idx].project_id = p.project_id;
+}
+
+console.log(JSON.stringify(_allSessions.map(s => ({id: s.session_id, project_id: s.project_id}))));
+"""
+    result = subprocess.run(
+        ["node", "-e", script], check=True, capture_output=True, text=True
+    )
+    rows = json.loads(result.stdout)
+    assert rows == [
+        {"id": "sa", "project_id": None},
+        {"id": "sb", "project_id": "proj-new"},
+    ], (
+        "Cache write must replace project_id on the _allSessions entry, "
+        "which is what renderSessionListFromCache reads (issue #2551)."
+    )
+
+
+def test_new_project_branch_still_uses_authoritative_refetch():
+    """The '+ New project' path was already correct: it calls
+    `await renderSessionList()` (a full /api/sessions refetch) after
+    creating the project. The minimal fix must not change that.
+    """
+    create_idx = PICKER_BODY.find("'+ New project'")
+    assert create_idx != -1, "'+ New project' branch not located"
+    window = PICKER_BODY[create_idx: create_idx + 900]
+    assert "await renderSessionList()" in window, (
+        "'+ New project' branch must keep its authoritative refetch — the "
+        "new project_id is only known to the server until /api/sessions is "
+        "re-fetched."
+    )