fix: keep Later plans conflict-safe across devices (#377)

README.md

@@ -224,8 +224,11 @@ or changing any Gitea issue or pull request. They automatically return to their
 existing priority position at the wake time, and **Bring back now** restores them
 early. Later wake times are scoped to the confirmed Gitea login and synchronize
 across signed-in tabs and devices. Offline changes apply immediately, survive reload,
-and replay after reconnect; `STACKCHAIN_LATER_DB` can override the default durable
+and replay after reconnect. Each queued edit carries the account revision it was based
-store at `.stackchain-state/later.sqlite3`.
+on; if another device has since changed the same item, Stackchain keeps the newer
+account plan and reports the conflict instead of silently overwriting it. Unrelated
+items continue syncing in the same batch. `STACKCHAIN_LATER_DB` can override the
+default durable store at `.stackchain-state/later.sqlite3`.
 
 After one successful online load, the installed dashboard precaches a versioned,
 subpath-scoped application shell. During a network outage or a dashboard HTTP

frontend/dashboard.js

@@ -186,9 +186,10 @@
     },
     onStatus: (state, detail = {}) => {
       qs('#later-sync-status').textContent = state === 'saved' ? 'Later saved to account.' :
+        (state === 'conflict' ? `Another device changed this Later item${detail.count > 1 ? 's' : ''} · account plan kept.` :
           (state === 'retrying' ? `Later saved on this device · retrying in ${Math.ceil(detail.delayMs / 1000)}s.` :
             (state === 'pending' ? 'Later saved on this device · sync pending.' :
-            'Later sync unavailable · changes stay on this device.'));
+              'Later sync unavailable · changes stay on this device.')));
     },
   });
   laterSync.startLifecycle({ window, document });

frontend/later-sync.js

@@ -115,7 +115,11 @@ function createLaterSync({ storage, getLogin, fetchJson, onRemoteRecords, onStat
         knownOperationKeys.delete(record.recordKey);
       });
       return records.filter(record => latestByItem.get(record.operation.item_id) === record)
-        .map(record => record.operation).filter(operation =>
+        .map(record => ({
+          ...record.operation,
+          base_revision: Number.isInteger(record.operation.base_revision)
+            ? record.operation.base_revision : 0,
+        })).filter(operation =>
           operation && typeof operation.operation_id === 'string' &&
           ['defer', 'restore'].includes(operation.action) && typeof operation.item_id === 'string' &&
           (operation.action === 'restore' || typeof operation.wake_at === 'string'));
@@ -148,7 +152,10 @@ function createLaterSync({ storage, getLogin, fetchJson, onRemoteRecords, onStat
         (action === 'defer' && typeof wakeAt !== 'string')) return false;
     pending().filter(operation => operation.item_id === itemId)
       .forEach(operation => removeOperation(operation.operation_id));
-    const operation = { operation_id: operationId(), action, item_id: itemId, wake_at: wakeAt };
+    const operation = {
+      operation_id: operationId(), action, item_id: itemId, wake_at: wakeAt,
+      base_revision: Math.max(0, savedRevision()),
+    };
     const storageKey = key();
     if (!storageKey || !storage) return false;
     const recordKey = storageKey + '.operation.' + encodeURIComponent(operation.operation_id);
@@ -186,6 +193,7 @@ function createLaterSync({ storage, getLogin, fetchJson, onRemoteRecords, onStat
     try {
       let operations = pending();
       let plan;
+      let conflictCount = 0;
       if (!operations.length) plan = await fetchJson('api/v1/later');
       while (operations.length) {
         if (key() !== ownerKey) return false;
@@ -202,6 +210,8 @@ function createLaterSync({ storage, getLogin, fetchJson, onRemoteRecords, onStat
           ...(plan.duplicate_operation_ids || []),
           ...(plan.rejected_operations || []).map(item => item.operation_id),
         ] : batch.map(item => item.operation_id);
+        conflictCount += (plan.rejected_operations || [])
+          .filter(item => item.reason === 'stale_intent').length;
         for (const operationId of received) {
           if (pending().some(candidate => candidate.operation_id === operationId) &&
               !removeOperation(operationId)) {
@@ -211,7 +221,8 @@ function createLaterSync({ storage, getLogin, fetchJson, onRemoteRecords, onStat
         operations = pending();
       }
       adopt(plan);
-      onStatus?.(pending().length ? 'pending' : 'saved');
+      onStatus?.(pending().length ? 'pending' :
+        (conflictCount ? 'conflict' : 'saved'), conflictCount ? { count: conflictCount } : {});
       retryAttempt = 0;
       cancelRetry();
       return true;

frontend/service-worker.js

@@ -1,6 +1,6 @@
 const BASE = new URL('./', self.location.href).pathname;
 importScripts(BASE + 'static/background-issue-sync.js');
-const CACHE = 'stackchain-dashboard-shell-v54';
+const CACHE = 'stackchain-dashboard-shell-v55';
 const OUTAGE_STATUSES = new Set([500, 502, 503, 504]);
 const NAVIGATION_TIMEOUT_MS = self.__STACKCHAIN_NAVIGATION_TIMEOUT_MS || 4000;
 const SHELL = [

src/later_store.py

@@ -33,6 +33,16 @@ class LaterStore:
             )
             """
         )
+        connection.execute(
+            """
+            CREATE TABLE IF NOT EXISTS later_item_revisions (
+                login TEXT NOT NULL,
+                item_id TEXT NOT NULL,
+                revision INTEGER NOT NULL,
+                PRIMARY KEY (login, item_id)
+            )
+            """
+        )
         return connection
 
     @staticmethod
@@ -74,54 +84,16 @@ class LaterStore:
         item_id: str,
         *,
         wake_at: str | None = None,
+        base_revision: int | None = None,
     ) -> dict:
-        login = self._normalize_login(login)
+        result = self.apply_batch(login, [{
-        if not operation_id or not item_id:
+            "operation_id": operation_id,
-            raise ValueError("operation_id and item_id are required")
+            "action": action,
-        if action not in {"defer", "restore"}:
+            "item_id": item_id,
-            raise ValueError("unsupported Later action")
+            "wake_at": wake_at,
-        if action == "defer":
+            "base_revision": base_revision,
-            wake_at = self._validate_wake_at(wake_at)
+        }])
-
+        return {"revision": result["revision"], "records": result["records"]}
-        with self._connect() as connection:
-            connection.execute("BEGIN IMMEDIATE")
-            row = connection.execute(
-                "SELECT revision, records FROM later_plans WHERE login = ?", (login,)
-            ).fetchone()
-            snapshot = self._snapshot(row)
-            duplicate = connection.execute(
-                "SELECT 1 FROM later_operations WHERE login = ? AND operation_id = ?",
-                (login, operation_id),
-            ).fetchone()
-            if duplicate:
-                return snapshot
-
-            records = dict(snapshot["records"])
-            before = records.get(item_id)
-            if action == "defer":
-                records[item_id] = wake_at
-                changed = before != wake_at
-            else:
-                changed = item_id in records
-                records.pop(item_id, None)
-
-            revision = snapshot["revision"] + (1 if changed else 0)
-            serialized = json.dumps(records, separators=(",", ":"), sort_keys=True)
-            if row is None:
-                connection.execute(
-                    "INSERT INTO later_plans(login, revision, records) VALUES (?, ?, ?)",
-                    (login, revision, serialized),
-                )
-            elif changed:
-                connection.execute(
-                    "UPDATE later_plans SET revision = ?, records = ? WHERE login = ?",
-                    (revision, serialized, login),
-                )
-            connection.execute(
-                "INSERT INTO later_operations(login, operation_id) VALUES (?, ?)",
-                (login, operation_id),
-            )
-            return {"revision": revision, "records": records}
 
     def apply_batch(self, login: str, operations: list[dict]) -> dict:
         """Apply ordered deferrals with one SQLite write transaction."""
@@ -136,6 +108,20 @@ class LaterStore:
             revision = snapshot["revision"]
             accepted: list[str] = []
             duplicates: list[str] = []
+            rejected: list[dict[str, str]] = []
+
+            # Existing databases predate per-item revisions. Conservatively mark
+            # active deferrals as changed at the latest known plan revision.
+            for item_id in records:
+                connection.execute(
+                    "INSERT OR IGNORE INTO later_item_revisions(login, item_id, revision) VALUES (?, ?, ?)",
+                    (login, item_id, revision),
+                )
+            item_revisions = dict(connection.execute(
+                "SELECT item_id, revision FROM later_item_revisions WHERE login = ?",
+                (login,),
+            ).fetchall())
+            batch_start_item_revisions = dict(item_revisions)
 
             for operation in operations:
                 operation_id = operation.get("operation_id", "")
@@ -156,6 +142,22 @@ class LaterStore:
                     duplicates.append(operation_id)
                     continue
 
+                base_revision = operation.get("base_revision")
+                if base_revision is None:
+                    base_revision = snapshot["revision"]
+                if not isinstance(base_revision, int) or isinstance(base_revision, bool) or base_revision < 0:
+                    raise ValueError("base_revision must be a non-negative integer")
+                if batch_start_item_revisions.get(item_id, 0) > base_revision:
+                    connection.execute(
+                        "INSERT INTO later_operations(login, operation_id) VALUES (?, ?)",
+                        (login, operation_id),
+                    )
+                    rejected.append({
+                        "operation_id": operation_id,
+                        "reason": "stale_intent",
+                    })
+                    continue
+
                 before = records.get(item_id)
                 if action == "defer":
                     records[item_id] = wake_at
@@ -164,6 +166,13 @@ class LaterStore:
                     changed = item_id in records
                     records.pop(item_id, None)
                 revision += 1 if changed else 0
+                if changed:
+                    item_revisions[item_id] = revision
+                    connection.execute(
+                        "INSERT INTO later_item_revisions(login, item_id, revision) VALUES (?, ?, ?) "
+                        "ON CONFLICT(login, item_id) DO UPDATE SET revision = excluded.revision",
+                        (login, item_id, revision),
+                    )
                 connection.execute(
                     "INSERT INTO later_operations(login, operation_id) VALUES (?, ?)",
                     (login, operation_id),
@@ -186,5 +195,5 @@ class LaterStore:
                 "records": records,
                 "accepted_operation_ids": accepted,
                 "duplicate_operation_ids": duplicates,
-                "rejected_operations": [],
+                "rejected_operations": rejected,
             }

src/main.py

@@ -222,6 +222,7 @@ class LaterOperation(BaseModel):
     action: Literal["defer", "restore"]
     item_id: str = Field(min_length=1, max_length=500)
     wake_at: str | None = Field(default=None, max_length=100)
+    base_revision: int | None = Field(default=None, ge=0)
 
 
 class TodayOperationBatch(BaseModel):
@@ -969,6 +970,7 @@ async def update_later_plan(payload: LaterOperation | LaterOperationBatch):
             payload.action,
             payload.item_id,
             wake_at=payload.wake_at,
+            base_revision=payload.base_revision,
         )
     except ValueError as error:
         raise HTTPException(status_code=422, detail=str(error))

tests/test_later_store.py

@@ -86,6 +86,57 @@ def test_batch_applies_in_one_ordered_idempotent_unit(tmp_path):
     assert replay["duplicate_operation_ids"] == ["first", "second"]
 
 
+def test_batch_rejects_stale_same_item_intent_without_blocking_other_items(tmp_path):
+    store = LaterStore(tmp_path / "later.sqlite3")
+    first = store.apply_batch("timmy", [{
+        "operation_id": "newer-device",
+        "action": "defer",
+        "item_id": "issue:r:1:",
+        "wake_at": "2026-08-12T09:00:00.000Z",
+        "base_revision": 0,
+    }])
+
+    replay = store.apply_batch("timmy", [
+        {
+            "operation_id": "stale-device",
+            "action": "defer",
+            "item_id": "issue:r:1:",
+            "wake_at": "2026-08-10T09:00:00.000Z",
+            "base_revision": 0,
+        },
+        {
+            "operation_id": "unrelated-item",
+            "action": "defer",
+            "item_id": "issue:r:2:",
+            "wake_at": "2026-08-11T09:00:00.000Z",
+            "base_revision": 0,
+        },
+    ])
+
+    assert first["revision"] == 1
+    assert replay == {
+        "revision": 2,
+        "records": {
+            "issue:r:1:": "2026-08-12T09:00:00.000Z",
+            "issue:r:2:": "2026-08-11T09:00:00.000Z",
+        },
+        "accepted_operation_ids": ["unrelated-item"],
+        "duplicate_operation_ids": [],
+        "rejected_operations": [
+            {"operation_id": "stale-device", "reason": "stale_intent"}
+        ],
+    }
+    duplicate = store.apply_batch("timmy", [{
+        "operation_id": "stale-device",
+        "action": "restore",
+        "item_id": "issue:r:2:",
+        "base_revision": 2,
+    }])
+    assert duplicate["duplicate_operation_ids"] == ["stale-device"]
+    assert duplicate["revision"] == 2
+    assert duplicate["records"] == replay["records"]
+
+
 @pytest.mark.anyio
 async def test_authenticated_later_api_uses_confirmed_account_and_csrf(monkeypatch, tmp_path):
     monkeypatch.setenv("STACKCHAIN_DASHBOARD_AUTH_MODE", "operator")
@@ -129,6 +180,21 @@ async def test_authenticated_later_api_uses_confirmed_account_and_csrf(monkeypat
                 "X-CSRF-Token": client.cookies["stackchain_csrf"],
             },
         )
+        stale = await client.patch(
+            "/api/v1/later",
+            json={
+                "operations": [{
+                    "operation_id": "offline-stale",
+                    "action": "restore",
+                    "item_id": "issue:stackchain/dashboard:363:",
+                    "base_revision": 0,
+                }],
+            },
+            headers={
+                "Origin": "https://test",
+                "X-CSRF-Token": client.cookies["stackchain_csrf"],
+            },
+        )
         fetched = await client.get("/api/v1/later")
 
     assert forbidden.status_code == 403
@@ -143,6 +209,10 @@ async def test_authenticated_later_api_uses_confirmed_account_and_csrf(monkeypat
         "duplicate_operation_ids": [],
         "rejected_operations": [],
     }
+    assert stale.json()["rejected_operations"] == [
+        {"operation_id": "offline-stale", "reason": "stale_intent"}
+    ]
+    assert stale.json()["revision"] == 2
     assert fetched.json() == {"revision": 2, "records": {
         "issue:stackchain/dashboard:363:": "2026-08-10T09:00:00.000Z",
         "issue:stackchain/dashboard:365:": "2026-08-11T09:00:00.000Z",

tests/test_later_sync.py

@@ -90,12 +90,44 @@ sync.enqueue('defer','issue:r:2:','2026-08-10T09:00:00.000Z');
         "action": "defer",
         "item_id": "issue:r:2:",
         "wake_at": "2026-08-10T09:00:00.000Z",
+        "base_revision": 0,
     }]}
     assert result["records"]["issue:r:2:"] == "2026-08-10T09:00:00.000Z"
     assert result["status"] == "saved"
     assert result["pending"] == []
 
 
+def test_stale_receipt_adopts_server_truth_and_reports_another_device_conflict():
+    script = f"""
+const createLaterSync=require({json.dumps(str(LATER_SYNC))});
+const values=new Map();const requests=[];const statuses=[];const adopted=[];
+const storage={{getItem:k=>values.get(k)||null,setItem:(k,v)=>values.set(k,v),removeItem:k=>values.delete(k)}};
+const sync=createLaterSync({{
+ storage,getLogin:()=> 'timmy',createOperationId:()=> 'offline-old',
+ fetchJson:async(_url,options={{}})=>{{
+   if(!options.method)return {{revision:3,records:{{'issue:r:1:':'2026-08-12T09:00:00.000Z'}}}};
+   const body=JSON.parse(options.body);requests.push(body);
+   return {{revision:4,records:{{'issue:r:1:':'2026-08-13T09:00:00.000Z'}},accepted_operation_ids:[],duplicate_operation_ids:[],rejected_operations:[{{operation_id:'offline-old',reason:'stale_intent'}}]}};
+ }},onRemoteRecords:records=>adopted.push(records),onStatus:(state,detail={{}})=>statuses.push([state,detail]),
+}});
+(async()=>{{await sync.flush();sync.enqueue('defer','issue:r:1:','2026-08-10T09:00:00.000Z');await sync.flush();
+process.stdout.write(JSON.stringify({{requests,statuses,adopted,pending:sync.pending()}}));}})();
+"""
+    result = run_node(script)
+    assert result["requests"] == [{"operations": [{
+        "operation_id": "offline-old",
+        "action": "defer",
+        "item_id": "issue:r:1:",
+        "wake_at": "2026-08-10T09:00:00.000Z",
+        "base_revision": 3,
+    }]}]
+    assert result["statuses"][-1] == ["conflict", {"count": 1}]
+    assert result["adopted"][-1] == {
+        "issue:r:1:": "2026-08-13T09:00:00.000Z"
+    }
+    assert result["pending"] == []
+
+
 def test_pending_later_edits_are_sent_as_one_batch_without_a_preflight_get():
     script = f"""
 const createLaterSync=require({json.dumps(str(LATER_SYNC))});
@@ -136,6 +168,7 @@ sync.enqueue('restore','issue:r:2:');
                 "action": "restore",
                 "item_id": "issue:r:2:",
                 "wake_at": None,
+                "base_revision": 0,
             }
         ],
         "status": "retrying",
@@ -283,10 +316,11 @@ async def test_dashboard_syncs_every_later_change_and_exposes_account_status():
     assert "laterSync.migrate(laterWork.read());" in html
     assert "laterSync.flush();" in html
     assert "Later saved to account." in html
+    assert "Another device changed this Later item" in html
 
 
 def test_later_sync_ships_atomically_in_the_offline_shell():
     source = (Path(__file__).parents[1] / "frontend" / "service-worker.js").read_text()
 
-    assert "stackchain-dashboard-shell-v54" in source
+    assert "stackchain-dashboard-shell-v55" in source
     assert "BASE + 'static/later-sync.js'" in source

tests/test_markdown_renderer.py

@@ -137,4 +137,4 @@ def test_markdown_work_bodies_are_mobile_safe_block_containers():
     assert ".markdown-content { min-width:0; max-width:100%; overflow-wrap:anywhere;" in css
     assert ".markdown-content pre { max-width:100%; overflow-x:auto;" in css
     assert ".markdown-content a { min-height:44px;" in css
-    assert "stackchain-dashboard-shell-v54" in worker
+    assert "stackchain-dashboard-shell-v55" in worker

tests/test_mobile_composer_integration.py

@@ -35,4 +35,4 @@ def test_offline_shell_contains_every_local_dashboard_runtime_asset():
     shell_assets = set(re.findall(r"BASE \+ '([^']+)'", worker.split("async function sessionCsrf", 1)[0]))
 
     assert local_assets <= shell_assets, f"Offline shell is missing: {sorted(local_assets - shell_assets)}"
-    assert "stackchain-dashboard-shell-v54" in worker
+    assert "stackchain-dashboard-shell-v55" in worker

tests/test_service_worker.py

@@ -108,7 +108,7 @@ async function dispatchNotificationClick(route) {{
 def test_duplicate_aware_capture_ships_in_a_new_offline_shell():
     source = WORKER.read_text()
 
-    assert "stackchain-dashboard-shell-v54" in source
+    assert "stackchain-dashboard-shell-v55" in source
     assert "BASE + 'static/create-issue-sheet.js'" in source
     assert "BASE + 'static/dashboard.js'" in source
 
@@ -116,14 +116,14 @@ def test_duplicate_aware_capture_ships_in_a_new_offline_shell():
 def test_exact_later_picker_ships_atomically_in_a_new_offline_shell():
     source = WORKER.read_text()
 
-    assert "stackchain-dashboard-shell-v54" in source
+    assert "stackchain-dashboard-shell-v55" in source
     assert "BASE + 'static/later-picker.js'" in source
 
 
 def test_navigation_deadline_ships_in_a_new_shell_cache():
     source = WORKER.read_text()
 
-    assert "stackchain-dashboard-shell-v54" in source
+    assert "stackchain-dashboard-shell-v55" in source
     assert "BASE + 'static/dashboard.css'" in source
     assert "BASE + 'static/dashboard.js'" in source
     assert "BASE + 'static/install-app.js'" in source
@@ -132,21 +132,21 @@ def test_navigation_deadline_ships_in_a_new_shell_cache():
 def test_today_convergence_ships_in_a_new_shell_cache():
     source = WORKER.read_text()
 
-    assert "stackchain-dashboard-shell-v54" in source
+    assert "stackchain-dashboard-shell-v55" in source
     assert "BASE + 'static/today-sync.js'" in source
 
 
 def test_mobile_search_viewport_ships_in_a_new_offline_shell():
     source = WORKER.read_text()
 
-    assert "stackchain-dashboard-shell-v54" in source
+    assert "stackchain-dashboard-shell-v55" in source
     assert "BASE + 'static/mobile-search-viewport.js'" in source
 
 
 def test_update_ownership_flow_ships_atomically_in_a_new_offline_shell():
     source = WORKER.read_text()
 
-    assert "stackchain-dashboard-shell-v54" in source
+    assert "stackchain-dashboard-shell-v55" in source
     assert "BASE + 'static/update-ownership.js'" in source
 
 

tests/test_today_sync.py

@@ -86,7 +86,7 @@ sync.enqueue('add', 'issue:r:1:');
 def test_inflight_today_drain_ships_in_a_new_offline_shell():
     source = (Path(__file__).parents[1] / "frontend" / "service-worker.js").read_text()
 
-    assert "stackchain-dashboard-shell-v54" in source
+    assert "stackchain-dashboard-shell-v55" in source
     assert "BASE + 'static/today-sync.js'" in source