fix(server-storage): adopted writes without a known version conflict instead of overwriting

A page that never read the server has no version tags, so an adopted
write went out unconditionally and replaced newer server data with its
cached value. Adopted edits now use the never-matching version when this
page knows none (and for a queued write without a tag), so the server
answers 412 and the edits are replayed on its value.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/architecture/pwa-self-hosted.md

@@ -233,7 +233,9 @@ settings and guards read them in every build.
   which copies `sessionStorage`, leaves the running tab its writes. A page
   load that still looked live (or whose close flag storage refused) is
   checked again every 30 s and, once it does not, adopted like a closed
-  tab's: its edits go ahead of this page's newer ones; the writes of a tab closed before it
+  tab's: its edits go ahead of this page's newer ones, and without a
+  server version this page read they are sent so that they conflict and
+  replay; the writes of a tab closed before it
   could send them are queued, ahead of its own, by the next re-read in
   another tab once that tab's record has gone stale; the result replays the
   closed tab's edits first and this tab's newer ones last. Tabs never clear each other's.

libs/services/src/lib/server-storage/server-user-data-adopt.ts

@@ -24,6 +24,12 @@ export function adoptEdits(
     const key = `${namespace}|${playlistId}`;
     const adopted = uncertain(steps);
     const queued = writes.isQueued(key) ? writes.unsent(key) : undefined;
+    // Without a server version this page read, the write must conflict and
+    // be replayed on the server's value, never overwrite it blindly.
+    const unknown =
+        foreign ||
+        (queued ? queued.tag : writes.tags.of(namespace, playlistId)) ===
+            undefined;
     if (queued) {
         // This tab's queued edits are newer: they replay last.
         const all = [...adopted, ...queued.steps];
@@ -32,12 +38,12 @@ export function adoptEdits(
             ...queued,
             value,
             steps: all,
-            tag: foreign ? UNKNOWN_TAG : queued.tag,
+            tag: unknown ? UNKNOWN_TAG : queued.tag,
         });
         return value;
     }
     const value = replaySteps(current, steps);
-    writes.queue(namespace, playlistId, value, value, { foreign });
+    writes.queue(namespace, playlistId, value, value, { foreign: unknown });
     const entry = writes.unsent(key);
     if (entry) {
         writes.put({ ...entry, steps: [...adopted, ...entry.steps] });

libs/services/src/lib/server-storage/server-user-data-sync.spec.ts

@@ -1182,5 +1182,39 @@ describe('ServerUserDataStorage with other devices', () => {
 
             expect(server.state['xtream-favorites']['p1']).toEqual(['S', 'X']);
         });
+
+        it("replays its writes on the server's value when this page never read it", async () => {
+            const server = fakeServer({ 'xtream-favorites': { p1: ['S'] } });
+            const local = memoryStorage();
+            const tabStore = memoryStorage();
+            const clock = jest.spyOn(Date, 'now').mockReturnValue(1_000);
+            await lastPageLoad(server, local, tabStore, async (page) => {
+                await page.hydrate();
+                page.setItem(
+                    'xtream-favorites',
+                    JSON.stringify({ p1: ['S', 'X'] })
+                );
+                await page.flush();
+            });
+            // Another device saves Z; this page's reads keep failing.
+            server.state['xtream-favorites']['p1'] = ['S', 'Z'];
+            const reloaded = new ServerUserDataStorage(
+                { ...server.api, getJson: jest.fn(offline) } as never,
+                local,
+                jest.fn(),
+                'default',
+                tabStore
+            );
+
+            clock.mockReturnValue(1_000 + UNCONFIRMED_TTL_MS + 1);
+            reloaded.touch();
+            await reloaded.flush();
+            await reloaded.flush();
+            clock.mockRestore();
+
+            expect(
+                [...(server.state['xtream-favorites']['p1'] as string[])].sort()
+            ).toEqual(['S', 'X', 'Z']);
+        });
     });
 });