fix(web): re-apply the write that settles after an overlapping one failed

Review round 5 on #2091, both findings.

The other overlap order was still wrong. Write 1 (`true`) is in flight
when write 2 (`false`) fails, so the rollback resolves to the stale
entry's `false` — correct at that instant, nothing had landed. Write 1
then lands `true` and only touched refs, so if its own list reload had
failed too, no render would ever correct the UI or the live client while
disk held `true`.

Writes now report both outcomes: `landed` returns whether this write is
the settled state for its server — recorded, with nothing later still in
flight — and `failed` takes a write out of flight so an earlier one that
lands afterwards settles. The toggle re-applies the settled value to the
override and the client, gated on its server still being active.

Serializing per server was the alternative and was not taken: it makes
the modal's debounced saves queue behind each other and changes the write
path to fix a UI-reconciliation concern, and it still could not order two
requests already in flight.

The override reset also moves from a `useEffect` to `useValueChange`,
which is what this repo requires for resetting state from render data —
the entry is referentially stable between reads, and keying on it alone
subsumes the persisted boolean and the server id.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UL9retfvAXRgvi6EWk4SY4
Signed-off-by: cliffhall <cliff@futurescale.com>

clients/web/src/hooks/useLastPersistedSettings.test.tsx

@@ -149,6 +149,35 @@ describe("useLastPersistedSettings", () => {
     expect(api.resolve("A")).toBe(newest);
   });
 
+  it("reports settled only for the last write issued", () => {
+    // The flag is what tells a caller it is safe to re-apply the value to the
+    // UI: while a later write is still in flight, that write will describe disk
+    // when it reports, and re-applying now would fight it.
+    const { api } = harness([entry("A", settings())]);
+    const first = api.begin("A");
+    expect(first.landed(settings({ paginatedLists: true }))).toBe(true);
+    const second = api.begin("A");
+    const third = api.begin("A");
+    expect(second.landed(settings({ paginatedLists: false }))).toBe(false);
+    expect(third.landed(settings({ paginatedLists: true }))).toBe(true);
+    // A superseded straggler is neither recorded nor settled.
+    expect(second.landed(settings({ paginatedLists: false }))).toBe(false);
+  });
+
+  it("treats an earlier write as settled once the later one has failed", () => {
+    // The order that leaves the UI wrong: the later write fails first, rolling
+    // the UI back to a baseline the earlier write then replaces on disk. Once
+    // the failed write stops counting as in flight, the earlier one settles and
+    // its caller can re-apply the value.
+    const { api } = harness([entry("A", settings())]);
+    const first = api.begin("A");
+    const second = api.begin("A");
+    second.failed();
+    const written = settings({ paginatedLists: true });
+    expect(first.landed(written)).toBe(true);
+    expect(api.resolve("A")).toBe(written);
+  });
+
   it("does not let a straggler resurrect a record a fresh read dropped", () => {
     // The high-water mark outlives the record, so an earlier write reporting
     // after `resolve` invalidated things cannot reinstate a superseded value.

clients/web/src/hooks/useLastPersistedSettings.ts

@@ -87,8 +87,22 @@ export interface SettingsWrite {
   /**
    * Record that this write reached disk. A no-op if a write issued after this
    * one has already been confirmed for the same server.
+   *
+   * Returns whether this write is now the **settled** state for that server —
+   * recorded, with no later write still in flight to describe disk after it.
+   * Callers that own UI derived from the setting use it to re-apply the value:
+   * an overlapping write that failed *first* will have rolled that UI back to a
+   * baseline this write has since replaced, and if the list read behind this
+   * one failed too, nothing else would ever correct it.
    */
-  landed: (written: InspectorServerSettings) => void;
+  landed: (written: InspectorServerSettings) => boolean;
+  /**
+   * Report that this write is over without reaching disk, so it stops counting
+   * as in flight. An earlier write that lands afterwards is then the settled
+   * state — which is exactly the order that leaves the UI on a rolled-back
+   * value nothing on disk holds.
+   */
+  failed: () => void;
 }
 
 interface WriteRecord {
@@ -108,6 +122,10 @@ export function useLastPersistedSettings(
   // record dropped by `resolve` can't be resurrected by a straggler that was
   // issued earlier: the high-water mark outlives the record it produced.
   const confirmedRef = useRef<Map<string, number>>(new Map());
+  // Issue orders still in flight per server, so a write that lands can tell
+  // whether it is the last word or whether something later will still report.
+  // A write leaves this set through `landed` or `failed` alike.
+  const pendingRef = useRef<Map<string, Set<number>>>(new Map());
   // Read the list through a ref so a write pairs with the entry as it stands
   // when it finishes, not the one captured when it was issued. Mirrored in an
   // effect rather than assigned during render: writing a ref mid-render is an
@@ -120,16 +138,29 @@ export function useLastPersistedSettings(
 
   const begin = useCallback((serverId: string): SettingsWrite => {
     const sequence = ++nextSequenceRef.current;
+    const pending = pendingRef.current.get(serverId) ?? new Set<number>();
+    pending.add(sequence);
+    pendingRef.current.set(serverId, pending);
+    const settle = () => {
+      pending.delete(sequence);
+    };
     return {
       landed: (written: InspectorServerSettings) => {
+        settle();
         const confirmed = confirmedRef.current.get(serverId) ?? 0;
         // A write issued after this one already reported; it describes disk
         // more recently, whichever of the two happened to finish first.
-        if (confirmed > sequence) return;
+        if (confirmed > sequence) return false;
         confirmedRef.current.set(serverId, sequence);
         const entry = serversRef.current.find((s) => s.id === serverId);
         recordsRef.current.set(serverId, { written, entry });
+        // Settled only while nothing later is still in flight — such a write
+        // will describe disk once it reports, so re-applying this value in the
+        // meantime would fight it.
+        for (const other of pending) if (other > sequence) return false;
+        return true;
       },
+      failed: settle,
     };
   }, []);