fix(desktop): fence forum clipboard settlement before invitation

Preserve the inherited clipboard wait through restack and gate its pre-preparation continuation by mounted visit and authored revision. Adapt the real composer harness to the clipboard seam and cover late settlement across edit, navigation, return and unmount.

Signed-off-by: Logan Johnson <loganj@squareup.com>

Author: loganj

desktop/src/features/forum/ui/ForumComposer.lifecycle.test.mjs

@@ -121,6 +121,9 @@ async function setup(options = {}) {
     "@/features/messages/lib/normalizeMentionClipboard": {
       hasMentionClipboardHtml: () => false,
     },
+    "@/features/messages/lib/mentionClipboardPaste": {
+      handleMentionClipboardPaste: () => false,
+    },
     "@/features/messages/lib/useLinkEditor": { useLinkEditor: () => ({}) },
     "./useCompactComposerInteractions": {
       useCompactComposerInteractions: () => ({ shouldIgnoreBlur: () => false }),
@@ -131,6 +134,9 @@ async function setup(options = {}) {
         mentionState = state.current;
         return {
           knownNames: {},
+          settlePendingMentionBindings: async () => {
+            if (control.settle) await control.settle.promise;
+          },
           cancelMentionAutocomplete: noop,
           updateMentionQuery: noop,
           clearMentions: () => {
@@ -544,3 +550,26 @@ for (const result of ["failure", "success"]) {
     assert.equal(s.calls.filter((c) => c[0] === "add").length, 1);
   });
 }
+
+for (const action of ["navigation", "return", "edit", "unmount"]) {
+  test(`clipboard settlement after ${action} cannot prepare another forum draft`, async () => {
+    const s = await setup();
+    s.edit();
+    const gate = deferred();
+    s.control.settle = gate;
+    await s.submit();
+    if (action === "navigation" || action === "return") {
+      s.navigate("b");
+      s.edit("B draft", []);
+      if (action === "return") s.navigate("a");
+    }
+    if (action === "edit") s.edit("new authored draft", []);
+    if (action === "unmount") s.unmount();
+    await s.finish(gate);
+    assert.equal(s.calls.length, 0);
+    assert.equal(s.prompt.open, false);
+    if (action === "navigation") assert.equal(s.text, "B draft");
+    if (action === "return") assert.equal(s.text, TEXT);
+    if (action === "edit") assert.equal(s.text, "new authored draft");
+  });
+}

desktop/src/features/forum/ui/ForumComposer.tsx

@@ -340,6 +340,7 @@ function ForumComposerVisit({
       }
 
       claimDraftSend(draftKey);
+      const composerRevision = draftLifecycle.getComposerRevision();
       isSubmissionPendingRef.current = true;
       setIsSubmissionPending(true);
       mentions.cancelMentionAutocomplete();
@@ -349,6 +350,12 @@ function ForumComposerVisit({
         // A pasted mention's identity check can still be in flight; extracting
         // first would publish the label with no `p` tag. Bounded internally.
         await mentions.settlePendingMentionBindings();
+        // This await precedes the preparation adapter's own visit fence.
+        if (
+          !mountedRef.current ||
+          draftLifecycle.getComposerRevision() !== composerRevision
+        )
+          return;
         const pubkeys = await prepareMentionPubkeys(
           mentions.extractMentionPubkeys(trimmed),
           trimmed,
@@ -406,6 +413,7 @@ function ForumComposerVisit({
       draftKey,
       drafts.clearDraft,
       draftLifecycle.runComposerUpdate,
+      draftLifecycle.getComposerRevision,
       mentions.getDraftMentionRefs,
       captureRecovery,
       media.pendingImetaRef,