feat(suggestions): visible, reversible rejection in the modal rail

A red-✗ dismissal no longer makes the suggestion vanish. The rejected tag
stays in the rail — dimmed, struck-through, with a "rejected" pill and a
one-click undo (↶) in place of the ✗ — so a misclick is recoverable and the
operator can see what they've said no to (operator-asked 2026-06-27).

Backend: SuggestionService.for_image now KEEPS rejected tags, flagged
rejected=True, sorted to the bottom of their category, instead of dropping
them. New AllowlistService.undismiss + POST /suggestions/undismiss clears the
TagSuggestionRejection. Rejected items are still excluded from bulk consensus
(for_selection) and the type-to-add dropdown, whose jobs are unchanged.

Frontend: store.dismiss flags in place (canonical tags) rather than dropping;
new store.undismiss reverts. SuggestionItem renders the rejected state and
swaps ✗→↶; ✓ still accepts (which clears the rejection server-side).

Tests: rejected-surfaced-flagged-then-reversible (service) + undismiss
endpoint idempotency (API).

Completes #1134's reversible-rejection half. Heads-as-suggestion-source is
the remaining piece.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ttrj5P7upUTueSfoJcxEqa

backend/app/services/ml/allowlist.py

@@ -89,6 +89,12 @@ class AllowlistService:
         )
         await self.session.execute(stmt)
 
+    async def undismiss(self, image_id: int, tag_id: int) -> None:
+        """Undo a per-image dismissal — drop the TagSuggestionRejection so the
+        suggestion reverts to a live (un-rejected) state. Backs the rail's
+        one-click reject-recovery (operator-asked 2026-06-27)."""
+        await self._clear_rejection(image_id, tag_id)
+
     async def reject_applied_tag(self, image_id: int, tag_id: int) -> None:
         """Operator removed an applied tag from an image. Remove the
         image_tag row AND record a rejection so the allowlist won't

backend/app/services/ml/suggestions.py

@@ -39,6 +39,11 @@ class Suggestion:
     # via_alias = this suggestion was surfaced because an operator alias remapped
     # the raw prediction to this canonical tag. Lets the UI mark it + offer undo.
     via_alias: bool = False
+    # rejected = the operator dismissed this tag for this image (a stored
+    # TagSuggestionRejection). It stays in the list — flagged, not dropped — so
+    # the rejection is VISIBLE and REVERSIBLE in the rail (misclick recovery,
+    # operator-asked 2026-06-27) instead of silently vanishing or re-suggesting.
+    rejected: bool = False
 
 
 @dataclass
@@ -174,12 +179,15 @@ class SuggestionService:
                     # augmentation, so it's always the first writer for a key.
                     raw_name=existing.raw_name,
                     via_alias=existing.via_alias,
+                    # rejected is a property of the tag_id, so both writers for a
+                    # key agree — preserve it through the higher-score rebuild.
+                    rejected=existing.rejected,
                 )
 
         for raw, display, category, conf in candidates:
             canonical = alias_map.get((raw, category))
             if canonical is not None:
-                if canonical.id in applied or canonical.id in rejected:
+                if canonical.id in applied:
                     continue
                 _merge(
                     canonical.id,
@@ -192,6 +200,7 @@ class SuggestionService:
                         creates_new_tag=False,
                         raw_name=raw,
                         via_alias=True,
+                        rejected=canonical.id in rejected,
                     ),
                 )
             else:
@@ -209,10 +218,7 @@ class SuggestionService:
                     )
                 ).scalars().first()
                 if existing_tag is not None:
-                    if (
-                        existing_tag.id in applied
-                        or existing_tag.id in rejected
-                    ):
+                    if existing_tag.id in applied:
                         continue
                     _merge(
                         existing_tag.id,
@@ -225,6 +231,7 @@ class SuggestionService:
                             creates_new_tag=False,
                             raw_name=raw,
                             via_alias=False,
+                            rejected=existing_tag.id in rejected,
                         ),
                     )
                 else:
@@ -247,7 +254,7 @@ class SuggestionService:
         for hit in hits:
             if hit.similarity < settings.centroid_similarity_threshold:
                 continue
-            if hit.tag_id in applied or hit.tag_id in rejected:
+            if hit.tag_id in applied:
                 continue
             tag = await self.session.get(Tag, hit.tag_id)
             if tag is None:
@@ -263,6 +270,7 @@ class SuggestionService:
                     score=hit.similarity,
                     source="centroid",
                     creates_new_tag=False,
+                    rejected=hit.tag_id in rejected,
                 ),
             )
 
@@ -270,7 +278,9 @@ class SuggestionService:
         for sug in merged.values():
             result.by_category.setdefault(sug.category, []).append(sug)
         for cat in result.by_category:
-            result.by_category[cat].sort(key=lambda s: s.score, reverse=True)
+            # Live suggestions first (by score), rejected ones sink to the
+            # bottom of the category — visible for recovery, out of the way.
+            result.by_category[cat].sort(key=lambda s: (s.rejected, -s.score))
         return result
 
     async def for_selection(
@@ -297,6 +307,11 @@ class SuggestionService:
                 for s in items:
                     if s.canonical_tag_id is None or s.creates_new_tag:
                         continue
+                    # for_image now keeps rejected tags (flagged) for the rail;
+                    # bulk consensus must still ignore them — a tag dismissed on
+                    # an image isn't a suggestion for that image.
+                    if s.rejected:
+                        continue
                     st = stats.get(s.canonical_tag_id)
                     if st is None:
                         st = {