duplicates: library-aware visibility — only hide a demoted row when its survivor is reachable

Soft-marked rows used to disappear from /photos globally, including
from a library-scoped view that didn't contain the survivor at all.
A user browsing lib A who'd promoted a file from lib B as the
survivor would silently lose visibility on their own copy in lib A,
even though lib B's file isn't reachable from lib A's view.

Library-scoped queries now keep a demoted row visible when its
survivor lives in a library outside the current scope. Implemented
as a NOT EXISTS subquery against the same image_exif table aliased
as `survivor`. The unscoped (all-libraries) view is unchanged — every
survivor is reachable, so demoted rows stay hidden as before.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/database/mod.rs

@@ -1222,7 +1222,38 @@ impl ExifDao for SqliteExifDao {
             }
 
             if !include_duplicates {
+                if library_ids.is_empty() {
+                    // Unscoped (all-libraries) view — every survivor is
+                    // reachable somewhere, so a soft-marked row is
+                    // genuinely a duplicate from the user's perspective.
+                    // Hide it.
                     query = query.filter(duplicate_of_hash.is_null());
+                } else {
+                    // Scoped to specific libraries: only hide a
+                    // soft-marked row when the survivor is reachable
+                    // *in this view*. If the survivor lives in a
+                    // library the user can't see right now, the
+                    // demoted file is the only copy of those bytes
+                    // they have access to — keep it visible.
+                    //
+                    // Implemented as a correlated NOT EXISTS subquery
+                    // over an aliased image_exif. Library ids are i32
+                    // so format!-inlining the integer list is safe.
+                    use diesel::sql_types::Bool;
+                    let lib_list = library_ids
+                        .iter()
+                        .map(i32::to_string)
+                        .collect::<Vec<_>>()
+                        .join(",");
+                    let raw = format!(
+                        "(image_exif.duplicate_of_hash IS NULL OR NOT EXISTS \
+                         (SELECT 1 FROM image_exif AS survivor \
+                          WHERE survivor.content_hash = image_exif.duplicate_of_hash \
+                            AND survivor.library_id IN ({})))",
+                        lib_list
+                    );
+                    query = query.filter(diesel::dsl::sql::<Bool>(&raw));
+                }
             }
 
             query