From 2ef055a41af6a6a0399055525d77d39957281e65 Mon Sep 17 00:00:00 2001
From: Masahiko AMANO <hiko-19@ya.ru>
Date: Wed, 10 Jun 2026 14:53:26 +0300
Subject: [PATCH] fix(backend): pool reorder no longer drops omitted members

Reorder did DELETE all pool memberships then re-inserted only the passed
file_ids, so a paginated client that sent just the loaded pages silently
removed every other file from the pool. Reorder now places the requested
files in order and appends any members the request omitted (in their
current order), so a partial reorder is safe and correct.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
---
 backend/internal/db/postgres/pool_repo.go | 52 +++++++++++++++++++++--
 1 file changed, 48 insertions(+), 4 deletions(-)

diff --git a/backend/internal/db/postgres/pool_repo.go b/backend/internal/db/postgres/pool_repo.go
index 868239e..e5b373e 100644
--- a/backend/internal/db/postgres/pool_repo.go
+++ b/backend/internal/db/postgres/pool_repo.go
@@ -656,10 +656,54 @@ func (r *PoolRepo) RemoveFiles(ctx context.Context, poolID uuid.UUID, fileIDs []
 // Reorder
 // ---------------------------------------------------------------------------
 
-// Reorder replaces the full ordered sequence with positions 1000, 2000, …
-// Only file IDs already in the pool are allowed; unknown IDs are silently
-// skipped to avoid integrity violations.
+// Reorder applies the requested order to the pool. Files actually in the pool
+// are placed in the given order; any pool members the request omitted are kept
+// and appended in their current order. This makes a partial request (e.g. a
+// paginated client that only loaded the first pages) reorder the visible prefix
+// without deleting the rest. Unknown IDs are ignored.
 func (r *PoolRepo) Reorder(ctx context.Context, poolID uuid.UUID, fileIDs []uuid.UUID) error {
 	q := connOrTx(ctx, r.pool)
-	return r.reassignPositions(ctx, q, poolID, fileIDs)
+
+	// Current membership, in position order.
+	rows, err := q.Query(ctx,
+		`SELECT file_id FROM data.file_pool WHERE pool_id = $1 ORDER BY position ASC, file_id ASC`, poolID)
+	if err != nil {
+		return fmt.Errorf("PoolRepo.Reorder fetch: %w", err)
+	}
+	var current []uuid.UUID
+	for rows.Next() {
+		var fid uuid.UUID
+		if err := rows.Scan(&fid); err != nil {
+			rows.Close()
+			return fmt.Errorf("PoolRepo.Reorder scan: %w", err)
+		}
+		current = append(current, fid)
+	}
+	rows.Close()
+	if err := rows.Err(); err != nil {
+		return fmt.Errorf("PoolRepo.Reorder rows: %w", err)
+	}
+
+	inPool := make(map[uuid.UUID]bool, len(current))
+	for _, fid := range current {
+		inPool[fid] = true
+	}
+
+	ordered := make([]uuid.UUID, 0, len(current))
+	placed := make(map[uuid.UUID]bool, len(current))
+	for _, fid := range fileIDs {
+		if inPool[fid] && !placed[fid] {
+			ordered = append(ordered, fid)
+			placed[fid] = true
+		}
+	}
+	// Preserve any members the request did not mention.
+	for _, fid := range current {
+		if !placed[fid] {
+			ordered = append(ordered, fid)
+			placed[fid] = true
+		}
+	}
+
+	return r.reassignPositions(ctx, q, poolID, ordered)
 }
\ No newline at end of file