Refacto load all functions

Unbounded LoadAll* loaders materialised an entire result set in one
query with no ceiling. A table that is small in development can grow
without bound in production, so these loaders were a latent memory
and query-time hazard.

Remove the LoadAll* methods from pkg/coredata and walk the cursor-
paginated LoadBy* siblings instead through a shared page.LoadAll
helper. The helper advances a MaxCursorSize forward cursor until the
result set is exhausted and concatenates the pages. It caps a single
call at MaxLoadAllPages (20) batches of 500 rows and errors past that
rather than materialising an unbounded set, so a runaway caller fails
loudly instead of exhausting memory.

Callers that genuinely need every row now express that explicitly,
and the coredata load-naming rule and docs are updated to discourage
new unbounded loaders.

Signed-off-by: Sacha Al Himdani <sacha@probo.com>

pkg/page/load_all.go

@@ -0,0 +1,76 @@
+// Copyright (c) 2025-2026 Probo Inc <hello@probo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package page
+
+import (
+	"context"
+	"fmt"
+)
+
+// MaxLoadAllPages caps how many pages LoadAll walks, bounding a single
+// call to MaxLoadAllPages*MaxCursorSize rows. Past that, LoadAll errors
+// rather than materialising an unbounded set.
+const MaxLoadAllPages = 20
+
+// Loader runs one paginated query for the given cursor and returns the
+// rows it loaded. Callers bind the connection, scope, parent key and
+// filter in a closure, exposing only ctx and cursor (typically a coredata
+// LoadBy* on a fresh receiver).
+type Loader[T Paginable[U], U OrderField] func(ctx context.Context, cursor *Cursor[U]) ([]T, error)
+
+// LoadAll walks every matching row via keyset pagination, advancing a
+// MaxCursorSize forward cursor until no rows remain, and returns them
+// concatenated. fetch runs the paginated query for the cursor. It errors
+// past MaxLoadAllPages pages.
+func LoadAll[T Paginable[U], U OrderField](
+	ctx context.Context,
+	orderBy OrderBy[U],
+	fetch Loader[T, U],
+) ([]T, error) {
+	var (
+		all []T
+		key *CursorKey
+	)
+
+	for page := 0; ; page++ {
+		if page >= MaxLoadAllPages {
+			return nil, fmt.Errorf(
+				"cannot load all rows: result set exceeds %d rows (%d pages of %d)",
+				MaxLoadAllPages*MaxCursorSize,
+				MaxLoadAllPages,
+				MaxCursorSize,
+			)
+		}
+
+		cursor := NewCursor(MaxCursorSize, key, Head, orderBy)
+
+		rows, err := fetch(ctx, cursor)
+		if err != nil {
+			return nil, fmt.Errorf("cannot load all rows: %w", err)
+		}
+
+		p := NewPage(rows, cursor)
+		all = append(all, p.Data...)
+
+		if !p.Info.HasNext {
+			break
+		}
+
+		k := p.Last().CursorKey(orderBy.Field)
+		key = &k
+	}
+
+	return all, nil
+}