s3tables: fix shared table-location bucket mapping collisions (#8286)

* s3tables: prevent shared table-location bucket mapping overwrite

* Update weed/s3api/bucket_paths.go

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

weed/s3api/s3tables/table_location_mapping_test.go

@@ -0,0 +1,77 @@
+package s3tables
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestGetTableLocationMappingEntryPathPerTable(t *testing.T) {
+	tableLocationBucket := "shared-location--table-s3"
+	tablePathA := GetTablePath("warehouse", "analytics", "orders")
+	tablePathB := GetTablePath("warehouse", "analytics", "customers")
+
+	entryPathA := GetTableLocationMappingEntryPath(tableLocationBucket, tablePathA)
+	entryPathARepeat := GetTableLocationMappingEntryPath(tableLocationBucket, tablePathA)
+	entryPathB := GetTableLocationMappingEntryPath(tableLocationBucket, tablePathB)
+
+	if entryPathA != entryPathARepeat {
+		t.Fatalf("mapping entry path should be deterministic: %q != %q", entryPathA, entryPathARepeat)
+	}
+	if entryPathA == entryPathB {
+		t.Fatalf("mapping entry path should differ per table path: %q == %q", entryPathA, entryPathB)
+	}
+
+	expectedPrefix := GetTableLocationMappingPath(tableLocationBucket) + "/"
+	if !strings.HasPrefix(entryPathA, expectedPrefix) {
+		t.Fatalf("mapping entry path %q should start with %q", entryPathA, expectedPrefix)
+	}
+	if strings.TrimPrefix(entryPathA, expectedPrefix) == "" {
+		t.Fatalf("mapping entry name should not be empty: %q", entryPathA)
+	}
+}
+
+func TestTableBucketPathFromTablePath(t *testing.T) {
+	testCases := []struct {
+		name      string
+		tablePath string
+		expected  string
+		ok        bool
+	}{
+		{
+			name:      "valid table path",
+			tablePath: GetTablePath("warehouse", "analytics", "orders"),
+			expected:  GetTableBucketPath("warehouse"),
+			ok:        true,
+		},
+		{
+			name:      "valid table bucket root",
+			tablePath: GetTableBucketPath("warehouse"),
+			expected:  GetTableBucketPath("warehouse"),
+			ok:        true,
+		},
+		{
+			name:      "invalid non-tables path",
+			tablePath: "/tmp/warehouse/analytics/orders",
+			expected:  "",
+			ok:        false,
+		},
+		{
+			name:      "invalid empty bucket segment",
+			tablePath: "/buckets/",
+			expected:  "",
+			ok:        false,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			actual, ok := tableBucketPathFromTablePath(tc.tablePath)
+			if ok != tc.ok {
+				t.Fatalf("tableBucketPathFromTablePath(%q) ok=%v, want %v", tc.tablePath, ok, tc.ok)
+			}
+			if actual != tc.expected {
+				t.Fatalf("tableBucketPathFromTablePath(%q)=%q, want %q", tc.tablePath, actual, tc.expected)
+			}
+		})
+	}
+}