Add selected single-file persistent tree store

store-tree.c keeps every document in one append-only file as a persistent
B-tree of byte extents, with the key catalog in the same structure. A splice
writes only the changed leaf and path; unchanged extents are shared between
versions, readers take no lock, and two alternating head slots publish a
commit after its nodes are durable. Compaction rewrites reachable nodes.

On the recorded ext4 host a durable 1-byte middle insert into a 1 MiB
document took 8.58 ms against 78.51 ms for the default store, and the real
TUI's Ctrl+S after typing took 16.60 ms against 84.59 ms. check-tree runs the
store's crash/oracle tests and the unchanged runtime, splice, async and
real-PTY editor checks on it. It stays opt-in: linked code is 12.7 KB larger
and contiguous multi-leaf reads copy.

1 files changed, 3 insertions, 0 deletions

diff --git a/prototypes/connections/test-splice.c b/prototypes/connections/test-splice.c
index bf3c0a9..51970d3 100644
--- a/prototypes/connections/test-splice.c
+++ b/prototypes/connections/test-splice.c
@@ -126,12 +126,15 @@ static void storage(const char *path) {
     expect(path, "work", revision, (PureSpan){oracle, length});
     CHECK(pure_store_splice(path, "work", revision, 0, length, (PureSpan){0}, PURE_OBJECT_LIMIT, &revision) == PURE_OK);
     expect(path, "work", revision, (PureSpan){0});
+#ifndef PURE_STORE_TREE
+    /* Per-object file formats; test-tree-store covers the same limit. */
     char file[256];
     snprintf(file, sizeof(file), "%s/obj-work", path);
     int fd = open(file, O_WRONLY);
     const unsigned char maximum[] = {255,255,255,255,255,255,255,127};
     CHECK(fd >= 0 && pwrite(fd, maximum, 8, 8) == 8 && close(fd) == 0);
     CHECK(pure_store_splice(path, "work", INT64_MAX, 0, 0, (PureSpan){0}, PURE_OBJECT_LIMIT, &revision) == PURE_LIMIT);
+#endif
 }
 
 static void runtime(const char *path) {