test: complete runtime config lease matrix

harness/tht/runtime_config_lease_io.py

@@ -236,6 +236,18 @@ def write_all(fd: int, data: bytes) -> None:
         pos += n
 
 
+def publication_fsync(fd: int, stage: str) -> None:
+    """Fsync one publication boundary, with an explicit test-only fault seam.
+
+    The seam is inert unless the caller opts in with the exact stage name.  It is
+    intentionally kept here (rather than in TypeScript) so the real helper's
+    durable ordering can be exercised without weakening production behaviour.
+    """
+    if os.environ.get("THT_RUNTIME_CONFIG_FSYNC_FAIL") == stage:
+        fail(f"runtime config fsync failed at {stage}")
+    os.fsync(fd)
+
+
 def read_all(fd: int, limit: int = 16 * 1024 * 1024) -> bytes:
     os.lseek(fd, 0, os.SEEK_SET)
     chunks: list[bytes] = []
@@ -361,7 +373,7 @@ def publish(inp: dict) -> dict:
             try:
                 write_all(fd, content)
                 os.fchmod(fd, 0o400)
-                os.fsync(fd)
+                publication_fsync(fd, "config-file")
                 try:
                     _rename_noreplace(stage, name, cfgdir, "config")
                 except FileExistsError:
@@ -384,7 +396,7 @@ def publish(inp: dict) -> dict:
                     fail("same-revision runtime configuration changed")
             finally:
                 os.close(fd)
-            os.fsync(cfgdir)
+            publication_fsync(cfgdir, "config-parent")
         # Identity is deliberately recorded after final no-replace publication.
         got = current(cfgdir, name, 0o400)
         assert got
@@ -423,7 +435,7 @@ def publish(inp: dict) -> dict:
             try:
                 write_all(fd, mb)
                 os.fchmod(fd, 0o600)
-                os.fsync(fd)
+                publication_fsync(fd, "manifest-file")
                 try:
                     _rename_noreplace(stage, mname, mandir, "manifest")
                 except FileExistsError:
@@ -449,7 +461,7 @@ def publish(inp: dict) -> dict:
                     os.unlink(stage, dir_fd=mandir)
                 except FileNotFoundError:
                     pass
-            os.fsync(mandir)
+            publication_fsync(mandir, "manifest-parent")
         return {
             "path": f"{root}/sessions/{wid}/preprocessing/runtime-config/{name}",
             "manifestPath": f"{root}/sessions/{wid}/preprocessing/runtime-config-manifests/{mname}",