feat: 'disable' renames to sync.json.disabled; new 'enable' rename-back

Pause/resume sync without losing the instance_id.

  disable  sync.json -> sync.json.disabled
  enable   sync.json.disabled -> sync.json

Re-enabling preserves the original ULID + url so the same restic
repo continues. No new instance_id minted, no orphaned snapshot
history. Tradeoff vs the previous 'disable = delete' semantics:
the on-disk artifact survives, so a truly fresh start now needs
'disable && rm sync.json.disabled' before 'setup'.

Implementation:

  config.disable(pack)  os.rename(sync.json -> sync.json.disabled).
                        False if no sync.json.
  config.enable(pack)   os.rename(sync.json.disabled -> sync.json).
                        Refuses if sync.json already exists
                        (caller must disable first).
  config.delete(pack)   now sweeps BOTH forms (escape hatch / tests).

setup_flow gains a precheck: if sync.json.disabled is present, point
the user at 'enable' instead of silently minting a fresh ULID over
their existing instance.

Opt-in gate (cfgmod.exists) is unchanged — only literal sync.json
counts. The .disabled sibling is invisible to pull/push, so the
silent-no-op behavior for paused instances Just Works.

cli adds 'enable' subcommand alongside 'disable'. _run_disable prints
'already disabled' when called twice; _run_enable refuses to clobber
an active config (exits 2 with the FileExistsError message).

7 new tests for disable/enable behavior + edge cases (idempotency,
nothing-to-X, refuse-clobber). 80 tests total.

cloud_sync/cli.py

@@ -80,10 +80,22 @@ def build_parser() -> argparse.ArgumentParser:
         help="discord_id:password token (read from stdin if omitted)",
     )
 
-    # --- disable: rm sync.json ---
+    # --- disable: rename sync.json → sync.json.disabled ---
     sp = sub.add_parser(
         "disable",
-        help="remove sync.json — re-noops the instance. Cloud data untouched.",
+        help="pause sync on this instance (renames sync.json -> sync.json.disabled). "
+             "Re-enable with `enable`. Cloud data untouched.",
+    )
+    sp.add_argument(
+        "--pack-folder", default=".", type=Path,
+        help="Minecraft instance directory (default: cwd)",
+    )
+
+    # --- enable: rename sync.json.disabled → sync.json ---
+    sp = sub.add_parser(
+        "enable",
+        help="resume sync on this instance (renames sync.json.disabled -> sync.json). "
+             "Preserves the original instance_id + url so snapshots continue.",
     )
     sp.add_argument(
         "--pack-folder", default=".", type=Path,
@@ -159,6 +171,8 @@ def main(argv: list[str] | None = None) -> int:
 
     if cmd == "disable":
         return _run_disable(ns)
+    if cmd == "enable":
+        return _run_enable(ns)
     if cmd in ("setup", "init"):
         return _run_setup(ns, cmd)
 
@@ -186,13 +200,42 @@ def main(argv: list[str] | None = None) -> int:
 def _run_disable(ns: argparse.Namespace) -> int:
     from . import config as cfgmod
     pack = Path(ns.pack_folder).absolute().resolve()
-    if cfgmod.delete(pack):
-        print(f"instance-sync: removed {cfgmod.config_path(pack)}")
-    else:
-        print(f"instance-sync: no sync.json at {cfgmod.config_path(pack)} (already disabled)")
+    if cfgmod.disable(pack):
+        print(
+            f"instance-sync: disabled — moved {cfgmod.config_path(pack).name} "
+            f"to {cfgmod.disabled_path(pack).name} in {cfgmod.config_path(pack).parent}. "
+            "Re-enable with `instance-sync enable`."
+        )
+        return 0
+    if cfgmod.disabled_path(pack).exists():
+        print(f"instance-sync: already disabled ({cfgmod.disabled_path(pack)} present)")
+        return 0
+    print(f"instance-sync: not enabled — no sync.json at {cfgmod.config_path(pack)}")
     return 0
 
 
+def _run_enable(ns: argparse.Namespace) -> int:
+    from . import config as cfgmod
+    pack = Path(ns.pack_folder).absolute().resolve()
+    try:
+        renamed = cfgmod.enable(pack)
+    except FileExistsError as e:
+        print(f"instance-sync: {e}", file=sys.stderr)
+        return 2
+    if renamed:
+        print(f"instance-sync: enabled — restored {cfgmod.config_path(pack)}")
+        return 0
+    if cfgmod.config_path(pack).exists():
+        print(f"instance-sync: already enabled ({cfgmod.config_path(pack)} present)")
+        return 0
+    print(
+        f"instance-sync: no sync.json.disabled at {cfgmod.disabled_path(pack)}. "
+        "Run `instance-sync setup` to opt in this instance fresh.",
+        file=sys.stderr,
+    )
+    return 2
+
+
 def _run_setup(ns: argparse.Namespace, cmd: str) -> int:
     """Wire `setup` (interactive) and `init` (flags-only) through the same
     flow module so both share the dialog/CLI logic."""