fix(cli): refuse to overwrite corrupt config.json on gitt config set (entrius#845)

When `~/.gittensor/config.json` failed to parse, `config_set` printed a
yellow warning, set `config = {}`, then wrote a fresh single-key file —
silently destroying every previously-configured key (network,
contract_address, ws_endpoint, hotkey, ...).

Mirror PR entrius#817's read-side fix: `JSONDecodeError` now aborts with a clear
message and `SystemExit(1)`, leaving the corrupt file untouched so the
operator can inspect or recover it.

New regression tests in `tests/cli/test_config_set.py` cover the
abort-with-nonzero-exit, byte-for-byte preservation of the corrupt file,
non-regression of the valid-file merge path, and the first-run case.

Closes entrius#845

Author: plind-junior

gittensor/cli/main.py

@@ -117,13 +117,23 @@ def config_set(key: str, value: str):
     # Ensure config directory exists
     GITTENSOR_DIR.mkdir(parents=True, exist_ok=True)
 
-    # Load existing config or start fresh
+    # Load existing config or start fresh.
+    # On JSONDecodeError refuse to overwrite — the file may contain values the
+    # operator still relies on (network, contract_address, ws_endpoint, hotkey).
+    # Silently writing a fresh single-key config would erase those and fall
+    # through to mainnet defaults on the next read. Mirrors load_config's
+    # read-side fix (PR #817 / #816).
     config = {}
     if CONFIG_FILE.exists():
         try:
             config = json.loads(CONFIG_FILE.read_text())
-        except json.JSONDecodeError:
-            console.print('[yellow]Warning: Existing config was invalid, starting fresh[/yellow]')
+        except json.JSONDecodeError as e:
+            console.print(
+                f'[red]Error: Config file at {CONFIG_FILE} is not valid JSON ({e}).[/red]\n'
+                f'[red]Refusing to overwrite — inspect or move the file aside before retrying[/red]\n'
+                f'[red]so previously-configured keys (network, contract_address, ws_endpoint, ...) are not lost.[/red]'
+            )
+            raise SystemExit(1)
 
     # Set the value
     old_value = config.get(key)

tests/cli/test_config_set.py

@@ -0,0 +1,91 @@
+# The MIT License (MIT)
+# Copyright © 2025 Entrius
+
+"""
+Tests for `gitt config set` corrupt-file handling.
+
+Regression: a single corrupt-config recovery used to wipe every previously-set
+key and replace the file with `{key: value}`. Operator's `network`,
+`contract_address`, `ws_endpoint`, and `hotkey` would silently disappear and
+the next `gitt issues ...` would fall through to finney mainnet. Companion to
+PR #817 / issue #816 (read side) and closes issue #845 (write side).
+"""
+
+import json
+from pathlib import Path
+from unittest.mock import patch
+
+import pytest
+from click.testing import CliRunner
+
+from gittensor.cli.main import config_group
+
+
+@pytest.fixture
+def temp_config_dir(tmp_path: Path):
+    """Redirect CONFIG_FILE/GITTENSOR_DIR to a temp dir for one test."""
+    config_dir = tmp_path / '.gittensor'
+    config_file = config_dir / 'config.json'
+    with (
+        patch('gittensor.cli.main.GITTENSOR_DIR', config_dir),
+        patch('gittensor.cli.main.CONFIG_FILE', config_file),
+    ):
+        yield config_dir, config_file
+
+
+def _read(config_file: Path) -> dict:
+    return json.loads(config_file.read_text()) if config_file.exists() else {}
+
+
+class TestConfigSetCorruption:
+    """`gitt config set` must not destroy other keys when the file is corrupt."""
+
+    def test_corrupt_config_aborts_with_nonzero_exit(self, temp_config_dir):
+        config_dir, config_file = temp_config_dir
+        config_dir.mkdir(parents=True)
+        # Truncated JSON — simulates an interrupted write or manual edit.
+        config_file.write_text('{"network": "test"')
+
+        runner = CliRunner()
+        result = runner.invoke(config_group, ['set', 'hotkey', 'default'])
+
+        assert result.exit_code != 0
+        assert 'not valid JSON' in result.output
+        assert 'Refusing to overwrite' in result.output
+
+    def test_corrupt_config_preserves_existing_file(self, temp_config_dir):
+        """The whole point: the bad file is left alone, not clobbered."""
+        config_dir, config_file = temp_config_dir
+        config_dir.mkdir(parents=True)
+        original_bytes = b'{"network": "test"'
+        config_file.write_bytes(original_bytes)
+
+        runner = CliRunner()
+        runner.invoke(config_group, ['set', 'hotkey', 'default'])
+
+        # Byte-for-byte identical: the operator can recover the values they
+        # had configured before the corruption.
+        assert config_file.read_bytes() == original_bytes
+
+    def test_valid_config_still_round_trips(self, temp_config_dir):
+        """Non-corrupt files must still merge new keys without loss."""
+        config_dir, config_file = temp_config_dir
+        config_dir.mkdir(parents=True)
+        config_file.write_text(json.dumps({'network': 'test', 'wallet': 'alice'}))
+
+        runner = CliRunner()
+        result = runner.invoke(config_group, ['set', 'hotkey', 'default'])
+
+        assert result.exit_code == 0, result.output
+        assert _read(config_file) == {'network': 'test', 'wallet': 'alice', 'hotkey': 'default'}
+
+    def test_missing_config_creates_fresh(self, temp_config_dir):
+        """First-run case: no existing file is fine — write a fresh one."""
+        _, config_file = temp_config_dir
+        assert not config_file.exists()
+
+        runner = CliRunner()
+        result = runner.invoke(config_group, ['set', 'wallet', 'alice'])
+
+        assert result.exit_code == 0, result.output
+        assert _read(config_file) == {'wallet': 'alice'}