refactor(config): pydantic-settings revamp + drop `is_whitebox` plumbing

Replaces 200+ lines of bespoke env-loader / persist / change-detection
machinery with ``pydantic_settings.BaseSettings`` (already a transitive
of ``openai-agents → mcp``, no new direct dep).

What was wrong with ``Config``:

- 14 knobs flat in one namespace, weak grouping by comment-block.
- ``Config._applied_from_default`` and ``Config._config_file_override``
  were externally mutated from ``interface/main.py:532-534``. Private
  members were part of the public contract.
- Stringly-typed values: every caller had to coerce
  (``int(Config.get("llm_timeout") or "300")``,
  ``... not in {"0", "false", "no", "off"}``).
- Dead knob: ``strix_llm_max_retries`` declared, persisted, listed in
  ``_LLM_CANONICAL_NAMES`` — zero readers (``DEFAULT_RETRY``
  hardcodes ``max_retries=5``). Dropped.
- ``_LLM_CANONICAL_NAMES`` tuple maintained alongside class vars —
  duplicate source of truth.
- ``_tracked_names()`` introspected ``vars(cls).items()`` filtered on
  ``(v is None or isinstance(v, str))`` — fragile.
- Awkward path: ``strix/config/config.py`` inside ``strix/config/``
  with ``__init__.py`` just re-exporting.
- Dual access for the same fact: ``web_search`` read
  ``os.getenv("PERPLEXITY_API_KEY")`` while ``main.py`` read
  ``Config.get("perplexity_api_key")``.

New shape:

- ``strix/config/settings.py`` — typed dataclass tree:
  ``Settings.{llm,runtime,telemetry,integrations}``. Each sub-model is
  its own ``BaseSettings`` so it reads env independently. Field-level
  ``alias=`` and ``validation_alias=AliasChoices(...)`` mirror the
  existing flat env-var names — user-facing env contract is unchanged.
  Bool fields auto-parse ``"0"``/``"false"``/``"no"``/``"off"``;
  int fields auto-coerce.
- ``strix/config/loader.py`` — thin ``load_settings()``,
  ``apply_config_override(path)``, ``persist_current()`` with module
  cache. JSON file reader walks aliases to populate sub-models, dropping
  entries already covered by env (so env still wins).
- 13 callsites migrated from ``Config.get("...")`` to
  ``load_settings().<group>.<field>``.
- ``posthog._is_enabled()`` collapses to one line.
- ``--config <path>`` flow simplified: one
  ``apply_config_override(...)`` call replaces three lines of
  class-private mutation.

Drive-by — drop ``is_whitebox`` from ``scan_config`` dict:

- It was being derived as ``bool(args.local_sources)`` in three places
  (``cli.py``, ``tui.py``, ``main.py``) and stuffed into the dict for
  ``entry.py`` to read back. The fact is fully derivable from
  ``scan_config["targets"]`` — any target with ``type == "local_code"``.
- New helper ``is_whitebox_scan(targets)`` in ``interface/utils.py``
  alongside the other target-classification utilities.
- ``entry.py`` computes once; ``main.py``'s posthog start uses the same
  helper. Triplicate derivation gone.

Verified: ruff at baseline (3), mypy at baseline (69). Six smoke tests
pass — defaults / JSON-only / env-wins-over-JSON / alias-chain
fallback / bool parsing / ``is_whitebox_scan``.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

strix/config/loader.py

@@ -0,0 +1,123 @@
+"""Settings loader, override switch, and disk persistence.
+
+Process-wide module cache so repeated ``load_settings()`` calls in the
+same scan are free. ``apply_config_override(path)`` invalidates the
+cache so the next ``load_settings()`` re-resolves with the new file.
+"""
+
+from __future__ import annotations
+
+import contextlib
+import json
+import os
+from pathlib import Path
+from typing import TYPE_CHECKING, Any
+
+from pydantic import AliasChoices, BaseModel
+
+from strix.config.settings import Settings
+
+
+if TYPE_CHECKING:
+    from pydantic.fields import FieldInfo
+
+
+_DEFAULT_PATH: Path = Path.home() / ".strix" / "cli-config.json"
+_override: Path | None = None
+_cached: Settings | None = None
+
+
+def load_settings() -> Settings:
+    """Resolve settings from env + JSON file + defaults. Memoized.
+
+    Precedence: env vars win, then the JSON file, then field defaults.
+    """
+    global _cached  # noqa: PLW0603
+    if _cached is None:
+        init_kwargs: dict[str, Any] = _read_json_overrides(_override or _DEFAULT_PATH)
+        _cached = Settings(**init_kwargs)
+    return _cached
+
+
+def apply_config_override(path: Path) -> None:
+    """Switch the JSON source to ``path`` and invalidate the cache."""
+    global _override, _cached  # noqa: PLW0603
+    _override = path
+    _cached = None
+
+
+def persist_current() -> None:
+    """Write currently-set env vars to the active config file (0o600)."""
+    s = load_settings()
+    target = _override or _DEFAULT_PATH
+    target.parent.mkdir(parents=True, exist_ok=True)
+
+    env_block: dict[str, str] = {}
+    for sub_name in s.model_fields:
+        sub_model = getattr(s, sub_name)
+        if not isinstance(sub_model, BaseModel):
+            continue
+        for finfo in type(sub_model).model_fields.values():
+            for alias in _aliases_for(finfo):
+                value = os.environ.get(alias.upper())
+                if value:
+                    env_block[alias.upper()] = value
+                    break
+
+    target.write_text(json.dumps({"env": env_block}, indent=2), encoding="utf-8")
+    with contextlib.suppress(OSError):
+        target.chmod(0o600)
+
+
+# --- internals ---------------------------------------------------------
+
+
+def _aliases_for(finfo: FieldInfo) -> list[str]:
+    """Collect every env-var name that should populate ``finfo``."""
+    aliases: list[str] = []
+    if finfo.alias:
+        aliases.append(finfo.alias)
+    va = finfo.validation_alias
+    if isinstance(va, AliasChoices):
+        aliases.extend(c for c in va.choices if isinstance(c, str))
+    elif isinstance(va, str):
+        aliases.append(va)
+    return aliases
+
+
+def _read_json_overrides(path: Path) -> dict[str, dict[str, Any]]:
+    """Read ``{"env": {...}}`` from ``path`` and remap to nested kwargs.
+
+    Only includes keys whose env var is NOT already set, so env always
+    wins over the persisted file.
+    """
+    if not path.exists():
+        return {}
+    try:
+        data = json.loads(path.read_text(encoding="utf-8"))
+    except (json.JSONDecodeError, OSError):
+        return {}
+    env_block = data.get("env", {}) if isinstance(data, dict) else {}
+    if not isinstance(env_block, dict):
+        return {}
+
+    # Normalize to upper-case keys for matching.
+    env_block_upper = {str(k).upper(): v for k, v in env_block.items()}
+
+    nested: dict[str, dict[str, Any]] = {}
+    for sub_name, sub_finfo in Settings.model_fields.items():
+        sub_cls = sub_finfo.annotation
+        if not (isinstance(sub_cls, type) and issubclass(sub_cls, BaseModel)):
+            continue
+        sub_data: dict[str, Any] = {}
+        for fname, finfo in sub_cls.model_fields.items():
+            for alias in _aliases_for(finfo):
+                key = alias.upper()
+                if key in os.environ:
+                    break  # env wins; skip JSON for this field
+                if key in env_block_upper:
+                    sub_data[fname] = env_block_upper[key]
+                    break
+        if sub_data:
+            nested[sub_name] = sub_data
+    return nested