feat(logging): per-scan `{run_dir}/strix.log` with scan/agent context tagging

Every scan now writes a complete log file at ``{run_dir}/strix.log``
captured from the moment ``run_dir`` is resolved through teardown.
Stdlib ``logging`` only — no parallel framework.

New ``strix/telemetry/logging.py``:
  * ``setup_scan_logging(run_dir, debug=)`` attaches a ``FileHandler``
    (DEBUG, all ``strix.*``) plus a ``StreamHandler`` (ERROR by
    default; DEBUG via ``STRIX_DEBUG=1``).
  * ``ContextVar``-backed ``scan_id`` and ``agent_id`` injected by a
    ``Filter`` so every line is auto-tagged across asyncio tasks
    without callers passing them explicitly.
  * Third-party noise (``httpx``, ``litellm``, ``openai``,
    ``anthropic``, ``urllib3``, ``httpcore``) capped at WARNING.
  * Returns a teardown handle for ``finally`` cleanup.

Wiring:
  * ``orchestration/scan.py`` calls ``setup_scan_logging`` once per
    scan after ``run_dir`` resolves; sets scan_id; tears down in
    ``finally``. Adds INFO logs for sandbox bring-up + scan
    start/end.
  * ``orchestration/hooks.py`` sets/clears ``agent_id`` ContextVar in
    ``on_agent_start`` / ``on_agent_end`` and emits INFO for agent
    lifecycle, DEBUG for every tool start/end and LLM call.
  * ``interface/main.py`` drops the ``setLevel(ERROR)`` silencer.

Coverage expanded across ~20 files (orchestration, agents, runtime,
llm, tools, interface, config, skills) with INFO for lifecycle and
DEBUG for verbose detail. Per the system instructions in
``logger.warning(f"…{e}")`` were converted to module logger calls.

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

strix/agents/factory.py

@@ -166,6 +166,16 @@ def build_strix_agent(
         tools = [*_BASE_TOOLS, agent_finish]
         stop_at = ("agent_finish",)
 
+    logger.info(
+        "Built %s agent '%s' (skills=%d, tools=%d, scan_mode=%s, whitebox=%s)",
+        "root" if is_root else "child",
+        name,
+        len(skills or []),
+        len(tools),
+        scan_mode,
+        is_whitebox,
+    )
+
     return SandboxAgent(
         name=name,
         instructions=instructions,

strix/agents/prompt.py

@@ -122,4 +122,12 @@ def render_system_prompt(
         logger.exception("render_system_prompt failed; returning empty prompt")
         return ""
     else:
+        logger.debug(
+            "render_system_prompt: scan_mode=%s root=%s whitebox=%s skills=%d prompt_len=%d",
+            scan_mode,
+            is_root,
+            is_whitebox,
+            len(skill_content),
+            len(rendered),
+        )
         return str(rendered)