feat(mcp): add observability to MCP service

[aminghadersohi]

SUMMARY

The MCP service emitted zero StatsD/Prometheus metrics, and its middleware swallowed every exception before any error tracker could see them. This adds:

• Per-tool metrics: success/error counters and timing in LoggingMiddleware.on_call_tool, plus a user-vs-system error counter split in GlobalErrorHandlerMiddleware._handle_error — mirrors the @statsd_metrics pattern already used in views/base_api.py.
• Fixed silently-dropped audit rows: LoggingMiddleware skipped its event_logger.log(...) call entirely when has_app_context() was False at the time the middleware finally block ran (the per-tool app context had already exited). Both call sites now wrap the log call in the existing _get_app_context_manager() helper instead of skipping it.
• Pluggable MCP_ERROR_HOOK config: a vendor-neutral Callable[[Exception, dict], None] | None hook invoked for system-class errors in GlobalErrorHandlerMiddleware._handle_error (primary capture point) and in StructuredContentStripperMiddleware.on_call_tool's last-resort except block (for exceptions that bypass the primary handler entirely). This lets operators wire an external error tracker (e.g. Sentry) without the OSS repo taking a hard dependency on any vendor SDK. PRODUCTION.md is updated to note that FlaskIntegration does not cover the FastMCP tool-execution path and shows wiring Sentry via the hook instead.
• error_type extraction: LoggingMiddleware previously substring-sniffed "error_type" in serialized tool responses only to decide success/failure, discarding the actual value. It's now parsed and included in the log line, curated payload, and metric tag.
• Small fixes: the generic "Internal error" branch used a second-granularity f"err_{int(time.time())}" ID that collides under concurrent failures — replaced with the existing per-call mcp_call_id. Added event_logger.log_context instrumentation to get_chart_type_schema (previously the only uninstrumented tool). Added server-side logger.warning/logger.exception calls next to several return XError(...) sites in get_chart_data, get_tag_info, and query_dataset that only logged to the MCP client (ctx.error/ctx.warning, which never reaches server logs) or didn't log at all.

BEFORE/AFTER

Before: grep -r "stats_logger\|statsd\|incr(\|timing(" superset/mcp_service/ → no hits. No error tracker could ever see an MCP tool failure, and DB audit rows for mcp_tool_call/mcp_message were silently dropped whenever the ambient Flask app context had already exited.

After: Per-tool mcp.tool.{name}.{success|error} counters and mcp.tool.{name}.time timing are emitted on every tool call. Audit rows are always written. Operators can wire MCP_ERROR_HOOK to forward system-class errors to an external tracker.

TESTING INSTRUCTIONS

• Extended tests/unit_tests/mcp_service/test_middleware.py and test_middleware_logging.py with unit tests covering: metrics emission (success/error counters + timing, including the call_tool proxy tool-name resolution case), error_type extraction from structured responses, the MCP_ERROR_HOOK invocation/no-op/exception-swallowing paths in both middlewares, the mcp_call_id-as-error_id fix, and regression tests confirming both LoggingMiddleware.on_call_tool and on_message route their audit-row log call through _get_app_context_manager() rather than conditionally skipping it.
• pytest tests/unit_tests/mcp_service/ — 2691 passed.
• ruff check / ruff format --check / mypy / pylint all pass on the changed files.

ADDITIONAL INFORMATION

• Has associated tests
• Has screenshots (N/A — backend-only observability change)
• Changes UI
• Introduces new feature or API
• Removes existing feature

[codecov]

Codecov Report

❌ Patch coverage is 3.07692% with 63 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.72%. Comparing base (0ff52d4) to head (9ab2905).
⚠️ Report is 217 commits behind head on master.

Files with missing lines	Patch %	Lines
superset/mcp_service/middleware.py	0.00%	44 Missing ⚠️
superset/mcp_service/chart/tool/get_chart_data.py	0.00%	15 Missing ⚠️
...et/mcp_service/chart/tool/get_chart_type_schema.py	33.33%	2 Missing ⚠️
superset/mcp_service/dataset/tool/query_dataset.py	0.00%	1 Missing ⚠️
superset/mcp_service/tag/tool/get_tag_info.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #41921      +/-   ##
==========================================
- Coverage   64.74%   64.72%   -0.03%     
==========================================
  Files        2738     2738              
  Lines      152950   153009      +59     
  Branches    35055    35059       +4     
==========================================
- Hits        99032    99028       -4     
- Misses      52018    52081      +63     
  Partials     1900     1900              

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hive	38.96% <3.07%> (-0.03%)	⬇️
mysql	57.88% <3.07%> (-0.05%)	⬇️
postgres	57.94% <3.07%> (-0.05%)	⬇️
presto	40.92% <3.07%> (-0.03%)	⬇️
python	59.33% <3.07%> (-0.05%)	⬇️
sqlite	57.55% <3.07%> (-0.05%)	⬇️
unit	100.00% <ø> (ø)

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