[BUG] Fix #220 #221 #222 — PandasAdapter dead code, negative limit validation, async background loop

[harsh2025-sketch]

Summary

Fixes three confirmed bugs found during ESoC 2026 codebase audit.

Fixes #220
Fixes #221
Fixes #222

---

Fix #220 — PandasAdapter auto-detection dead code

File: src/sktime_mcp/data/adapters/pandas_adapter.py

Condition was always False — pd.Index is base class of all pandas
index types so _detect_time_column was never called.

Fix: Removed pd.Index from check — detection now triggers correctly
on RangeIndex inputs.

---

Fix #221 — Negative limit returns 400+ results

File: src/sktime_mcp/tools/list_estimators.py

limit was never validated. limit=-5 caused all_estimators[0:-5]
to return 410 results, flooding LLM agent context window.

Fix: Added guard before slice:
if limit is not None and limit < 0: return error

---

Fix #222 — Async jobs stay pending forever

Files: _background_loop.py (new), fit_predict.py, data_tools.py

run_coroutine_threadsafe was submitting to a loop never started
in a background thread. All async jobs stayed pending forever.

Fix: Created _BackgroundLoop with daemon thread running
loop.run_forever(). All async tools now submit via BG_LOOP.submit(coro).

---

Tests — all passing

Test	Result
test_list_estimators_negative_limit_rejected	done
test_list_estimators_zero_limit_returns_empty	done
test_pandas_adapter_auto_detects_time_column	done
test_async_fit_predict_tool_completes_background_job	done

[Copilot]

Pull request overview

This PR fixes three audited bugs across data loading, estimator listing, and async background job execution in sktime_mcp, and adds regression tests to prevent recurrence.

Changes:

• Fix PandasAdapter time-column auto-detection so _detect_time_column() is reachable when the index is a default RangeIndex.
• Validate limit in list_estimators_tool to reject negative values that would otherwise return a near-full page.
• Introduce a shared background asyncio loop (BG_LOOP) and route async tool submissions through it so background jobs actually execute.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/sktime_mcp/data/adapters/pandas_adapter.py	Adjusts index-type guard so time-column detection runs when time_column is omitted.
src/sktime_mcp/tools/list_estimators.py	Adds negative limit validation before slicing.
src/sktime_mcp/runtime/_background_loop.py	Adds a singleton background event loop running in a daemon thread and a submit() API.
src/sktime_mcp/tools/fit_predict.py	Uses BG_LOOP.submit(...) for async fit/predict jobs instead of submitting to a non-running loop.
src/sktime_mcp/tools/data_tools.py	Uses BG_LOOP.submit(...) for async data-loading jobs instead of submitting to a non-running loop.
tests/test_core.py	Adds regression tests for negative/zero limit and pandas time-column auto-detection.
tests/test_background_jobs.py	Adds a tool-level regression test ensuring async fit/predict jobs move beyond pending.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.