fix(mcp): Skip misleading trend analysis for categorical ASCII charts

[alexandrusoare]

SUMMARY

Problem

When an LLM asks for an ASCII chart preview of categorical data (e.g., countries sorted alphabetically), the trend analysis compares first vs last data points and reports statements like "Strong downward trend." This is meaningless — the ordering is alphabetical, not temporal — and misleads LLMs into drawing incorrect conclusions about the data.

Root Cause

_analyze_trend() unconditionally compares values[0] vs values[-1] to determine directional trend, assuming the data is temporally ordered. It has no awareness of whether the x-axis represents time or categories. _extract_time_series_data() already distinguishes date columns from categorical ones (via keyword matching on column names), but this signal was discarded — never propagated to the trend analysis.

Fix

• _extract_time_series_data now returns an is_temporal flag (True when the label column name contains date/time keywords)
• _analyze_trend accepts this flag and replaces directional trend statements with a categorical caveat when is_temporal=False
• Range and volatility stats are preserved regardless — they remain valid for any data

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

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• Introduces new feature or API
• Removes existing feature or API

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• Files reviewed - 2 · Commit Range: ebb9801..ebb9801

  • superset/mcp_service/chart/ascii_charts.py
  • tests/unit_tests/mcp_service/chart/test_ascii_charts.py
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[codecov]

Codecov Report

❌ Patch coverage is 8.33333% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.86%. Comparing base (0a3a350) to head (30e063e).
⚠️ Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
superset/mcp_service/chart/ascii_charts.py	8.33%	22 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #39761      +/-   ##
==========================================
- Coverage   64.16%   63.86%   -0.30%     
==========================================
  Files        2591     2585       -6     
  Lines      138302   136940    -1362     
  Branches    32084    31522     -562     
==========================================
- Hits        88736    87457    -1279     
+ Misses      48036    47953      -83     
  Partials     1530     1530              

Flag	Coverage Δ
hive	39.41% <8.33%> (-0.03%)	⬇️
mysql	59.08% <8.33%> (-0.05%)	⬇️
postgres	59.16% <8.33%> (-0.05%)	⬇️
presto	41.10% <8.33%> (-0.03%)	⬇️
python	60.59% <8.33%> (-0.05%)	⬇️
sqlite	58.79% <8.33%> (-0.05%)	⬇️
unit	100.00% <ø> (ø)

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