fix(mcp): fall back to form_data spatial query for Deck.gl charts

[aminghadersohi]

SUMMARY

get_chart_data MCP tool was returning a MissingQueryContext error for
Deck.gl charts (deck_scatter, deck_arc, deck_hex, etc.) when those charts had
no saved query_context. Instead of offering a data retrieval path, the tool
told users to re-open and re-save the chart in Superset.

Deck.gl charts use spatial column configs (lat/lon pairs, geohash, delimited
coordinates, GeoJSON) rather than the standard metrics/groupby structure.
This PR teaches the form_data fallback path how to extract those columns.

Changes:

• Add _deck_gl_spatial_cols (private helper) and resolve_deck_gl_columns
  to chart_helpers.py. The helper reads spatial, start_spatial,
  end_spatial, line_column, geojson, dimension, and js_columns
  fields from form_data and returns the SQL column names needed by the
  underlying query — mirroring BaseDeckGLViz.query_obj() semantics.

• Route deck_* viz types through the new helpers inside
  build_query_dicts_from_form_data. When a size/metric field is present
  (e.g., point-radius or weight metric), it is included in the query; spatial
  columns become the groupby dimensions. Without a metric, spatial columns
  become raw-select columns.

• Remove the hard error block in get_chart_data.py that rejected all
  Deck.gl charts with MissingQueryContext. The existing safety-net (empty
  columns + empty metrics) still covers charts whose spatial config is
  completely missing.

• Add unit tests covering: latlong, delimited, geohash spatial types;
  arc start/end spatial; line_column; geojson; dimension;
  js_columns; column deduplication; the build_query_dicts_from_form_data
  Deck.gl branch with and without metrics.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

N/A (backend-only change to MCP tool data retrieval)

TESTING INSTRUCTIONS

1. Find or create a Deck.gl chart (e.g., Scatter, Arc, Hex) in Superset
   whose params JSON has a spatial field but no saved
   query_context.
2. Call the get_chart_data MCP tool with that chart's ID.
3. Before: ChartError with error_type: "MissingQueryContext" and a
   message asking the user to re-save the chart.
4. After: The tool queries the underlying dataset using the lat/lon (or
   geohash/delimited) columns from form_data and returns tabular data.

Run the new unit tests:

pytest tests/unit_tests/mcp_service/chart/test_chart_helpers.py -x -q \
  -k "deck"

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

❌ Patch coverage is 6.89655% with 27 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.11%. Comparing base (d203f0d) to head (ed15be8).
⚠️ Report is 28 commits behind head on master.

Files with missing lines	Patch %	Lines
superset/mcp_service/chart/chart_helpers.py	6.89%	27 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #40339      +/-   ##
==========================================
- Coverage   64.18%   64.11%   -0.08%     
==========================================
  Files        2591     2592       +1     
  Lines      138459   138930     +471     
  Branches    32118    32223     +105     
==========================================
+ Hits        88875    89069     +194     
- Misses      48052    48329     +277     
  Partials     1532     1532              

Flag	Coverage Δ
hive	39.28% <6.89%> (-0.13%)	⬇️
mysql	58.78% <6.89%> (-0.28%)	⬇️
postgres	58.87% <6.89%> (-0.28%)	⬇️
presto	40.95% <6.89%> (-0.15%)	⬇️
python	60.42% <6.89%> (-0.15%)	⬇️
sqlite	58.51% <6.89%> (-0.28%)	⬇️
unit	100.00% <ø> (ø)

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[bito-code-review]

Code Review Agent Run #7b748a

Actionable Suggestions - 0

Additional Suggestions - 1

• superset/mcp_service/chart/tool/get_chart_data.py - 1

  • Missing test for deck.gl fallback · Line 340-367
    The deleted deck.gl special-case block lacks test coverage. While the removal is correct (build_query_dicts_from_form_data handles deck_* viz types via resolve_deck_gl_columns), adding a test ensures the fallback path works for deck.gl charts without query_context.

Review Details

• Files reviewed - 3 · Commit Range: ed15be8..ed15be8

  • superset/mcp_service/chart/chart_helpers.py
  • superset/mcp_service/chart/tool/get_chart_data.py
  • tests/unit_tests/mcp_service/chart/test_chart_helpers.py
• Files skipped - 0
• Tools

  • Whispers (Secret Scanner) - ✔︎ Successful
  • Detect-secrets (Secret Scanner) - ✔︎ Successful
  • MyPy (Static Code Analysis) - ✔︎ Successful
  • Astral Ruff (Static Code Analysis) - ✔︎ Successful

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