Use double consistently for JSON decimal conversion

[Mike Krüger (mkrueger)]

Summary

• Return double for JSON decimal conversion, matching shell decimal values and arithmetic consumers.
• Fix numeric JSON strings failing decimal arithmetic and ordered comparisons with invalid casts.
• Extend the literal/JSON/loop/function value-origin matrix, direct conversion tests, and invariant-culture coverage.
• Document numeric string coercion while preserving addition as concatenation.

Validation

• 1570 focused parser and script-scope tests passed.
• App and test projects build with zero warnings/errors.
• CLI reproduction now returns 3 for a JSON string containing 2 multiplied by 1.5.

[Copilot]

Copilot review overview

🟢 Approval recommended

The implementation consistently matches existing shell numeric semantics and includes focused regression coverage and documentation.

Review effort: Balanced
Findings: None

What changed in this PR

Aligns JSON decimal conversion with the shell’s double representation, fixing numeric-string arithmetic and comparisons.

Changes:

• Converts JSON numbers and numeric strings to invariant-culture double.
• Expands conversion, value-origin, and culture tests.
• Documents numeric-string coercion behavior.

File	Description
README.md	Summarizes numeric-string behavior.
docs/​programming.md	Documents coercion rules and examples.
ShellJson.cs	Uses double for decimal conversion.
StatementExecutionTests.cs	Tests operators across value origins.
ShellObjectConversionTests.cs	Verifies direct double conversion.
CultureInvariantConversionTests.cs	Tests invariant-culture parsing.
CHANGELOG.md	Records the fix.

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[github-code-quality]

Code Coverage Overview

Languages: C#

C# / code-coverage/dotnet

The overall line coverage in commit 46aff4a in the dev/mkrueger/fix/jso... branch remains at 66%, unchanged from commit fa2b09c in the main branch.

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_{Updated October 07, 2026 09:33 UTC}

[Mike Krüger (mkrueger)]

Copilot resolve the merge conflicts in this pull request

[Copilot]

Copilot review overview

🟢 Approval recommended

The implementation consistently fixes the conversion mismatch with comprehensive tests and aligned documentation.

Review effort: Balanced
Findings: None

[Copilot]

Copilot resolve the merge conflicts in this pull request

Merged main cleanly; no conflict resolution was needed. Merge commit: a6e5467. Focused tests and both builds passed.

[Copilot]

Copilot review overview

🟢 Approval recommended

The conversion is consistent with existing shell numeric semantics and is covered across direct, culture-specific, and value-origin scenarios.

Review effort: Balanced
Findings: None