Fix four scripting parser and value-conversion bugs

[Mike Krüger (mkrueger)]

Summary

Fix four scripting bugs that could execute malformed loop headers, select the wrong array element, fail decimal arithmetic on JSON string values, or reject valid dynamic command arguments.

Changes

• Require the case-insensitive in keyword in for headers and while after do bodies. Invalid headers produce parser diagnostics before any statements in the input execute.
• Reject filter array indexes that exceed Int32.MaxValue, including optional access, instead of silently substituting index zero. Representable indexes outside an array still return null.
• Make JSON-to-decimal conversion return the same culture-invariant double representation as other shell values. Numeric JSON strings work in decimal arithmetic and comparisons; string concatenation with + remains unchanged.
• Share command argument parsing between ordinary commands and exec, supporting options with space-separated, =, and : values, negative arguments, URLs, and file patterns while preserving typed expressions.
• Add regression coverage for parser diagnostics, prevention of earlier execution, script scope restoration, filter errors, value origins, culture invariance, and dynamic command binding.
• Update the changelog, README, scripting documentation, and filter specification.

Release scope

This is a follow-up for a future release and should not be included in the current release.

[Copilot]

Copilot review overview

🟡 Changes recommended

The value-conversion regression coverage does not follow the repository’s required value-origin matrix.

Review effort: Balanced
Findings: 1

Open (1)

• Expand value-semantics regression matrix for JSON origins and operand order · New

What changed in this PR

Fixes four scripting issues involving loop validation, filter indexes, JSON numeric conversion, and dynamic exec arguments.

Changes:

• Validates loop keywords and filter index ranges.
• Aligns JSON decimal conversion with shell doubles.
• Reuses command argument parsing for exec and adds regression coverage and documentation.

File	Description
README.md	Summarizes corrected scripting behavior.
docs/​programming.md	Documents conversion, loops, and exec arguments.
docs/​filter-v1-spec.md	Defines valid filter index bounds.
StatementParser.cs	Validates keywords and shares argument parsing.
ShellJson.cs	Returns invariant doubles for decimal conversion.
ExpressionParser.cs	Rejects overflowing filter indexes.
ScriptExecutionScopeTests.cs	Tests invalid scripts and scope restoration.
StatementParserEdgeTests.cs	Tests keywords and exec parsing.
StatementExecutionTests.cs	Tests loop preflight and numeric strings.
ShellObjectConversionTests.cs	Updates JSON conversion expectations.
FilterPathExpressionTests.cs	Tests index boundaries and overflow.
CultureInvariantConversionTests.cs	Tests culture-independent JSON conversion.
CommandExecutionTests.cs	Tests dynamic command argument execution.
FilterCommandTests.cs	Tests filter overflow handling.
CHANGELOG.md	Records the four fixes.

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[github-code-quality]

Code Coverage Overview

Languages: C#

C# / code-coverage/dotnet

The overall line coverage in commit aed1c2b in the dev/mkrueger/fix-scr... branch remains at 66%, unchanged from commit dc14571 in the main branch.

Show a line coverage summary of the most impacted files.

File	main dc14571	dev/mkrueger/fix-scr... aed1c2b	+/-
D:\a\CosmosDBSh...tementParser.cs	77%	78%	+1%
D:\a\CosmosDBSh...essionParser.cs	84%	85%	+1%
D:\a\CosmosDBSh...llWordParser.cs	97%	99%	+2%
D:\a\CosmosDBSh...xecStatement.cs	77%	79%	+2%
D:\a\CosmosDBSh...onExpression.cs	69%	73%	+4%
D:\a\CosmosDBSh...OptionBinder.cs	57%	74%	+17%