Reject oversized filter array indexes

[Mike Krüger (mkrueger)]

Summary

• Reject filter indexes outside the Int32 range instead of silently selecting index zero.
• Preserve null results for valid out-of-range indexes and reject overflow even on optional paths.
• Add parser and command regressions; document the index range.

Validation

• 145 focused filter/parser tests passed.
• App and test projects build with zero warnings/errors.
• CLI reproduction now rejects index 2147483648 instead of returning the first element.

[Copilot]

Copilot review overview

🟢 Approval recommended

The focused validation change is consistent with documented behavior and covered by parser and command tests.

Review effort: Balanced
Findings: None

What changed in this PR

Rejects oversized filter array indexes instead of silently treating them as index zero.

Changes:

• Validates indexes against the Int32 range.
• Adds parser and command regression tests.
• Documents index limits and null behavior.

File	Description
README.md	Documents index limits.
docs/​filter-v1-spec.md	Defines index-range semantics.
ExpressionParser.cs	Reports overflowing indexes as errors.
FilterPathExpressionTests.cs	Tests overflow and maximum indexes.
FilterCommandTests.cs	Verifies command rejection preserves input.
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 8eb1c81 in the dev/mkrueger/fix/fil... branch remains at 66%, unchanged from commit b9aec70 in the main branch.

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_{Updated October 06, 2026 11:16 UTC}

[Mike Krüger (mkrueger)]

Copilot resolve the merge conflicts in this pull request

[Copilot]

Copilot resolve the merge conflicts in this pull request

Merged main into the PR branch; the merge completed without conflicts. Merge commit: 8eb1c81.

[Copilot]

Copilot review overview

🟢 Approval recommended

The implementation, tests, and documentation consistently address oversized indexes without changing valid out-of-range semantics.

Review effort: Balanced
Findings: None