Dictionary Keys Guards

[feO2x]

Closes #148

[Copilot]

Pull request overview

This PR reintroduces dictionary key guard clauses (MustContainKey / MustNotContainKey) to Light.GuardClauses using the v4-era conventions, including new exception types, throw helpers, source-export support, documentation, and test coverage.

Changes:

• Added MustContainKey / MustNotContainKey guards for IReadOnlyDictionary<TKey, TValue> plus shape-preserving overloads for Dictionary<TKey, TValue>.
• Introduced MissingKeyException / ExistingKeyException and corresponding Throw.MissingKey / Throw.ExistingKey helpers.
• Updated source-export whitelists/settings, regenerated the .NET Standard single-file distribution, expanded docs, and added comprehensive automated tests.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tools/source-export/Light.GuardClauses.SourceCodeTransformation/settings.json	Adds the new assertion families to the source-export configuration.
tools/source-export/Light.GuardClauses.SourceCodeTransformation/AssertionWhitelist.cs	Extends the whitelist model with MustContainKey / MustNotContainKey entries.
src/Light.GuardClauses/Check.MustContainKey.cs	Implements MustContainKey guards for IReadOnlyDictionary and Dictionary (shape-preserving) with factory overloads.
src/Light.GuardClauses/Check.MustNotContainKey.cs	Implements MustNotContainKey guards for IReadOnlyDictionary and Dictionary (shape-preserving) with factory overloads.
src/Light.GuardClauses/Exceptions/MissingKeyException.cs	Adds the new exception type thrown when a key is missing.
src/Light.GuardClauses/Exceptions/ExistingKeyException.cs	Adds the new exception type thrown when a key unexpectedly exists.
src/Light.GuardClauses/ExceptionFactory/Throw.MissingKey.cs	Provides the default exception construction/message for missing-key failures (including key listing).
src/Light.GuardClauses/ExceptionFactory/Throw.ExistingKey.cs	Provides the default exception construction/message for existing-key failures.
tests/Light.GuardClauses.Tests/CollectionAssertions/MustContainKeyTests.cs	Adds behavioral, null-handling, comparer-sensitivity, factory, message, and binding tests for MustContainKey.
tests/Light.GuardClauses.Tests/CollectionAssertions/MustNotContainKeyTests.cs	Adds behavioral, null-handling, comparer-sensitivity, factory, message, and binding tests for MustNotContainKey.
tests/Light.GuardClauses.SourceCodeTransformation.Tests/SourceFileMergerWhitelistTests.cs	Verifies source-export whitelist output includes the new guards/exceptions/throw helpers and trims factory overloads when disabled.
Light.GuardClauses.SingleFile.cs	Regenerates the .NET Standard single-file distribution to include the new guards and exceptions.
docs/assertion-overview.md	Documents the new dictionary key guards and the IDictionary<TKey, TValue> limitation/workaround.
ai-plans/0148-dictionary-key-guards.md	Adds the implementation plan/acceptance criteria record for issue #148.
AGENTS.md	Removes a previously recorded “notes” entry from the “Here is Your Space” section.

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