Fix #519, #576, #696 + regression guards for #590, #608, #581, #606

[YogeshPraj]

Summary

Tier 2 follow-up to #727 (perf) and our batch-1 PR. Three real fixes, four already-fixed-on-main verifications turned into regression tests. Each fix has a dedicated test file.

Fixes #576 — ActionContext ctor NRE when Context is null

ActionContext's constructor unconditionally iterates context and dereferences each kv.Value.GetType(). Custom actions that don't need configuration commonly leave OnSuccess.Context = null, which crashed before the action could even run.

Added a null guard on the dictionary itself and on each value. A null value now stores null in the internal map instead of throwing.

Fixes #519 — ExecuteActionWorkflowAsync skipped FormatErrorMessages

ExecuteAllRulesAsync interpolates Rule.ErrorMessage ($(input.foo)) into RuleResultTree.ExceptionMessage via FormatErrorMessages. ExecuteActionWorkflowAsync did not, so users got an unpopulated ExceptionMessage on the same workflow.

Added the call in ExecuteActionWorkflowAsync right before invoking the action. Result-tree shape and ordering are unchanged; only ExceptionMessage is now populated consistently.

Fixes #696 — Multi-level dotted ErrorMessage interpolation

UpdateErrorMessage split the dotted path but only used segments [0] (typeName) and [1] (propertyName). For $([input1.Inner.Name](https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Finput1.inner.name%2F&data=05%7C02%7CYogesh.Prajapati%40microsoft.com%7C8276de067a704d3c502608debc07dec3%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C639154939190866661%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=mjtWuqX8oJIvyRkxLPcQCYkCg8c2bh%2Ffv%2BzGl88fcNw%3D&reserved=0)) it set typeName=input1, propertyName=Inner — and then the replacement was the raw JSON of Inner ({"Name":"deep-value"}) instead of "deep-value".

Rewrote the helper to walk the full path via JsonNode, returning the leaf scalar unquoted (for JsonValue strings) or nested JSON otherwise. The single-level case is unchanged.

Regression guards (verified already fixed on master)

#	Title	Fixed by
#590	Exception message from prior run leaks into next successful run	Commit 4ca3cc2 (PR #592)
#608	UseFastExpressionCompiler=true + chained scoped-param sums NRE'd	FastExpressionCompiler / Dynamic.Core version bumps
#581	Custom parameter name not honored ("Enum type 'endpoint' not found")	Likely the AutoRegisterInputType work in PR #501
#606	Lambda parameter l reported as unknown identifier	Dynamic.Core 1.4.3 → 1.6.7 bumps

Each repro from the linked issue now passes on master. Added explicit tests so we'd notice if any of these regressed.

Not fixed in this PR

#390 (ActionContext receives literal string instead of evaluated value) is a design decision rather than a bug — ActionContext is documented as a static key/value config dict; users who want evaluation should use OutputExpression. Happy to revisit in a separate PR if the maintainers want to introduce a $(...)-evaluating mode.

Test plan

• 7 new test files (Issue519/576/581/590/606/608/696), 11 new tests total.
• All 142 unit tests pass on net6.0 / net8.0 / net9.0 / net10.0.
• No changes to public API surface; behavior changes only on the documented-but-broken paths.