Cover single evaluation of direct nullable nested-updater sources

[AGiorgetti]

Summary

Direct nullable source members passed to explicitly selected nested update mappings need a regression proving single evaluation under NullableMismatch.Throw.

Evidence

The nested-updater branch only creates a capture for configured paths. For a direct nullable source member, the generated precondition reads source.Child and the updater invocation reads it again. Relevant logic begins at src/Mammoth.LiteMapper.Generator/LiteMapperGenerator.cs:745, with the precondition path at line 771 and update assignment rendering at line 4150.

Risk

A side-effecting direct source getter can run twice before the nested updater is invoked, violating the source-path and existing-target single-evaluation contract.

Acceptance criteria

• Add a regression with a direct nullable source property whose getter records invocation count.
• Exercise an explicitly selected nested updater under NullableMismatch.Throw.
• Assert the generated mapping evaluates the source property exactly once for both non-null and null behavior.
• If the regression fails, apply the smallest generator fix that preserves patch/nullability semantics.
• Verify focused nested-update tests and required full validation suite pass.

Specification references

Sections 9.4, 11.4, 12.4, 14.4, 16.1, and 22.13.

[AGiorgetti]

Agent claim registered for autonomous execution.

[AGiorgetti]

AgentStack Protocol: execution-plan

1. Add a red compile-and-run regression proving a direct nullable source expression passed to a nested updater is evaluated exactly once for non-null and null cases. 2. Trace the existing updater source capture, null precondition, and invocation rendering. 3. Apply the smallest generator fix that binds the direct source once under NullableMismatch.Throw while preserving patch and nullable semantics. 4. Run focused nested-update tests, full generator tests, Release build, and full solution tests, then submit review.

[AGiorgetti]

AgentStack Protocol: progress

• Implementation complete in commit 5770334. Added a red direct nullable nested-updater regression with side-effecting getter, covering present and null behavior under NullableMismatch.Throw. Minimal generator fix pattern-captures direct nullable updater sources so the getter is evaluated once. Focused regression: 1/1 passed after fix
• nested-update suite: 17/17
• full generator tests: 568/568
• Release build: 0 warnings/errors
• packaging: 61 passed plus 1 expected Native AOT prerequisite skip
• runtime: 5/5
• integration: 1/1. Push and review submission are pending explicit authorization for this issue Cover single evaluation of direct nullable nested-updater sources #13 payload.