fix(dynamodb): SET complex RHS into nested paths

[vieiralucas]

Summary

• The nested-path SET branch short-circuited to plain resolve_value, so SET a.b = a.b + :d, SET a.b = list_append(a.b, :list), and SET a.b = if_not_exists(a.b, :v) all fell through to None and errored with ValidationException. Real DynamoDB allows every SET RHS shape against every SET LHS, including dotted paths.
• Split SET's RHS evaluation out of the three apply_set_* helpers into a single evaluate_set_rhs that returns Option<Value>. The caller then picks a destination: item.insert (top-level), assign_list_index (indexed), or assign_nested_path (dotted).
• resolve_ref_or_path replaces resolve_value as the single SET-side operand resolver: handles value refs (:x) and document paths (top-level, #name, dotted) by chaining resolve_projection_path with resolve_nested_path.
• Unignore update_set_nested_path_complex_rhs and expand it to cover arithmetic (+/-), list_append, and both if_not_exists branches (skip-when-present, write-when-missing) through a dotted LHS.
• Remove the now-obsolete update_set_nested_path_complex_rhs_errors_cleanly guard: its assertion ("dotted complex RHS must error") directly contradicts the positive test that now passes ("dotted arithmetic yields count = 8"). The positive test is strictly stronger coverage; silent-drop prevention is still locked in by the untouched update_set_nested_path_errors_on_missing_parent and by evaluate_arithmetic_rhs returning ValidationException on type mismatches.

Last of the 4 PRs (#670, #671, #672 already merged) that together close every #[ignore] in expression_corpus_tests.rs.

Test plan

• cargo test -p fakecloud-dynamodb --lib (216 pass, 0 ignored — full corpus green)
• cargo test -p fakecloud-e2e --test dynamodb (46 pass)
• cargo clippy -p fakecloud-dynamodb --all-targets -- -D warnings
• cargo fmt --all

---

Summary by cubic

Enables complex SET RHS on nested/dotted paths in DynamoDB updates (arithmetic, list_append, if_not_exists), fixing previous ValidationException errors and matching real DynamoDB behavior.

• Bug Fixes

  • SET a.b = a.b +/- :d, SET a.b = list_append(a.b, :l), and SET a.b = if_not_exists(a.b, :v) now work with dotted paths and #name placeholders.
  • RHS operands can be value refs (:x) or document paths (top-level, #name, dotted).
  • Honors no-op behavior for if_not_exists when the target already has a value; structural path errors still surface.

• Refactors

  • Added evaluate_set_rhs to compute RHS once and return Option<Value>; callers route to top-level insert, list index, or nested path.
  • Replaced resolve_value with resolve_ref_or_path by chaining resolve_projection_path and resolve_nested_path.
  • Unignored and expanded nested-path tests; removed the obsolete error-guard test.

^{Written for commit dd528ed. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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