feat(stepfunctions): real UpdateExpression eval for dynamodb:updateItem

[vieiralucas]

Summary

• Replaces the simplified Key + ExpressionAttributeValues merge with a real UpdateExpression evaluator that parses up to four clauses in any order (SET, REMOVE, ADD, DELETE)
• SET supports path = :v, path = path + :inc, path = path - :dec, and path = if_not_exists(path, :default)
• ADD is numeric increment with implicit initialization when the attribute is absent
• DELETE subtracts set elements from SS / NS / BS and drops the attribute when the resulting set is empty
• DynamoDB number wire format ({"N":"<str>"}) preserved on arithmetic; comma splitting respects parentheses so if_not_exists(a, :b) doesn't fragment assignments

Test plan

• 7 new unit tests: SET arithmetic increment + decrement, REMOVE, ADD existing + absent, DELETE set elements, if_not_exists both branches, multi-clause SET ... ADD ... REMOVE
• All 137 existing fakecloud-stepfunctions tests still green (legacy set keyword + alias attribute names included)
• cargo clippy --workspace --all-targets -- -D warnings clean
• cargo fmt --check clean

---

Summary by cubic

Adds a real DynamoDB UpdateExpression evaluator for dynamodb:updateItem, supporting SET, REMOVE, ADD, and DELETE. Fixes incorrect merges so increments, conditional sets, attribute removal, and set deletes follow DynamoDB semantics.

• New Features

  • Parses clauses in any order and splits on top-level commas (parentheses respected).
  • SET: assign value, arithmetic +/-, and if_not_exists.
  • ADD: numeric increment; initializes when absent.
  • DELETE: removes elements from SS/NS/BS; drops the attribute when empty.
  • Preserves DynamoDB number wire format and upserts from Key when no item exists.

• Bug Fixes

  • Number formatting: range-checks f64 before i64 cast and uses an exclusive i64::MAX bound to avoid truncation or saturation on large whole numbers.

^{Written for commit 29b99c0. Summary will update on new commits.}

[cubic-dev-ai]

1 issue found across 1 file

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="crates/fakecloud-stepfunctions/src/interpreter.rs">

<violation number="1" location="crates/fakecloud-stepfunctions/src/interpreter.rs:1619">
P2: `n as i64` saturates for whole-number f64 values outside the i64 range, silently corrupting the formatted number. Add a range check before the cast.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

1 issue found across 1 file (changes from recent commits).

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="crates/fakecloud-stepfunctions/src/interpreter.rs">

<violation number="1" location="crates/fakecloud-stepfunctions/src/interpreter.rs:1618">
P2: The inclusive `f64` bound check still allows `2^63`, which then saturates on `as i64` and formats to an incorrect value.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[codecov]

Codecov Report

❌ Patch coverage is 92.23602% with 25 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/fakecloud-stepfunctions/src/interpreter.rs	92.23%	25 Missing ⚠️

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