feat(stepfunctions): implement States.JsonMerge intrinsic

[abanna]

Summary

Adds the States.JsonMerge intrinsic function to the Step Functions executor. Previously any state using it failed with Unsupported intrinsic function: States.JsonMerge.

• Implements the shallow merge form States.JsonMerge($.a, $.b, false): the result is a's top-level fields with b's top-level fields merged in, and b wins on a key conflict.
• Rejects the deep-merge form (third argument true) and non-object arguments, matching AWS (which only supports false).
• Also resolves true/false/null literal intrinsic arguments in resolveIntrinsicArg, so the third argument evaluates to a real boolean rather than falling through to path resolution.

Type of change

• New feature (feat:)

AWS Compatibility

States.JsonMerge(json1, json2, isDeepMerge) performs a shallow merge of two JSON objects; the only supported isDeepMerge value is false, and conflicting top-level keys take the value from the second object. Deep merge (true) is rejected. Verified against the documented AWS intrinsic behavior and covered by AslExecutorJsonMergeTest.

Checklist

• ./mvnw test passes locally (AslExecutorJsonMergeTest: 4 tests; sibling AslExecutorCatchTest regression green — run in an eclipse-temurin:25-jdk container)
• New or updated integration test added (AslExecutorJsonMergeTest)
• Commit messages follow Conventional Commits

[greptile-apps]

Greptile Summary

This PR implements the States.JsonMerge intrinsic function in Floci's Step Functions executor, resolving a hard failure for state machines that rely on it. It also adds true/false/null literal recognition to resolveIntrinsicArg, which was needed to correctly evaluate the boolean third argument.

• Shallow merge is performed by iterating a's then b's fields into a fresh ObjectNode, so b wins on key conflicts — matching AWS semantics.
• The guard order is correct: argument count → boolean type check → object type check → deep-merge rejection, aligning with AWS error precedence.
• Six targeted unit tests cover the happy path, all four rejection cases, and the error-ordering invariant.

Confidence Score: 5/5

Safe to merge — the change is self-contained, all validation paths are exercised, and the previously flagged issues with type coercion and error ordering have been corrected.

The implementation correctly handles all relevant validation cases for States.JsonMerge: argument count, boolean type guard (no silent coercion), object-type check before deep-merge rejection, and the shallow merge itself. The boolean/null literal additions to resolveIntrinsicArg are minimal and well-scoped. Six unit tests cover every branch including the error-ordering invariant.

No files require special attention.

Important Files Changed

Filename	Overview
src/main/java/io/github/hectorvent/floci/services/stepfunctions/AslExecutor.java	Adds the States.JsonMerge case to the intrinsic switch and boolean/null literal handling to resolveIntrinsicArg; validation order and type guards are correct.
src/test/java/io/github/hectorvent/floci/services/stepfunctions/AslExecutorJsonMergeTest.java	New test class with 6 focused unit tests covering the happy path, all rejection paths, and the object-type-before-deep-merge error-ordering invariant.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["States.JsonMerge(arg1, arg2, arg3)"] --> B{"Exactly 3 args?"}
    B -- No --> E1["FailState: requires exactly 3 arguments"]
    B -- Yes --> C["resolveIntrinsicArg for all 3"]
    C --> D{"deepArg.isBoolean()"}
    D -- No --> E2["FailState: third argument must be a boolean"]
    D -- Yes --> F{"a.isObject() AND b.isObject()"}
    F -- No --> E3["FailState: requires two JSON objects"]
    F -- Yes --> G{"deep == true"}
    G -- Yes --> E4["FailState: supports only shallow merge"]
    G -- No --> H["Create new ObjectNode, set all fields from a, overwrite with all fields from b"]
    H --> I["Return merged ObjectNode"]

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flowchart TD
    A["States.JsonMerge(arg1, arg2, arg3)"] --> B{"Exactly 3 args?"}
    B -- No --> E1["FailState: requires exactly 3 arguments"]
    B -- Yes --> C["resolveIntrinsicArg for all 3"]
    C --> D{"deepArg.isBoolean()"}
    D -- No --> E2["FailState: third argument must be a boolean"]
    D -- Yes --> F{"a.isObject() AND b.isObject()"}
    F -- No --> E3["FailState: requires two JSON objects"]
    F -- Yes --> G{"deep == true"}
    G -- Yes --> E4["FailState: supports only shallow merge"]
    G -- No --> H["Create new ObjectNode, set all fields from a, overwrite with all fields from b"]
    H --> I["Return merged ObjectNode"]

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_{Reviews (5): Last reviewed commit: "Merge branch 'main' into feat/stepfuncti..." | Re-trigger Greptile}

[abanna]

Applied the Greptile P2 on error precedence: the object-type check now runs before the deep-merge-flag rejection, so States.JsonMerge with two non-object arguments and true reports requires two JSON objects (type validation first) rather than shallow merge only, matching AWS's ordering. Added a precedence test. Branch is up to date with main (merge) and green.