Harden $create-changelog and improve artifact-diff fidelity

[c-schuler]

Summary

Makes the $create-changelog operation (and the shared $artifact-diff engine it builds on) robust against real-world manifests and produces a cleaner, less noisy diff. Two threads of work: a series of null-safety fixes that were each blocking the operation on progressively more complex inputs, and diff-quality improvements that remove spurious and redundant entries from the result.

Robustness (NPE fixes)

Each surfaced after the prior was unblocked, all on the diff/changelog path:

1. HapiArtifactDiffProcessor.extensionEquals - dereferenced extension.getValue() unconditionally, NPE-ing on complex extensions that carry only nested sub-extensions and no top-level value (e.g. the package-source extension emitted by $data-requirements). Now null-guards both sides and falls back to Extension.equalsDeep.

2. Page.addInsertOperation / addDeleteOperation / addReplaceOperation - dereferenced oldData/newData, which are legitimately null for pages representing a resource that exists on only one side of the diff (insert-only or delete-only). Now each side is guarded independently.

3. Null parameter names - HAPI's Parameters.getParameter(String) NPEs when the list contains a component with a null name (which arises when a malformed canonical parses to null and is stored back on a component). Added a null-safe hasParameterNamed helper and switched the remaining .getName().equals(...) / .equalsIgnoreCase(...) call sites in both processors to literal-first form.

Diff fidelity

4. Set-match contained expansion parameters - the contained Parameters.parameter[] array is order-independent, but FhirPatch.diff compares arrays positionally, so a reordered manifest produced a cascade of meaningless replace ops pairing unrelated entries by index. Extended the existing match-and-reorder machinery (already used for relatedArtifact, compose.include, expansion.contains) to expansion parameters, matching by name + version-stripped URL. A pure reorder now produces no ops; a genuine version bump produces a single replace; add/remove produce clean insert/delete.

5. Skip unchanged dependencies - handleSourceMatches recursed into and re-fetched every matched dependency even when the source and target referenced the identical version-pinned canonical (the same immutable artifact). Now short-circuits when the full canonicals are equal — no wasted fetch, no spurious sub-diff entry.

6. Suppress futile retrieval-failure placeholders - when a recursive sub-diff couldn't resolve a side (commonly external code systems like LOINC/SNOMED/ICD/CPT that are never stored as full resources), the processor baked a "Target/Source could not be retrieved" string into the diff payload. These were both futile (external systems can't be content-diffed) and redundant (any reference-level change is already reported as a relatedArtifact operation). Now logged at debug instead of polluting the output.

[github-actions]

Formatting check succeeded!

[Chris0296]

Great improvements - nice work Chris!

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
85.4% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud