perf(workbench): avoid copying unused dictionary items

[mldangelo-oai]

Summary

Dictionary previews create a list of every item before selecting the first 20. Use itertools.islice to enforce the existing limit without allocating that temporary list.

Changes

• Import islice and use it for the dictionary preview loop.
• Preserve insertion order, field limits, byte budgets, depth limits and text handling.

One production file changes. There is no net line-count change or dependency change.

Testing

Opened as a draft: local validation and independent review are incomplete.

• git diff --check: passed.
• node --experimental-strip-types .github/scripts/check_plugin_source_compatibility.mts: passed against the complete source checker. This does not replace the required compiled invocation.
• node sdk/typescript/scripts/check-plugin-source.mjs: passed.
• Focused pytest and required Ruff check could not start because their modules are unavailable.
• The original SDK finding-preview/report-limit tests had three setup failures because the generated bundled plugin is absent.
• SDK build and remaining required checks were not run because build dependencies are unavailable.
• Independent review is pending. No clean review receipt is claimed.

Risk and rollout

The production caller projects freshly decoded JSON dictionaries. For that path, the change retains the first-20-item order and projection behavior, including invalid-Unicode handling. It changes no CLI arguments, response schemas, persisted data or resource limit.

Custom dictionary subclasses with side effects during iteration, or concurrent mutation, could observe different behavior; the identified production path does not supply those objects. The benefit is avoiding an unnecessary allocation, not a claimed production benchmark improvement. Complete the required validation and review before merging.

Public disclosure review

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• No credentials, personal data, private source, scan findings, or nonpublic links or tickets are included.
• I reviewed the branch name, title, description, commits, changes, comments, logs, screenshots, attachments, and links for public disclosure.