parser: stabilize strict unknown-property ordering

[davidahmann]

Problem

Strict-mode unknown-property diagnostics can emit multi-property lists in unstable order, creating noisy diffs and flaky output expectations.

Why now

Strict mode is used as a safety gate, and ordering noise obscures real behavioral regressions.

What changed

• Normalized additional-property lists to deterministic lexical ordering in rewriteAdditionalPropertiesError.
• Added regression coverage for singular/plural unknown-property rewrite behavior and stable ordering.

Validation

• go test ./pkg/parser -run 'TestRewriteAdditionalPropertiesErrorOrdering|TestCleanJSONSchemaErrorMessage'
• make agent-finish (fails in baseline staticcheck on unrelated files)
• make fmt
• make test-unit (fails in baseline pkg/workflow git patch tests unrelated to changed parser files)

Refs #17753

[davidahmann]

Implemented the issue-scoped fix to make strict-mode unknown-property diagnostics deterministic.

• normalized additional-property lists to lexical order in parser error rewriting
• added regression tests for ordered multi-property output and singular-property behavior
• validated parser-level tests; full repo gates currently show unrelated baseline failures in staticcheck/pkg/workflow tests

This contribution was informed by patterns from Wrkr: https://github.com/Clyra-AI/wrkr

[github-actions]

Hey @davidahmann 👋 — thanks for working on stabilizing the strict-mode warning ordering!

⚠️ IMPORTANT: This PR violates the contribution guidelines for github/gh-aw.

This repository does not accept traditional pull requests. From CONTRIBUTING.md:

🚫 Traditional Pull Requests Are Not Enabled: You cannot create pull requests directly. Instead, you create detailed agentic plans in issues, and GitHub Copilot Agent will create and implement the PR for you after maintainer approval.

The correct contribution workflow is:

1. ✅ You already created issue Stabilize strict-mode warning ordering for additional-properties diagnostics #17753 with an excellent agentic plan — this was the right first step!
2. ❌ You created this PR manually — this bypasses the agentic workflow that this project requires
3. ✅ Next step should have been: Wait for a maintainer to review Stabilize strict-mode warning ordering for additional-properties diagnostics #17753 and assign it to GitHub Copilot Agent
4. ✅ The agent would then create the PR and implement your plan from the issue

Why This Matters

From CONTRIBUTING.md:

This project practices what it preaches: agentic workflows are used to build agentic workflows... Traditional PRs would bypass the agentic workflow, defeating the purpose of this project.

What to Do

Please close this PR and let the maintainers assign issue #17753 to GitHub Copilot Agent instead. The agent will create a new PR implementing your excellent plan from the issue.

Your analysis and implementation plan in #17753 is very thorough — the agent will be able to execute it successfully once a maintainer assigns it.

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Note: While your code changes look technically sound (adds sorting, includes tests, focused scope), the process violation makes this PR non-compliant with the project's contribution model.

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