[claude] Defer change-type freeze until JsonSerializerOptions is first used

[myieye]

Reading config.JsonSerializerOptions now freezes ChangeTypeListBuilder eagerly (introduced in #80), so a consumer that reads the options mid-configuration — e.g. to layer its own TypeInfoResolver modifier onto ours — and then registers more change types throws ChangeTypeListBuilder is frozen. This breaks FWL.

Fix: Make more stuff lazy.

[coderabbitai]

📝 Walkthrough

Walkthrough

CrdtConfig now defers discriminator map materialization, allowing additional change types to be registered after accessing serializer options. The converter resolves known types lazily, and a regression test verifies JSON round-tripping.

Changes

Change type registration

Layer / File(s)	Summary
Lazy discriminator resolution src/SIL.Harmony/Changes/PeekThenConcreteChangeConverter.cs	The converter accepts a discriminator-map factory and lazily resolves known types during discriminator matching and deserialization.
Configuration wiring and regression coverage src/SIL.Harmony/CrdtConfig.cs, src/SIL.Harmony.Tests/ConfigTests.cs	CrdtConfig passes the lazy discriminator map, while a test registers a change type after accessing serializer options and verifies JSON round-tripping.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• sillsdev/harmony#80: Introduced the converter and opaque $type handling that this configuration-timing update extends.

Suggested reviewers: hahn-kev-bot, hahn-kev

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: deferring change-type freezing until JsonSerializerOptions is first used.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch claude/new-session-7248e6

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[myieye]

Actually, I'm thinking consumers/we can probably just avoid referencing the serialization options early.