fix: default input-select select_type to 'from-options'

[sLightlyDev]

Problem

New Input Select blocks were created with deepnote_variable_select_type set to null. The @deepnote/blocks serializer validates this field against a strict 'from-options' | 'from-variable' enum and rejects null, so freshly-added Input Select blocks could not be saved.

Fix

Default deepnote_variable_select_type to 'from-options' in DeepnoteSelectInputMetadataSchema so new blocks serialize cleanly.

Tests

Added regression tests in inputConverters.unit.test.ts:

• New input-select metadata defaults select_type to a valid enum value (not null).
• Block → cell → block → cell round-trip is idempotent — guards against repeated JSON.stringify escaping growing the cell value.

Full unit suite green (2333 passing).

CI note

The required Build & Test check is red, but the tests pass (2333 passing in the job log). The failure is in the later "Upload test results to Codecov" step:

gpg: Can't check signature: No public key
==> Could not verify signature. Please contact Codecov if problem continues

This is a Codecov CLI / infrastructure issue unrelated to this change — it currently fails the same step on other open PRs as well. No action needed in this PR to address it.

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR fixes a serialization bug in select input metadata where null or undefined deepnote_variable_select_type values could not be saved and triggered content-reformat loops. The fix applies Zod schema validation to coerce null/undefined to the non-null default 'from-options'. Two regression tests validate the schema's default behavior and confirm round-trip conversion remains idempotent without runaway escaping of quoted cell values.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title directly describes the main change: defaulting input-select select_type to 'from-options', which matches the core fix in DeepnoteSelectInputMetadataSchema.
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.
Updates Docs	✅ Passed	Bug fix for internal schema validation, not a user-facing feature. Changes default null enum to 'from-options' to prevent serialization errors.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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