fix: backfill schemaDefined on replicas missing the flag

[ldt1996]

No description provided.

[claude]

Missing test for the backfill path

What: The needsSchemaDefinedBackfill check introduces a two-leg runtime-shape branch (schemaDefined === undefined vs present) with no test covering the backfill leg. The normal leg (descriptor already has schemaDefined) is exercised by existing tests; the new leg is not.

Why it matters: A regression here — e.g. the write silently no-ops or persists the wrong value — would leave replica tables still missing the flag after a restart. The fix looks correct today, but without a test this is invisible to CI.

Suggested fix: Add a unit test (alongside the existing unitTests/resources/databases.test.js suite) that:

1. Opens or creates a table (so schemaDefined=true is written to the descriptor).
2. Manually overwrites the primary-key entry in attributesDbi with a copy that omits schemaDefined (simulating an old replica).
3. Calls table() again with the same definition.
4. Asserts that Table.schemaDefined === true and that the stored descriptor now contains schemaDefined: true.

[claude]

1. Missing test for the needsSchemaDefinedBackfill backfill path

File: resources/databases.ts:1064–1085
What: The new needsSchemaDefinedBackfill branch (attributeDescriptor.schemaDefined === undefined) has no test covering the backfill leg. Existing tests only exercise the normal path where the descriptor already carries the flag.
Why it matters: A regression (wrong value written, write silently skipped) would leave replica tables still missing schemaDefined after restart, with no CI signal.
Suggested fix: Add a test that strips schemaDefined from a stored primary-key descriptor via a direct attributesDbi.put, re-calls table(), then asserts both Table.schemaDefined === true and that the stored descriptor was updated — see inline comment for detail.

[cb1kenobi]

I don't know much about this, but makes sense. It would be nice if it was easy to add a test that demonstrates this fixes things.

[kriszyp]

What is the situation where this can occur? I thought line 907 in databases.ts consistently set this flag.
And reminder: please try to use /harper-engineering-guidelines skill to file PRs, this should automatically ensure there is an AI review prior to the PR being filed.