fix(sync-rules): length() and instr() should count code points to match SQLite

[sravan27]

Follow-up to the substring() code-point fix — the same UTF-16-vs-code-point divergence affects two sibling functions.

Problem

length() used JS String.length (UTF-16 code units) and instr() used String.indexOf (a UTF-16 index), so both diverge from SQLite for text containing non-BMP characters (emoji, mathematical alphanumerics, etc.):

expression	SQLite	sync-rules (before)
length('😀')	1	2
length('a😀b')	3	4
instr('😀x', 'x')	2	3

Because sync-rule expressions are evaluated client-side and must agree with the source database, a filter like length(name) > 10 or instr(...) over text containing emoji could include/exclude rows differently on the client than on the server — silent sync divergence.

Fix

Both functions now iterate by code point (spreading the string / counting code points in the prefix), matching SQLite and the existing substring() behaviour. Blob handling is unchanged (still byte counts, which is correct per SQLite).

Tests

Added regression cases to sql_functions.test.ts for length and instr covering non-BMP characters, including the case where a non-BMP character precedes the match (the one that actually diverges). Full sync-rules suite passes.

Verified against the system sqlite3 as ground truth.

🤖 Generated with Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: 2e6fd14

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 17 packages

Name	Type
@powersync/service-sync-rules	Patch
@powersync/service-core	Patch
@powersync/lib-services-framework	Patch
@powersync/service-module-convex	Patch
@powersync/service-module-mongodb-storage	Patch
@powersync/service-module-mongodb	Patch
@powersync/service-module-mssql	Patch
@powersync/service-module-mysql	Patch
@powersync/service-module-postgres-storage	Patch
@powersync/service-module-postgres	Patch
@powersync/service-module-core	Patch
@powersync/service-image	Patch
test-client	Patch
@powersync/service-rsocket-router	Patch
@powersync/lib-service-mongodb	Patch
@powersync/lib-service-postgres	Patch
@powersync/service-schema	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

---

Sravan Sridhar seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[rkistner]

@sravan27 As mentioned before, we're moving towards using the node:sqlite engine, and are not fixing further compatibility differences with our JS engine. See #666.