Replace SELECT * with explicit column lists in metadata queries

[deepjoy]

Description

SQL queries in the metadata layer use SELECT *, which loads all columns including potentially heavy ones like metadata JSON blobs. This is wasteful when only a subset of columns is needed (e.g., listing object keys).

Location

• src/metadata/sqlite.rs:74

Details

Queries like:

sqlx::query_as::<_, ObjectRecord>("SELECT * FROM objects WHERE key = ?")

should be replaced with explicit column lists to:

• Avoid loading heavy columns (e.g., metadata JSON) when not needed
• Improve query performance for list operations
• Make the code more resilient to schema changes

Acceptance Criteria

• Audit all SELECT * queries in sqlite.rs
• Replace with explicit column lists
• Consider adding lightweight query variants for list/prefix operations that skip heavy columns