Function store 

pub fn store(
    conn: &Connection,
    namespace: &str,
    content: &str,
    ttl: Option<Duration>,
) -> Result<Transcript>

Compress content with zstd-3 and write a row to memory_transcripts.

ttl is interpreted as a duration from “now”; None means no expiry (the row is retained until explicitly deleted by I3’s archive-prune sweeper).

The returned Transcript handle lets callers persist the id + metadata (e.g. into the I2 join table) without re-reading the row.

Errors

Returns an error if zstd encoding fails (out-of-memory) or the SQLite INSERT fails (disk full, schema mismatch, etc.).