Function project_template_launch_row 

fn project_template_launch_row(
    conn: &Connection,
    root: &LegacyInstance,
) -> Result<bool, String>

Create the consolidated row for a template-launch chain whose head has no db_agents row yet — the “Phase 3a stamped, db_agents partially populated” upgrade shape (codex P1 on #3075). Without this the UPDATE below affects zero rows, the migration is still recorded applied, and the chain’s session/status is unreachable once readers flip. Frozen copy of the consolidate pass-3 / dual-write head-INSERT column mapping as of v29, INSERT OR IGNORE so it can never clobber a row that appeared in between. Ok(false) when the definition itself is gone — nothing to project against (the legacy FK cascade would have removed such an instance; if it survived it is an orphan).