consensus-db: schema migration aborts with TableDoesNotExist when data tables are missing

[Dusk1e]

Summary

On a consensus DB whose data tables have not been created yet, schema migration aborts with TableDoesNotExist("certificates") and the node cannot start. Two of the four per-table migration functions open their table in a read transaction (which errors on a missing table), while the other two use a write transaction (which creates it) — so the behaviour is inconsistent and the read-transaction path is fatal.

Affected code

crates/consensus-db/src/migrations.rs

migrate_certificates and migrate_decided_blocks open the table in a read transaction:

let mut next_height = if let Some((min_height, _)) = self
    .db
    .begin_read()?
    .open_table(CERTIFICATES_TABLE)?   // -> TableError::TableDoesNotExist if absent
    .first()?

redb's open_table on a read transaction returns TableError::TableDoesNotExist when the table was never created. By contrast, migrate_undecided_blocks and migrate_pending_parts open their table in a write transaction, which creates it, so they already treat a missing table as empty. The two read-transaction functions abort the entire migration instead.

How it is reached

The tables do not always exist when migration runs:

1. Db::new runs the migration, and only afterwards does Store::open call create_tables.
2. needs_migration treats "database file exists, no schema version recorded" as v0 and requests a migration.
3. redb::Database::create creates the file before that schema version is written.

So a first start interrupted between (1) creating the file and (3) writing the version leaves a database file with a metadata table but no data tables. Every subsequent start then runs the migration, hits the read-transaction open_table, and fails. arc-node-consensus db migrate fails the same way, including --dry-run (which goes through preview_migrate → the same functions).

Observed error

Error: Table(TableDoesNotExist("certificates"))

The node is stuck: it cannot start and cannot migrate, even though the datadir is recoverable.

Proposed fix

Make migrate_certificates and migrate_decided_blocks treat a missing table as empty — matching what migrate_undecided_blocks / migrate_pending_parts already do — by handling TableError::TableDoesNotExist as "no rows" instead of propagating it.

Verification

I have a patch plus a regression test that reproduces the failure. On main the test fails with Table(TableDoesNotExist("certificates")); with the fix it passes, and the full arc-consensus-db suite (107 tests) stays green (cargo fmt/clippy clean). Happy to open a PR referencing this issue once assigned.

Environment

• Reproduced against the current main on x86_64-unknown-linux-gnu, Rust 1.93.0.