fix(sqlite): preserve session metadata contracts

packages/session-persistence/session-persistence-sqlite/README.md

@@ -10,7 +10,7 @@ A SQLite durable session-persistence backend — a second `SessionPersistence` i
 
 Each `SessionEvent` maps 1:1 onto a row in an `events` table `(session_id, seq, type, time, data, source_event_seqs, surface_op)` — `data` is the event payload as JSON text, so the row shape is the event verbatim (including `assistant/chunk`, keeping `seq` contiguous). The two `TEXT` columns `source_event_seqs` and `surface_op` are nullable; they store the event's optional surface-metadata fields (see [session surface](../../../.agents/notes/implemented/architecture/2026-06-18-session-surface.md)). Out-of-log metadata (`SessionHeader`), a per-materialization incarnation id, and a monotonic per-log revision live in a `sessions` row; a singleton state row carries the immutable store id. A `sessions` row is written only by the first `append` — its existence is the lazy-materialization signal (`list` reports exactly the sessions that have a row).
 
-The repository's Node range supports unflagged `node:sqlite`. The database enables foreign keys and uses the configured journal mode (`wal` by default; use a rollback mode where WAL shared-memory files are unsuitable). `PRAGMA user_version` stores the table-layout version; databases with any other version are rejected because this unreleased format has no migrations.
+The repository's Node range supports unflagged `node:sqlite`. The database enables foreign keys and uses the configured journal mode (`wal` by default; use a rollback mode where WAL shared-memory files are unsuitable). `PRAGMA user_version` stores the table-layout version. A fresh empty database is initialized at the current version; nonempty unversioned databases and every other version are rejected because this unreleased format has no migrations. Rejection occurs before changing journal mode or stamping the file.
 
 On filesystems with POSIX modes, the backend requests mode `0700` for missing directories and exclusively creates a missing database with mode `0600` before SQLite opens it; the process umask may further restrict both. New WAL, shared-memory, and persistent rollback-journal sidecars receive the database's resulting owner-only mode. Existing directories, database files, and sidecars keep their modes; filesystem setup errors other than an existing database fail initialization. These defaults prevent incidental exposure through a permissive process umask, but do not protect database confidentiality or integrity when another principal can replace the database entry in its parent directory.
 
@@ -55,5 +55,5 @@ SQLite storage does not mutate live request prefixes. A resumed loop can reuse p
 
 - **`DatabaseSync` is synchronous** — every append transaction blocks the event loop for its duration; acceptable for local stores, a throughput ceiling for busy multi-session servers.
 - **Write contention has no wait or retry policy** — the backend sets no busy timeout and retries no locked-database error, so another connection holding a write transaction makes the operation reject immediately.
-- **Only the current `SCHEMA_VERSION` opens** — a database with any other schema version is rejected rather than migrated (unreleased software; no persisted user data to preserve).
+- **Only an empty new database or the current `SCHEMA_VERSION` opens** — a nonempty unversioned database or any other schema version is rejected rather than migrated (unreleased software; no persisted user data to preserve).
 - **Nothing deletes stored sessions** — rows accumulate until removed externally (the seam has no deletion surface; `ON DELETE CASCADE` is wired for such out-of-band cleanup).