fix(core): import credentials from previous channel database - #40920

What

The channel database consolidation (#40723) pointed the next channel at the shared opencode.db and imported legacy credentials from V1 auth.json only. Credentials that existed only in the previous channel database (opencode-next.db) were dropped: the next-database import copies project, session, and session_message rows, and nothing copies the credential table.

Before / After

Before

1. On the next channel, connect OpenCode Zen through the integration dialog. The credential is stored in opencode-next.db's credential table — it never existed in V1 auth.json.
2. Update to a build containing feat(core): migrate v1 data to v2 #40723. The service now opens opencode.db; 20260805200742_import_legacy_credentials imports auth.json (Anthropic/OpenAI/Copilot OAuth entries survive), and the next-database import copies sessions only.
3. Zen is silently disconnected: the integration shows no connections, every paid opencode/* model disappears from the catalog (only the free list remains), and sessions pinned to a paid Zen model fail with ModelUnavailableError.

After

A new migration, 20260806200000_import_next_credentials, copies credential rows from opencode-next.db (opened read-only) into the consolidated database. Existing credentials win: an integration that already has a credential row is left untouched, so users who already reconnected are unaffected, and reruns are no-ops.

How

• packages/core/src/database/migration/20260806200000_import_next_credentials.ts — opens opencode-next.db read-only via bun:sqlite, validates each row's value against Credential.Value, skips integrations that already have a credential in the target, and preserves original ids, labels, method ids, and timestamps. An unreadable or incompatible source logs a warning and skips instead of failing startup. The source database is never modified.
• packages/core/src/database/migration.gen.ts — registry line matches bun script/migration.ts output (no schema changes).

Scope

• Overlap priority is unchanged: for a not-yet-migrated database the auth.json import runs first and wins for integrations present in both sources.
• Fresh database bootstraps mark migrations completed without executing them, so this migration (like the existing auth.json import) only takes effect on existing databases.
• wellknown:sources kv entries from the previous channel database are not merged.

Testing

• cd packages/core && bun test test/database-migration.test.ts — new test covers import, skip-if-integration-exists, invalid-value rows, idempotent rerun, and missing source file (9 pass).
• cd packages/core && bun typecheck
• Full bun test in packages/core: 1524 pass; the single failure (Config > loads authenticated wellknown config at highest priority) also fails on clean origin/v2.
• Real-world verification: ran the importer against the actual opencode-next.db from the machine that hit this bug, into a scratch database — it recovered exactly the dropped opencode Zen credential and left everything else alone.