fix: update plugin for OpenCode 1.16.0+ compatibility and add schema migration

[High-cla]

Summary

Fixes two compatibility issues between CodeNomad and OpenCode v1.16.0+:

Issue #525 — Plugin Compatibility with OpenCode 1.16.0+

Changes:

• packages/opencode-plugin/package.json: Bumped @opencode-ai/plugin from 1.3.7 to ^1.16.0 and added the "oc-plugin" field for npm plugin discovery
• packages/opencode-plugin/plugin/codenomad.ts: Updated to the new Plugin type from @opencode-ai/plugin, replaced the old chat.message hook with experimental.chat.system.transform, and added export const server: Plugin for the PluginModule format (required by the v1.16+ loader)
• packages/opencode-plugin/plugin/lib/background-process.ts: Changed tool import from @opencode-ai/plugin/tool to @opencode-ai/plugin (tool is now re-exported from the main entry)

Issue #31204 — session_message.seq NOT NULL Constraint Failure

Changes:

• packages/server/src/workspaces/migration.ts (new): Non-blocking schema migration utility that checks the OpenCode database and fixes the seq column if needed
• packages/server/src/workspaces/runtime.ts: Calls checkAndFixOpencodeSchema() before spawning OpenCode instances

The migration handles three cases:

1. Column missing → ALTER TABLE ADD COLUMN seq INTEGER NOT NULL DEFAULT 0
2. Column exists, no default → Full table recreation via SQL
3. Already has DEFAULT 0 → No-op

Testing

• tsc --noEmit on both packages: Zero errors
• Integration tests added for migration module (4 tests, all passing)
• All existing tests continue to pass
• Uses opencode db command (no external dependencies)

[github-actions]

PR builds are available as GitHub Actions artifacts:

https://github.com/NeuralNomadsAI/CodeNomad/actions/runs/27087761913

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[shantur]

Hi @High-cla

Thanks for the PR. I have made some fixes in dev for the 1.16+ support. Can you check if that works for you