feat: add Kimchi agent harness support

[vytautas-petrikas]

Summary

Adds Kimchi (@kimchi-dev/cli, binary kimchi) as a new supported agent harness. Kimchi is a coding-agent CLI built on @earendil-works/pi-coding-agent. AO drives it non-interactively with --print mode, delivers the initial prompt as a trailing positional argument, appends system prompts via --append-system-prompt, and maps AO permission modes onto Kimchi's --plan/--auto/--yolo flags.

Session restore uses --session <id> — the native session id is captured from hook metadata and stored in AO session metadata. Hooks use Kimchi's Claude Code hook compatibility extension (.claude/settings.local.json), installed via ao hooks kimchi <event> commands.

Changes

New adapter package (backend/internal/adapters/agent/kimchi/):

• kimchi.go — adapter: launch, restore, prompt construction, permission flag mapping
• auth.go — auth probe (checks for API key / credentials)
• hooks.go — hook command generation for Claude Code-compatible hook events
• activity.go — activity state derivation from Kimchi output
• install.go — install path for the Kimchi binary
• kimchi_test.go, auth_test.go — unit tests (640+ lines)

Domain & registry wiring:

• backend/internal/domain/harness.go — add HarnessKimchi constant and register in AllHarnesses
• backend/internal/adapters/agent/registry/registry.go — register kimchi.New() constructor

Database migration:

• backend/internal/storage/sqlite/migrations/0022_allow_kimchi_harness.sql — allow kimchi as a valid harness value

Frontend wiring:

• frontend/src/renderer/types/workspace.ts — add "kimchi" to AgentProvider union
• frontend/src/renderer/lib/agent-options.ts — add Kimchi to agent options list

OpenAPI spec fix (follow-up commit):

• backend/internal/httpd/controllers/dto.go — add kimchi to SpawnSessionRequest.Harness enum tag
• backend/internal/httpd/apispec/openapi.yaml — regenerated
• frontend/src/api/schema.ts — regenerated (adds kimchi to harness union)

Testing

• go test ./internal/adapters/agent/kimchi/... — 46 tests pass
• go test ./internal/httpd/... — 146 tests pass (spec parity + drift checks)
• go test ./... — full backend suite green
• npm run typecheck (frontend) — clean, no errors

Migration note

Migration 0022_allow_kimchi_harness.sql adds kimchi to the allowed harness values. No data migration needed — purely additive.

[somewherelostt]

Thanks for contributing to Agent Orchestrator.

This PR is being picked up by the current external contributor on-call pair:

• @neversettle17-101
• @somewherelostt

If someone is already working on this, please continue as usual.
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