feat(aircoding): AirCoding V2 baseline — deterministic multi-agent architecture

Forked from OpenCode v1.17.4 with multi-agent system:
- 5 agents: aircoding, scheduler, worker, architect, reviewer
- Deterministic DAG scheduling engine (coordinator_tick)
- Tool whitelists as hard enforcement
- AirCoding validation plugin
- V1 requirements: C4 docs, ADR, AGENTS.md, debug-log.md
- Design documents in docs/

packages/opencode/specs/effect/server-package.md

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+# Server Package Extraction
+
+Practical reference for a future `packages/server` split after the opencode
+server moved to the Effect HttpApi backend.
+
+## Current State
+
+- The server still lives in `packages/opencode`.
+- The runtime and app layer are centralized in `src/effect/app-runtime.ts` and
+  `src/effect/run-service.ts`.
+- The route tree lives under `src/server/routes/instance/httpapi` and is hosted
+  from `src/server/server.ts`.
+- OpenAPI generation is based on the HttpApi contract plus compatibility
+  translation in `src/server/routes/instance/httpapi/public.ts`.
+- There is no standalone `packages/server` workspace yet.
+
+## Future State
+
+Target package layout:
+
+- `packages/core` - shared domain services and schemas
+- `packages/server` - HTTP contracts, handlers, OpenAPI generation, and an
+  embeddable server API
+- `packages/cli` - TUI and CLI entrypoints
+- `packages/sdk` - generated from the server OpenAPI spec
+- `packages/plugin` - plugin authoring surface
+
+## Extraction Rule
+
+Do not create a package cycle.
+
+Until enough shared service code lives outside `packages/opencode`, a future
+`packages/server` should either:
+
+- own pure HttpApi contracts only, or
+- accept host-provided services/layers/callbacks from `packages/opencode`
+
+It should not import `packages/opencode` services while `packages/opencode`
+imports it to host routes.
+
+## Suggested PR Sequence
+
+1. Keep shrinking OpenAPI compatibility shims in `httpapi/public.ts`.
+2. Move stable domain schemas into shared packages only when they no longer
+   depend on opencode-local runtime modules.
+3. Extract pure HttpApi contract modules into `packages/server` once the contract
+   can compile without importing `packages/opencode` implementation details.
+4. Extract handler factories after their service dependencies can be supplied by
+   a host layer instead of imported directly.
+5. Move server hosting last, after package ownership is clear.
+
+## Non-Goals
+
+- Do not revive the old dual-backend migration shape.
+- Do not split server hosting before service dependencies have a clean package
+  boundary.
+- Do not switch SDK generation to a new package until generated output is known
+  to remain compatible.