refactor(main): add runtime domain registry and fan-in guardrails

Introduce runtime domain barrel exports and registry composition support, and document/check main runtime fan-in workflow with related backlog planning artifacts.

docs/subagents/agents/opencode-task95-config-20260221T031843Z-m4k9.md

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+# Agent Log: opencode-task95-config-20260221T031843Z-m4k9
+
+- alias: `opencode-task95-config`
+- mission: `Implement TASK-95 config extraction for src/config/service.ts with unchanged public API/behavior`
+- status: `done`
+- last_update_utc: `2026-02-21T03:26:57Z`
+
+## Intent
+
+- Extract collaborators from `src/config/service.ts` under `src/config/` (load/parse/warnings/resolve as fits).
+- Keep `ConfigService` API and behavior unchanged.
+- Add/update seam tests in `src/config/config.test.ts` for loader precedence, strict parse non-mutation, warning determinism.
+- Run `bun run build && bun run test:config:dist`.
+
+## Planned Files
+
+- `src/config/service.ts`
+- `src/config/config.test.ts`
+- `src/config/*` (new collaborator modules)
+
+## Assumptions
+
+- TASK-95 exists and this is the config-only slice.
+- No backlog markdown edits allowed in this run.
+
+## Activity
+
+- 2026-02-21T03:18:43Z: started; loaded backlog workflow overview + TASK-95 context; initialized subagent coordination files.
+- 2026-02-21T03:26:57Z: extracted collaborators `src/config/load.ts`, `src/config/parse.ts`, `src/config/warnings.ts`, `src/config/resolve.ts`; rewired `src/config/service.ts` as facade; added seam tests for loader precedence, strict parse non-mutation, warning determinism; ran `bun run build && bun run test:config:dist` (pass).
+
+## Touched Files
+
+- `src/config/service.ts`
+- `src/config/load.ts`
+- `src/config/parse.ts`
+- `src/config/warnings.ts`
+- `src/config/resolve.ts`
+- `src/config/config.test.ts`
+
+## Handoff
+
+- ConfigService API unchanged (`constructor`, `get*`, `reload*`, `saveRawConfig`, `patchRawConfig`).
+- Behavior preserved by moving logic (no semantic changes intended) and passing full config dist suite.