refactor: remove OpenRouter rollback, shims, and redundant layers

- OpenRouter: native Anthropic only; remove chat_request and OPENROUTER_TRANSPORT
- Drop OpenAICompatibleProvider alias, api.request_utils, voice_pipeline facade
- Simplify OpenRouter SSE, generic reasoning in conversion, messaging dispatch
- Shared markdown table helpers; API optimization response helper; contract guards
- Restore PLAN.md; update docs and tests

PLAN.md

@@ -0,0 +1,87 @@
+# Architecture Plan
+
+This document is the baseline architecture guide referenced by `AGENTS.md`. It
+records the intended dependency direction and the migration target for keeping
+the project modular as providers, clients, and smoke tests grow.
+
+## Current Product Shape
+
+`free-claude-code` is an Anthropic-compatible proxy with optional messaging
+workers:
+
+- `api/` owns the HTTP routes, request orchestration, model routing, auth, and
+  server lifecycle.
+- `providers/` owns upstream model adapters, request conversion, stream
+  conversion, provider rate limiting, and provider error mapping.
+- `messaging/` owns Discord and Telegram adapters, command handling, tree
+  threading, session persistence, transcript rendering, and voice intake.
+- `cli/` owns package entrypoints and managed Claude CLI subprocess sessions.
+- `config/` owns environment-backed settings and logging setup.
+- `smoke/` owns opt-in product smoke scenarios and the public coverage
+  inventory used by contract tests.
+
+## Intended Dependency Direction
+
+The repo should preserve this dependency order:
+
+```mermaid
+flowchart TD
+    config[config] --> api[api]
+    config --> providers[providers]
+    config --> messaging[messaging]
+    core[core.anthropic] --> api
+    core --> providers
+    core --> messaging
+    providers --> api
+    cli --> messaging
+    messaging --> api
+```
+
+The practical rule is simpler than the graph: shared protocol helpers belong in
+neutral core modules, not under a provider package. Provider adapters may depend
+on the neutral protocol layer, but API and messaging code should not import
+provider internals.
+
+## Target Boundaries
+
+- `core/anthropic/`: Anthropic protocol helpers, stream primitives, content
+  extraction, token estimation, user-facing error strings, request conversion,
+  thinking, and tool helpers shared across API, providers, messaging, and tests.
+- `api/runtime.py`: application composition, optional messaging startup,
+  session store restoration, and cleanup ownership.
+- `providers/`: provider descriptors, credential resolution, transport
+  factories, scoped rate limiters, upstream request builders, and stream
+  transformers.
+- `messaging/`: platform-neutral orchestration split from command dispatch,
+  rendering, voice handling, and persistence.
+- `cli/`: typed Claude CLI runner config, subprocess management, and packaged
+  user-facing entrypoints.
+
+## Smoke Coverage Policy
+
+Default CI stays deterministic and runs `uv run pytest` against `tests/`.
+Product smoke lives under `smoke/` and is enabled with `FCC_LIVE_SMOKE=1`.
+Smoke runs should use `-n 0` unless a scenario is explicitly known to be safe
+under xdist.
+
+Live smoke has two valid skip classes:
+
+- `missing_env`: credentials, local services, binaries, or explicit opt-in flags
+  are absent.
+- `upstream_unavailable`: real providers, bot APIs, or local model servers are
+  unreachable.
+
+`product_failure` and `harness_bug` are regressions. When a provider is
+explicitly selected by `FCC_SMOKE_PROVIDER_MATRIX`, missing configuration should
+fail instead of being silently skipped.
+
+## Refactor Rules
+
+- Keep public request/response shapes stable while moving internals.
+- Complete module migrations in one change: update imports to the new owner and
+  remove old compatibility shims unless preserving a published interface is
+  explicitly required.
+- Lock behavior with focused tests before moving shared protocol or runtime
+  code.
+- Run checks in this order: `uv run ruff format`, `uv run ruff check`,
+  `uv run ty check`, `uv run pytest`.