Update: Refactor native auth routing and harness attachment

[SI-RUI-ZHANG]

原问题
The middleware native-auth branch had accumulated fallback-style auth logic, inconsistent OpenClaw and OpenCode support decisions, and harness-specific setup behavior embedded directly in the CLI flow. Live smoke was not strict enough to act as a reliable release gate, and Codex remained a special case because harness attachment was not modeled as a first-class abstraction.

本次修复
Refactored the native-auth stack around strict harness-owned auth reuse and exact selected-state preservation. Added a shared provider-policy layer, split runtime request/upstream planning, extracted first-class harness adapters for Codex/OpenCode/OpenClaw/Claude, removed remaining OpenClaw managed-mode normal-path behavior, tightened smoke infrastructure and live smoke gating, and aligned supported-client documentation with the actual product contract.

Changed files list
CONTRIBUTING.md
QUICKSTART.md
README.md
findings.md
modeio_middleware/cli/gateway.py
modeio_middleware/cli/harness_adapters/init.py
modeio_middleware/cli/harness_adapters/base.py
modeio_middleware/cli/harness_adapters/claude.py
modeio_middleware/cli/harness_adapters/codex.py
modeio_middleware/cli/harness_adapters/openclaw.py
modeio_middleware/cli/harness_adapters/opencode.py
modeio_middleware/cli/harness_adapters/registry.py
modeio_middleware/cli/setup.py
modeio_middleware/cli/setup_lib/common.py
modeio_middleware/cli/setup_lib/openclaw.py
modeio_middleware/cli/setup_lib/openclaw_common.py
modeio_middleware/cli/setup_lib/openclaw_routes.py
modeio_middleware/cli/setup_lib/openclaw_transaction.py
modeio_middleware/cli/setup_lib/opencode.py
modeio_middleware/cli/setup_lib/upstream.py
modeio_middleware/connectors/anthropic_http.py
modeio_middleware/connectors/openai_http.py
modeio_middleware/core/client_auth.py
modeio_middleware/core/contracts.py
modeio_middleware/core/engine.py
modeio_middleware/core/pipeline_orchestrator.py
modeio_middleware/core/plugin_manager.py
modeio_middleware/core/provider_auth.py
modeio_middleware/core/provider_policy.py
modeio_middleware/core/request_context.py
modeio_middleware/core/stream_orchestrator.py
modeio_middleware/core/upstream_client.py
modeio_middleware/core/upstream_plan.py
modeio_middleware/core/upstream_strategy.py
modeio_middleware/core/upstream_transport.py
modeio_middleware/http_transport.py
modeio_middleware/plugins/redact_utils.py
modeio_middleware/runtime_control.py
progress.md
scripts/smoke_agent_matrix.py
scripts/smoke_e2e.sh
scripts/smoke_matrix/agents.py
scripts/smoke_matrix/common.py
scripts/smoke_matrix/models.py
scripts/smoke_matrix/openclaw_family.py
scripts/smoke_matrix/outcome.py
scripts/smoke_matrix/runner.py
scripts/smoke_matrix/sandbox.py
scripts/upstream_tap_proxy.py
task_plan.md
tests/README.md
tests/helpers/gateway_harness.py
tests/helpers/inspection_builder.py
tests/helpers/openclaw_builder.py
tests/integration/test_gateway_contract.py
tests/integration/test_monitoring_api.py
tests/integration/test_plugin_management_api.py
tests/integration/test_protocol_stdio_runtime.py
tests/smoke/test_smoke_agent_matrix_support.py
tests/smoke/test_smoke_client_setup_flows.py
tests/smoke/test_smoke_opencode_flow.py
tests/unit/test_client_auth.py
tests/unit/test_harness_adapters.py
tests/unit/test_http_transport.py
tests/unit/test_provider_policy.py
tests/unit/test_setup_gateway.py
tests/unit/test_upstream_client.py
tests/unit/test_upstream_tap_proxy.py

Reviewer: @SI-RUI-ZHANG