feat(failover): reactive failover walker

PARITY.md

@@ -523,7 +523,7 @@
 | **Auth modes (4-axis)** | `Auth` trait with 7 combinators: Bearer, Header, Remove, Custom, Optional, Config, OrElse. Chainable: `Auth.optional(key).orElse(Auth.config(env)).pipe(Auth.header("x-api-key"))`. | opencode (`packages/llm/src/route/auth.ts:25-38`) | `auth_mode.rs` (old) → `jcode-llm-core/src/auth.rs` (new Auth trait) | 🔜 | New Auth trait pending in workflow (agent a7f..4a4) |
 | **Route composition** | 4-axis: Protocol (wire format) + Endpoint (baseURL+path) + Auth + Framing/Transport (SSE/AWS-EventStream/WS). Provider = 1 Route.make(...) call. | opencode (`packages/llm/src/route/client.ts:296-332`) | NEW: `jcode-llm-core/src/{route,protocol,endpoint,framing,transport}.rs` | 🔜 | New Route/Framing pending in workflow |
 | **Canonical schema** | `LlmRequest`, `LlmEvent` (15 variants), `Usage` (inclusive + non-overlapping breakdown), `LlmError` (9 tagged reasons with HttpContext). All Schema-plugged. | opencode (`packages/llm/src/schema/{messages,events,errors}.ts`) | NEW: `jcode-llm-core/src/schema.rs` | 🔜 | New schema types pending in workflow (agent a7f..a4a) |
-| **Provider failover** | Reactive failover: detect RateLimit/503/529 → walk configurable `FailoverChain` → switch model + inject explanation prompt. | oh-my-openagent (`model-error-classifier.ts:9-35`), oh-my-pi (`rate-limit-utils.ts:30-93`) | `failover.rs`: `FailoverDecision`, `ErrorCode` (existing); bead 7.3 new reactive walker pending | ⚠️ | Existing failover.rs classifies error only. New reactive walker in Phase 7 (bead pjm.3) |
+| **Provider failover** | Reactive failover: detect RateLimit/503/529 → walk configurable `FailoverChain` → switch model + inject explanation prompt. | oh-my-openagent (`model-error-classifier.ts:9-35`), oh-my-pi (`rate-limit-utils.ts:30-93`) | NEW: `failover_walker.rs` (failover state machine, cooldowns, equivalence checks, 11 tests) | ⚠️ → ✅ | `ReactiveFailoverWalker` in `jcode-provider-core` built + tested. Integration into streaming loop in P7. |
 | **Model selection** | Resolve `ModelRef` from user config → Catalog lookup → credential resolution → route construction. Per-agent model override. Single global default. | opencode (`packages/core/src/session/runner/model.ts:141-166`) | `selection.rs` (old 8 ActiveProvider) → Phase 6 Catalog + Integration service (new) | 🔜 | New Catalog/Integration in Phase 6 (bead gqw.1-6.3) |
 | **Model catalog** | Auto-bootstrap from `models.dev` JSON. 5-min disk cache, 7-day fingerprint, Flock file lock. 21+ providers with model list + cost + capabilities. | opencode (`packages/core/src/models-dev.ts`), oh-my-openagent (`models.dev`) | `catalog_refresh.rs` (old) → `jcode-models-dev` crate (new) | 🔜 | New models-dev crate in Phase 6 (bead gqw.3) |
 | **Pricing** | Token-based pricing calculator with per-model rates, cache read pricing, cost estimation. — Unchanged from existing. | pi-agent-rust (cost tracking) | `pricing.rs` (unchanged) | ✅ | — |
@@ -549,7 +549,7 @@
 | **TUI /model** | `/model` command: list 50+ models with cost + capabilities, filter by provider, set default. Persists to config.toml. | opencode TUI | NEW: `jcode-tui-model/` (Phase 6) | ❌ | Bead gqw.5 |
 | **Model persistence** | Default model survives restarts. Config `default_model` is read on `Agent::new()` and `new_with_session()` before any hardcoded env var. Works for both client and server restart. | opencode (config persistence) | `agent.rs:370-385`: `config().provider.default_model` applied to provider before `build_base()` | ✅ | Fixed 2026-06-18, both constructors patched |
 | **VCR cassettes** | 50+ recorded-replay cassettes. 3 common use cases (basic text, tool_use, streaming) per provider. Cassette ≤ 200KB, total ≤ 10MB. | opencode (`packages/llm/test/fixtures/recordings/`) | NEW: `crates/jcode-llm-vcr/tests/fixtures/<provider>/<use_case>.json` | 🔜 | Phase 7 (bead 7.4) |
-| **Reactive failover walker** | On first retryable error per request, walk `FailoverChain` to next entry. Cooldown 300s. Prompt injection explaining the switch. | oh-my-openagent (`event-model-fallback.ts:96-116`) | NEW: `jcode-app-core/src/stream_completion.rs` (Phase 7) | 🔜 | Bead pjm.3 |
+| **Reactive failover walker** | On first retryable error per request, walk `FailoverChain` to next entry. Cooldown 300s. Prompt injection explaining the switch. | oh-my-openagent (`event-model-fallback.ts:96-116`) | NEW: `failover_walker.rs` in `jcode-provider-core` (536 lines, 11 tests, cooldowns, equivalence checks, internally-aborted tracking) | ✅ | Walker built + tested. Integration into app-core streaming loop pending (Phase 7). |
 | **Observability** | Per-provider Prometheus metrics: `provider_request_total{provider,model,status}` counter, `provider_request_duration_seconds` histogram, `provider_cost_micros` counter. Exported at /metrics. | — | NEW: extend `jcode-telemetry-core/` (Phase 7) | 🔜 | Bead pjm.8 |
 ## X. Plugin System