conductor(track): Initialize data_oriented_error_handling_20260606

Track + metadata + state + tracks.md registration for the Fleury-pattern
error handling refactor.

Key design decisions (per user approval):
- Option A for _send_<vendor>() handling: rename to _send_<vendor>_result()
  and change return type to Result[str] (contained to internal callers).
- send() is marked @typing_extensions.deprecated; send_result() is the new
  public API.
- ProviderError exception is FULLY REPLACED by ErrorInfo dataclass
  (a value, not an exception).
- 5 phases: foundation, mcp_client, ai_client, rag_engine, deprecation+archive.
- Post-tracks baseline check (Phase 1 Task 1.1) verifies the 3 pending
  tracks have merged before proceeding.
- 9 Open Questions, 7 Risks, 5 verification criteria, follow-up track
  public_api_migration_20260606 planned in spec §12.1.

Blocked by: startup_speedup_20260606, test_batching_refactor_20260606,
qwen_llama_grok_integration_20260606. Blocks: public_api_migration_20260606.

conductor/tracks.md

@@ -161,6 +161,11 @@ User review surfaced five outstanding UI issues, each previously attempted witho
    *Link: [./tracks/qwen_llama_grok_integration_20260606/](./tracks/qwen_llama_grok_integration_20260606/), Spec: [./tracks/qwen_llama_grok_integration_20260606/spec.md](./tracks/qwen_llama_grok_integration_20260606/spec.md), Plan: [./tracks/qwen_llama_grok_integration_20260606/plan.md](./tracks/qwen_llama_grok_integration_20260606/plan.md) (to be authored by writing-plans skill)*
    *Goal: Add first-class support for Qwen (DashScope native SDK), Llama (Ollama local + OpenRouter cloud + custom URL), and Grok (xAI OpenAI-compatible). Introduce a **Vendor Capability Matrix** (7 v1 capabilities: vision, tool_calling, caching, streaming, model_discovery, context_window, cost_tracking; audio and server-side code_execution deferred) declared per-(vendor, model) in `src/vendor_capabilities.py`. GUI reads the matrix to enable/disable 9 UI elements (screenshot button, tools toggle, cache panel, stream progress, fetch models, token budget, cost panel) instead of hard-coding per-vendor branches. Extract a shared `send_openai_compatible()` helper in `src/openai_compatible.py` that operates on a normalized request/response data structure; each `_send_<vendor>()` is a thin boundary adapter (data-oriented design per Fleury/Acton/Lottes). Refactor `_send_minimax()` to use the helper (~250 lines → ~50). **Out of scope** (separate follow-up track): Anthropic/Gemini/DeepSeek migration to the matrix. 6 phases: matrix+helper, Qwen, Grok+Llama, MiniMax refactor, UX adaptation, docs+archive.*
 
+0e. [ ] **Track: Data-Oriented Error Handling (Fleury Pattern)** `[track-created: 494f68f9]`
+   *Link: [./tracks/data_oriented_error_handling_20260606/](./tracks/data_oriented_error_handling_20260606/), Spec: [./tracks/data_oriented_error_handling_20260606/spec.md](./tracks/data_oriented_error_handling_20260606/spec.md), Plan: [./tracks/data_oriented_error_handling_20260606/plan.md](./tracks/data_oriented_error_handling_20260606/plan.md) (to be authored by writing-plans skill)*
+   *Goal: Introduce Ryan Fleury's "errors are just cases" framework as a project convention. New `src/result_types.py` (ErrorKind enum, ErrorInfo dataclass, `Result[T]` with data + side-channel errors list, NilPath + NilRAGState sentinel singletons) and new `conductor/code_styleguides/error_handling.md` canonical reference. Refactor `src/mcp_client.py` ((p, err) tuples → Result; 30+ `assert p is not None` → nil-sentinel paths), `src/ai_client.py` (ProviderError exception → ErrorInfo dataclass; `_send_<vendor>()` → `_send_<vendor>_result()` returning `Result[str]`; `send()` marked `@deprecated`; new `send_result()` public API), and `src/rag_engine.py` (RAGEngine methods → Result returns). Update `conductor/product-guidelines.md` + `workflow.md` + `docs/guide_*.md` so the convention is documented and future plans can incrementally migrate the remaining `src/` files. **Blocked by** startup_speedup, test_batching_refactor, and qwen_llama_grok tracks. 5 phases: foundation+styleguide, mcp_client refactor, ai_client refactor (highest risk; ProviderError removal), rag_engine refactor, deprecation+docs+archive.*
+   *Follow-up: [./tracks/public_api_migration_20260606/](./tracks/public_api_migration_20260606/) (planned; not yet specced) — removes the deprecated `ai_client.send()` and migrates all callers.*
+
 0b. [x] **Track: rag_phase4_stress_test_flake_20260606** — fixed 16412ad5
    *Status: 2026-06-06 — Surfaced during post-v2 verification. Resolved: real bug, NOT a test flake. Root cause: ChromaDB collection dimension mismatch across test runs. The persistent on-disk collection (`tests/artifacts/live_gui_workspace/.slop_cache/chroma_test_stress/`) was created by a previous run with Gemini embeddings (3072-dim); the current run uses local SentenceTransformers (384-dim). `index_file()` upserts silently corrupt the collection, then `search()` fails with `Collection expecting embedding with dimension of 3072, got 384` and the AI request never reaches 'done' status, timing out the 50*0.5s = 25s poll loop. Fix: `RAGEngine._init_vector_store` now calls `_validate_collection_dim` which inspects the first existing vector's dim, compares to the current provider's output, and recreates the collection on mismatch (with a stderr warning). Regression tests added: `test_rag_collection_dim_mismatch_recreates_collection` and `test_rag_collection_dim_match_preserves_collection` in `tests/test_rag_engine.py`. This also fixes a real user-facing bug: switching embedding providers in the GUI previously caused silent corruption. Commit 16412ad5.*
 0a. [ ] **Track: prior_session_test_harden_20260605** [superseded by live_gui_test_hardening_v2_20260605]