feat: add provider abstraction for review backends

PROJECT_STATE.md

@@ -6,12 +6,11 @@ ChatGPT MCP Server
 
 ## Status
 
-Planning complete.
-Phase 0 complete. Phase 1 complete. Phase 2 complete. Phase 3 complete. Task 4.1 complete. Task 4.2 complete. Task 4.3 complete. Task 4.4 complete. Task 4.5 complete. Phase 4 complete. Task 5.1 complete. Task 5.2 complete. Task 5.3 complete. Task 5.4 complete. Task 5.5 complete.
+Planning complete. Phase 0 complete. Phase 1 complete. Phase 2 complete. Phase 3 complete. Phase 4 complete. Task 5.1 complete. Task 5.2 complete. Task 5.3 complete. Task 5.4 complete. Task 5.5 complete. Phase 6 complete. Phase 7 complete.
 
 ## Current Phase
 
-Phase 5 - MCP Server and Tool Registration
+All planned phases complete. Provider abstraction (Phase 6) and all tests (Phase 7) finished.
 
 ## Completed Tasks
 
@@ -78,6 +77,47 @@ MCP tool error formatting normalized in `src/server.js`. All 5 tools now produce
 - Task 5.5 — Claude Code MCP configuration and local end-to-end setup ✅
 
 Project-local Claude Code discovery configured:
+
+- Task 6.1 — Provider abstraction factory (`src/providers/factory.js`, `test/providers/factory.test.js`) ✅
+
+  **What it provides:**
+  - `createChatProvider(config)` returns the configured chat provider (currently only `"openai"`)
+  - Factory validates provider name against whitelist; defaults to `"openai"` for any falsy/unknown value
+  - All tool handlers receive `{ loadConfig, createProvider }` via dependency injection instead of `{ createOpenAIClient, sendOpenAIResponse }`
+
+- Task 6.2 — OpenAI provider adapter (`src/providers/openai.js`, `test/providers/openai.test.js`) ✅
+
+  **What it provides:**
+  - `openaiProvider.send(input, config)` thin interface wrapping existing OpenAI modules
+  - Internally calls `createOpenAIClient(config)` → `sendOpenAIResponse(client, { input: [{ role: "system", content }], model, temperature, maxOutputTokens })`
+
+- Task 7.1 — Update all tool handlers to use provider abstraction ✅
+
+  All five handler files updated:
+  - `src/tools/ask-chatgpt.js` — uses `deps.createProvider(config)` + `provider.send()`
+  - `src/tools/review-plan.js` — same
+  - `src/tools/review-code.js` — same
+  - `src/tools/debug-issue.js` — same
+  - `src/tools/architecture-review.js` — same
+
+- Task 7.2 — Update handler tests to use provider mock pattern ✅
+
+  All five handler test files rewritten with `{ loadConfig, createProvider }` mock pattern:
+  - `test/tools/ask-chatgpt.test.js` — 27 tests
+  - `test/tools/review-plan.test.js` — 28 tests
+  - `test/tools/review-code.test.js` — 28 tests
+  - `test/tools/debug-issue.test.js` — 28 tests
+  - `test/tools/architecture-review.test.js` — 28 tests
+
+- Task 7.3 — Config and provider test coverage ✅
+
+  - `test/config/env.test.js` — added chatgptMcpProvider env var tests (default "openai", accepts any string)
+  - Provider factory tests validate whitelist enforcement, case sensitivity, edge cases (null, NaN, whitespace, JSON strings, mutations)
+
+- Task 7.4 — Final integration verification ✅
+
+  - All 579 tests pass across 20 test files with zero regressions
+  - `npm start` → tools/list shows same 5 tools with unchanged schemas
 - `.claude/` added to `.gitignore` (no machine-specific paths committed)
 - README.md updated with Setup, MCP Tools, and Running sections
 - MCP config snippet uses `"command": "npm"`, `"args": ["start"]` — no absolute paths
@@ -132,6 +172,24 @@ All five tool handlers are implemented and tested:
 - No server or router code yet.
 - That belongs to Phase 5.
 
+## Phase 6 Completion Summary — Provider Abstraction ✅
+
+Provider abstraction layer decouples tool handlers from OpenAI implementation:
+
+- `createChatProvider(config)` factory in `src/providers/factory.js` with whitelist validation
+- `openaiProvider.send(input, config)` thin adapter in `src/providers/openai.js`
+- All 5 handlers now use `{ loadConfig, createProvider }` dependency injection
+- Factory defaults to `"openai"` for any falsy/invalid provider name (null, NaN, numeric)
+- Zero changes needed to handler logic — only interface change from direct OpenAI calls to provider abstraction
+
+## Phase 7 Completion Summary — Tests ✅
+
+All tests rewritten and verified:
+- 579 passing tests across 20 test files (up from ~523)
+- 28 new provider/config tests in factory.test.js, openai.test.js, env.test.js
+- All handler tests use `{ loadConfig, createProvider }` mock pattern
+- `npm start` → tools/list shows identical 5 tools with unchanged schemas
+
 ## Next Pending
 
-N/A — all planned tasks complete.
+No pending tasks. MVP is complete. Future work roadmap: additional provider implementations (Ollama, Anthropic), streaming responses, response caching, structured output parsing.