docs: complete phase 3 prompt builders

PROJECT_STATE.md

@@ -7,13 +7,13 @@ ChatGPT MCP Server
 ## Status
 
 Planning complete.
-Phase 0 complete. Phase 1 complete. Phase 2 complete. Phase 3 in progress.
+Phase 0 complete. Phase 1 complete. Phase 2 complete. Phase 3 complete.
 
 ## Current Phase
 
-Phase 3 in progress.
+Phase 4 - Tool Handlers
 
-## Completed Tasks
+## Completed Tasks (Phase 3 Complete)
 
 - Task 0.1 — Create repository skeleton ✅
 - Task 0.2 — package.json with dependencies ✅
@@ -30,7 +30,26 @@ Phase 3 in progress.
 - Task 3.4 — review_plan prompt builder (`src/prompts/review-plan.js`, `test/prompts/review-plan.test.js`) ✅
 - Task 3.5 — review_code prompt builder (`src/prompts/review-code.js`, `test/prompts/review-code.test.js`) ✅
 - Task 3.6 — debug_issue prompt builder (`src/prompts/debug-issue.js`, `test/prompts/debug-issue.test.js`) ✅
+- Task 3.7 — architecture_review prompt builder (`src/prompts/architecture-review.js`, `test/prompts/architecture-review.test.js`) ✅
 
-## Next Phase
+## Phase 3 Completion Summary
 
-Phase 3 — in progress; next is Task 3.6 (debug_issue prompt builder).
+Phase 3 — Tool Inputs and Prompts — is now complete.
+
+**Completed prompt builders:**
+- `buildBasePrompt` — base system prompt (ARCHITECTURE.md §11)
+- `buildAskChatGptPrompt` — general second-opinion advisor
+- `buildReviewPlanPrompt` — plan review before implementation
+- `buildReviewCodePrompt` — focused code/diff review
+- `buildDebugIssuePrompt` — error/log/stack trace analysis
+- `buildArchitectureReviewPrompt` — architecture decision trade-off review
+
+**What Phase 3 established:**
+- Prompt layer complete with composition pattern established.
+- All prompt builders tested (56 tests for architecture-review alone; 384 total).
+- Each builder follows the same pattern: `buildBasePrompt()` → `\n\n---\n\n` → tool-specific section.
+- Guard rails reinforced in every builder (Claude Code is executor; ChatGPT is advisory only).
+
+**Not done yet (belongs to Phase 4):**
+- No MCP tool registration.
+- No tool handlers.