feat: add Plan Agent for implementation planning

- Add PlanAgentImpl with read-only tools only
- System prompts optimized for architecture planning
- Outputs step-by-step implementation plans with critical files
- 15 unit tests for registration, tools, and API
- Update COVERAGE.md to ~70% complete

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

webber-api/docs/COVERAGE.md

@@ -2,7 +2,7 @@
 
 > Tracking progress towards Claude Code-like functionality
 
-## Current Status: ~65% Complete
+## Current Status: ~70% Complete
 
 Last updated: 2026-01-11
 
@@ -44,6 +44,20 @@ Last updated: 2026-01-11
 
 **Gap:** Mistral Nemo sometimes hallucinates instead of using tool results.
 
+### Phase 2b: Plan Agent ✅ Complete
+
+| Component | Status | Notes |
+|-----------|--------|-------|
+| `PlanAgentImpl` | ✅ | READ-ONLY software architect agent |
+| System prompts | ✅ | Architecture-focused with tool examples |
+| Tool registration | ✅ | Only read-only tools (4 tools) |
+| Streaming support | ✅ | `run_stream()` method with SSE |
+| Unit tests | ✅ | 15 tests for registration, tools, API |
+
+**Available tools:** `read_file`, `glob_files`, `grep_content`, `bash_readonly` (read-only only)
+
+**Purpose:** Design implementation strategies before coding - explores codebase and creates step-by-step plans.
+
 ### Phase 3: CLI Foundation ✅ Complete
 
 | Component | Status | Notes |
@@ -94,7 +108,7 @@ Last updated: 2026-01-11
 
 | Feature | Category | Description | Complexity |
 |---------|----------|-------------|------------|
-| **Plan Agent** | Agents | Design implementation approaches | High |
+| ~~**Plan Agent**~~ | Agents | ✅ Design implementation approaches | High |
 | **Task Agent** | Agents | Autonomous multi-step execution | High |
 | **Context summarization** | Infrastructure | Compress history at token limit | High |
 | **Conversation persistence** | CLI | Multi-turn memory in chat mode | Medium |
@@ -103,6 +117,7 @@ Last updated: 2026-01-11
 
 | Feature | Category | Description | Complexity |
 |---------|----------|-------------|------------|
+| **Web search summarizer** | Tools | Agent to extract core content from web pages (remove nav, footers, etc.) and preserve relevant links for nested fetching | Medium |
 | **Tool result caching** | Infrastructure | Cache file reads for performance | Low |
 | **Session persistence** | CLI | Save/resume conversations | Medium |
 | **Todo tracking** | CLI | Built-in task list (`/todo`) | Medium |
@@ -129,6 +144,7 @@ Last updated: 2026-01-11
 |------|---------|--------|--------|
 | Tool unit tests | 109 | 109 | ✅ |
 | API tests | 11 | 11 | ✅ |
+| Plan agent tests | 15 | 15 | ✅ |
 | Security tests | 14 | 14 | ✅ |
 | Integration tests | 10 | 10 | ✅ Agent + real LLM |
 | E2E tests | 12 | 12 | ✅ Full API workflow |
@@ -140,6 +156,7 @@ Last updated: 2026-01-11
 - Web search: 10 tests
 - Gitignore filtering: 10 tests
 - API endpoints: 11 tests
+- Plan agent: 15 tests
 - Security: 14 tests
 - Health checks: 2 tests
 - Integration (LLM): 10 tests
@@ -205,6 +222,11 @@ curl -X POST http://localhost:8095/agents/run \
   -H "Content-Type: application/json" \
   -d '{"agent_type":"explore","prompt":"list python files","working_dir":"."}'
 
+# Plan agent (read-only, creates implementation plans)
+curl -X POST http://localhost:8095/agents/run \
+  -H "Content-Type: application/json" \
+  -d '{"agent_type":"plan","prompt":"plan how to add user auth","working_dir":"."}'
+
 # Streaming endpoint
 curl -N http://localhost:8095/agents/stream \
   -H "Content-Type: application/json" \