feat(skills): add /understand-domain skill for business domain knowledge extraction

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Lum1104

understand-anything-plugin/skills/understand-domain/SKILL.md

@@ -0,0 +1,67 @@
+---
+name: understand-domain
+description: Extract business domain knowledge from a codebase and generate an interactive domain flow graph. Works standalone (lightweight scan) or derives from an existing /understand knowledge graph.
+argument-hint: [--full]
+---
+
+# /understand-domain
+
+Extracts business domain knowledge — domains, business flows, and process steps — from a codebase and produces an interactive horizontal flow graph in the dashboard.
+
+## How It Works
+
+- If a knowledge graph already exists (`.understand-anything/knowledge-graph.json`), derives domain knowledge from it (cheap, no file scanning)
+- If no knowledge graph exists, performs a lightweight scan: file tree + entry point detection + sampled files
+- Use `--full` flag to force a fresh scan even if a knowledge graph exists
+
+## Instructions
+
+### Phase 1: Detect Existing Graph
+
+1. Check if `.understand-anything/knowledge-graph.json` exists in the current project
+2. If it exists AND `--full` was NOT passed → proceed to Phase 3 (derive from graph)
+3. Otherwise → proceed to Phase 2 (lightweight scan)
+
+### Phase 2: Lightweight Scan (Path 1)
+
+1. Run the preprocessing script bundled with this skill:
+   ```
+   python understand-anything-plugin/skills/understand-domain/extract-domain-context.py <project-root>
+   ```
+   This outputs `.understand-anything/intermediate/domain-context.json` containing:
+   - File tree (respecting `.gitignore`)
+   - Detected entry points (HTTP routes, CLI commands, event handlers, cron jobs, exported handlers)
+   - File signatures (exports, imports per file)
+   - Code snippets for each entry point (signature + first few lines)
+2. Read the generated `domain-context.json` as context for Phase 4
+3. Proceed to Phase 4
+
+### Phase 3: Derive from Existing Graph (Path 2)
+
+1. Read `.understand-anything/knowledge-graph.json`
+2. Format the graph data as structured context:
+   - All nodes with their types, names, summaries, and tags
+   - All edges with their types (especially `calls`, `imports`, `contains`)
+   - All layers with their descriptions
+   - Tour steps if available
+3. This is the context for the domain analyzer — no file reading needed
+4. Proceed to Phase 4
+
+### Phase 4: Domain Analysis
+
+1. Read the domain-analyzer agent prompt from `agents/domain-analyzer.md`
+2. Dispatch a subagent with the domain-analyzer prompt + the context from Phase 2 or 3
+3. The agent writes its output to `.understand-anything/intermediate/domain-analysis.json`
+
+### Phase 5: Validate and Save
+
+1. Read the domain analysis output
+2. Validate using the standard graph validation pipeline (the schema now supports domain/flow/step types)
+3. If validation fails, log warnings but save what's valid (error tolerance)
+4. Save to `.understand-anything/domain-graph.json`
+5. Clean up `.understand-anything/intermediate/domain-analysis.json`
+
+### Phase 6: Launch Dashboard
+
+1. Auto-trigger `/understand-dashboard` to visualize the domain graph
+2. The dashboard will detect `domain-graph.json` and show the domain view by default