understand-domain

# /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 (`.ua/knowledge-graph.json`, or the legacy `.understand-anything/knowledge-graph.json` when that directory is present), 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 0: Resolve `PROJECT_ROOT`

Set `PROJECT_ROOT` to the current working directory.

**Worktree redirect.** If `PROJECT_ROOT` is inside a git worktree (not the main checkout), redirect output to the main repository root. Worktrees managed by Claude Code are ephemeral — the data directory (`.ua/`, or legacy `.understand-anything/`) written there is destroyed when the session ends, taking the domain graph with it (issue #133). Detect a worktree by comparing `git rev-parse --git-dir` against `git rev-parse --git-common-dir`; in a normal checkout or submodule they resolve to the same path, in a worktree they differ and the parent of `--git-common-dir` is the main repo root.

```bash
COMMON_DIR=$(git -C "$PROJECT_ROOT" rev-parse --git-common-dir 2>/dev/null)
GIT_DIR=$(git -C "$PROJECT_ROOT" rev-parse --git-dir 2>/dev/null)
if [ -n "$COMMON_DIR" ] && [ -n "$GIT_DIR" ]; then
  COMMON_ABS=$(cd "$PROJECT_ROOT" && cd "$COMMON_DIR" 2>/dev/null && pwd -P)
  GIT_ABS=$(cd "$PROJECT_ROOT" && cd "$GIT_DIR" 2>/dev/null && pwd -P)
  if [ -n "$COMMON_ABS" ] && [ "$COMMON_ABS" != "$GIT_ABS" ]; then
    MAIN_ROOT=$(dirname "$COMMON_ABS")
    if [ -d "$MAIN_ROOT" ] && [ "${UNDERSTAND_NO_WORKTREE_REDIRECT:-0}" != "1" ]; then
      echo "[understand-domain] Detected git worktree at $PROJECT_ROOT"
      echo "[understand-domain] Redirecting output to main repo root: $MAIN_ROOT"
      echo "[understand-domain] (Set UNDERSTAND_NO_WORKTREE_REDIRECT=1 to keep PROJECT_ROOT as the worktree.)"
      PROJECT_ROOT="$MAIN_ROOT"
    fi
  fi
fi
```

Use `$PROJECT_ROOT` (not the bare CWD) for every reference to "the current project" / `<project-root>` in subsequent phases.

**Resolve the data directory `$UA_DIR`.** All Understand-Anything artifacts live in the project's data directory. Resolve it once, now that `$PROJECT_ROOT` is known, and reuse `$UA_DIR` for every read and write in later phases:
```bash
UA_DIR="$PROJECT_ROOT/$([ -d "$PROJECT_ROOT/.understand-anything" ] && echo .understand-anything || echo .ua)"
```
This keeps the legacy `.understand-anything/` directory when it already exists (existing projects keep working with no migration) and uses the new `.ua/` otherwise. Because each phase may run in a fresh shell, carry `$UA_DIR` forward like `$PROJECT_ROOT`, re-resolving it with the line above if a later command block needs it.

**Important:** do **not** assume the plugin root is simply two directories above the skill path string. In many installations `~/.agents/skills/understand-domain` is a symlink into the real plugin checkout. Prefer runtime-provided plugin roots first (for Claude), then fall back to universal symlinks, skill symlink resolution, and common clone-based install paths.

Resolve the plugin root like this:

```bash
SKILL_REAL=$(realpath ~/.agents/skills/understand-domain 2>/dev/null || readlink -f ~/.agents/skills/understand-domain 2>/dev/null || echo "")
SELF_RELATIVE=$([ -n "$SKILL_REAL" ] && cd "$SKILL_REAL/../.." 2>/dev/null && pwd || echo "")
COPILOT_SKILL_REAL=$(realpath ~/.copilot/skills/understand-domain 2>/dev/null || readlink -f ~/.copilot/skills/understand-domain 2>/dev/null || echo "")
COPILOT_SELF_RELATIVE=$([ -n "$COPILOT_SKILL_REAL" ] && cd "$COPILOT_SKILL_REAL/../.." 2>/dev/null && pwd || echo "")

PLUGIN_ROOT=""
for candidate in \
  "${CLAUDE_PLUGIN_ROOT}" \
  "$HOME/.understand-anything-plugin" \
  "$SELF_RELATIVE" \
  "$COPILOT_SELF_RELATIVE" \
  "$HOME/.codex/understand-anything/understand-anything-plugin" \
  "$HOME/.opencode/understand-anything/understand-anything-plugin" \
  "$HOME/.pi/understand-anything/understand-anything-plugin" \
  "$HOME/understand-anything/understand-anything-plugin"; do
  if [ -n "$candidate" ] && [ -f "$candidate/package.json" ] && [ -f "$candidate/pnpm-workspace.yaml" ]; then
    PLUGIN_ROOT="$candidate"
    break
  fi
done

if [ -z "$PLUGIN_ROOT" ]; then
  echo "Error: Cannot find the understand-anything plugin root."
  echo "Checked:"
  echo "  - ${CLAUDE_PLUGIN_ROOT:-<unset CLAUDE_PLUGIN_ROOT>}"
  echo "  - $HOME/.understand-anything-plugin"
  echo "  - ${SELF_RELATIVE:-<unresolved path derived from ~/.agents/skills/understand-domain>}"
  echo "  - ${COPILOT_SELF_RELATIVE:-<unresolved path derived from ~/.copilot/skills/understand-domain>}"
  echo "  - $HOME/.codex/understand-anything/understand-anything-plugin"
  echo "  - $HOME/.opencode/understand-anything/understand-anything-plugin"
  echo "  - $HOME/.pi/understand-anything/understand-anything-plugin"
  echo "  - $HOME/understand-anything/understand-anything-plugin"
  echo "Make sure the plugin is installed correctly."
  exit 1
fi
```

Use `$PLUGIN_ROOT` for every reference to agent definitions in subsequent phases.

### Phase 1: Detect Existing Graph

1. Check if `$UA_DIR/knowledge-graph.json` exists
2. If it exists AND `--full` was NOT passed, check freshness before deriving from it:
   - Read `project.gitCommitHash` from the graph metadata as `GRAPH_COMMIT_RAW`. Change to `$PROJECT_ROOT`, resolve it as a commit before using it in any Git diff, compare the resolved commit with `git rev-parse HEAD`, and inspect project-scoped committed and working-tree changes:
     ```bash
     GRAPH_COMMIT=$(git rev-parse --verify --end-of-options "${GRAPH_COMMIT_RAW}^{commit}" 2>/dev/null)
     git rev-parse HEAD
     git diff --name-only "$GRAPH_COMMIT" HEAD -- .
     git diff --ca