Add standalone P&ID designer app

.github/workflows/pid-designer-ci.yml

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+name: P&ID Designer CI
+
+'on':
+  push:
+    paths:
+      - 'pid-designer/**'
+      - '.github/workflows/pid-designer-ci.yml'
+  pull_request:
+    paths:
+      - 'pid-designer/**'
+      - '.github/workflows/pid-designer-ci.yml'
+  workflow_dispatch:
+
+jobs:
+  frontend:
+    name: Frontend (TypeScript build)
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - uses: actions/setup-node@v4
+      with:
+        node-version: '20.x'
+        cache: 'npm'
+        cache-dependency-path: pid-designer/frontend/package-lock.json
+
+    - name: Install dependencies
+      working-directory: pid-designer/frontend
+      run: npm ci || npm install
+
+    - name: TypeScript build
+      working-directory: pid-designer/frontend
+      run: npm run build
+
+  backend:
+    name: Backend (import check)
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - uses: actions/setup-python@v5
+      with:
+        python-version: '3.11'
+
+    - name: Install dependencies
+      run: pip install "fastapi>=0.128" "uvicorn[standard]>=0.34" "pydantic>=2.12"
+
+    - name: Verify imports
+      working-directory: pid-designer
+      run: python3 -c "import backend.main; print('backend imports OK')"

pid-designer/.gitignore

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+node_modules/
+__pycache__/
+*.pyc
+*.pyo
+.vite/
+dist/

pid-designer/backend/main.py

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+"""Standalone FastAPI backend for the P&ID Designer.
+
+Run with:
+    cd pid-designer
+    uvicorn backend.main:app --reload --port 8001
+"""
+
+from fastapi import FastAPI
+from fastapi.middleware.cors import CORSMiddleware
+
+from backend.routers import pid
+
+app = FastAPI(title="P&ID Designer API", version="1.0.0")
+
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=[
+        "http://localhost:5173",
+        "http://localhost:5174",
+        "http://127.0.0.1:5173",
+        "http://127.0.0.1:5174",
+    ],
+    allow_credentials=True,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+app.include_router(pid.router)
+
+
+@app.get("/api/health")
+async def health():
+    return {"status": "healthy"}

pid-designer/backend/routers/pid.py

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+"""PID diagram persistence and git-backed version control."""
+
+import json
+import subprocess
+from pathlib import Path
+
+from fastapi import APIRouter, HTTPException
+from pydantic import BaseModel
+from typing import Any
+
+router = APIRouter(prefix="/api/pid", tags=["pid"])
+
+REPO_ROOT = Path(__file__).resolve().parents[2]
+DIAGRAM_PATH = REPO_ROOT / "diagrams" / "pid_main.json"
+
+def _git_root() -> Path:
+    r = subprocess.run(["git", "rev-parse", "--show-toplevel"], cwd=REPO_ROOT,
+                       capture_output=True, text=True)
+    return Path(r.stdout.strip())
+
+GIT_ROOT = _git_root()
+# Path used in `git show <hash>:<path>` — must be relative to the git repo root.
+GIT_DIAGRAM_PATH = str(DIAGRAM_PATH.relative_to(GIT_ROOT))
+
+
+def _run_git(*args: str) -> str:
+    """Run a git command in the repo root, return stdout. Raises RuntimeError on failure."""
+    result = subprocess.run(
+        ["git", *args],
+        cwd=REPO_ROOT,
+        capture_output=True,
+        text=True,
+        timeout=30,
+    )
+    if result.returncode != 0:
+        raise RuntimeError(result.stderr.strip() or result.stdout.strip())
+    return result.stdout
+
+
+def _read_diagram() -> dict:
+    if not DIAGRAM_PATH.exists():
+        return {"nodes": [], "edges": []}
+    return json.loads(DIAGRAM_PATH.read_text())
+
+
+def _write_diagram(data: dict) -> None:
+    DIAGRAM_PATH.parent.mkdir(parents=True, exist_ok=True)
+    DIAGRAM_PATH.write_text(json.dumps(data, indent=2))
+
+
+# ── Request models ────────────────────────────────────────────────────────────
+
+class DiagramPayload(BaseModel):
+    nodes: list[Any]
+    edges: list[Any]
+
+
+class CheckpointPayload(BaseModel):
+    nodes: list[Any]
+    edges: list[Any]
+    title: str
+    description: str = ""
+
+
+# ── Endpoints ─────────────────────────────────────────────────────────────────
+
+@router.get("/load")
+async def load_diagram():
+    """Load the current diagram from disk."""
+    return _read_diagram()
+
+
+@router.post("/autosave")
+async def autosave_diagram(payload: DiagramPayload):
+    """Write diagram to disk silently — no git commit."""
+    _write_diagram({"nodes": payload.nodes, "edges": payload.edges})
+    return {"ok": True}
+
+
+@router.post("/pull")
+async def pull_latest():
+    """Git pull then return the updated diagram."""
+    try:
+        _run_git("pull")
+    except RuntimeError as e:
+        raise HTTPException(status_code=500, detail=f"git pull failed: {e}")
+    return _read_diagram()
+
+
+@router.post("/checkpoint")
+async def checkpoint(payload: CheckpointPayload):
+    """Write diagram, commit, and push with a user-provided title + description."""
+    _write_diagram({"nodes": payload.nodes, "edges": payload.edges})
+
+    commit_message = payload.title.strip()
+    if payload.description.strip():
+        commit_message += f"\n\n{payload.description.strip()}"
+
+    try:
+        rel_path = str(DIAGRAM_PATH.relative_to(REPO_ROOT))
+        _run_git("add", rel_path)
+        _run_git("commit", "-m", commit_message)
+        _run_git("push")
+    except RuntimeError as e:
+        raise HTTPException(status_code=500, detail=f"git operation failed: {e}")
+
+    commit_hash = _run_git("rev-parse", "--short", "HEAD").strip()
+    return {"ok": True, "commit": commit_hash}
+
+
+@router.get("/history")
+async def get_history():
+    """Return the last 10 commits that touched diagrams/pid_main.json."""
+    rel_path = str(DIAGRAM_PATH.relative_to(REPO_ROOT))
+    try:
+        log = _run_git("log", "--format=%H|%s|%aI", "-10", "--", rel_path)
+    except RuntimeError as e:
+        raise HTTPException(status_code=500, detail=f"git log failed: {e}")
+
+    entries = []
+    for line in log.splitlines():
+        line = line.strip()
+        if not line:
+            continue
+        parts = line.split("|", 2)
+        if len(parts) == 3:
+            entries.append({"hash": parts[0], "title": parts[1], "timestamp": parts[2]})
+    return entries
+
+
+@router.get("/version/{commit_hash}")
+async def get_version(commit_hash: str):
+    """Return the diagram snapshot at a specific commit."""
+    try:
+        content = _run_git("show", f"{commit_hash}:{GIT_DIAGRAM_PATH}")
+    except RuntimeError as e:
+        raise HTTPException(status_code=404, detail=f"Version not found: {e}")
+    try:
+        return json.loads(content)
+    except json.JSONDecodeError:
+        raise HTTPException(status_code=500, detail="Snapshot at that commit is not valid JSON")

pid-designer/dev.sh

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+#!/usr/bin/env bash
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+cd "$SCRIPT_DIR"
+
+cleanup() {
+  echo ""
+  echo "Shutting down..."
+  kill "$BACKEND_PID" "$FRONTEND_PID" 2>/dev/null
+  wait "$BACKEND_PID" "$FRONTEND_PID" 2>/dev/null
+}
+trap cleanup EXIT INT TERM
+
+# Install frontend deps if needed
+if [ ! -d "frontend/node_modules" ]; then
+  echo "Installing frontend dependencies..."
+  (cd frontend && npm install)
+fi
+
+echo "Starting backend on http://localhost:8001"
+uvicorn backend.main:app --reload --port 8001 &
+BACKEND_PID=$!
+
+echo "Starting frontend on http://localhost:5174"
+(cd frontend && npm run dev) &
+FRONTEND_PID=$!
+
+wait "$BACKEND_PID" "$FRONTEND_PID"

pid-designer/frontend/index.html

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+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>P&ID Designer</title>
+  </head>
+  <body>
+    <div id="root"></div>
+    <script type="module" src="/src/main.tsx"></script>
+  </body>
+</html>