Initial artdag-common shared library

Shared components for L1 and L2 servers:
- Jinja2 template system with base template and components
- Middleware for auth and content negotiation
- Pydantic models for requests/responses
- Utility functions for pagination, media, formatting
- Constants for Tailwind/HTMX/Cytoscape CDNs

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

artdag_common/rendering.py

@@ -0,0 +1,160 @@
+"""
+Jinja2 template rendering system for Art-DAG servers.
+
+Provides a unified template environment that can load from:
+1. The shared artdag_common/templates directory
+2. App-specific template directories
+
+Usage:
+    from artdag_common import create_jinja_env, render
+
+    # In app initialization
+    templates = create_jinja_env("app/templates")
+
+    # In route handler
+    return render(templates, "runs/detail.html", request, run=run, user=user)
+"""
+
+from pathlib import Path
+from typing import Any, Optional, Union
+
+from fastapi import Request
+from fastapi.responses import HTMLResponse
+from jinja2 import Environment, ChoiceLoader, FileSystemLoader, PackageLoader, select_autoescape
+
+from .constants import (
+    TAILWIND_CDN,
+    HTMX_CDN,
+    CYTOSCAPE_CDN,
+    DAGRE_CDN,
+    CYTOSCAPE_DAGRE_CDN,
+    TAILWIND_CONFIG,
+    NODE_COLORS,
+    STATUS_COLORS,
+)
+
+
+def create_jinja_env(*template_dirs: Union[str, Path]) -> Environment:
+    """
+    Create a Jinja2 environment with the shared templates and optional app-specific dirs.
+
+    Args:
+        *template_dirs: Additional template directories to search (app-specific)
+
+    Returns:
+        Configured Jinja2 Environment
+
+    Example:
+        env = create_jinja_env("/app/templates", "/app/custom")
+    """
+    loaders = []
+
+    # Add app-specific directories first (higher priority)
+    for template_dir in template_dirs:
+        path = Path(template_dir)
+        if path.exists():
+            loaders.append(FileSystemLoader(str(path)))
+
+    # Add shared templates from this package (lower priority, fallback)
+    loaders.append(PackageLoader("artdag_common", "templates"))
+
+    env = Environment(
+        loader=ChoiceLoader(loaders),
+        autoescape=select_autoescape(["html", "xml"]),
+        trim_blocks=True,
+        lstrip_blocks=True,
+    )
+
+    # Add global context available to all templates
+    env.globals.update({
+        "TAILWIND_CDN": TAILWIND_CDN,
+        "HTMX_CDN": HTMX_CDN,
+        "CYTOSCAPE_CDN": CYTOSCAPE_CDN,
+        "DAGRE_CDN": DAGRE_CDN,
+        "CYTOSCAPE_DAGRE_CDN": CYTOSCAPE_DAGRE_CDN,
+        "TAILWIND_CONFIG": TAILWIND_CONFIG,
+        "NODE_COLORS": NODE_COLORS,
+        "STATUS_COLORS": STATUS_COLORS,
+    })
+
+    # Add custom filters
+    env.filters["truncate_hash"] = truncate_hash
+    env.filters["format_size"] = format_size
+    env.filters["status_color"] = status_color
+
+    return env
+
+
+def render(
+    env: Environment,
+    template_name: str,
+    request: Request,
+    status_code: int = 200,
+    **context: Any,
+) -> HTMLResponse:
+    """
+    Render a template to an HTMLResponse.
+
+    Args:
+        env: Jinja2 environment
+        template_name: Template file path (e.g., "runs/detail.html")
+        request: FastAPI request object
+        status_code: HTTP status code (default 200)
+        **context: Template context variables
+
+    Returns:
+        HTMLResponse with rendered content
+    """
+    template = env.get_template(template_name)
+    html = template.render(request=request, **context)
+    return HTMLResponse(html, status_code=status_code)
+
+
+def render_fragment(
+    env: Environment,
+    template_name: str,
+    **context: Any,
+) -> str:
+    """
+    Render a template fragment to a string (for HTMX partial updates).
+
+    Args:
+        env: Jinja2 environment
+        template_name: Template file path
+        **context: Template context variables
+
+    Returns:
+        Rendered HTML string
+    """
+    template = env.get_template(template_name)
+    return template.render(**context)
+
+
+# Custom Jinja2 filters
+
+def truncate_hash(value: str, length: int = 16) -> str:
+    """Truncate a hash to specified length with ellipsis."""
+    if not value:
+        return ""
+    if len(value) <= length:
+        return value
+    return f"{value[:length]}..."
+
+
+def format_size(size_bytes: Optional[int]) -> str:
+    """Format file size in human-readable form."""
+    if size_bytes is None:
+        return "Unknown"
+    if size_bytes < 1024:
+        return f"{size_bytes} B"
+    elif size_bytes < 1024 * 1024:
+        return f"{size_bytes / 1024:.1f} KB"
+    elif size_bytes < 1024 * 1024 * 1024:
+        return f"{size_bytes / (1024 * 1024):.1f} MB"
+    else:
+        return f"{size_bytes / (1024 * 1024 * 1024):.1f} GB"
+
+
+def status_color(status: str) -> str:
+    """Get Tailwind CSS class for a status."""
+    return STATUS_COLORS.get(status, STATUS_COLORS["pending"])