Add SPA-style navigation for plan nodes

- Add /run/{run_id}/plan/node/{step_id} endpoint for node details
- Node click updates URL without full page reload (pushState)
- Browser back/forward works correctly
- Refreshing page preserves selected node via ?node= parameter
- Node details loaded via fetch with partial HTML response

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

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

server.py

@@ -1335,8 +1335,159 @@ PLAN_CACHE_DIR = CACHE_DIR / 'plans'
 ANALYSIS_CACHE_DIR = CACHE_DIR / 'analysis'
 
 
+@app.get("/run/{run_id}/plan/node/{step_id}", response_class=HTMLResponse)
+async def run_plan_node_detail(run_id: str, step_id: str, request: Request):
+    """HTMX partial: Get node detail HTML fragment."""
+    ctx = await get_user_context_from_cookie(request)
+    if not ctx:
+        return HTMLResponse('<p class="text-red-400">Login required</p>', status_code=401)
+
+    run = await asyncio.to_thread(load_run, run_id)
+    if not run:
+        return HTMLResponse(f'<p class="text-red-400">Run not found</p>', status_code=404)
+
+    # Load plan data
+    plan_data = None
+    PLAN_CACHE_DIR.mkdir(parents=True, exist_ok=True)
+    for plan_file in PLAN_CACHE_DIR.glob("*.json"):
+        try:
+            with open(plan_file) as f:
+                data = json.load(f)
+                plan_inputs = data.get("input_hashes", {})
+                if set(plan_inputs.values()) == set(run.inputs):
+                    plan_data = data
+                    break
+        except (json.JSONDecodeError, IOError):
+            continue
+
+    if not plan_data:
+        return HTMLResponse('<p class="text-gray-400">Plan not found</p>')
+
+    # Find the step
+    step = None
+    for s in plan_data.get("steps", []):
+        if s.get("step_id") == step_id:
+            step = s
+            break
+
+    if not step:
+        return HTMLResponse(f'<p class="text-gray-400">Step {step_id} not found</p>')
+
+    # Get step info
+    step_name = step.get("name", step_id[:20])
+    node_type = step.get("node_type", "EFFECT")
+    cache_id = step.get("cache_id", "")
+    config = step.get("config", {})
+    level = step.get("level", 0)
+    input_steps = step.get("input_steps", [])
+
+    # Check for IPFS CID
+    step_cid = None
+    if run.step_results:
+        res = run.step_results.get(step_id)
+        if isinstance(res, dict) and res.get("cid"):
+            step_cid = res["cid"]
+
+    has_cached = cache_manager.has_content(cache_id) if cache_id else False
+    color = NODE_COLORS.get(node_type, NODE_COLORS["default"])
+
+    # Build preview HTML
+    preview_html = ""
+    if has_cached and cache_id:
+        media_type = detect_media_type(get_cache_path(cache_id))
+        if media_type == "video":
+            preview_html = f'''
+            <div class="mb-4">
+                <video src="/cache/{cache_id}/raw" controls muted class="w-full max-h-64 rounded-lg"></video>
+            </div>'''
+        elif media_type == "image":
+            preview_html = f'''
+            <div class="mb-4">
+                <img src="/cache/{cache_id}/raw" class="w-full max-h-64 rounded-lg object-contain">
+            </div>'''
+    elif step_cid:
+        ipfs_gateway = IPFS_GATEWAY_URL.rstrip('/') if IPFS_GATEWAY_URL else "https://ipfs.io/ipfs"
+        preview_html = f'''
+        <div class="mb-4">
+            <video src="{ipfs_gateway}/{step_cid}" controls muted class="w-full max-h-64 rounded-lg"></video>
+        </div>'''
+
+    # Build output link
+    output_html = ""
+    if step_cid:
+        output_html = f'''
+        <div class="mt-4">
+            <h5 class="text-sm font-medium text-gray-400 mb-2">Output (IPFS)</h5>
+            <a href="/ipfs/{step_cid}" class="flex items-center justify-between bg-dark-600 rounded p-3 hover:bg-dark-500 transition-colors">
+                <span class="font-mono text-xs text-gray-300 truncate">{step_cid}</span>
+                <span class="px-3 py-1 bg-blue-600 text-white text-xs rounded ml-2">View</span>
+            </a>
+        </div>'''
+    elif has_cached and cache_id:
+        output_html = f'''
+        <div class="mt-4">
+            <h5 class="text-sm font-medium text-gray-400 mb-2">Output</h5>
+            <a href="/cache/{cache_id}" class="flex items-center justify-between bg-dark-600 rounded p-3 hover:bg-dark-500 transition-colors">
+                <span class="font-mono text-xs text-gray-300 truncate">{cache_id}</span>
+                <span class="px-3 py-1 bg-blue-600 text-white text-xs rounded ml-2">View</span>
+            </a>
+        </div>'''
+
+    # Config display
+    config_html = ""
+    if config:
+        config_json = json.dumps(config, indent=2)
+        config_html = f'''
+        <div class="mt-4">
+            <h5 class="text-sm font-medium text-gray-400 mb-2">Config</h5>
+            <pre class="text-xs bg-dark-600 p-3 rounded overflow-x-auto max-h-40">{config_json}</pre>
+        </div>'''
+
+    # Input steps
+    inputs_html = ""
+    if input_steps:
+        inputs_list = "".join([
+            f'<span class="px-2 py-1 bg-dark-500 rounded text-xs font-mono">{inp[:16]}...</span>'
+            for inp in input_steps
+        ])
+        inputs_html = f'''
+        <div class="mt-4">
+            <h5 class="text-sm font-medium text-gray-400 mb-2">Input Steps</h5>
+            <div class="flex flex-wrap gap-2">{inputs_list}</div>
+        </div>'''
+
+    status = "cached" if (has_cached or step_cid) else ("completed" if run.status == "completed" else "pending")
+    status_color = "green" if status in ("cached", "completed") else "yellow"
+
+    return HTMLResponse(f'''
+    <div class="flex justify-between items-start mb-4">
+        <div>
+            <h4 class="text-lg font-semibold text-white">{step_name}</h4>
+            <div class="flex items-center gap-2 mt-1">
+                <span class="px-2 py-0.5 rounded text-xs" style="background-color: {color}; color: white">{node_type}</span>
+                <span class="text-{status_color}-400 text-xs">{status}</span>
+                <span class="text-gray-500 text-xs">Level {level}</span>
+            </div>
+        </div>
+        <button onclick="closeNodeDetail()" class="text-gray-400 hover:text-white p-1">
+            <svg class="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+                <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M6 18L18 6M6 6l12 12"/>
+            </svg>
+        </button>
+    </div>
+    {preview_html}
+    <div class="text-sm space-y-2">
+        <div><span class="text-gray-400">Step ID:</span> <span class="font-mono text-xs">{step_id}</span></div>
+        <div><span class="text-gray-400">Cache ID:</span> <span class="font-mono text-xs">{cache_id[:32] if cache_id else "N/A"}...</span></div>
+    </div>
+    {output_html}
+    {inputs_html}
+    {config_html}
+    ''')
+
+
 @app.get("/run/{run_id}/plan", response_class=HTMLResponse)
-async def run_plan_visualization(run_id: str, request: Request):
+async def run_plan_visualization(run_id: str, request: Request, node: Optional[str] = None):
     """Visualize execution plan as interactive DAG."""
     ctx = await get_user_context_from_cookie(request)
     if not ctx:
@@ -1504,7 +1655,7 @@ async def run_plan_visualization(run_id: str, request: Request):
     nodes_json = json.dumps(nodes)
     edges_json = json.dumps(edges)
 
-    dag_html = render_dag_cytoscape(nodes_json, edges_json)
+    dag_html = render_dag_cytoscape(nodes_json, edges_json, run_id=run_id, initial_node=node or "")
 
     # Stats summary - count from built nodes to reflect actual execution status
     total = len(nodes)
@@ -4712,34 +4863,82 @@ def render_run_sub_tabs(run_id: str, active: str = "overview") -> str:
     return html
 
 
-def render_dag_cytoscape(nodes_json: str, edges_json: str, container_id: str = "cy") -> str:
-    """Render Cytoscape.js DAG visualization HTML with WebSocket-ready architecture."""
+def render_dag_cytoscape(nodes_json: str, edges_json: str, container_id: str = "cy", run_id: str = "", initial_node: str = "") -> str:
+    """Render Cytoscape.js DAG visualization HTML with HTMX SPA-style navigation."""
     return f'''
     <div id="{container_id}" class="w-full h-96 bg-dark-800 rounded-lg border border-dark-500"></div>
-    <div id="{container_id}-details" class="mt-4 p-4 bg-dark-700 rounded-lg hidden">
-        <div class="flex justify-between items-start mb-3">
-            <div>
-                <h4 id="{container_id}-node-name" class="text-lg font-semibold text-white"></h4>
-                <span id="{container_id}-node-type" class="text-xs text-gray-400"></span>
-            </div>
-            <button id="{container_id}-close-btn" class="text-gray-400 hover:text-white">
-                <svg class="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24">
-                    <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M6 18L18 6M6 6l12 12"/>
-                </svg>
-            </button>
-        </div>
-        <div id="{container_id}-artifact-preview" class="mb-4 hidden">
-            <div class="bg-dark-800 rounded-lg overflow-hidden">
-                <video id="{container_id}-video-player" class="w-full max-h-64" controls muted></video>
-            </div>
-        </div>
-        <div id="{container_id}-node-info" class="text-gray-200 font-mono text-xs space-y-1"></div>
-        <div id="{container_id}-outputs-list" class="mt-4 hidden">
-            <h5 class="text-sm font-medium text-gray-400 mb-2">Outputs</h5>
-            <div id="{container_id}-outputs-container" class="space-y-2"></div>
+    <div id="{container_id}-details" class="mt-4 p-4 bg-dark-700 rounded-lg {"" if initial_node else "hidden"}">
+        <div id="{container_id}-details-content">
+            {"Loading..." if initial_node else ""}
         </div>
     </div>
     <script>
+        // SPA-style node detail functions
+        var currentRunId = '{run_id}';
+        var currentNodeId = '{initial_node}';
+
+        function loadNodeDetail(stepId) {{
+            if (!currentRunId || !stepId) return;
+            currentNodeId = stepId;
+
+            var detailsEl = document.getElementById('{container_id}-details');
+            var contentEl = document.getElementById('{container_id}-details-content');
+
+            detailsEl.classList.remove('hidden');
+            contentEl.innerHTML = '<div class="text-gray-400">Loading...</div>';
+
+            // Update URL without full page reload
+            var newUrl = '/run/' + currentRunId + '/plan?node=' + encodeURIComponent(stepId);
+            history.pushState({{ node: stepId }}, '', newUrl);
+
+            // Fetch node details via HTMX-style fetch
+            fetch('/run/' + currentRunId + '/plan/node/' + encodeURIComponent(stepId))
+                .then(function(response) {{ return response.text(); }})
+                .then(function(html) {{
+                    contentEl.innerHTML = html;
+                    // Trigger HTMX to process any dynamic content
+                    if (typeof htmx !== 'undefined') {{
+                        htmx.process(contentEl);
+                    }}
+                }})
+                .catch(function(err) {{
+                    contentEl.innerHTML = '<p class="text-red-400">Error loading node details</p>';
+                }});
+
+            // Select the node in cytoscape
+            if (window.artdagCy) {{
+                window.artdagCy.nodes().unselect();
+                var node = window.artdagCy.getElementById(stepId);
+                if (node && node.length) {{
+                    node.select();
+                }}
+            }}
+        }}
+
+        function closeNodeDetail() {{
+            var detailsEl = document.getElementById('{container_id}-details');
+            detailsEl.classList.add('hidden');
+            currentNodeId = '';
+
+            // Update URL to remove node parameter
+            var newUrl = '/run/' + currentRunId + '/plan';
+            history.pushState({{ node: null }}, '', newUrl);
+
+            // Unselect in cytoscape
+            if (window.artdagCy) {{
+                window.artdagCy.nodes().unselect();
+            }}
+        }}
+
+        // Handle browser back/forward
+        window.addEventListener('popstate', function(event) {{
+            if (event.state && event.state.node) {{
+                loadNodeDetail(event.state.node);
+            }} else {{
+                closeNodeDetail();
+            }}
+        }});
+
         document.addEventListener('DOMContentLoaded', function() {{
             // Register dagre layout
             if (typeof cytoscape !== 'undefined' && typeof cytoscapeDagre !== 'undefined') {{
@@ -4827,77 +5026,25 @@ def render_dag_cytoscape(nodes_json: str, edges_json: str, container_id: str = "
                 }}
             }});
 
-            // Close button handler
-            document.getElementById('{container_id}-close-btn').addEventListener('click', function() {{
-                document.getElementById('{container_id}-details').classList.add('hidden');
-                var player = document.getElementById('{container_id}-video-player');
-                if (player) player.pause();
-            }});
-
+            // Node click handler - SPA style with URL update
             window.artdagCy.on('tap', 'node', function(evt) {{
                 var node = evt.target;
-                var details = document.getElementById('{container_id}-details');
-                var info = document.getElementById('{container_id}-node-info');
-                var nameEl = document.getElementById('{container_id}-node-name');
-                var typeEl = document.getElementById('{container_id}-node-type');
-                var previewEl = document.getElementById('{container_id}-artifact-preview');
-                var videoPlayer = document.getElementById('{container_id}-video-player');
-                var outputsList = document.getElementById('{container_id}-outputs-list');
-                var outputsContainer = document.getElementById('{container_id}-outputs-container');
-
-                details.classList.remove('hidden');
-
-                // Set name and type
-                var nodeName = node.data('name') || node.data('label') || node.data('id');
-                nameEl.textContent = nodeName;
-                typeEl.textContent = node.data('nodeType') || '';
-
-                // Handle artifact preview
-                var cacheId = node.data('cacheId');
-                var status = node.data('status');
-                var hasCached = node.data('hasCached');
-
-                // Show video preview if artifact is cached
-                if (hasCached && cacheId) {{
-                    previewEl.classList.remove('hidden');
-                    videoPlayer.src = '/cache/' + cacheId + '/raw';
-                }} else {{
-                    previewEl.classList.add('hidden');
-                    videoPlayer.src = '';
-                }}
-
-                // Show artifact link if cached
-                if (hasCached && cacheId) {{
-                    outputsList.classList.remove('hidden');
-                    outputsContainer.innerHTML = '<div class="flex items-center justify-between bg-dark-600 rounded p-2">' +
-                        '<div class="flex-1 min-w-0">' +
-                        '<div class="text-sm text-gray-200">Output Artifact</div>' +
-                        '<div class="text-xs text-gray-500 font-mono truncate">' + cacheId.substring(0, 16) + '...</div>' +
-                        '</div>' +
-                        '<a href="/cache/' + cacheId + '" class="px-3 py-1 bg-blue-600 hover:bg-blue-700 text-white text-xs rounded transition-colors">View</a>' +
-                        '</div>';
-                }} else {{
-                    outputsList.classList.add('hidden');
-                }}
-
-                // Show basic info
-                var configStr = node.data('config') ? JSON.stringify(node.data('config'), null, 2) : null;
-                info.innerHTML =
-                    '<div><span class="text-gray-400">ID:</span> ' + node.data('id').substring(0, 24) + '...</div>' +
-                    '<div><span class="text-gray-400">Level:</span> ' + (node.data('level') !== undefined ? node.data('level') : 'N/A') + '</div>' +
-                    '<div><span class="text-gray-400">Cache ID:</span> ' + (cacheId ? cacheId.substring(0, 24) + '...' : 'N/A') + '</div>' +
-                    '<div><span class="text-gray-400">Status:</span> <span class="' + (status === 'cached' || status === 'completed' ? 'text-green-400' : 'text-yellow-400') + '">' + (status || 'N/A') + '</span></div>' +
-                    (configStr ? '<div class="mt-2"><span class="text-gray-400">Config:</span><pre class="mt-1 text-xs bg-dark-600 p-2 rounded overflow-x-auto max-h-32">' + configStr + '</pre></div>' : '');
+                var stepId = node.data('id');
+                loadNodeDetail(stepId);
             }});
 
+            // Click on background closes detail
             window.artdagCy.on('tap', function(evt) {{
                 if (evt.target === window.artdagCy) {{
-                    document.getElementById('{container_id}-details').classList.add('hidden');
-                    var player = document.getElementById('{container_id}-video-player');
-                    if (player) player.pause();
+                    closeNodeDetail();
                 }}
             }});
 
+            // Load initial node from URL if specified
+            if (currentNodeId) {{
+                loadNodeDetail(currentNodeId);
+            }}
+
             // WebSocket update function for real-time status updates
             window.updateNodeStatus = function(stepId, status, cacheId, hasCached) {{
                 if (!window.artdagCy) return;