v0.7.0 - Pre-flight launch validation (Test button on every model card)

validate.py:
- Builds the same args list a real swap would pass to 'vllm serve'
- SSHes into Spark 1 and runs vLLM's own argparse layer inside the running vllm_node container, WITHOUT initializing the engine
- Uses FlexibleArgumentParser (from vllm.utils.argparse_utils, with fallback to engine.arg_utils) + make_arg_parser — the exact same parser the 'vllm serve' CLI uses. Earlier attempt with bare argparse.ArgumentParser was too strict (rejected '--moe_backend' with underscore that the real CLI accepts via FlexibleArgumentParser's normalization)
- Returns structured {ok, stage, error, cmd_args, launch_cmd} so the UI can surface the exact failure cause

Endpoint: POST /api/swap/{key}/validate. Cheap (~5s), no engine init, no disruption to the currently-loaded model.

Frontend: 'Test' button on every model card, inline result below the action row (green check or red detailed error). Result stays visible until the user reloads or clicks Test again.

Catches: typos in flag names, deprecated/removed flags after a vLLM upgrade, type mismatches. Does NOT catch runtime-only failures (Mamba block-size assertion, OOM at load, kernel-compat). Ok=true is necessary-but-not-sufficient; ok=false is definitive 'don't bother running it'.

image/app/static/style.css

@@ -701,9 +701,24 @@ main {
 .card.active .btn { background: rgba(74, 222, 128, 0.12); color: var(--accent); border-color: rgba(74, 222, 128, 0.4); }
 .card-actions { display: flex; gap: 6px; }
 .card-actions .btn.primary { flex: 1; }
-.card .adv-btn { padding: 8px 12px; font-size: 12px; }
+.card .adv-btn,
+.card .test-btn { padding: 8px 12px; font-size: 12px; }
 .card .custom-pill { color: var(--info); border-color: rgba(96, 165, 250, 0.4); }
 
+.test-result {
+  font-size: 12px;
+  line-height: 1.45;
+  padding: 8px 10px;
+  border-radius: 5px;
+  margin-top: 4px;
+  border: 1px solid var(--border);
+  background: var(--surface-2);
+}
+.test-result.ok { border-color: rgba(74, 222, 128, 0.4); background: rgba(74, 222, 128, 0.04); }
+.test-result.fail { border-color: rgba(239, 68, 68, 0.45); background: rgba(239, 68, 68, 0.06); word-break: break-word; }
+.test-result .ok-mark { color: var(--accent); font-weight: 600; }
+.test-result .fail-mark { color: var(--error); font-weight: 600; }
+
 .footer {
   margin-top: 28px;
   padding-top: 16px;