fix: support /model alias switch for cross-provider custom models

Backend (api/config.py):
- resolve_model_provider(): check custom_providers for prefix match
  BEFORE the config_base_url branch. Previously, providers with a
  base_url set (e.g. deepseek) would catch all slash-delimited model
  ids and return the config provider, preventing custom provider
  routing.
- get_available_models(): include model aliases in response so the
  frontend can resolve them on /model commands.

Frontend (static/commands.js):
- cmdModel(): resolve aliases by fetching /api/models before fuzzy
  matching the dropdown.
- Add bare-model fallback when the alias resolves to a slash-delimited
  provider/model id (e.g. "deepseek/deepseek-v4-flash").
- Add cross-provider fallback: when the model is from a custom provider
  not in the active provider dropdown, call /api/session/update directly
  with the provider/model id and provider override.

api/config.py

@@ -1772,6 +1772,19 @@ def resolve_model_provider(model_id: str) -> tuple:
             and prefix != config_provider
         ):
             return model_id, "openrouter", None
+        # Cross-provider via custom_providers: if the prefix matches a named custom
+        # provider entry (e.g. "ollama-local/glm-4.7-flash:q4_k_m"), route through it
+        # instead of falling back to the default config provider. MUST come BEFORE
+        # the config_base_url branch because many providers have a base_url set.
+        if prefix and config_provider and prefix != config_provider:
+            _custom_cfg = cfg.get("custom_providers", [])
+            if isinstance(_custom_cfg, list):
+                for _entry in _custom_cfg:
+                    if isinstance(_entry, dict) and _entry.get("name", "").strip() == prefix:
+                        _slug = _custom_provider_slug_from_name(prefix)
+                        _base = (_entry.get("base_url") or "").strip()
+                        return model_id, _slug, _base or None
+
         # If a custom endpoint base_url is configured, don't reroute through OpenRouter
         # just because the model name contains a slash (e.g. google/gemma-4-26b-a4b).
         # The user has explicitly pointed at a base_url, so trust their routing config.
@@ -3812,11 +3825,21 @@ def get_available_models() -> dict:
             or (g.get("provider_id") or "").startswith("custom:")
         ]
 
+        # 12. Include model aliases so the WebUI frontend can resolve them.
+        model_aliases: dict[str, str] = {}
+        try:
+            raw_aliases = cfg.get("model", {}).get("aliases", {})
+            if isinstance(raw_aliases, dict):
+                model_aliases = {str(k).strip(): str(v).strip() for k, v in raw_aliases.items() if k and v}
+        except Exception:
+            pass
+
         return {
             "active_provider": active_provider,
             "default_model": default_model,
             "configured_model_badges": _build_configured_model_badges(),
             "groups": groups,
+            "aliases": model_aliases,
         }
 
     # ── FAST PATH ─────────────────────────────────────────────────────────────

static/commands.js

@@ -326,7 +326,22 @@ async function cmdModel(args){
   if(!args){showToast(t('model_usage'));return;}
   const sel=$('modelSelect');
   if(!sel)return;
-  const q=args.toLowerCase();
+  let q=args.toLowerCase();
+  // Resolve alias before fuzzy matching the dropdown.
+  // Fetch /api/models which now includes an "aliases" key.
+  try {
+    const resp=await fetch('/api/models');
+    if(resp.ok){
+      const data=await resp.json();
+      const aliases=data.aliases||{};
+      for(const [alias,modelId] of Object.entries(aliases)){
+        if(alias.toLowerCase()===q){
+          q=modelId; // resolve alias to real model id e.g. "deepseek/deepseek-v4-flash"
+          break;
+        }
+      }
+    }
+  } catch(_){/* non-critical, fall through to fuzzy match */}
   // Fuzzy match: find first option whose label or value contains the query
   let match=null;
   for(const opt of sel.options){
@@ -334,6 +349,39 @@ async function cmdModel(args){
       match=opt.value;break;
     }
   }
+  // Fallback: if q has provider/ prefix (e.g. "deepseek/deepseek-v4-flash"),
+  // try the bare model name (which is how options appear for the active provider)
+  if(!match && q.includes('/')){
+    const bare=q.slice(q.lastIndexOf('/')+1);
+    for(const opt of sel.options){
+      if(opt.value.toLowerCase().includes(bare)||opt.textContent.toLowerCase().includes(bare)){
+        match=opt.value;break;
+      }
+    }
+    // Cross-provider fallback: if still no match, the model is from a
+    // different provider not in the dropdown. Call /api/session/update directly.
+    if(!match && S&&S.session&&S.session.session_id){
+      const provider=q.slice(0,q.indexOf('/'));
+      try{
+        const resp=await fetch('/api/session/update',{
+          method:'POST',
+          headers:{'Content-Type':'application/json'},
+          body:JSON.stringify({
+            session_id:S.session.session_id,
+            model:q,
+            model_provider:provider,
+          }),
+        });
+        if(resp.ok){
+          S.session.model=q;
+          S.session.model_provider=provider;
+          if(typeof syncTopbar==='function') syncTopbar();
+          showToast(t('switched_to')+q);
+          return;
+        }
+      }catch(_){/* fall through to "no model match" */}
+    }
+  }
   if(!match){showToast(t('no_model_match')+`"${args}"`);return;}
   sel.value=match;
   await sel.onchange();