Label eval runs with the model the server actually loaded (#379)

The phrasing eval printed "llm (0.8B, ...)" no matter which gguf
llama-server had loaded, so two runs of two different models came out
named the same and were easy to mix up when comparing.

It now asks llama-server over /v1/models, same as the router eval
already did. The helper moved to internal/llm so both share it, and it
now errors instead of returning a blank name when the id field is
missing — an unreachable server gets labelled "unknown-model", never a
plausible-looking guess.

Both eval paths stay opt-in behind MAVEN_LLM_URL; no server needed for
go test.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CGeSZxh1DCtRxmFVSYVGvJ

internal/llm/modelid.go

@@ -0,0 +1,70 @@
+package llm
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strings"
+	"time"
+)
+
+// UnknownModel is the label to print when the server would not say what it has
+// loaded. Deliberately ugly: an honest "unknown" is fine, a plausible-looking
+// but wrong model name is the bug this whole file exists to prevent.
+const UnknownModel = "unknown-model"
+
+// llama-server is local, so never send this through a proxy: this box's
+// http_proxy answers 503 for loopback, which would look like "server won't say
+// which model it has" when the server is right there and fine.
+// A Transport with no Proxy set bypasses http_proxy entirely.
+var modelHTTP = &http.Client{Timeout: 10 * time.Second, Transport: &http.Transport{}}
+
+// ModelID asks llama-server which model it has loaded, so a scoring run can
+// label itself. Without this a bake-off between two models produces two tables
+// that look identical, and the operator has to remember which server was up.
+//
+// Read from the server rather than passed in on purpose: a hand-typed label
+// goes stale the moment someone restarts the server with a different -m.
+func ModelID(ctx context.Context, base string) (string, error) {
+	req, err := http.NewRequestWithContext(ctx, "GET", strings.TrimSuffix(base, "/")+"/v1/models", nil)
+	if err != nil {
+		return "", err
+	}
+	resp, err := modelHTTP.Do(req)
+	if err != nil {
+		return "", err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != 200 {
+		return "", fmt.Errorf("models: status %d", resp.StatusCode)
+	}
+	var out struct {
+		Data []struct {
+			ID string `json:"id"`
+		} `json:"data"`
+	}
+	if err := json.NewDecoder(resp.Body).Decode(&out); err != nil {
+		return "", err
+	}
+	if len(out.Data) == 0 {
+		return "", fmt.Errorf("models: empty list")
+	}
+	short := shortModelID(out.Data[0].ID)
+	if short == "" {
+		// Server answered but the id field was missing or blank. Say so
+		// instead of handing back an empty label that reads as a real name.
+		return "", fmt.Errorf("models: no id in response")
+	}
+	return short, nil
+}
+
+// shortModelID trims the path and the .gguf suffix — llama-server reports the
+// file name it was started with, which is too long for a table header.
+func shortModelID(id string) string {
+	id = strings.TrimSpace(id)
+	if i := strings.LastIndexAny(id, "/\\"); i >= 0 {
+		id = id[i+1:]
+	}
+	return strings.TrimSpace(strings.TrimSuffix(id, ".gguf"))
+}

internal/llm/modelid_test.go

@@ -0,0 +1,64 @@
+package llm
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+// The point of these tests: a wrong-but-plausible model label is the bug, so
+// every path that cannot learn the real name must return an error instead of a
+// guess. No llama-server needed — a stub server stands in.
+func TestModelID(t *testing.T) {
+	cases := []struct {
+		name string
+		body string
+		code int
+		want string // "" ⇒ expect an error
+	}{
+		{"full path", `{"data":[{"id":"/mnt/hdd1/llms/qwen3.5/Qwen3.5-0.8B.Q4_K_M.gguf"}]}`, 200, "Qwen3.5-0.8B.Q4_K_M"},
+		{"bare name", `{"data":[{"id":"LFM2.5-1.2B"}]}`, 200, "LFM2.5-1.2B"},
+		{"empty list", `{"data":[]}`, 200, ""},
+		{"id missing", `{"data":[{}]}`, 200, ""},
+		{"id blank", `{"data":[{"id":"  "}]}`, 200, ""},
+		{"server error", `nope`, 500, ""},
+		{"not json", `<html>`, 200, ""},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				if r.URL.Path != "/v1/models" {
+					t.Errorf("asked for %s, want /v1/models", r.URL.Path)
+				}
+				w.WriteHeader(c.code)
+				_, _ = w.Write([]byte(c.body))
+			}))
+			defer srv.Close()
+
+			got, err := ModelID(context.Background(), srv.URL+"/")
+			if c.want == "" {
+				if err == nil {
+					t.Fatalf("want an error, got label %q", got)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("ModelID: %v", err)
+			}
+			if got != c.want {
+				t.Errorf("got %q, want %q", got, c.want)
+			}
+		})
+	}
+}
+
+func TestModelIDUnreachable(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(http.ResponseWriter, *http.Request) {}))
+	url := srv.URL
+	srv.Close() // nothing listening now
+
+	if got, err := ModelID(context.Background(), url); err == nil {
+		t.Fatalf("want an error from a dead server, got label %q", got)
+	}
+}