fix: floor token budgets and surface truncation, add live progress

Reasoning models burn thousands of completion tokens before the
answer. Small per-test caps caused silent truncation and zero scores.
The runner now floors max_tokens at the config default (12000). The
client parses finish_reason. Reports mark truncated cells and the
JSON format carries response text for debugging. A stderr progress
reporter prints one line per completed request; --quiet disables it.

cmd/llmtest/progress.go

@@ -0,0 +1,63 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"sync"
+
+	"github.com/lukaszraczylo/llm-testbench/internal/runner"
+)
+
+// stderrProgressReporter implements runner.ProgressReporter, writing one
+// line per event to w (os.Stderr in production). Run's stdout stays
+// pipeable (table/markdown/json only): all progress goes here instead.
+type stderrProgressReporter struct {
+	w  io.Writer
+	mu sync.Mutex
+}
+
+// newStderrProgressReporter builds a stderrProgressReporter writing to w.
+func newStderrProgressReporter(w io.Writer) *stderrProgressReporter {
+	return &stderrProgressReporter{w: w}
+}
+
+// ReportStart implements runner.ProgressReporter.
+func (r *stderrProgressReporter) ReportStart(totalTests, totalModels, concurrency int) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	// A write failure on this side-channel progress stream (a closed pipe,
+	// a full/broken stderr) is not actionable and must not abort the run
+	// that produces the actual report on stdout.
+	_, _ = fmt.Fprintf(r.w, "running %d tests x %d models = %d requests, concurrency %d\n",
+		totalTests, totalModels, totalTests*totalModels, concurrency)
+}
+
+// ReportDone implements runner.ProgressReporter. Safe for concurrent calls
+// from up to Config.Concurrency goroutines at once: the mutex serializes
+// each printed line so concurrent completions cannot interleave mid-line.
+func (r *stderrProgressReporter) ReportDone(done, total int, result runner.Result) {
+	status := resultStatus(result)
+	truncated := ""
+	if result.Truncated() {
+		truncated = " TRUNCATED"
+	}
+
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	// See ReportStart: a write failure here is not actionable.
+	_, _ = fmt.Fprintf(r.w, "[%d/%d] model=%s test=%s score=%s tokens=%d (%s)%s\n",
+		done, total, result.Model, result.TestID, status, result.TotalTokens(), result.Latency, truncated)
+}
+
+// resultStatus renders a Result's score for one progress line: the numeric
+// score, or ERR/skip.
+func resultStatus(result runner.Result) string {
+	switch {
+	case result.Err != nil:
+		return "ERR"
+	case result.Score.Skipped:
+		return "skip"
+	default:
+		return fmt.Sprintf("%.2f", result.Score.Value)
+	}
+}