diff --git a/docs/maxusai/tasks/upstream-sync-2026-09-04.md b/docs/maxusai/tasks/upstream-sync-2026-09-04.md
index 3cb150bafe7..efbe74e8b1b 100644
--- a/docs/maxusai/tasks/upstream-sync-2026-09-04.md
+++ b/docs/maxusai/tasks/upstream-sync-2026-09-04.md
@@ -623,9 +623,16 @@ The two fixes differ:
 | log output | **degraded**: `sync.Mutex` is not reentrant, so the **11 of ~25 log sites that already hold `refMu`** (sched.go 343, 408, 415, 417, 428, 433, 439, 451, 483, 762, 766) *always* fail the TryLock and permanently lose `name`, `inference`, `pid`, `num_ctx` | unchanged at every site |
 | regression test | none — `server/sched_test.go` untouched upstream | `TestRunnerRefLogValueDuringUnload`, reproduces all three reported races on unfixed code |
 
-**Decision (2026-09-10): keep ours at the sync**, because the scheduler debug lines that lose
-their fields under upstream's version are exactly the ones this fork reads when diagnosing runner
-behaviour, and because upstream ships no test. Expect a conflict in `LogValue` and resolve it in
+**Decision (2026-09-10): keep ours at the sync**, because upstream's version silently strips
+those four attrs from the eleven in-lock sites — the lines you get when you raise the level to
+diagnose a runner — and because upstream ships no test. Measured, not assumed:
+`TestRunnerRefLogValueKeepsFieldsUnderRefMu` logs a runner while holding `refMu` exactly as
+`sched.go:433` does and asserts the attrs survive; it passes on ours and fails on all four attrs
+with upstream's `LogValue` pasted in. (A caveat on an earlier phrasing of this note: those are
+`slog.Debug` lines, and only one run this week — the array-trace probe of 2026-09-06,
+`preflight-runs/trace-arrays-runner.log` — was captured at debug level, e.g.
+`sched.go:433 … runner.name=…gemma4:12b-nvfp4 runner.pid=316 runner.num_ctx=65536`. The routine
+campaign logs run at INFO and never carried them.) Expect a conflict in `LogValue` and resolve it in
 our favour; carry our test either way, since it also covers upstream's implementation. Worth
 offering upstream as a follow-up so the divergence can be retired.
 
diff --git a/server/sched_test.go b/server/sched_test.go
index e4230d1378b..007ba365b4b 100644
--- a/server/sched_test.go
+++ b/server/sched_test.go
@@ -2452,3 +2452,42 @@ func TestRunnerRefLogValueDuringUnload(t *testing.T) {
 		t.Fatalf("LogValue after unload = %v, want a group", got.Kind())
 	}
 }
+
+// TestRunnerRefLogValueKeepsFieldsUnderRefMu pins the behaviour that separates
+// our logMu fix from upstream's TryLock one (ollama/ollama#18319): eleven of
+// the scheduler's ~25 runner log sites hold refMu when they log, and slog
+// resolves the value there. sync.Mutex is not reentrant, so a TryLock inside
+// LogValue always fails at those sites and drops name, inference, pid and
+// num_ctx from exactly the lines used to diagnose a runner. Ours keeps them.
+// See tasks/upstream-sync-2026-09-04.md, "One deliberate divergence".
+func TestRunnerRefLogValueKeepsFieldsUnderRefMu(t *testing.T) {
+	opts := api.Options{Runner: api.Runner{NumCtx: 65536}}
+	runner := &runnerRef{
+		model:       &Model{Name: "registry/library/gemma4:12b-nvfp4"},
+		modelPath:   "/models/gemma4",
+		llama:       &mockLlm{vramByGPU: map[ml.DeviceID]uint64{}},
+		Options:     &opts,
+		gpus:        []ml.DeviceID{{ID: "0"}},
+		numParallel: 1,
+		pid:         316,
+	}
+
+	var buf bytes.Buffer
+	logger := slog.New(slog.NewTextHandler(&buf, &slog.HandlerOptions{Level: slog.LevelDebug}))
+
+	// Exactly what sched.go:433 does: log the runner while holding refMu.
+	runner.refMu.Lock()
+	logger.Debug("after processing request finished event", "runner", runner)
+	runner.refMu.Unlock()
+
+	for _, want := range []string{
+		"runner.name=registry/library/gemma4:12b-nvfp4",
+		"runner.pid=316",
+		"runner.num_ctx=65536",
+		"runner.inference=",
+	} {
+		if !bytes.Contains(buf.Bytes(), []byte(want)) {
+			t.Errorf("log line lost %q when logged under refMu:\n%s", want, buf.String())
+		}
+	}
+}