test(core): cover the unschedulable bookkeeping directly

Removing a job clears its recorded refusal, so a job deleted from the
config stops holding /health degraded. That path had no test. Also
covers that the returned map is a copy, which the health checker reads
on every check.

Signed-off-by: Sebastian Mendel <github@sebastianmendel.de>

Author: CybotTM

core/scheduler_unschedulable_test.go

@@ -0,0 +1,68 @@
+// Copyright (c) 2025-2026 Netresearch DTT GmbH
+// SPDX-License-Identifier: MIT
+
+package core
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// A refused job is remembered so /health can name it. That memory has to end
+// when the job does, or an operator who fixed the problem by deleting the job
+// would be left with a permanently degraded daemon and no job to blame it on.
+
+func TestSchedulerRecordsRefusedJob(t *testing.T) {
+	t.Parallel()
+
+	job := &TestJob{}
+	job.Name = "broken"
+	job.Schedule = "not-a-schedule"
+
+	sc := NewScheduler(newDiscardLogger())
+	require.Error(t, sc.AddJob(job))
+
+	refused := sc.GetUnschedulableJobs()
+	require.Contains(t, refused, "broken")
+	assert.NotEmpty(t, refused["broken"], "the recorded reason is what makes the report actionable")
+}
+
+// TestSchedulerRemoveJobClearsUnschedulable covers the removal half: dropping
+// the job from the config has to drop the complaint with it.
+func TestSchedulerRemoveJobClearsUnschedulable(t *testing.T) {
+	t.Parallel()
+
+	job := &TestJob{}
+	job.Name = "broken"
+	job.Schedule = "not-a-schedule"
+
+	sc := NewScheduler(newDiscardLogger())
+	require.Error(t, sc.AddJob(job))
+	require.Contains(t, sc.GetUnschedulableJobs(), "broken")
+
+	require.NoError(t, sc.RemoveJob(job))
+
+	assert.NotContains(t, sc.GetUnschedulableJobs(), "broken",
+		"a job removed from the config still held /health degraded")
+}
+
+// TestSchedulerGetUnschedulableJobsIsACopy pins that callers cannot reach into
+// the scheduler's state through the returned map: the health checker reads it
+// on every check, and a shared map would be a data race as well as a way to
+// silently erase a refusal.
+func TestSchedulerGetUnschedulableJobsIsACopy(t *testing.T) {
+	t.Parallel()
+
+	job := &TestJob{}
+	job.Name = "broken"
+	job.Schedule = "not-a-schedule"
+
+	sc := NewScheduler(newDiscardLogger())
+	require.Error(t, sc.AddJob(job))
+
+	delete(sc.GetUnschedulableJobs(), "broken")
+
+	assert.Contains(t, sc.GetUnschedulableJobs(), "broken")
+}