chore: update golangci-lint to v2.12.2 with canonical config (#54)

Canonical v2-schema `.golangci.yml`, golangci-lint pins bumped to v2.12.2 in `Dockerfile` and `script/bootstrap`, and the tree brought to `0 issues.` under it.

Three behaviour deltas: `Cache.StoreVariant` takes a context (cancelled requests skip the accounting row, recovered by reconciliation); `MetadataStorage.Store` no longer leaks `.tmp-*.json` on Write/Close/Rename failure (dead-defer bug fix); the `signing_key` too-short error text gained a `value too short:` prefix.

Eviction-loop context cancellation deferred to #102.

internal/config/cache_max_bytes_internal_test.go

@@ -0,0 +1,305 @@
+package config
+
+import (
+	"errors"
+	"log/slog"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+// Static errors returned by the stub free-space probes below.
+var (
+	errTestStatfsFailed     = errors.New("statfs failed")
+	errTestProbeNotExpected = errors.New("probe must not be called")
+)
+
+// discardLogger returns a logger that swallows all output, for tests
+// that exercise code paths which log.
+func discardLogger() *slog.Logger {
+	return slog.New(slog.DiscardHandler)
+}
+
+// TestCacheMaxBytesExplicitValueUsedWithoutFloor verifies that an
+// explicitly configured cache_max_bytes value is used exactly as
+// given: the 500 MiB floor applies only to the computed default, never
+// to explicit values.
+func TestCacheMaxBytesExplicitValueUsedWithoutFloor(t *testing.T) {
+	t.Parallel()
+
+	yamlContent := "signing_key: " + validTestSigningKey + "\ncache_max_bytes: 1024\n"
+
+	c, err := configFromYAML(t, yamlContent)
+	if err != nil {
+		t.Fatalf("explicit cache_max_bytes must be accepted, got error: %v", err)
+	}
+
+	if c.CacheMaxBytes != 1024 {
+		t.Errorf("CacheMaxBytes = %d, want 1024 (no floor for explicit values)",
+			c.CacheMaxBytes)
+	}
+}
+
+// TestCacheMaxBytesZeroIsValidAndDisablesCache verifies that an
+// explicit zero is a valid value (it disables the disk cache), not an
+// error.
+func TestCacheMaxBytesZeroIsValidAndDisablesCache(t *testing.T) {
+	t.Parallel()
+
+	yamlContent := "signing_key: " + validTestSigningKey + "\ncache_max_bytes: 0\n"
+
+	c, err := configFromYAML(t, yamlContent)
+	if err != nil {
+		t.Fatalf("cache_max_bytes: 0 must be accepted, got error: %v", err)
+	}
+
+	if c.CacheMaxBytes != 0 {
+		t.Errorf("CacheMaxBytes = %d, want 0", c.CacheMaxBytes)
+	}
+}
+
+// TestCacheMaxBytesLargeExplicitValueParses verifies that values above
+// 32-bit range parse correctly (the field is an int64 byte count).
+func TestCacheMaxBytesLargeExplicitValueParses(t *testing.T) {
+	t.Parallel()
+
+	yamlContent := "signing_key: " + validTestSigningKey +
+		"\ncache_max_bytes: 10737418240\n"
+
+	c, err := configFromYAML(t, yamlContent)
+	if err != nil {
+		t.Fatalf("large cache_max_bytes must be accepted, got error: %v", err)
+	}
+
+	if c.CacheMaxBytes != 10737418240 {
+		t.Errorf("CacheMaxBytes = %d, want 10737418240", c.CacheMaxBytes)
+	}
+}
+
+// TestCacheMaxBytesInvalidValuesAbortStartup verifies that a SET but
+// invalid cache_max_bytes value aborts startup naming the key and the
+// offending value, per the no-silent-fallback rule: defaults apply
+// only to omitted keys.
+func TestCacheMaxBytesInvalidValuesAbortStartup(t *testing.T) {
+	t.Parallel()
+
+	signingKeyLine := "signing_key: " + validTestSigningKey + "\n"
+
+	cases := []struct {
+		name string
+		yaml string
+		// wantErrSubstrings must all appear in the error message.
+		wantErrSubstrings []string
+	}{
+		{
+			name:              "negative",
+			yaml:              signingKeyLine + "cache_max_bytes: -1024\n",
+			wantErrSubstrings: []string{keyCacheMaxBytes, "-1024"},
+		},
+		{
+			name:              "float",
+			yaml:              signingKeyLine + "cache_max_bytes: 3.5\n",
+			wantErrSubstrings: []string{keyCacheMaxBytes, "3.5"},
+		},
+		{
+			name:              "non-numeric string",
+			yaml:              signingKeyLine + "cache_max_bytes: banana\n",
+			wantErrSubstrings: []string{keyCacheMaxBytes, "banana"},
+		},
+		{
+			name:              "explicit null",
+			yaml:              signingKeyLine + "cache_max_bytes: null\n",
+			wantErrSubstrings: []string{keyCacheMaxBytes, "null"},
+		},
+		{
+			name:              "bare key no value",
+			yaml:              signingKeyLine + "cache_max_bytes:\n",
+			wantErrSubstrings: []string{keyCacheMaxBytes, "null"},
+		},
+		{
+			name:              "boolean",
+			yaml:              signingKeyLine + "cache_max_bytes: true\n",
+			wantErrSubstrings: []string{keyCacheMaxBytes, "true"},
+		},
+		{
+			name:              "list",
+			yaml:              signingKeyLine + "cache_max_bytes:\n  - 1\n",
+			wantErrSubstrings: []string{keyCacheMaxBytes},
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			c, err := configFromYAML(t, tc.yaml)
+			if err == nil {
+				t.Fatalf(
+					"config with %s cache_max_bytes must abort startup, got config: %+v",
+					tc.name, c)
+			}
+
+			t.Logf("got expected error: %v", err)
+
+			for _, want := range tc.wantErrSubstrings {
+				if !strings.Contains(err.Error(), want) {
+					t.Errorf("error %q does not mention %q", err.Error(), want)
+				}
+			}
+		})
+	}
+}
+
+// TestComputeDefaultCacheMaxBytesUses75PercentOfFreeSpace verifies the
+// computed default is 75% of the probed free space when that exceeds
+// the floor.
+func TestComputeDefaultCacheMaxBytesUses75PercentOfFreeSpace(t *testing.T) {
+	t.Parallel()
+
+	// 4 GiB free -> 3 GiB default.
+	probe := func(string) (uint64, error) { return 4294967296, nil }
+
+	got, err := ComputeDefaultCacheMaxBytes(t.TempDir(), probe)
+	if err != nil {
+		t.Fatalf("ComputeDefaultCacheMaxBytes returned error: %v", err)
+	}
+
+	if got != 3221225472 {
+		t.Errorf("ComputeDefaultCacheMaxBytes = %d, want 3221225472 (75%% of 4 GiB)",
+			got)
+	}
+}
+
+// TestComputeDefaultCacheMaxBytesAppliesFloorToComputedDefault
+// verifies that when 75% of free space is below 500 MiB, the computed
+// default is floored at DefaultCacheMaxBytesFloor.
+func TestComputeDefaultCacheMaxBytesAppliesFloorToComputedDefault(t *testing.T) {
+	t.Parallel()
+
+	cases := []struct {
+		name      string
+		freeBytes uint64
+	}{
+		{name: "100 MiB free", freeBytes: 104857600},
+		{name: "zero free", freeBytes: 0},
+		{name: "just below floor threshold", freeBytes: 699050665},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			probe := func(string) (uint64, error) { return tc.freeBytes, nil }
+
+			got, err := ComputeDefaultCacheMaxBytes(t.TempDir(), probe)
+			if err != nil {
+				t.Fatalf("ComputeDefaultCacheMaxBytes returned error: %v", err)
+			}
+
+			if got != DefaultCacheMaxBytesFloor {
+				t.Errorf("ComputeDefaultCacheMaxBytes = %d, want floor %d",
+					got, DefaultCacheMaxBytesFloor)
+			}
+		})
+	}
+}
+
+// TestComputeDefaultCacheMaxBytesPropagatesProbeError verifies that a
+// failing free-space probe produces an error naming the config key,
+// instead of a silently wrong default.
+func TestComputeDefaultCacheMaxBytesPropagatesProbeError(t *testing.T) {
+	t.Parallel()
+
+	probe := func(string) (uint64, error) { return 0, errTestStatfsFailed }
+
+	_, err := ComputeDefaultCacheMaxBytes(t.TempDir(), probe)
+	if err == nil {
+		t.Fatal("probe failure must produce an error, got nil")
+	}
+
+	t.Logf("got expected error: %v", err)
+
+	if !strings.Contains(err.Error(), keyCacheMaxBytes) {
+		t.Errorf("error %q does not name the config key cache_max_bytes", err.Error())
+	}
+}
+
+// TestResolveCacheMaxBytesComputesDefaultWhenOmitted verifies that an
+// omitted cache_max_bytes key resolves to the computed default, that
+// the probe is pointed at <state_dir>/cache/ (which must be created
+// first so statfs measures the right filesystem), and that the result
+// lands on the Config.
+func TestResolveCacheMaxBytesComputesDefaultWhenOmitted(t *testing.T) {
+	t.Parallel()
+
+	c, err := configFromYAML(t, "signing_key: "+validTestSigningKey+"\n")
+	if err != nil {
+		t.Fatalf("minimal config should be valid, got error: %v", err)
+	}
+
+	c.StateDir = t.TempDir()
+	wantCacheDir := filepath.Join(c.StateDir, "cache")
+
+	var probedPath string
+
+	// 4 GiB free -> 3 GiB default.
+	probe := func(path string) (uint64, error) {
+		probedPath = path
+
+		return 4294967296, nil
+	}
+
+	err = c.resolveCacheMaxBytes(discardLogger(), probe)
+	if err != nil {
+		t.Fatalf("resolveCacheMaxBytes returned error: %v", err)
+	}
+
+	if c.CacheMaxBytes != 3221225472 {
+		t.Errorf("CacheMaxBytes = %d, want computed default 3221225472",
+			c.CacheMaxBytes)
+	}
+
+	if probedPath != wantCacheDir {
+		t.Errorf("free space probed at %q, want cache directory %q",
+			probedPath, wantCacheDir)
+	}
+
+	info, err := os.Stat(wantCacheDir)
+	if err != nil || !info.IsDir() {
+		t.Errorf("cache directory %q was not created before probing: info=%v err=%v",
+			wantCacheDir, info, err)
+	}
+}
+
+// TestResolveCacheMaxBytesDoesNotOverrideExplicitValue verifies that
+// an explicitly configured value survives resolution untouched and
+// that the free-space probe is never consulted for it.
+func TestResolveCacheMaxBytesDoesNotOverrideExplicitValue(t *testing.T) {
+	t.Parallel()
+
+	yamlContent := "signing_key: " + validTestSigningKey + "\ncache_max_bytes: 1024\n"
+
+	c, err := configFromYAML(t, yamlContent)
+	if err != nil {
+		t.Fatalf("explicit cache_max_bytes must be accepted, got error: %v", err)
+	}
+
+	c.StateDir = t.TempDir()
+
+	probe := func(string) (uint64, error) {
+		t.Error("free-space probe must not be consulted for explicit values")
+
+		return 0, errTestProbeNotExpected
+	}
+
+	err = c.resolveCacheMaxBytes(discardLogger(), probe)
+	if err != nil {
+		t.Fatalf("resolveCacheMaxBytes returned error: %v", err)
+	}
+
+	if c.CacheMaxBytes != 1024 {
+		t.Errorf("CacheMaxBytes = %d, want explicit 1024 (no floor, no recompute)",
+			c.CacheMaxBytes)
+	}
+}