fix(linkcheck): keep the write when the link index cannot be built (#178)

StripUnresolvedLinks runs before every brain_write and brain_update. Any
walk error below a linked tree's root (e.g. one unreadable subdirectory)
made it return an error, and the write was refused: the learning was
lost. Already true on main.

It now logs a warning and returns the content unchanged: a partial index
cannot tell an invented link from one into the unreadable part, so it
unwraps nothing (never inventing a resolution) and the note is written
with its links as given.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ingestion/internal/api/write_keeps_learning_test.go

@@ -0,0 +1,34 @@
+package api_test
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/mathiasbq/hyperguild/ingestion/internal/api"
+)
+
+// hyperguild#178: an unreadable directory under wiki/ made the link check
+// fail and brain_write refuse the note, losing the learning. The note is now
+// written with its links as given.
+func TestWriteNoteKeepsTheLearningWhenTheLinkCheckCannotIndex(t *testing.T) {
+	if os.Geteuid() == 0 {
+		t.Skip("root ignores directory permissions")
+	}
+	brain := t.TempDir()
+	require.NoError(t, os.MkdirAll(filepath.Join(brain, "wiki", "w", "facts"), 0o755))
+	require.NoError(t, os.WriteFile(filepath.Join(brain, "wiki", "w", "facts", "real.md"), []byte("x"), 0o644))
+	locked := filepath.Join(brain, "wiki", "other", "locked")
+	require.NoError(t, os.MkdirAll(locked, 0o755))
+	require.NoError(t, os.Chmod(locked, 0o000))
+	t.Cleanup(func() { _ = os.Chmod(locked, 0o755) })
+
+	rel, err := api.WriteNote(brain, api.WriteNoteOptions{Wing: "w", Hall: "facts", Filename: "n", Content: "learning [[real]] and [[gone]]"})
+	require.NoError(t, err)
+	got, err := os.ReadFile(filepath.Join(brain, filepath.FromSlash(rel)))
+	require.NoError(t, err)
+	assert.Contains(t, string(got), "[[gone]]", "links kept as given when the index is partial")
+}

ingestion/internal/brain/linkcheck.go

@@ -47,7 +47,12 @@ var (
 func StripUnresolvedLinks(brainDir, content string) (string, []string, error) {
 	index, err := entryIndex(brainDir)
 	if err != nil {
-		return "", nil, err
+		// A partial index cannot tell an invented link from one into the
+		// part it could not read, so unwrap nothing, and do not refuse the
+		// write either: this runs before every brain_write, and a refused
+		// write is a lost learning (hyperguild#178).
+		slog.Warn("link check skipped: cannot index the brain", "err", err)
+		return content, nil, nil
 	}
 	if len(index) == 0 {
 		return content, nil, nil

ingestion/internal/brain/linkcheck_fallback_test.go

@@ -0,0 +1,41 @@
+package brain_test
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/mathiasbq/hyperguild/ingestion/internal/brain"
+)
+
+// hyperguild#178: StripUnresolvedLinks runs before every brain_write and
+// brain_update. An unreadable directory under knowledge/ or wiki/ made it
+// error, the write was refused and the learning lost. When the link index
+// cannot be built, the content is now returned unchanged (no link is
+// unwrapped, none is invented) and no error stops the write.
+func TestStripUnresolvedLinksKeepsContentWhenTheIndexCannotBeBuilt(t *testing.T) {
+	if os.Geteuid() == 0 {
+		t.Skip("root ignores directory permissions")
+	}
+	b := t.TempDir()
+	require.NoError(t, os.MkdirAll(filepath.Join(b, "wiki", "w", "facts"), 0o755))
+	require.NoError(t, os.WriteFile(filepath.Join(b, "wiki", "w", "facts", "real.md"), []byte("x"), 0o644))
+	locked := filepath.Join(b, "wiki", "other", "locked")
+	require.NoError(t, os.MkdirAll(locked, 0o755))
+	require.NoError(t, os.Chmod(locked, 0o000))
+	t.Cleanup(func() { _ = os.Chmod(locked, 0o755) })
+
+	in := "learning [[real]] and [[gone]]"
+	out, unlinked, err := brain.StripUnresolvedLinks(b, in)
+	require.NoError(t, err)
+	assert.Equal(t, in, out, "content unchanged: no link unwrapped on a partial index")
+	assert.Empty(t, unlinked)
+
+	require.NoError(t, os.Chmod(locked, 0o755))
+	out, _, err = brain.StripUnresolvedLinks(b, in)
+	require.NoError(t, err)
+	assert.NotContains(t, out, "[[gone]]", "positive control: with a readable tree the strip runs")
+}