fix(brain): unwrap wikilinks that name no entry at the write boundary

Every brain write accepted [[targets]] that resolve to nothing — skill
names, repo names, agent-local memory-file slugs — and each one became a
permanent [high] broken-link finding. The brain-audit digest grew 19 -> 63
high findings between 2026-08-26 and 2026-09-16; 53 of the 63 were exactly
this, and none are fixable by brain-gardener's BrokenLinkFixer, which only
repoints edit-distance-1 renames. There is no target to repoint to.

StripUnresolvedLinks resolves each link against knowledge/ + wiki/ using
brain-gardener's own resolver semantics (bare slug or wing/hall/slug path
form, code spans excluded) and unwraps the misses to plain text, reporting
them as Ref.Unlinked / the MCP `unlinked` field.

Unwrap rather than reject: a refused write on claudewatcher's unattended
ingest path is a lost learning, and the author's words are worth keeping
even when the link is not. An empty corpus is a no-op, so a misconfigured
brainDir cannot strip every link in a note.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

ingestion/internal/brainstore/store_test.go

@@ -83,3 +83,45 @@ func TestStoreGetRoundTripsHash(t *testing.T) {
 	assert.Equal(t, "a", note.Frontmatter["wing"])
 	assert.Contains(t, note.Body, "# Body")
 }
+
+func TestStoreWriteUnwrapsUnresolvedWikilinks(t *testing.T) {
+	dir := t.TempDir()
+	s := brainstore.New(dir)
+	_, err := s.Write(context.Background(), capture.Note{
+		Content: "# Target\n\nbody\n", Filename: "target", Wing: "a", Hall: "facts",
+	})
+	require.NoError(t, err)
+
+	ref, err := s.Write(context.Background(), capture.Note{
+		Content:  "See [[target]] and [[secret-hygiene]].\n",
+		Filename: "src", Wing: "a", Hall: "facts",
+	})
+	require.NoError(t, err)
+	assert.Equal(t, []string{"secret-hygiene"}, ref.Unlinked)
+
+	got, err := os.ReadFile(filepath.Join(dir, "wiki/a/facts/src.md"))
+	require.NoError(t, err)
+	assert.Contains(t, string(got), "[[target]]")
+	assert.Contains(t, string(got), "and secret-hygiene.")
+	assert.NotContains(t, string(got), "[[secret-hygiene]]")
+}
+
+func TestStoreUpdateUnwrapsUnresolvedWikilinks(t *testing.T) {
+	dir := t.TempDir()
+	s := brainstore.New(dir)
+	_, err := s.Write(context.Background(), capture.Note{
+		Content: "old\n", Filename: "n", Wing: "a", Hall: "facts",
+	})
+	require.NoError(t, err)
+
+	ref, err := s.Update(context.Background(), "n", capture.Note{
+		Content: "Related: [[cad-babysit]].\n", Wing: "a", Hall: "facts", Reason: "r",
+	})
+	require.NoError(t, err)
+	assert.Equal(t, []string{"cad-babysit"}, ref.Unlinked)
+
+	got, err := os.ReadFile(filepath.Join(dir, "wiki/a/facts/n.md"))
+	require.NoError(t, err)
+	assert.Contains(t, string(got), "Related: cad-babysit.")
+	assert.NotContains(t, string(got), "[[cad-babysit]]")
+}