merge: land #195 (watcher/pipeline writes through the brain root, #158 part B) on top of inbox zero and the wing resolver

Reconciled with v0.25.0 semantics:
- markers are only the fallback when the original cannot be removed, and are
  now written through the brain root; the refused set (size+mtime keyed) replaces
  the path-only 'stuck' set
- #195's tests updated for inbox zero (archive written, original retired, no
  marker), and the planted-marker-link test keeps its point: nothing is ever
  written through the link, and the note is processed once
- the 'cannot retire' test now counts archive copies; it counted LLM calls,
  which pipeline.Run's source-hash check hides (mutation: removing the
  remember step left it green)

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

ingestion/internal/pipeline/pipeline.go

@@ -10,8 +10,6 @@ import (
 	"github.com/mathiasbq/hyperguild/ingestion/internal/brain"
 	"github.com/mathiasbq/hyperguild/ingestion/internal/brainfs"
 	"io/fs"
-	"os"
-	"path/filepath"
 	"strings"
 	"time"
 
@@ -143,10 +141,6 @@ func buildAndWrite(ctx context.Context, wing string, rawPages []RawPage, sourceS
 	var written []string
 	for _, page := range merged {
 		if !dryRun {
-			dest := filepath.Join(brainDir, filepath.FromSlash(page.Path))
-			if err := os.MkdirAll(filepath.Dir(dest), 0o755); err != nil {
-				return Result{}, fmt.Errorf("mkdir for %s: %w", page.Path, err)
-			}
 			content, conflicts, err := reviseOrCreate(brainDir, page)
 			if err != nil {
 				return Result{}, err
@@ -165,7 +159,9 @@ func buildAndWrite(ctx context.Context, wing string, rawPages []RawPage, sourceS
 			if err != nil {
 				return Result{}, fmt.Errorf("stamp %s: %w", page.Path, err)
 			}
-			if err := os.WriteFile(dest, []byte(stamped), 0o644); err != nil {
+			// Written through the brain root, never through a symlinked
+			// directory or page (hyperguild#158).
+			if err := writeBrainFile(brainDir, page.Path, []byte(stamped)); err != nil {
 				return Result{}, fmt.Errorf("write %s: %w", page.Path, err)
 			}
 		}
@@ -224,6 +220,17 @@ func readSourcePage(brainDir, wing, sourceSlug string) string {
 	return string(raw)
 }
 
+// writeBrainFile creates or replaces one brain-relative file through the
+// brain root (hyperguild#158).
+func writeBrainFile(brainDir, rel string, data []byte) error {
+	bfs, err := brainfs.Open(brainDir)
+	if err != nil {
+		return err
+	}
+	defer func() { _ = bfs.Close() }()
+	return bfs.PutRegular(rel, data)
+}
+
 // readBrainFile reads one brain-relative file through the brain root,
 // regular files only (hyperguild#157).
 func readBrainFile(brainDir, rel string) ([]byte, error) {