fix(pipeline,api,wing): never archive a note as processed when nothing was ingested; titles do not merge sources; ties prefer the page on disk (review of #211, pass 3)

- in a wing, an ingest that writes no source page is an error: the note goes to
  raw/failed with the warnings in log.md instead of leaving the inbox as
  'processed' (model returned [], only invalid types, only clashing entities)
- the wing's source path is deterministic, so Resolve no longer redirects a
  source onto another note's page because the model gave both the same title
  ('Home'); that overwrote the hash and the text
- a batch tie between concept and entity prefers the page already on disk, so
  its update is not lost; the wing's own source page keeps its slug even when a
  foreign page shares it
- brain_pending lists an unreadable (over-cap) note with the reason instead of
  dropping it; the client filter's 4 KiB match-span limit is documented
Each has a test that fails without it (mutation-checked).

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

ingestion/internal/pipeline/pipeline.go

@@ -113,7 +113,19 @@ func Run(ctx context.Context, cfg Config, brainDir, content, source string, dryR
 	meta.BodyHash = bodyHash
 	applySourceMeta(allRaw, meta)
 
-	return buildAndWrite(ctx, cfg.Wing, allRaw, sourceSlug, date, brainDir, source, inventory, allWarnings, dryRun)
+	res, err := buildAndWrite(ctx, cfg.Wing, allRaw, sourceSlug, date, brainDir, source, inventory, allWarnings, dryRun)
+	if err != nil || cfg.Wing == "" {
+		return res, err
+	}
+	// In a wing every ingest must leave its source page: it is what ties the
+	// note to the wiki (and carries the hash the drift check reads). Without one
+	// nothing of the note exists, and the caller would archive it as processed.
+	for _, p := range res.Pages {
+		if isSourcePath(p) {
+			return res, nil
+		}
+	}
+	return res, fmt.Errorf("no source page was written for %q; nothing of the note was ingested (%s)", source, strings.Join(res.Warnings, "; "))
 }
 
 // RunRaw runs the pipeline on pre-parsed RawPages, skipping the LLM extraction
@@ -357,13 +369,19 @@ func resolveSourceSlug(brainDir, wing, base string) (string, error) {
 			return "", fmt.Errorf("check source slug: %w", err)
 		}
 		own := "wiki/" + wing + "/sources/" + cand + ".md"
-		free := true
+		free, hasOwn := true, false
 		for _, p := range existing {
-			if p != own {
+			if p == own {
+				hasOwn = true
+			} else {
 				free = false
-				break
 			}
 		}
+		// The wing's own page is its identity: keep using it even if some other
+		// page shares the slug (that other page is the one dropSlugClashes skips).
+		if hasOwn {
+			return cand, nil
+		}
 		if free {
 			return cand, nil
 		}
@@ -399,12 +417,42 @@ func dropSlugClashes(brainDir string, pages []wiki.Page) ([]wiki.Page, []string,
 	}
 	slugOf := func(p wiki.Page) string { return strings.TrimSuffix(filepath.Base(p.Path), ".md") }
 
-	winner := map[string]wiki.Page{}
+	// Group by slug; where several pages with different paths want one slug,
+	// the source wins, then a page that already exists on disk (so its update
+	// is not lost), then entity over concept.
+	bySlug := map[string][]wiki.Page{}
 	for _, p := range pages {
-		w, seen := winner[slugOf(p)]
-		if !seen || (w.Path != p.Path && rank(p) < rank(w)) {
-			winner[slugOf(p)] = p
+		bySlug[slugOf(p)] = append(bySlug[slugOf(p)], p)
+	}
+	winner := map[string]wiki.Page{}
+	for slug, group := range bySlug {
+		best := group[0]
+		if distinctPaths(group) > 1 {
+			existing, err := wiki.FindSlugs(brainDir, slug)
+			if err != nil {
+				return nil, nil, fmt.Errorf("check slug %q: %w", slug, err)
+			}
+			onDisk := func(p wiki.Page) int {
+				for _, e := range existing {
+					if e == p.Path {
+						return 0
+					}
+				}
+				return 1
+			}
+			for _, p := range group[1:] {
+				if rank(p) != rank(best) && (rank(p) == 0 || rank(best) == 0) {
+					if rank(p) < rank(best) {
+						best = p
+					}
+					continue
+				}
+				if onDisk(p) < onDisk(best) || (onDisk(p) == onDisk(best) && rank(p) < rank(best)) {
+					best = p
+				}
+			}
 		}
+		winner[slug] = best
 	}
 
 	var kept []wiki.Page
@@ -438,3 +486,11 @@ func dropSlugClashes(brainDir string, pages []wiki.Page) ([]wiki.Page, []string,
 	}
 	return kept, warnings, nil
 }
+
+func distinctPaths(pages []wiki.Page) int {
+	seen := map[string]bool{}
+	for _, p := range pages {
+		seen[p.Path] = true
+	}
+	return len(seen)
+}