fix(brain): a one-word tunnel title must match the prose case-exactly

AutoTunnel matched note titles case-insensitively, so a one-word title linked
every entry that happened to use that word. Measured on the live corpus: 185
entries carry an auto-written See-also link to wiki/telos/decisions/wrong.md
(title "WRONG") and 136 to .../status.md — the two most-linked nodes in the
whole graph, and both of them artifacts of the English language rather than
references. telos's projects/problems/strategies/goals/beliefs entries account
for another ~60 between them.

That pollution is not cosmetic: inbound-link count is what the duplicate
Fixer picks survivors by, what orphan detection reads, and what brain_graph
shows.

One-word titles now need the title's own casing in the prose ("WRONG", "BERT",
"NLP" — an entity name in a sentence still links). Multi-word titles keep the
case-insensitive match: "risk tier middleware" is a real mention however it is
capitalised, and a three-word collision is not an accident.

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

ingestion/internal/brain/tunnel.go

@@ -54,11 +54,24 @@ func DetectTunnels(brainDir, content string) ([]TunnelCandidate, error) {
 			return nil
 		}
 		title, _ := readTitleAndCreated(path, strings.TrimSuffix(d.Name(), ".md"))
-		needle := strings.ToLower(strings.TrimSpace(title))
-		if needle == "" {
+		title = strings.TrimSpace(title)
+		if title == "" {
 			return nil
 		}
-		idx := strings.Index(lowerContent, needle)
+
+		// A one-word title has to match the prose case-exactly. Matched
+		// case-insensitively, it links every entry that happens to use the
+		// word: "WRONG" (wiki/telos/decisions/wrong.md) collected 185 inbound
+		// See-also links and "Status" 136, making the two most-linked nodes in
+		// the graph artifacts of the English language rather than references.
+		// Multi-word titles keep the case-insensitive match — "risk tier
+		// middleware" in prose is a real mention however it is capitalised,
+		// and a three-word collision is not an accident.
+		haystack, needle := lowerContent, strings.ToLower(title)
+		if isSingleWord(title) {
+			haystack, needle = content, title
+		}
+		idx := strings.Index(haystack, needle)
 		if idx == -1 {
 			return nil
 		}
@@ -69,7 +82,7 @@ func DetectTunnels(brainDir, content string) ([]TunnelCandidate, error) {
 		out = append(out, TunnelCandidate{
 			TargetPath:  filepath.ToSlash(rel),
 			MatchedTerm: title,
-			Exact:       isWholeWord(lowerContent, idx, len(needle)),
+			Exact:       isWholeWord(haystack, idx, len(needle)),
 		})
 		return nil
 	})
@@ -79,6 +92,11 @@ func DetectTunnels(brainDir, content string) ([]TunnelCandidate, error) {
 	return out, nil
 }
 
+// isSingleWord reports whether title is one whitespace-free token.
+func isSingleWord(title string) bool {
+	return !strings.ContainsAny(title, " \t")
+}
+
 // isWholeWord reports whether the substring at [idx, idx+n) in s is
 // bounded by non-alphanumeric characters (or string edges).
 func isWholeWord(s string, idx, n int) bool {