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 {

ingestion/internal/brain/tunnel_test.go

@@ -102,16 +102,29 @@ func TestDetectTunnels_ExactTitleMatch(t *testing.T) {
 
 func TestDetectTunnels_FuzzyMatch(t *testing.T) {
 	dir := t.TempDir()
-	seedNote(t, dir, "wiki/x/facts/routing.md",
-		"---\ntitle: Routing\n---\nbody.\n")
+	seedNote(t, dir, "wiki/x/facts/routing-table.md",
+		"---\ntitle: 'Routing Table'\n---\nbody.\n")
 
 	// Substring of title appears in content, but not as a whole word.
-	candidates, err := brain.DetectTunnels(dir, "rerouting handles failover")
+	candidates, err := brain.DetectTunnels(dir, "the routing tables were rebuilt")
 	require.NoError(t, err)
 	require.Len(t, candidates, 1)
 	assert.False(t, candidates[0].Exact, "substring-only match should be fuzzy")
 }
 
+// A one-word title whose only appearance is lowercase inside another word is
+// not even a candidate: it would fill the review file with English rather than
+// with references.
+func TestDetectTunnels_SingleWordSubstringIsNotACandidate(t *testing.T) {
+	dir := t.TempDir()
+	seedNote(t, dir, "wiki/x/facts/routing.md",
+		"---\ntitle: Routing\n---\nbody.\n")
+
+	candidates, err := brain.DetectTunnels(dir, "rerouting handles failover")
+	require.NoError(t, err)
+	assert.Empty(t, candidates)
+}
+
 func TestDetectTunnels_NoFrontmatterFallsBackToSlug(t *testing.T) {
 	dir := t.TempDir()
 	seedNote(t, dir, "wiki/x/facts/widget-flags.md", "# widget flags\n\nbody.\n")
@@ -126,20 +139,21 @@ func TestDetectTunnels_NoFrontmatterFallsBackToSlug(t *testing.T) {
 
 func TestAutoTunnel_FuzzyGoesToCandidatesFile(t *testing.T) {
 	dir := t.TempDir()
-	// Existing note in a different wing whose title is "Routing".
-	seedNote(t, dir, "wiki/other/facts/routing.md",
-		"---\nwing: other\nhall: facts\ntitle: Routing\n---\nbody.\n")
-	// Source note in another wing whose body mentions "rerouting" (substring match only).
+	// Existing note in a different wing whose title is "Routing Table".
+	seedNote(t, dir, "wiki/other/facts/routing-table.md",
+		"---\nwing: other\nhall: facts\ntitle: 'Routing Table'\n---\nbody.\n")
+	// Source note in another wing whose body mentions "routing tables"
+	// (substring match only — the title is not there as a whole word).
 	seedNote(t, dir, "wiki/jepa-fx/facts/new.md",
-		"---\nwing: jepa-fx\nhall: facts\n---\nrerouting traffic\n")
+		"---\nwing: jepa-fx\nhall: facts\n---\nrouting tables rebuilt\n")
 
 	require.NoError(t, brain.AutoTunnel(dir,
-		"wiki/jepa-fx/facts/new.md", "rerouting traffic"))
+		"wiki/jepa-fx/facts/new.md", "routing tables rebuilt"))
 
 	// Source must not get auto-linked (fuzzy).
 	got, err := os.ReadFile(filepath.Join(dir, "wiki/jepa-fx/facts/new.md"))
 	require.NoError(t, err)
-	assert.NotContains(t, string(got), "[[other/facts/routing]]")
+	assert.NotContains(t, string(got), "[[other/facts/routing-table]]")
 
 	// Candidates file must list the pair.
 	matches, err := filepath.Glob(filepath.Join(dir, "raw", "tunnel-candidates-*.md"))
@@ -148,7 +162,7 @@ func TestAutoTunnel_FuzzyGoesToCandidatesFile(t *testing.T) {
 	body, err := os.ReadFile(matches[0])
 	require.NoError(t, err)
 	assert.Contains(t, string(body), "wiki/jepa-fx/facts/new.md")
-	assert.Contains(t, string(body), "wiki/other/facts/routing.md")
+	assert.Contains(t, string(body), "wiki/other/facts/routing-table.md")
 	assert.Contains(t, string(body), "Routing")
 }
 
@@ -175,3 +189,35 @@ func TestWriteTunnel_AppendsToExistingSeeAlso(t *testing.T) {
 	assert.Contains(t, s, "[[a/facts/old]]")
 	assert.Contains(t, s, "[[b/facts/y]]")
 }
+
+// A one-word title matched case-insensitively links every entry that happens
+// to use that word. Live cost before this rule: 185 entries auto-linked to
+// wiki/telos/decisions/wrong.md (title "WRONG") and 136 to .../status.md,
+// making the two most-linked nodes in the graph pure artifacts.
+func TestDetectTunnels_SingleWordTitleNeedsAnExactCaseMatch(t *testing.T) {
+	dir := t.TempDir()
+	seedNote(t, dir, "wiki/telos/decisions/wrong.md",
+		"---\nwing: telos\nhall: decisions\ntitle: WRONG\n---\n# WRONG\n\nRetired beliefs.\n")
+
+	got, err := brain.DetectTunnels(dir, "The obvious fix was to reject the write. Wrong here.")
+	require.NoError(t, err)
+	for _, c := range got {
+		assert.False(t, c.Exact, "a lowercase prose word must not auto-link a one-word title: %+v", c)
+	}
+
+	got, err = brain.DetectTunnels(dir, "The beliefs listed under WRONG were retired.")
+	require.NoError(t, err)
+	require.Len(t, got, 1)
+	assert.True(t, got[0].Exact, "the title's own casing appearing in prose is a real reference")
+}
+
+func TestDetectTunnels_MultiWordTitleStaysCaseInsensitive(t *testing.T) {
+	dir := t.TempDir()
+	seedNote(t, dir, "wiki/homelab/facts/risk-tier.md",
+		"---\nwing: homelab\nhall: facts\ntitle: 'Risk Tier Middleware'\n---\nbody\n")
+
+	got, err := brain.DetectTunnels(dir, "We rebuilt the risk tier middleware last week.")
+	require.NoError(t, err)
+	require.Len(t, got, 1)
+	assert.True(t, got[0].Exact)
+}