feat(ingestion): add full-text wiki search package

Implements search.Query which walks brainDir/wiki/**/*.md, scores files
by term-frequency across query tokens, and returns results sorted by
score descending. Uses only stdlib — no external search deps.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ingestion/internal/search/search.go

@@ -0,0 +1,110 @@
+// ingestion/internal/search/search.go
+package search
+
+import (
+	"bufio"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+)
+
+// Result is a single search hit from the brain wiki.
+type Result struct {
+	Path    string `json:"path"`
+	Title   string `json:"title"`
+	Excerpt string `json:"excerpt"`
+	Score   int    `json:"score"`
+}
+
+// Query searches all .md files under brainDir/wiki/ for pages containing
+// any of the whitespace-separated terms in query. Returns up to limit results
+// sorted by score descending.
+func Query(brainDir, query string, limit int) ([]Result, error) {
+	if limit <= 0 {
+		limit = 5
+	}
+	terms := strings.Fields(strings.ToLower(query))
+	if len(terms) == 0 {
+		return nil, nil
+	}
+
+	var results []Result
+
+	err := filepath.WalkDir(filepath.Join(brainDir, "wiki"), func(path string, d os.DirEntry, err error) error {
+		if err != nil || d.IsDir() || !strings.HasSuffix(path, ".md") {
+			return err
+		}
+
+		content, err := os.ReadFile(path)
+		if err != nil {
+			return nil // skip unreadable files
+		}
+
+		lower := strings.ToLower(string(content))
+		score := 0
+		for _, term := range terms {
+			score += strings.Count(lower, term)
+		}
+		if score == 0 {
+			return nil
+		}
+
+		rel, _ := filepath.Rel(brainDir, path)
+		rel = filepath.ToSlash(rel)
+
+		results = append(results, Result{
+			Path:    rel,
+			Title:   extractTitle(string(content), d.Name()),
+			Excerpt: excerpt(string(content), 300),
+			Score:   score,
+		})
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	sort.Slice(results, func(i, j int) bool {
+		return results[i].Score > results[j].Score
+	})
+	if len(results) > limit {
+		results = results[:limit]
+	}
+	return results, nil
+}
+
+func extractTitle(content, filename string) string {
+	scanner := bufio.NewScanner(strings.NewReader(content))
+	inFrontmatter := false
+	for scanner.Scan() {
+		line := scanner.Text()
+		if strings.TrimSpace(line) == "---" {
+			if !inFrontmatter {
+				inFrontmatter = true
+				continue
+			}
+			break
+		}
+		if inFrontmatter {
+			key, val, ok := strings.Cut(line, ":")
+			if ok && strings.TrimSpace(key) == "title" {
+				return strings.Trim(strings.TrimSpace(val), `"'`)
+			}
+		}
+	}
+	return strings.TrimSuffix(filename, ".md")
+}
+
+func excerpt(content string, maxLen int) string {
+	// Skip frontmatter, return first maxLen chars of body.
+	parts := strings.SplitN(content, "---", 3)
+	body := content
+	if len(parts) == 3 {
+		body = strings.TrimSpace(parts[2])
+	}
+	if len(body) > maxLen {
+		return body[:maxLen] + "…"
+	}
+	return body
+}

ingestion/internal/search/search_test.go

@@ -0,0 +1,54 @@
+// ingestion/internal/search/search_test.go
+package search_test
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/mathiasbq/hyperguild/ingestion/internal/search"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestSearch_ReturnsMatchingPages(t *testing.T) {
+	dir := t.TempDir()
+	require.NoError(t, os.MkdirAll(filepath.Join(dir, "wiki", "concepts"), 0o755))
+
+	// Write a concept page mentioning "retry"
+	require.NoError(t, os.WriteFile(
+		filepath.Join(dir, "wiki", "concepts", "retry-logic.md"),
+		[]byte("---\ntitle: Retry Logic\ndomain: software\n---\n\nRetry logic handles transient failures by re-attempting operations.\n"),
+		0o644,
+	))
+	// Write an unrelated page
+	require.NoError(t, os.WriteFile(
+		filepath.Join(dir, "wiki", "concepts", "database.md"),
+		[]byte("---\ntitle: Database\ndomain: software\n---\n\nA database stores structured data.\n"),
+		0o644,
+	))
+
+	results, err := search.Query(dir, "retry transient", 5)
+	require.NoError(t, err)
+	require.Len(t, results, 1)
+	assert.Equal(t, "wiki/concepts/retry-logic.md", results[0].Path)
+	assert.Equal(t, "Retry Logic", results[0].Title)
+	assert.Greater(t, results[0].Score, 0)
+	assert.Contains(t, results[0].Excerpt, "Retry")
+}
+
+func TestSearch_RespectsLimit(t *testing.T) {
+	dir := t.TempDir()
+	require.NoError(t, os.MkdirAll(filepath.Join(dir, "wiki", "concepts"), 0o755))
+	for i := 0; i < 5; i++ {
+		require.NoError(t, os.WriteFile(
+			filepath.Join(dir, "wiki", "concepts", fmt.Sprintf("page-%d.md", i)),
+			[]byte(fmt.Sprintf("---\ntitle: Page %d\n---\n\nThis page mentions retry.\n", i)),
+			0o644,
+		))
+	}
+	results, err := search.Query(dir, "retry", 3)
+	require.NoError(t, err)
+	assert.LessOrEqual(t, len(results), 3)
+}