fix(session): AX-6 sweep on parser.go (#398) — bufio/maps/path → core

Removed bufio (replaced with local streaming line reader capped at 8 MiB),
maps (replaced with explicit for range), and path (replaced with
core.CleanPath / core.JoinPath). Preserves transcript line handling.

Co-authored-by: Codex <noreply@openai.com>
Closes tasks.lthn.sh/view.php?id=398

parser.go

@@ -2,12 +2,9 @@
 package session
 
 import (
-	"bufio"   // Note: intrinsic — streaming JSONL scan with an explicit bounded buffer; no core equivalent
-	"io"      // Note: intrinsic — Reader and ReadCloser contracts for transcript streams and hostFS handles; no core equivalent
+	"io"      // Note: intrinsic — Reader, ReadCloser, and EOF contracts for transcript streams and hostFS handles; no core equivalent
 	"io/fs"   // Note: intrinsic — fs.FileInfo metadata returned from hostFS.Stat; no core equivalent
 	"iter"    // Note: intrinsic — public lazy sequence API for sessions and events; no core equivalent
-	"maps"    // Note: intrinsic — maps.Keys exposes JSON fallback key sets for deterministic output; no core equivalent
-	"path"    // Note: intrinsic — slash-separated transcript path joining and base-name extraction; no core equivalent
 	"slices"  // Note: intrinsic — iterator collection, sorted keys, and session ordering; no core equivalent
 	"syscall" // Note: intrinsic — Stat_t.Mode lstat bits used to reject symlinked transcript files; no core equivalent
 	"time"    // Note: intrinsic — RFC3339 transcript timestamps and session age calculations; no core equivalent
@@ -153,7 +150,7 @@ func ListSessions(projectsDir string) ([]Session, error) {
 //	}
 func ListSessionsSeq(projectsDir string) iter.Seq[Session] {
 	return func(yield func(Session) bool) {
-		matches := core.PathGlob(path.Join(projectsDir, "*.jsonl"))
+		matches := core.PathGlob(transcriptPath(projectsDir, "*.jsonl"))
 
 		var sessions []Session
 		for _, filePath := range matches {
@@ -161,7 +158,7 @@ func ListSessionsSeq(projectsDir string) iter.Seq[Session] {
 				continue
 			}
 
-			base := path.Base(filePath)
+			base := core.PathBase(filePath)
 			id := core.TrimSuffix(base, ".jsonl")
 
 			infoResult := hostFS.Stat(filePath)
@@ -188,22 +185,21 @@ func ListSessionsSeq(projectsDir string) iter.Seq[Session] {
 				continue
 			}
 
-			scanner := bufio.NewScanner(f)
-			scanner.Buffer(make([]byte, 1024*1024), 1024*1024)
 			var firstTS, lastTS string
-			for scanner.Scan() {
+			scanTranscriptLines(f, maxScannerBuffer, func(line []byte) bool {
 				var entry rawEntry
-				if !core.JSONUnmarshal(scanner.Bytes(), &entry).OK {
-					continue
+				if !core.JSONUnmarshal(line, &entry).OK {
+					return true
 				}
 				if entry.Timestamp == "" {
-					continue
+					return true
 				}
 				if firstTS == "" {
 					firstTS = entry.Timestamp
 				}
 				lastTS = entry.Timestamp
-			}
+				return true
+			})
 			f.Close()
 
 			if firstTS != "" {
@@ -241,7 +237,7 @@ func ListSessionsSeq(projectsDir string) iter.Seq[Session] {
 // Example:
 // deleted, err := session.PruneSessions("/tmp/projects", 24*time.Hour)
 func PruneSessions(projectsDir string, maxAge time.Duration) (int, error) {
-	matches := core.PathGlob(path.Join(projectsDir, "*.jsonl"))
+	matches := core.PathGlob(transcriptPath(projectsDir, "*.jsonl"))
 
 	var deleted int
 	now := time.Now()
@@ -286,7 +282,7 @@ func FetchSession(projectsDir, id string) (*Session, *ParseStats, error) {
 		return nil, nil, core.E("FetchSession", "invalid session id", nil)
 	}
 
-	filePath := path.Join(projectsDir, id+".jsonl")
+	filePath := transcriptPath(projectsDir, id+".jsonl")
 	if !isSafeProjectFile(filePath) {
 		return nil, nil, core.E("FetchSession", "invalid session path", nil)
 	}
@@ -309,7 +305,7 @@ func ParseTranscript(filePath string) (*Session, *ParseStats, error) {
 	}
 	defer f.Close()
 
-	base := path.Base(filePath)
+	base := core.PathBase(filePath)
 	id := core.TrimSuffix(base, ".jsonl")
 
 	sess, stats, err := parseFromReader(f, id)
@@ -337,8 +333,8 @@ func ParseTranscriptReader(r io.Reader, id string) (*Session, *ParseStats, error
 }
 
 // parseFromReader is the shared implementation for both file-based and
-// reader-based parsing. It scans line-by-line using bufio.Scanner with
-// an 8 MiB buffer, gracefully skipping malformed lines.
+// reader-based parsing. It scans line-by-line with an 8 MiB buffer,
+// gracefully skipping malformed lines.
 func parseFromReader(r io.Reader, id string) (*Session, *ParseStats, error) {
 	sess := &Session{
 		ID: id,
@@ -354,20 +350,17 @@ func parseFromReader(r io.Reader, id string) (*Session, *ParseStats, error) {
 	}
 	pendingTools := make(map[string]toolUse)
 
-	scanner := bufio.NewScanner(r)
-	scanner.Buffer(make([]byte, 64*1024), maxScannerBuffer)
-
 	var lineNum int
 	var lastRaw string
 	var lastLineFailed bool
 
-	for scanner.Scan() {
+	scanErr := scanTranscriptLines(r, maxScannerBuffer, func(line []byte) bool {
 		lineNum++
 		stats.TotalLines++
 
-		raw := scanner.Text()
+		raw := string(line)
 		if core.Trim(raw) == "" {
-			continue
+			return true
 		}
 
 		lastRaw = raw
@@ -383,13 +376,13 @@ func parseFromReader(r io.Reader, id string) (*Session, *ParseStats, error) {
 			stats.Warnings = append(stats.Warnings,
 				core.Sprintf("line %d: skipped (bad JSON): %s", lineNum, preview))
 			lastLineFailed = true
-			continue
+			return true
 		}
 
 		ts, err := time.Parse(time.RFC3339Nano, entry.Timestamp)
 		if err != nil {
 			stats.Warnings = append(stats.Warnings, core.Sprintf("line %d: bad timestamp %q: %v", lineNum, entry.Timestamp, err))
-			continue
+			return true
 		}
 
 		if sess.StartTime.IsZero() && !ts.IsZero() {
@@ -404,7 +397,7 @@ func parseFromReader(r io.Reader, id string) (*Session, *ParseStats, error) {
 			var msg rawMessage
 			if !core.JSONUnmarshal(entry.Message, &msg).OK {
 				stats.Warnings = append(stats.Warnings, core.Sprintf("line %d: failed to unmarshal assistant message", lineNum))
-				continue
+				return true
 			}
 			for i, raw := range msg.Content {
 				var block contentBlock
@@ -445,7 +438,7 @@ func parseFromReader(r io.Reader, id string) (*Session, *ParseStats, error) {
 			var msg rawMessage
 			if !core.JSONUnmarshal(entry.Message, &msg).OK {
 				stats.Warnings = append(stats.Warnings, core.Sprintf("line %d: failed to unmarshal user message", lineNum))
-				continue
+				return true
 			}
 			for i, raw := range msg.Content {
 				var block contentBlock
@@ -487,15 +480,15 @@ func parseFromReader(r io.Reader, id string) (*Session, *ParseStats, error) {
 				}
 			}
 		}
-	}
+		return true
+	})
 
 	// Detect truncated final line.
 	if lastLineFailed && lastRaw != "" {
 		stats.Warnings = append(stats.Warnings, "truncated final line")
 	}
 
-	// Check for scanner buffer errors.
-	if scanErr := scanner.Err(); scanErr != nil {
+	if scanErr != nil {
 		return nil, stats, scanErr
 	}
 
@@ -569,7 +562,11 @@ func extractToolInput(toolName string, raw rawJSON) string {
 	// Fallback: show raw JSON keys
 	var m map[string]any
 	if core.JSONUnmarshal(raw, &m).OK {
-		parts := slices.Sorted(maps.Keys(m))
+		parts := make([]string, 0, len(m))
+		for key := range m {
+			parts = append(parts, key)
+		}
+		slices.Sort(parts)
 		return core.Join(", ", parts...)
 	}
 
@@ -605,6 +602,69 @@ func truncate(s string, max int) string {
 	return s[:max] + "..."
 }
 
+func scanTranscriptLines(r io.Reader, maxLineSize int, handle func([]byte) bool) error {
+	if maxLineSize <= 0 {
+		maxLineSize = maxScannerBuffer
+	}
+
+	readBuffer := make([]byte, 64*1024)
+	line := make([]byte, 0, 64*1024)
+
+	for {
+		n, readErr := r.Read(readBuffer)
+		if n > 0 {
+			chunk := readBuffer[:n]
+			start := 0
+			for i, b := range chunk {
+				if b != '\n' {
+					continue
+				}
+				if len(line)+i-start > maxLineSize {
+					return core.E("scanTranscriptLines", core.Sprintf("line exceeds %d bytes", maxLineSize), nil)
+				}
+				line = append(line, chunk[start:i]...)
+				if !handle(trimLineBreak(line)) {
+					return nil
+				}
+				line = line[:0]
+				start = i + 1
+			}
+			if start < len(chunk) {
+				if len(line)+len(chunk)-start > maxLineSize {
+					return core.E("scanTranscriptLines", core.Sprintf("line exceeds %d bytes", maxLineSize), nil)
+				}
+				line = append(line, chunk[start:]...)
+			}
+		}
+
+		if readErr == io.EOF {
+			if len(line) > 0 {
+				if !handle(trimLineBreak(line)) {
+					return nil
+				}
+			}
+			return nil
+		}
+		if readErr != nil {
+			return readErr
+		}
+	}
+}
+
+func trimLineBreak(line []byte) []byte {
+	if len(line) > 0 && line[len(line)-1] == '\r' {
+		return line[:len(line)-1]
+	}
+	return line
+}
+
+func transcriptPath(projectsDir, name string) string {
+	if projectsDir == "" {
+		return core.CleanPath(name, "/")
+	}
+	return core.CleanPath(core.JoinPath(projectsDir, name), "/")
+}
+
 func isSymlink(filePath string) bool {
 	var st syscall.Stat_t
 	if err := syscall.Lstat(filePath, &st); err != nil {