feat: DTail fork — server/client feature development

Squashed development of the snonux/dtail fork's product code (internal/, cmd/)
since diverging from mimecast/dtail. Major areas:

- Read/output path: the former "turbo" channel-less path is now the single,
  default server-side read/output path for cat/grep/tail and MapReduce; the old
  channel-based path and its config/env toggles were removed.
- MapReduce: single aggregate implementation (server + serverless) fed directly
  by a processor pipeline, with input-exhausted finalization via the shutdown
  coordinator; high-concurrency and data-race fixes.
- Journal source reads (journal:unit.service) via journalctl, Linux-gated behind
  a journal-v1 capability.
- Auth-key fast reconnect: in-memory per-user public-key cache with TTL/max-keys,
  registered over an authenticated session (AUTHKEY), checked before
  authorized_keys.
- Interactive query reload (--interactive-query) with SESSION START/UPDATE
  generation boundaries and capability negotiation.
- Client-side deadlines: --timeout / --shutdownAfter as context deadlines;
  follow shutdown handling.
- Client logging: diagnostics-only daily log by default, opt-in payload tee via
  --log-payload.
- Numerous correctness fixes (buffer-pool double-recycle races, EOF-sentinel
  leaks, glob-expansion cap, TOCTOU in CSV parsing) with accompanying unit tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

2 files changed, 25 insertions, 15 deletions

diff --git a/internal/io/line/line.go b/internal/io/line/line.go
index 97e7795..69cc667 100644
--- a/internal/io/line/line.go
+++ b/internal/io/line/line.go
@@ -30,6 +30,8 @@ type Line struct {
 	// directories in case multiple log files with the same basename are
 	// followed.
 	SourceID string
+	// Session generation this line belongs to. Zero means unscoped/legacy output.
+	Generation uint64
 }
 
 // New creaters a new line object. This is a DTail internal helper structure for reading files.
@@ -39,13 +41,7 @@ func New(content *bytes.Buffer, count uint64, transmittedPerc int, sourceID stri
 	l.Count = count
 	l.TransmittedPerc = transmittedPerc
 	l.SourceID = sourceID
-	return l
-}
-
-// Null returns a new line with all members initialized to their null value.
-func Null() *Line {
-	l := lineBuffer.Get().(*Line)
-	l.NullValues()
+	l.Generation = 0
 	return l
 }
 
@@ -65,11 +61,3 @@ func (l *Line) Recycle() {
 	//l.Reset()
 	lineBuffer.Put(l)
 }
-
-// NullValues nulls all line struct members to their default state.
-func (l *Line) NullValues() {
-	l.Content = nil
-	l.Count = 0
-	l.TransmittedPerc = 0
-	l.SourceID = ""
-}
diff --git a/internal/io/line/processor.go b/internal/io/line/processor.go
new file mode 100644
index 0000000..c7bec77
--- /dev/null
+++ b/internal/io/line/processor.go
@@ -0,0 +1,22 @@
+package line
+
+import (
+	"bytes"
+)
+
+// Processor defines an interface for processing lines read from files.
+// This interface replaces the channel-based approach for better performance.
+type Processor interface {
+	// ProcessLine handles a single line read from a file.
+	// The line buffer ownership is transferred to the processor.
+	// Returns error if processing should stop.
+	ProcessLine(line *bytes.Buffer, lineNum uint64, sourceID string) error
+	
+	// Flush ensures any buffered data is written out.
+	// Called when file reading completes or on periodic intervals.
+	Flush() error
+	
+	// Close cleans up any resources used by the processor.
+	// Called when processing is complete.
+	Close() error
+}
\ No newline at end of file