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>

1 files changed, 61 insertions, 0 deletions

diff --git a/internal/io/dlog/rotation_test.go b/internal/io/dlog/rotation_test.go
new file mode 100644
index 0000000..3cc2701
--- /dev/null
+++ b/internal/io/dlog/rotation_test.go
@@ -0,0 +1,61 @@
+package dlog
+
+import (
+	"context"
+	"os"
+	"sync/atomic"
+	"testing"
+	"time"
+)
+
+// TestRotateLoopHandlesMultipleSignals is a regression test for a bug where
+// rotateLoop returned after the first signal, so subsequent SIGHUPs were
+// silently dropped. Sending two signals on rotateCh must result in two
+// rotate() invocations before ctx is cancelled.
+func TestRotateLoopHandlesMultipleSignals(t *testing.T) {
+	prev := Common
+	Common = &DLog{maxLevel: None}
+	t.Cleanup(func() { Common = prev })
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	rotateCh := make(chan os.Signal, 2)
+	var count int32
+	rotated := make(chan struct{}, 2)
+	rotate := func() {
+		atomic.AddInt32(&count, 1)
+		rotated <- struct{}{}
+	}
+
+	done := make(chan struct{})
+	go func() {
+		rotateLoop(ctx, rotateCh, rotate)
+		close(done)
+	}()
+
+	rotateCh <- os.Interrupt
+	waitForRotate(t, rotated, "first")
+	rotateCh <- os.Interrupt
+	waitForRotate(t, rotated, "second")
+
+	cancel()
+	select {
+	case <-done:
+	case <-time.After(2 * time.Second):
+		t.Fatal("rotateLoop did not return after ctx cancel")
+	}
+
+	if got := atomic.LoadInt32(&count); got != 2 {
+		t.Fatalf("rotate() called %d times, want 2", got)
+	}
+}
+
+func waitForRotate(t *testing.T, rotated <-chan struct{}, label string) {
+	t.Helper()
+	select {
+	case <-rotated:
+	case <-time.After(2 * time.Second):
+		t.Fatalf("rotate() was not invoked for %s signal", label)
+	}
+}