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, 37 insertions, 0 deletions

diff --git a/internal/ssh/server/hostkey_test.go b/internal/ssh/server/hostkey_test.go
new file mode 100644
index 0000000..e318fb4
--- /dev/null
+++ b/internal/ssh/server/hostkey_test.go
@@ -0,0 +1,37 @@
+package server
+
+import (
+	"bytes"
+	"github.com/mimecast/dtail/internal/io/fs"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestPrivateHostKeyGeneratesAndReloadsExistingKey(t *testing.T) {
+	hostKeyFile := filepath.Join(t.TempDir(), "cache", "ssh_host_key")
+	if err := os.MkdirAll(filepath.Dir(hostKeyFile), 0o755); err != nil {
+		t.Fatalf("MkdirAll failed: %v", err)
+	}
+
+	hostKeyPath, err := fs.NewRootedPath(hostKeyFile)
+	if err != nil {
+		t.Fatalf("NewRootedPath failed: %v", err)
+	}
+
+	firstPEM, err := generatePrivateHostKey(1024)
+	if err != nil {
+		t.Fatalf("generatePrivateHostKey failed: %v", err)
+	}
+	if err := storePrivateHostKey(hostKeyPath, firstPEM); err != nil {
+		t.Fatalf("storePrivateHostKey failed: %v", err)
+	}
+
+	secondPEM, err := readPrivateHostKey(hostKeyPath)
+	if err != nil {
+		t.Fatalf("readPrivateHostKey failed: %v", err)
+	}
+	if !bytes.Equal(secondPEM, firstPEM) {
+		t.Fatalf("readPrivateHostKey returned different key data")
+	}
+}