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, 94 insertions, 0 deletions

diff --git a/internal/cli/authkeyflags_test.go b/internal/cli/authkeyflags_test.go
new file mode 100644
index 0000000..64c76c3
--- /dev/null
+++ b/internal/cli/authkeyflags_test.go
@@ -0,0 +1,94 @@
+package cli
+
+import (
+	"flag"
+	"testing"
+
+	"github.com/mimecast/dtail/internal/config"
+)
+
+func TestApplyAuthKeyPathCompatibilityLegacyOnly(t *testing.T) {
+	args := config.Args{}
+
+	if warning := ApplyAuthKeyPathCompatibility(&args, "/tmp/legacy.pem", false); warning != "" {
+		t.Fatalf("unexpected warning: %q", warning)
+	}
+
+	if got, want := args.SSHPrivateKeyFilePath, "/tmp/legacy.pem"; got != want {
+		t.Fatalf("unexpected auth key path: want %q got %q", want, got)
+	}
+}
+
+func TestApplyAuthKeyPathCompatibilityPrefersExplicitAuthKeyPath(t *testing.T) {
+	tests := []struct {
+		name string
+		args []string
+		want string
+		warn bool
+	}{
+		{
+			name: "legacy then auth",
+			args: []string{"-key", "/tmp/legacy.pem", "-auth-key-path", "/tmp/current.pem"},
+			want: "/tmp/current.pem",
+			warn: true,
+		},
+		{
+			name: "auth then legacy",
+			args: []string{"-auth-key-path", "/tmp/current.pem", "-key", "/tmp/legacy.pem"},
+			want: "/tmp/current.pem",
+			warn: true,
+		},
+		{
+			name: "explicit blank auth key path keeps blank",
+			args: []string{"-key", "/tmp/legacy.pem", "-auth-key-path="},
+			want: "",
+			warn: true,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			fs := flag.NewFlagSet(t.Name(), flag.ContinueOnError)
+			var args config.Args
+			var legacyKey string
+
+			BindAuthKeyFlags(fs, &legacyKey, &args)
+			if err := fs.Parse(tc.args); err != nil {
+				t.Fatalf("Parse failed: %v", err)
+			}
+
+			var authKeyPathSet bool
+			fs.Visit(func(f *flag.Flag) {
+				if f.Name == "auth-key-path" {
+					authKeyPathSet = true
+				}
+			})
+
+			warning := ApplyAuthKeyPathCompatibility(&args, legacyKey, authKeyPathSet)
+			if gotWarn := warning != ""; gotWarn != tc.warn {
+				t.Fatalf("unexpected warning presence: want %v got %v (%q)", tc.warn, gotWarn, warning)
+			}
+			if got, want := args.SSHPrivateKeyFilePath, tc.want; got != want {
+				t.Fatalf("unexpected auth key path: want %q got %q", want, got)
+			}
+		})
+	}
+}
+
+func TestBindAuthKeyFlagsHelpText(t *testing.T) {
+	fs := flag.NewFlagSet(t.Name(), flag.ContinueOnError)
+	var args config.Args
+	var legacyKey string
+
+	BindAuthKeyFlags(fs, &legacyKey, &args)
+
+	if got, want := fs.Lookup("key").Usage, "Deprecated alias for -auth-key-path"; got != want {
+		t.Fatalf("unexpected legacy flag help: want %q got %q", want, got)
+	}
+	if got, want := fs.Lookup("auth-key-path").Usage, authKeyPathHelpText; got != want {
+		t.Fatalf("unexpected auth-key-path help: want %q got %q", want, got)
+	}
+	if got, want := fs.Lookup("auth-key-path").DefValue, ""; got != want {
+		t.Fatalf("unexpected auth-key-path default: want %q got %q", want, got)
+	}
+}