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, 147 insertions, 0 deletions

diff --git a/internal/clients/session_spec_test.go b/internal/clients/session_spec_test.go
new file mode 100644
index 0000000..8133bc9
--- /dev/null
+++ b/internal/clients/session_spec_test.go
@@ -0,0 +1,147 @@
+package clients
+
+import (
+	"testing"
+
+	"github.com/mimecast/dtail/internal/config"
+	"github.com/mimecast/dtail/internal/omode"
+)
+
+func TestSessionSpecCommands(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name    string
+		spec    SessionSpec
+		want    []string
+		wantErr bool
+	}{
+		{
+			name: "tail read commands",
+			spec: SessionSpec{
+				Mode:    omode.TailClient,
+				Files:   []string{"/var/log/app.log"},
+				Options: "plain=true",
+				Regex:   "ERROR",
+			},
+			want: []string{"tail:plain=true /var/log/app.log regex:default,literal ERROR"},
+		},
+		{
+			name: "map client commands",
+			spec: SessionSpec{
+				Mode:    omode.MapClient,
+				Files:   []string{"/var/log/app.log"},
+				Options: "plain=true",
+				Query:   "from STATS select count(*)",
+				Regex:   ".",
+			},
+			want: []string{
+				"map:plain=true from STATS select count(*)",
+				"cat:plain=true /var/log/app.log regex:noop ",
+			},
+		},
+		{
+			name: "tail query with timeout",
+			spec: SessionSpec{
+				Mode:    omode.TailClient,
+				Files:   []string{"/var/log/app.log"},
+				Options: "plain=true",
+				Query:   "from STATS select count(*)",
+				Regex:   "WARN",
+				Timeout: 15,
+			},
+			want: []string{
+				"map:plain=true from STATS select count(*)",
+				"timeout 15 tail /var/log/app.log regex:default,literal WARN",
+			},
+		},
+		{
+			name: "health command",
+			spec: SessionSpec{
+				Mode: omode.HealthClient,
+			},
+			want: []string{"health"},
+		},
+		{
+			name: "invalid regex returns error",
+			spec: SessionSpec{
+				Mode:  omode.GrepClient,
+				Files: []string{"/var/log/app.log"},
+				Regex: "[",
+			},
+			wantErr: true,
+		},
+		{
+			name: "query with unsupported mode returns error",
+			spec: SessionSpec{
+				Mode:  omode.GrepClient,
+				Files: []string{"/var/log/app.log"},
+				Query: "from STATS select count(*)",
+				Regex: ".",
+			},
+			wantErr: true,
+		},
+	}
+
+	for _, tc := range tests {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			got, err := tc.spec.Commands()
+			if tc.wantErr {
+				if err == nil {
+					t.Fatalf("expected error, got nil")
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("Commands() error = %v", err)
+			}
+			if len(got) != len(tc.want) {
+				t.Fatalf("unexpected command count: got %d want %d (%v)", len(got), len(tc.want), got)
+			}
+			for i := range tc.want {
+				if got[i] != tc.want[i] {
+					t.Fatalf("command %d mismatch: got %q want %q", i, got[i], tc.want[i])
+				}
+			}
+		})
+	}
+}
+
+func TestNewSessionSpecSplitsFiles(t *testing.T) {
+	t.Parallel()
+
+	spec := NewSessionSpec(config.Args{
+		Mode:        omode.GrepClient,
+		What:        " a.log , , b.log ",
+		RegexStr:    "ERROR",
+		RegexInvert: true,
+		Timeout:     10,
+	})
+
+	if len(spec.Files) != 2 || spec.Files[0] != "a.log" || spec.Files[1] != "b.log" {
+		t.Fatalf("unexpected files: %#v", spec.Files)
+	}
+	if !spec.RegexInvert {
+		t.Fatalf("expected RegexInvert to be true")
+	}
+	if spec.Timeout != 10 {
+		t.Fatalf("unexpected timeout: %d", spec.Timeout)
+	}
+}
+
+func TestNewSessionSpecUsesPipeSentinelForServerlessStdin(t *testing.T) {
+	t.Parallel()
+
+	spec := NewSessionSpec(config.Args{
+		Mode:       omode.GrepClient,
+		Serverless: true,
+		RegexStr:   "ERROR",
+	})
+
+	if len(spec.Files) != 1 || spec.Files[0] != "-" {
+		t.Fatalf("unexpected files for serverless stdin: %#v", spec.Files)
+	}
+}