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, 45 insertions, 0 deletions

diff --git a/internal/io/journal/reader_unsupported.go b/internal/io/journal/reader_unsupported.go
new file mode 100644
index 0000000..83b4a73
--- /dev/null
+++ b/internal/io/journal/reader_unsupported.go
@@ -0,0 +1,45 @@
+//go:build !linux
+
+// Package journal provides a journalctl-backed file reader.
+package journal
+
+import (
+	"context"
+	"errors"
+	"runtime"
+
+	"github.com/mimecast/dtail/internal/io/line"
+	"github.com/mimecast/dtail/internal/lcontext"
+	"github.com/mimecast/dtail/internal/regex"
+)
+
+// ErrUnsupported reports that journal reading is only available on Linux.
+var ErrUnsupported = errors.New("journal reader is only supported on linux")
+
+// Reader is an unsupported journal reader stub on non-Linux systems.
+type Reader struct{}
+
+// NewReader returns an unsupported error on non-Linux systems.
+func NewReader(_ []string, _ string, _ bool, _ chan<- string) (*Reader, error) {
+	return nil, errors.Join(ErrUnsupported, errors.New(runtime.GOOS))
+}
+
+// StartWithProcessor returns an unsupported error on non-Linux systems.
+func (r *Reader) StartWithProcessor(context.Context, lcontext.LContext, line.Processor, regex.Regex) error {
+	return ErrUnsupported
+}
+
+// StartWithProcessorOptimized returns an unsupported error on non-Linux systems.
+func (r *Reader) StartWithProcessorOptimized(context.Context, lcontext.LContext, line.Processor, regex.Regex) error {
+	return ErrUnsupported
+}
+
+// FilePath returns the journalctl command name.
+func (r *Reader) FilePath() string {
+	return "journalctl"
+}
+
+// Retry returns false on non-Linux systems.
+func (r *Reader) Retry() bool {
+	return false
+}