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, 14 insertions, 0 deletions

diff --git a/internal/clients/session_spec.go b/internal/clients/session_spec.go
new file mode 100644
index 0000000..a5218f6
--- /dev/null
+++ b/internal/clients/session_spec.go
@@ -0,0 +1,14 @@
+package clients
+
+import (
+	"github.com/mimecast/dtail/internal/config"
+	sessionspec "github.com/mimecast/dtail/internal/session"
+)
+
+// SessionSpec captures the mutable, per-connection workload a DTail client wants to run.
+type SessionSpec = sessionspec.Spec
+
+// NewSessionSpec returns a session specification from client args.
+func NewSessionSpec(args config.Args) SessionSpec {
+	return sessionspec.NewSpec(args)
+}