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, 6 insertions, 2 deletions

diff --git a/internal/io/fs/filereader.go b/internal/io/fs/filereader.go
index e27d2a7..7f36a29 100644
--- a/internal/io/fs/filereader.go
+++ b/internal/io/fs/filereader.go
@@ -9,9 +9,13 @@ import (
 )
 
 // FileReader is the interface used on the dtail server to read/cat/grep/mapr...
-// a file.
+// a file. Line delivery is processor-based (line.Processor); the historic
+// channel-based Start(chan<- *line.Line) method was removed once every read path
+// migrated to the processor pipeline (task iv0).
 type FileReader interface {
-	Start(ctx context.Context, ltx lcontext.LContext, lines chan<- *line.Line,
+	StartWithProcessor(ctx context.Context, ltx lcontext.LContext, processor line.Processor,
+		re regex.Regex) error
+	StartWithProcessorOptimized(ctx context.Context, ltx lcontext.LContext, processor line.Processor,
 		re regex.Regex) error
 	FilePath() string
 	Retry() bool