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, 41 insertions, 0 deletions

diff --git a/internal/cli/pprof_test.go b/internal/cli/pprof_test.go
new file mode 100644
index 0000000..aa1cd05
--- /dev/null
+++ b/internal/cli/pprof_test.go
@@ -0,0 +1,41 @@
+package cli
+
+import (
+	"runtime"
+	"testing"
+)
+
+// TestEnableProfilingRatesSetsMutexFraction verifies that EnableProfilingRates
+// actually turns on mutex profiling. Without this the /debug/pprof/mutex
+// endpoint reports an empty profile. runtime.SetMutexProfileFraction(-1) reads
+// the current fraction without changing it, so it lets us assert the state.
+func TestEnableProfilingRatesSetsMutexFraction(t *testing.T) {
+	// Save and restore global runtime state so this test does not leak into
+	// other tests in the package. The block profile rate has no getter, so we
+	// simply disable it again on cleanup.
+	prevMutex := runtime.SetMutexProfileFraction(-1)
+	t.Cleanup(func() {
+		runtime.SetMutexProfileFraction(prevMutex)
+		runtime.SetBlockProfileRate(0)
+	})
+
+	// Start from a known-disabled state.
+	runtime.SetMutexProfileFraction(0)
+
+	EnableProfilingRates()
+
+	if got := runtime.SetMutexProfileFraction(-1); got != mutexProfileFraction {
+		t.Errorf("mutex profile fraction = %d, want %d", got, mutexProfileFraction)
+	}
+}
+
+// TestProfilingRateConstants pins the ss0-validated values so a change is a
+// conscious decision rather than an accident.
+func TestProfilingRateConstants(t *testing.T) {
+	if mutexProfileFraction != 5 {
+		t.Errorf("mutexProfileFraction = %d, want 5", mutexProfileFraction)
+	}
+	if blockProfileRateNanos != 100000 {
+		t.Errorf("blockProfileRateNanos = %d, want 100000", blockProfileRateNanos)
+	}
+}