Add meeting capture with explicit start and stop (#253)

Maven can record a meeting when she is told to, transcribe it through the
STT she already has, and write a summary note. The audio lives in the blob
store #252 introduced, under the same retention loop.

Nothing here listens. Recorder.Append is the only way audio enters and it
refuses every frame unless someone explicitly started a session, so audio
arriving at an idle core is dropped rather than buffered. The plan document
asked for a keyword trigger ("maven record" heard in the room) and that is
refused: noticing a keyword means listening to the room, which is the one
behaviour this capability must not have.

Off unless configured twice over. No media block means nowhere to keep
audio, no capture block means no recorder, and in either case the four IPC
methods answer ErrUnknownMethod. On an unconfigured box there is no wire
path that begins a recording at all.

A forgotten session ends itself at max_minutes, checked on every append,
and the audio collected before the cap is kept. Stop with discard set is
what "забудь, не записывай" maps to and it leaves nothing behind. The
verbatim transcript is not saved unless save_transcript says so; the
summary is.

Long audio against n_ctx 4096 is handled by map-reduce over 3000-rune
windows rather than by truncation, because a truncated meeting summary
reads as complete and is not. Transcription is windowed at five minutes so
the whisper worker stays responsive to the voice path.

No second STT: internal/capture takes the stt.Transcriber the voice path
already holds. Capture with voice off is refused rather than degraded,
since hours of unreadable audio of other people is worse than no recording.

The three write methods are AuthWrite, not AuthStepUp: step-up needs a
passkey gesture the voice path cannot make, which would leave "запиши
встречу" impossible by voice. capture_status is AuthRead.

make build and make test both pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TrVSBKe3RFDF4fGYKWYQnX

internal/auth/auth_test.go

@@ -416,3 +416,29 @@ func TestRequirement_SwapModel(t *testing.T) {
 		t.Errorf("SwapModel with no asserted step-up = %v; want ErrForbidden", err)
 	}
 }
+
+// TestRequirement_Capture — recording other people is a write, not a read: it
+// puts audio of them on disk. The read side, "что ты записываешь?", is not.
+//
+// It is deliberately NOT AuthStepUp. Step-up needs a passkey gesture, which the
+// voice path cannot make, so putting it there would mean "запиши встречу" could
+// never work by voice. The real gate on this capability is that the methods do
+// not exist at all unless the operator enabled a capture block.
+func TestRequirement_Capture(t *testing.T) {
+	for _, m := range []ipc.Method{
+		ipc.MethodCaptureStart, ipc.MethodCaptureAppend, ipc.MethodCaptureStop,
+	} {
+		if got := Requirement(m); got != AuthWrite {
+			t.Errorf("%s authority = %v; want AuthWrite", m, got)
+		}
+	}
+	if got := Requirement(ipc.MethodCaptureStatus); got != AuthRead {
+		t.Errorf("CaptureStatus authority = %v; want AuthRead", got)
+	}
+	// Voice can start one: it is the surface he will actually use to say
+	// "запиши встречу", and it carries AuthWrite.
+	voice := Scope{Surface: SurfaceVoice, Module: "voice", SourceScope: []string{"*"}}
+	if err := Can(ipc.MethodCaptureStart, voice, nil); err != nil {
+		t.Errorf("voice starting a capture = %v; want allowed", err)
+	}
+}

internal/auth/policy.go

@@ -60,6 +60,21 @@ func Requirement(m ipc.Method) Authority {
 		// and for the same reason: nothing Maven says or does may reach it.
 		// MethodModelStatus is only the read side, so it stays at AuthRead.
 		return AuthStepUp
+	case ipc.MethodCaptureStart, ipc.MethodCaptureAppend, ipc.MethodCaptureStop:
+		// Recording a meeting (Vikunja #253). AuthWrite, not AuthRead: it puts
+		// audio of other people on disk, which is a heavier thing than reading a
+		// fact, and it is not something a read-only surface should be able to
+		// begin. Append and Stop sit on the same rung as Start deliberately —
+		// a surface that may not start a recording has no business feeding or
+		// harvesting one either.
+		//
+		// Not AuthStepUp, and this is the interesting line: step-up needs a
+		// passkey gesture, which the voice path cannot make. Putting it here
+		// would mean "запиши встречу" could never work by voice, and the real
+		// gate on this capability is elsewhere and stronger — the methods do not
+		// exist at all unless the operator enabled a capture block, and no
+		// recording can begin without someone saying so.
+		return AuthWrite
 	case ipc.MethodWriteFact:
 		return AuthWrite
 	case ipc.MethodAssertStepUp:
@@ -95,6 +110,9 @@ func Requirement(m ipc.Method) Authority {
 		// the box, which internal/vision enforces by refusing a non-private
 		// endpoint.
 		ipc.MethodDescribeImage,
+		// "что ты записываешь?" — the read side of the recorder. It reports a
+		// label, a start time and a byte count, begins nothing and keeps nothing.
+		ipc.MethodCaptureStatus,
 		// The read side of the model swap: which model is resident, which ones are
 		// allowlisted. It loads nothing and changes nothing.
 		ipc.MethodModelStatus: