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/ipc/api.go

@@ -4,6 +4,8 @@ import (
 	"context"
 	"errors"
 	"time"
+
+	"github.com/kami/maven/internal/audio"
 )
 
 // DTOs — wire-level data. Decoupled from internal/store so the protocol is
@@ -221,6 +223,84 @@ type DescribeImageResp struct {
 	NoteID      int64  `json:"note_id,omitempty"`
 }
 
+// CaptureStartReq — begin recording a meeting (Vikunja #253).
+//
+// Label is what the meeting is called ("встреча с подрядчиком"); it goes into
+// the summary note so the note is findable later. Empty is allowed.
+//
+// There is no "auto", no keyword and no schedule in this request, and there will
+// not be: the only way audio enters the recorder is a client that was told to
+// start, appending frames it was told to append. All four capture methods answer
+// ErrUnknownMethod unless the operator enabled a capture block, so a surface
+// cannot start a recording by asking nicely.
+type CaptureStartReq struct {
+	Label string `json:"label,omitempty"`
+}
+
+// CaptureStartResp — the session that opened. MaxSeconds is the hard cap after
+// which it stops itself; the caller tells him, so a forgotten recording is his
+// own informed choice rather than a surprise.
+type CaptureStartResp struct {
+	Label      string    `json:"label,omitempty"`
+	Started    time.Time `json:"started"`
+	MaxSeconds int       `json:"max_seconds"`
+}
+
+// CaptureAppendReq — one chunk of audio for the running session. Refused with
+// "nothing is being recorded" when no session is open, which is the guard that
+// makes an ambient path impossible: audio arriving at an idle core is dropped on
+// the floor, not buffered "just in case".
+type CaptureAppendReq struct {
+	Audio audio.Audio `json:"audio"`
+}
+
+// CaptureAppendResp — how much has been collected, so a client can show a timer
+// and notice the cap coming. Expired means the session hit its limit and closed;
+// stop sending and call capture_stop, the audio so far is kept.
+type CaptureAppendResp struct {
+	Seconds float64 `json:"seconds"`
+	Expired bool    `json:"expired,omitempty"`
+}
+
+// CaptureStopReq — end the running session.
+//
+// Discard throws the recording away without transcribing, storing or
+// summarising anything. This is what "забудь, не записывай" maps to, and it is a
+// flag rather than a separate method so the client that says "stop" and the
+// client that says "stop and forget" take the same path to the same session.
+type CaptureStopReq struct {
+	Discard bool `json:"discard,omitempty"`
+}
+
+// CaptureStopResp — the finished capture. BlobID is the stored WAV, kept under
+// media.retention like any other blob and pruned with it.
+//
+// A response with a Transcript and an empty Summary is a degraded success: the
+// words exist, only the model failed. A response with a BlobID and neither is
+// the audio surviving a transcription failure — the same id can be run again.
+// Discarded is true when nothing was kept.
+type CaptureStopResp struct {
+	BlobID     string    `json:"blob_id,omitempty"`
+	Label      string    `json:"label,omitempty"`
+	Started    time.Time `json:"started,omitempty"`
+	Seconds    float64   `json:"seconds,omitempty"`
+	Transcript string    `json:"transcript,omitempty"`
+	Summary    string    `json:"summary,omitempty"`
+	Chunks     int       `json:"chunks,omitempty"`
+	NoteID     int64     `json:"note_id,omitempty"`
+	Discarded  bool      `json:"discarded,omitempty"`
+}
+
+// CaptureStatusResp — what "что ты записываешь?" needs, and what /dash shows.
+// Running=false with everything else empty is the normal state.
+type CaptureStatusResp struct {
+	Running bool      `json:"running"`
+	Label   string    `json:"label,omitempty"`
+	Started time.Time `json:"started,omitempty"`
+	Seconds float64   `json:"seconds,omitempty"`
+	Bytes   int       `json:"bytes,omitempty"`
+}
+
 // SwapModelReq — load another resident model without restarting the daemon
 // (Vikunja #250). ModelPath must be one of the paths in phraser.swap_models;
 // anything else is ErrForbidden, and an unconfigured allowlist makes the whole