initial commit: live meeting transcription pipeline

Go orchestrator: spawns audiotee for capture (system audio + mic, two
tracks), segments with an energy-threshold VAD, transcribes each segment
via qwen-asr (subprocess per segment, vendored as a pinned git submodule
in third_party/qwen-asr), and serves the live transcript over SSE while
also writing it durably to a text file. Includes a glossary/prompt-leakage
guard (internal/asr/leak.go) that discards a segment if the model echoes
the biasing prompt instead of transcribing.

cmd/transcriptor-ai is the main orchestrator; cmd/transcript-tail is a
minimal terminal SSE client. See CLAUDE.md for the full architecture and
the reasoning behind each choice (Go over Python/Swift/Rust, SSE over
WebSocket, why the VAD is a hand-rolled heuristic, etc).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

internal/asr/asr.go

@@ -0,0 +1,77 @@
+// Package asr transcribes bounded PCM segments via qwen-asr
+// (https://github.com/antirez/qwen-asr), invoked as a one-shot subprocess
+// per segment rather than a long-lived daemon.
+//
+// This was verified empirically, not assumed: `qwen_asr --stdin --stream
+// --silent` does not print incremental partial text as it processes a
+// single stdin stream — it prints only the final transcription once done,
+// even in --stream mode (that flag changes its internal chunked-encoding
+// strategy, not what gets written to stdout). Measured latency including
+// process startup and model load, on the 0.6B model, was ~0.15-0.2x
+// realtime for a ~6s clip — comfortably fast enough to spawn fresh per VAD
+// segment instead of keeping a persistent process fed over a pipe.
+// Our own VAD segment boundaries (internal/vad) are therefore what stands
+// in for "live" here: each vad.Segment.IsFinal maps directly to the
+// SSE message's is_final field described in CLAUDE.md.
+package asr
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+// Config points at a built qwen_asr binary and a downloaded model
+// directory. Neither has an established default location yet (unlike
+// audiotee's ~/bin convention), so both are required.
+type Config struct {
+	BinaryPath string
+	ModelDir   string
+	// Prompt biases transcription toward glossary terms, e.g.
+	// "Preserve spelling: Kubernetes, PostgreSQL". Optional.
+	Prompt string
+	// Threads sets qwen_asr's -t flag. Zero means "let it pick" (all CPUs).
+	Threads int
+}
+
+type Transcriber struct {
+	cfg Config
+	run runFunc // seam for testing without a real binary
+}
+
+func New(cfg Config) *Transcriber {
+	return &Transcriber{cfg: cfg, run: runCommand}
+}
+
+// Transcribe runs qwen_asr once against pcm (raw s16le, 16kHz, mono — the
+// format both audiotee and internal/vad produce) and returns the
+// transcribed text, trimmed.
+func (t *Transcriber) Transcribe(ctx context.Context, pcm []byte) (string, error) {
+	args := []string{"-d", t.cfg.ModelDir, "--stdin", "--stream", "--silent"}
+	if t.cfg.Prompt != "" {
+		args = append(args, "--prompt", t.cfg.Prompt)
+	}
+	if t.cfg.Threads > 0 {
+		args = append(args, "-t", strconv.Itoa(t.cfg.Threads))
+	}
+
+	stdout, stderr, err := t.run(ctx, t.cfg.BinaryPath, args, pcm)
+	if err != nil {
+		return "", fmt.Errorf("qwen_asr: %w (stderr: %s)", err, bytes.TrimSpace(stderr))
+	}
+	text := strings.TrimSpace(string(stdout))
+
+	if looksLikePromptLeak(text, t.cfg.Prompt) {
+		// Discard rather than return it as a genuine transcription — see
+		// leak.go. Logged here (not just silently dropped) since this
+		// package has no structured logger of its own; matches the plain
+		// stderr diagnostics the CLI already prints elsewhere.
+		fmt.Fprintf(os.Stderr, "asr: discarding segment, looks like a --prompt leak, not a transcription: %q\n", text)
+		return "", nil
+	}
+
+	return text, nil
+}