---
phase: 03-pipeline-integration-and-mvp
plan: 02
subsystem: cmd
tags: [pipeline-integration, mvp, encoding-feedback, end-to-end]
dependency_graph:
  requires: [03-01]
  provides: [end-to-end-mvp-pipeline]
  affects: [cmd/netsynth/main.go]
tech_stack:
  added: []
  patterns: [pipeline-wiring, encoding-feedback-ux]
key_files:
  created: []
  modified:
    - cmd/netsynth/main.go
decisions:
  - PrintSummary called before RunSynthesis per D-08 (user sees stats before waiting for encoding)
  - Audio duration computed from snapshot count * DefaultWindowMs (not wall-clock) per Pitfall 4
  - os.Stat called only after RunSynthesis returns nil per Pitfall 5
metrics:
  duration: ~5min
  completed: 2026-03-26T12:30:00Z
  tasks_completed: 1
  files_modified: 1
---

# Phase 03 Plan 02: Wire RunSynthesis and Encoding Feedback Summary

**One-liner:** Wire capture->classify->aggregate->synthesize->MP3 pipeline in main.go with protocol summary before encoding and "Encoding/Saved" status messages.

## What Was Built

Completed the v1 MVP end-to-end pipeline by wiring `encode.RunSynthesis` into `cmd/netsynth/main.go`. The complete flow is now:
1. Capture live packets from interface
2. Classify packets by protocol (14 traffic classes)
3. Aggregate into 500ms time windows
4. Print protocol summary to stderr (D-08: before encoding)
5. Print "Encoding N windows to path..." status (D-07)
6. Call `encode.RunSynthesis(collectedSnapshots, outputPath)` to synthesize and encode
7. Print "Saved path (Xs, N KB, encoded in Xs)" confirmation (D-09)

### Key Changes

**cmd/netsynth/main.go:**
- Added `"github.com/netsynth/netsynth/encode"` import
- Removed `// TODO(phase-3)` stub and `_ = collectedSnapshots` blank identifier
- Reordered: `PrintSummary` now appears BEFORE `encode.RunSynthesis` (D-08)
- Added encoding status line with window count and output path (D-07)
- Added encode timing (`encodeStart`/`encodeElapsed`)
- Added `RunSynthesis` call with error propagation via `fmt.Errorf("synthesis failed: %w", err)`
- Added audio duration calculation: `float64(len(collectedSnapshots)) * float64(aggregate.DefaultWindowMs) / 1000.0` (float64 avoids truncation)
- Added `os.Stat` post-encode for file size (only called after nil error from RunSynthesis)
- Added "Saved" confirmation with path, duration, KB size, encode time (D-09)
- Updated Long description: removed "(in future phases)" qualifier

### Zero-Packet Handling

`encode.RunSynthesis` already returns an error before creating any file when zero packets are captured (D-16/OUT-03). `main.go` propagates this as `"synthesis failed: <message>"` — no corrupt empty file is written.

## Commits

| Task | Commit | Description |
|------|--------|-------------|
| Task 1 | 0ab2c6e | feat(03-02): wire RunSynthesis and add encoding feedback messages |

## Checkpoint Status

**Task 2 (human-verify) is awaiting verification.** The binary builds successfully and all automated tests pass. Human verification is needed to confirm the live capture-to-MP3 flow works with real network traffic on a loopback interface.

### Verification Steps (for Task 2)

1. Build: `go build -o ./netsynth ./cmd/netsynth`
2. Run: `sudo ./netsynth -i lo -o /tmp/test-mvp.mp3`
3. In another terminal: `ping -c 5 127.0.0.1`
4. Press Ctrl+C
5. Verify stderr shows: protocol summary, then "Encoding...", then "Saved..."
6. Verify: `ls -la /tmp/test-mvp.mp3` shows non-zero size
7. Zero-packet test: run and immediately Ctrl+C — expect error, no file

## Test Results

```
ok  github.com/netsynth/netsynth/aggregate  0.147s
ok  github.com/netsynth/netsynth/capture    0.009s
ok  github.com/netsynth/netsynth/classify   0.017s
ok  github.com/netsynth/netsynth/cmd/netsynth 0.010s
ok  github.com/netsynth/netsynth/encode     0.329s
ok  github.com/netsynth/netsynth/synth      0.850s
```

All 6 packages pass. No regressions.

## Deviations from Plan

None - plan executed exactly as written.

## Known Stubs

None. All pipeline stages are wired. The binary produces a real MP3 from live traffic.

## Self-Check: PASSED