feat(v2): add reconnecting FFmpeg stream source

docs/superpowers/plans/2026-07-22-t304-go-demo-delivery.md

@@ -98,7 +98,7 @@ git commit -m "feat(v2): add safe runtime configuration"
 - Create: `v2/internal/source/stream_test.go`
 - Modify: `docs/04-architecture.md`
 
-- [ ] **Step 1: Write deterministic source tests before subprocess integration**
+- [x] **Step 1: Write deterministic source tests before subprocess integration**
 
 ```go
 func TestLatestFrameDropsStaleFrame(t *testing.T) {
@@ -114,12 +114,12 @@ func TestBackoffIsBoundedAndCancellationStopsRetry(t *testing.T) {
 }
 ```
 
-- [ ] **Step 2: Verify the tests fail**
+- [x] **Step 2: Verify the tests fail**
 
 Run: `Set-Location v2; go test ./internal/source -run 'Test(Latest|Backoff)' -v`  
 Expected: FAIL because `internal/source` does not exist.
 
-- [ ] **Step 3: Implement probe and worker ownership**
+- [x] **Step 3: Implement probe and worker ownership**
 
 ```go
 type Status string
@@ -136,14 +136,12 @@ func Start(ctx context.Context, cfg Config, commands CommandFactory) (Stream, er
 
 Use `-rtsp_transport`, `-rw_timeout`, low-latency FFmpeg input flags when configured, and `-f rawvideo -pix_fmt bgr24 -` output. Capture stderr internally but publish only a generic status code/message such as `视频流已断开，正在重连`; it must never contain command arguments or the RTSP URL. Cancellation kills the current process and closes channels exactly once.
 
-- [ ] **Step 4: Run source tests and a safe invalid-source smoke**
+- [x] **Step 4: Run source tests**
 
 Run: `Set-Location v2; go test ./internal/source -v`  
-Expected: PASS.  
-Run: `go run ./cmd/silver-pose --config config.example.json`  
-Expected: clean missing-environment configuration error without an RTSP address.
+Expected: PASS. The production command's missing-environment smoke is performed in Task 6 after `cmd/silver-pose` exists.
 
-- [ ] **Step 5: Commit the source slice**
+- [x] **Step 5: Commit the source slice**
 
 ```powershell
 git add v2/internal/source docs/04-architecture.md