fix(02): revise plans based on checker feedback

.planning/phases/02-audio-synthesis-engine/02-03-PLAN.md

@@ -25,7 +25,7 @@ must_haves:
       provides: "Integration test with ffprobe validation and zero-packet guard test"
       contains: "TestMP3Valid"
     - path: "cmd/netsynth/main.go"
-      provides: "-o flag wiring with timestamp default"
+      provides: "-o flag wiring with timestamp default, snapshot slice accumulator stub"
       contains: "outputPath"
   key_links:
     - from: "encode/mp3.go"
@@ -225,7 +225,7 @@ Write tests FIRST, using `os.CreateTemp` for output files and `exec.Command("ffp
 </task>
 
 <task type="auto">
-  <name>Task 2: Wire -o output flag into CLI</name>
+  <name>Task 2: Wire -o output flag and snapshot accumulator stub into CLI</name>
   <files>cmd/netsynth/main.go</files>
   <read_first>
     - cmd/netsynth/main.go (current Cobra flag setup, run function)
@@ -255,9 +255,16 @@ Add the `-o` / `--output` flag to main.go. Per D-15: defaults to `netsynth-<time
 
 4. Add `"time"` to the imports.
 
-5. Add a comment in the snapshot consumption loop marking where Phase 3 will wire synthesis:
+5. Add a snapshot slice accumulator alongside the existing snapshot consumption loop, and a TODO for Phase 3 wiring. Replace the current `for snap := range snapshots` block to also collect snapshots into a slice:
    ```go
-   // TODO(phase-3): Pass snapshots to encode.RunSynthesis(snapshots, outputPath)
+   // Accumulate snapshots for synthesis (Phase 3 will pass to encode.RunSynthesis)
+   var collectedSnapshots []classify.WindowSnapshot
+   for snap := range snapshots {
+       collectedSnapshots = append(collectedSnapshots, snap)
+       aggregate.AccumulateTotals(totals, snap)
+   }
+
+   // TODO(phase-3): Pass collectedSnapshots to encode.RunSynthesis(collectedSnapshots, outputPath)
    ```
 
 Do NOT import the encode package yet — Phase 3 handles that. The flag must be functional (parseable, shows in --help) even though the synthesis pipeline isn't wired.
@@ -271,10 +278,12 @@ Do NOT import the encode package yet — Phase 3 handles that. The flag must be
     - cmd/netsynth/main.go contains `netsynth-%s.mp3`
     - cmd/netsynth/main.go contains `time.Now().Format("20060102-150405")`
     - cmd/netsynth/main.go imports `"time"`
+    - cmd/netsynth/main.go contains `var collectedSnapshots []classify.WindowSnapshot`
+    - cmd/netsynth/main.go contains `TODO(phase-3)` referencing `encode.RunSynthesis`
     - `go build ./cmd/netsynth/` exits 0
     - `go run ./cmd/netsynth/ --help` output contains `-o, --output`
   </acceptance_criteria>
-  <done>The -o/--output flag is registered in Cobra, defaults to netsynth-<timestamp>.mp3, visible in --help. Build succeeds. Phase 3 will wire it to RunSynthesis.</done>
+  <done>The -o/--output flag is registered in Cobra, defaults to netsynth-<timestamp>.mp3, visible in --help. Snapshot slice accumulator stub is in place for Phase 3 wiring. Build succeeds.</done>
 </task>
 
 </tasks>
@@ -284,12 +293,14 @@ Do NOT import the encode package yet — Phase 3 handles that. The flag must be
 - `ffprobe` validates the test-generated MP3 (within encode test)
 - `go run ./cmd/netsynth/ --help` shows `-o, --output` flag
 - `grep "no packets captured" encode/mp3.go` confirms zero-packet error message
+- `grep "collectedSnapshots" cmd/netsynth/main.go` confirms snapshot accumulator stub
 </verification>
 
 <success_criteria>
 - encode/mp3.go produces valid MP3 files from synthetic WindowSnapshots (validated by ffprobe)
 - Zero-packet guard prevents file creation and returns descriptive error (OUT-03)
 - -o flag registered in CLI with timestamp default (OUT-01)
+- Snapshot slice accumulator ready for Phase 3 wiring
 - Full test suite passes: `CGO_ENABLED=1 go test ./...`
 - Complete Phase 2 audio pipeline validated end-to-end against synthetic data
 </success_criteria>