feat(ce-demo-reel): add local save as alternative to catbox upload (#647)

docs/brainstorms/2026-04-22-demo-reel-local-save-requirements.md

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+---
+date: 2026-04-22
+topic: demo-reel-local-save
+---
+
+# Demo Reel: Local Evidence Save
+
+## Problem Frame
+
+When `ce-demo-reel` captures evidence (GIFs, screenshots, terminal recordings), the local artifacts are deleted after uploading to catbox.moe. Users who want to keep evidence locally — for offline access, committing to the repo, or archival — have no way to do so without manually copying files from the temp directory before cleanup runs.
+
+---
+
+## Requirements
+
+**Destination choice**
+- R1. After capture completes, ask the user whether to upload to catbox (existing behavior) or save locally.
+- R2. The question must present the captured artifact(s) and clearly describe both options.
+
+**Local save behavior**
+- R3. When the user chooses local save, copy the final artifact(s) (GIF, PNG, or recording) to a stable OS-temp path (`$TMPDIR/compound-engineering/ce-demo-reel/`). Do not upload to catbox.
+- R4. Create the destination directory if it does not exist.
+- R5. Use a descriptive filename that includes the branch name or PR identifier and a timestamp to avoid collisions across runs.
+- R6. After saving, display the local file path(s) to the user for easy reference.
+
+---
+
+## Success Criteria
+
+- A user running `ce-demo-reel` can keep captured evidence on disk without manual intervention.
+- The saved artifacts are discoverable in a predictable, stable OS-temp location.
+
+---
+
+## Scope Boundaries
+
+- Catbox upload logic itself is unchanged — only the routing (local vs. upload) is new.
+- No automatic git-add or commit of saved artifacts.
+- No configurable save path — `$TMPDIR/compound-engineering/ce-demo-reel/` is the fixed default for now.
+- No retroactive save of previously captured evidence.
+
+---
+
+## Key Decisions
+
+- **Local save as an alternative to upload, not an addition**: The user chooses one destination per capture — either catbox or local. This keeps the flow simple and avoids redundant artifacts.
+- **OS-temp as the local target**: Uses `$TMPDIR/compound-engineering/ce-demo-reel/` per the repo's cross-invocation scratch-space convention. Stable prefix makes files findable without polluting the repo tree.
+
+---
+
+## Next Steps
+
+-> `/ce-plan` for structured implementation planning, or proceed directly to implementation given the small scope.