Add upload pipeline session summary

Session_Summaries/2026-03-01_Upload-Pipeline-Filesystem-Consolidation.md

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+# Session Summary: Upload Pipeline & Filesystem Consolidation
+
+Date: 2026-03-01
+
+---
+
+## Summary
+
+This session consolidated the file system architecture and resolved issues in the upload pipeline from browser to agent.
+
+---
+
+## Filesystem Architecture
+
+Game server filesystem operations are handled exclusively by the agent. The API proxies all requests — it never touches the filesystem directly.
+
+Capabilities documented:
+
+- Read (list, stat, read, download)
+- Write (server.properties, config/*.toml, config/*.json, config/*.properties)
+- Delete (constrained to mods-removed/, mods-uploaded/, logs/)
+- Upload (mods/*.jar, world/datapacks/*.zip)
+- Revert (shadow backup restore)
+
+Shadow backups created on first write. 7-day retention, 6h cleanup cycle.
+
+---
+
+## Provenance Tracking
+
+`.zlh_metadata.json` written after every upload:
+
+```json
+{
+  "mods/sodium.jar": {
+    "source": "user",
+    "uploaded_at": "2026-03-01T22:37:01Z"
+  }
+}
+```
+
+`stat` responses include `source: "user" | null`. No curated inference implemented.
+
+---
+
+## Upload Transport Fix (API Layer)
+
+Uploads initially failed with `502` errors when proxied from the API to the agent.
+
+Root cause:
+The Node API upload proxy was forwarding `Content-Length` incorrectly while streaming the request body.
+
+Resolution:
+The upload route now uses a raw Node `http.request` stream:
+
+- `req.pipe(proxyReq)`
+- `proxyRes.pipe(res)`
+- `Content-Type` preserved
+- `Content-Length` not forwarded
+- Upload timeout extended to 5 minutes
+
+This allows large multipart uploads to stream directly from the client → API → agent without buffering.