add granular session log: Mar 1 upload pipeline + filesystem consolidation

SESSION_LOG/2026-03-01-upload-pipeline-filesystem-consolidation.md

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+# 2026-03-01 – Upload Pipeline + Filesystem Consolidation
+
+**Type:** Implementation + Architecture Consolidation
+**Status:** Upload implemented, transport tuning in progress
+
+---
+
+## Completed
+
+### Upload Model
+- Implemented direct runtime upload model
+- Removed staging and symlink exploration entirely
+- Uploads write atomically to runtime root
+- Enforced by strict allowlist (`mods/*.jar`, `world/datapacks/*.zip`)
+- No directory creation, no staging folders, no symlinks
+
+### Provenance
+- Added `.zlh_metadata.json` provenance tracking
+- Extended `stat` response with `source` field (`"user" | null`)
+- No curated inference implemented (intentional)
+
+### API Transport
+- Identified `fetch()` streaming as source of upload proxy timing issues
+- Switched to raw `http.request` piping:
+  ```
+  req.pipe(proxyReq)
+  proxyRes.pipe(res)
+  ```
+- Confirmed agent upload via direct curl
+- Upload timeout tuning identified as remaining work
+
+### Documentation
+- Consolidated filesystem architecture docs (`filesystem-and-file-browser.md`, `mod-deployment-safety.md`)
+- Full grind repo consolidation pass (README, CONSTRAINTS, OPEN_THREADS, SESSION_START, ANTI_DRIFT, UPSTREAMS)
+
+---
+
+## System State
+
+- Read: Stable
+- Write: Stable with shadow backup
+- Delete: Constrained and safe
+- Upload: Implemented, transport tuning in progress
+- Console: Stable
+
+---
+
+## Known Architectural Decisions Locked In
+
+- Direct runtime upload — no staging, no symlinks
+- `.zlh_metadata.json` is the provenance layer; `stat` returns `source`
+- Raw `http.request` piping for upload proxy — no `fetch()` streaming
+- Upload allowlist enforced by agent, not API
+
+---
+
+## Remaining Issues
+
+### Upload Transport Timeout
+- Upload route timeout not yet increased
+- Need to distinguish:
+  - client abort
+  - upstream timeout
+  - socket reset
+- Upload route should log explicit error categories
+
+### Dev Server Filesystem Model
+- Not yet designed
+- Game server model is complete and stable
+- Dev runtime layout, artifact promotion strategy, and file editing scope all TBD
+
+---
+
+## Next Steps
+
+1. Increase upload route timeout
+2. Add explicit error category logging to upload route
+3. Begin dev server filesystem model planning