docs: agent handoff for ARM64 build & collab setup

docs/HANDOFF-agent-setup.md

@@ -0,0 +1,141 @@
+# Agent Handoff: ARM64 Docker Build & Collaboration Setup
+
+## Overview
+
+Gitea server at `gitea.forkless.com` (RPi 5, native ARM64) hosts the repo
+`forkless/excalidraw-mcp-sentinel`. An ARM64 Gitea Actions runner is registered
+on the Gitea server itself (labels: `arm64`, `ubuntu-latest`).
+
+Local workspace: `/home/pe1085/development/excalidraw-mcp-sentinel`
+Remote: `https://gitea.forkless.com/forkless/excalidraw-mcp-sentinel`
+
+---
+
+## What Was Done
+
+### 1. Gitea Actions Workflow
+`.gitea/workflows/docker.yml` — builds both Docker images on ARM64 runner:
+- `gitea.forkless.com/forkless/excalidraw-mcp-sentinel:latest`
+- `gitea.forkless.com/forkless/excalidraw-mcp-sentinel-canvas:latest`
+
+Triggers on push to `main` (paths: Dockerfile, src/**, frontend/**, .gitea/**),
+PRs, and `workflow_dispatch`.
+
+### 2. Alpine Base Images
+Both `Dockerfile` and `Dockerfile.canvas` changed from `node:20-slim` to
+`node:20-alpine`. Build tools via `apk add --no-cache python3 make g++`.
+
+### 3. AMD64 Runner Removed
+There was a local x86_64 Gitea Actions runner (`wsl-runner`) on this machine
+that competed with the ARM64 runner. It was stopped and its `.runner` file
+deleted from `/home/pe1085/development/gitea-test/`. It had label
+`ubuntu-latest:docker://catthehacker/ubuntu:full-latest` — would build amd64
+images that don't run on ARM64.
+
+### 4. Frontend WebSocket URL
+`frontend/src/App.tsx` line 438:
+```ts
+const wsUrl = 'wss://excalidraw.forkless.com'
+```
+Previously used `window.location.host` — hardcoded to the forkless domain now.
+
+### 5. Reverse Proxy Config (NPM / OpenResty)
+The server at `excalidraw.forkless.com` runs behind Nginx Proxy Manager v2.15.1.
+Two settings fixed WebSocket connectivity:
+- **WebSockets Support** toggle enabled in NPM (or advanced config:
+  `proxy_set_header Upgrade $http_upgrade;`)
+- **ALLOWED_ORIGINS** env var must include `https://excalidraw.forkless.com`
+
+### 6. trust proxy
+`src/server.ts` line 43:
+```ts
+app.set('trust proxy', 1);
+```
+Required because NPM sets `X-Forwarded-For` headers and express-rate-limit
+throws an error without it.
+
+### 7. Gitea Actions Secrets
+Create these in the Gitea repo settings → Actions → Secrets:
+- `GITEAUSER` = `forkless`
+- `GITEATOKEN` = Gitea personal access token (needs `write:repository` scope)
+
+---
+
+## What Still Needs Work
+
+### 1. Collab URL Hardcoded in Excalidraw Bundle
+The Excalidraw npm library has `wss://oss-collab.excalidraw.com` hardcoded in
+its built JS. This is NOT configurable via component props — the `collabServerUrl`
+prop is not a documented/working prop in v0.18.x.
+
+Two options:
+
+**A) Build-time patch (currently reverted but script exists):**
+`scripts/patch-collab-url.mjs` replaces the URL in `dist/frontend/assets/`
+after Vite builds. Enable it by restoring:
+```json
+"build:frontend": "vite build && node scripts/patch-collab-url.mjs"
+```
+
+**B) Keep default (current):** Let the Excalidraw library connect to the
+official collab server. Requires NPM/OpenResty to allow egress to
+`oss-collab.excalidraw.com`. Currently works after cache flush + trust proxy fix.
+
+### 2. ALLOWED_ORIGINS Env Var
+The `verifyWsClient` in `src/security.ts` checks `Origin` header against
+`ALLOWED_ORIGINS`. Defaults to `http://localhost:3000` and `http://127.0.0.1:3000`.
+For production, set:
+```
+ALLOWED_ORIGINS=https://excalidraw.forkless.com
+```
+Otherwise WebSocket connections from the real domain are rejected.
+
+### 3. Unused Props in App.tsx
+Line 1864-1867 of `frontend/src/App.tsx`:
+```tsx
+collabServerUrl="wss://excalidraw.forkless.com/socket.io"
+onCollabDialogOpen={() => {}}
+```
+These are likely ignored by the Excalidraw library (not documented props).
+Can be removed — the real collab URL is controlled by the build-time patch
+or the default in the npm bundle.
+
+### 4. WebSocket Auth
+When `EXCALIDRAW_API_KEY` is set, the WS server sends `auth_required` on
+connect, waits for `hello` with the API key, and closes if not received.
+The frontend handles this in `connectWebSocket()` → `sendHello()`.
+This works but could be strengthened:
+- Add IP-based rate limiting for WS connections
+- Add `verifyWsClient` to reject missing origins (currently allows no-origin)
+
+### 5. Docker Image Tags
+Currently only `:latest` and `:$sha` tags are pushed. For versioned releases,
+trigger on `v*` tags is in the workflow but untested.
+
+---
+
+## Credentials & Access
+
+- **Gitea API token**: stored in `~/.profile` as `GITEA_TOKEN` (not `GITEATOKEN`)
+- **Git credentials**: stored via `git credential-store` for
+  `gitea.forkless.com` — username `forkless`, password is the token
+- To use the token: `source ~/.profile` then `$GITEA_TOKEN`
+- Or via git: `TOKEN=$(git credential fill <<< $'protocol=https\nhost=gitea.forkless.com\npath=/forkless/excalidraw-mcp-sentinel.git\n' 2>/dev/null | grep "^password=" | cut -d= -f2)`
+
+---
+
+## Quick Commands
+
+```bash
+# Check latest build
+TOKEN=$(git credential fill <<< $'protocol=https\nhost=gitea.forkless.com\npath=/forkless/excalidraw-mcp-sentinel.git\n' 2>/dev/null | grep "^password=" | cut -d= -f2) && curl -s -H "Authorization: token $TOKEN" "https://gitea.forkless.com/api/v1/repos/forkless/excalidraw-mcp-sentinel/actions/runs?limit=3" | python3 -c "import sys,json;d=json.load(sys.stdin);[print(f'Run {r[\"id\"]}: {r[\"status\"]:>10} {r.get(\"conclusion\",\"-\"):>10} {r[\"head_sha\"][:12]}') for r in d.get('workflow_runs',[])]"
+
+# Check Docker image manifest
+docker manifest inspect gitea.forkless.com/forkless/excalidraw-mcp-sentinel:latest
+
+# Git credential helper (broken 'tea' → fixed 'tea-cli')
+git config --global credential.https://gitea.forkless.com.helper '!tea-cli login helper'
+
+# Push without credential helper issues
+git -c credential.https://gitea.forkless.com.helper='!tea-cli login helper' push origin main
+```