docs(cost): add upstream safety rules to cost optimization plan

Hard constraints: no dist edits, no undocumented config keys, no middleware.
Safe: documented openclaw.json knobs + workspace files only.
Includes update workflow and pre-implementation verification checklist.

memory/plans/inference-cost-optimization.md

@@ -282,6 +282,40 @@ Add a section documenting when to use which model tier for subagents, so the con
 
 ---
 
+## Upstream Safety Rules
+
+These are hard constraints. Any implementation that violates them is out of scope.
+
+### ❌ Never do
+- Edit files under `~/.npm-global/lib/node_modules/openclaw/` directly (dist, src, docs)
+- Patch or monkey-patch OpenClaw's runtime code, even for emergencies (exception: the existing TUI patch has a tracked upstream PR — document any new ones immediately)
+- Add config keys not documented in OpenClaw's own docs (guessing at undocumented keys can silently break on upgrade)
+- Modify `~/.openclaw/openclaw.json` in a way that would be overwritten or invalidated by `openclaw update`
+- Introduce any middleware, proxy, or hook that intercepts OpenClaw's internal request path
+
+### ✅ Safe to do
+- Edit `~/.openclaw/openclaw.json` using documented config knobs (agents, models, diagnostics, contextPruning, etc.)
+- Add/edit workspace files (`~/.openclaw/workspace/`) freely — these are never touched by OpenClaw updates
+- Install/update skills via `clawhub` — skills are workspace-local
+- Run `openclaw gateway restart` after config changes
+- Use `openclaw update status` / `scripts/openclaw-update-safe.sh` to check for upstream updates
+
+### Checking before applying
+Before implementing any config change:
+1. Verify the key exists in `/home/openclaw/.npm-global/lib/node_modules/openclaw/docs/` or `https://docs.openclaw.ai`
+2. If undocumented: skip it or open a question/issue — don't guess
+3. After `openclaw update`, re-verify config keys still work (check gateway logs for config parse errors)
+
+### Update workflow
+```bash
+# Before updating OpenClaw
+openclaw update status           # check what version is available
+# Review changelog for breaking config changes
+openclaw update                  # update (safe scripts handle local compat)
+openclaw gateway restart         # restart to pick up new version
+# Verify gateway health + session model still resolves correctly
+```
+
 ## What This Does NOT Change
 
 - **No OpenClaw code changes**: Everything is config-only in `openclaw.json`