stack: Upgrade-Pfad bekommt eine eigene manual-Instruktion, INSTALL.md verweist darauf (#108)

Files changed:
- CHANGES.md
- INSTALL.md
- VERSION
- instructions/session-setup.md
- instructions/upgrade-instance.md
- tools/CONTRACT.md
- tools/chemenu/commands/dist_cmd.py
- tools/chemenu/tests/test_dist_upgrade.py

instructions/session-setup.md

@@ -23,6 +23,21 @@ export WIKITOOL_SESSION_ID="wiki-$(date +%s)"
 tools/wikitool sync
 ```
 
+**An `export` only carries if the shell carries.** Several agent harnesses run every tool call in
+a freshly initialised shell: the working directory survives, shell state - environment variables,
+functions - does not, so the variable is gone by the next call and each call falls back to its own
+parent pid. The budget then counts a run of thirty calls as thirty sessions of one, and neither
+the 60-call ceiling nor the loop-breaker can ever trip. On such a harness, pass the id **inline on
+every call** instead, keeping the same value for the whole task:
+
+```bash
+WIKITOOL_SESSION_ID="wiki-1234" tools/wikitool sync
+WIKITOOL_SESSION_ID="wiki-1234" tools/wikitool new entity --name "..."
+```
+
+Which of the two applies is answerable in one call: run `tools/wikitool budget status` twice in
+separate calls after exporting, and see whether it names the same id both times.
+
 Check the current state at any time with `tools/wikitool budget status`, which is never
 counted against the budget itself and prints the id it is counting under.