stack: TOC-Pflicht fuer Referenzdateien ueber 100 Zeilen (docs toc); session-setup.md/gates.md nennen die tatsaechliche Budget-Ausnahmeliste (schliesst #73, #76)

Files changed:
- AGENTS.md
- CHANGES.md
- VERSION
- instructions/CONTRACT.md
- instructions/capture-session.md
- instructions/claude-code-model-selection.md
- instructions/dev/issue-tracking.md
- instructions/dev/testing-conventions.md
- instructions/dev/version-parts.md
- instructions/evolve-subtypes.md
- instructions/gates.md
- instructions/german-terminology.md
- instructions/ingest-large-tree.md
- instructions/kb-profiles.md
- instructions/link-taxonomy.md
- instructions/mcp-read-server.md
- instructions/migrate-corpus.md
- instructions/migrations/3.0.0-authoring-conventions.md
- instructions/migrations/4.0.0-link-taxonomy.md
- instructions/private-instance.md
- instructions/session-setup.md
- instructions/setup-instance.md
- kb/CONTRACT.md
- kb/CONVENTIONS.md
- kb/concepts/COLLECTION.md
- raw/CONTRACT.md
- tools/CONTRACT.md
- tools/chemenu/commands/docs_verify.py
- tools/chemenu/commands/instructions_cmd.py
- tools/chemenu/tests/test_docs_verify.py
- tools/chemenu/tests/test_instructions_cmd.py
- tools/chemenu/tests/test_toc.py
- tools/chemenu/toc.py
- types/type-spec.md

instructions/session-setup.md

@@ -15,7 +15,8 @@ shell inherits an unrelated count.
 
 ## Steps
 
-Run this **once per working session**, before the first `wikitool` call that changes anything:
+Run this **once per working session**, before the first `wikitool` call that is not exempt from
+the budget (see § Scope for what that means):
 
 ```bash
 export WIKITOOL_SESSION_ID="wiki-$(date +%s)"
@@ -56,7 +57,15 @@ refusal. See [gates.md](gates.md).
 
 ## Scope
 
-Read-only retrieval (`wikitool search`) is exempt from the budget and needs no setup. This
-matters only for commands that change the wiki.
+**The exemption is a fixed allowlist, not "read-only" or "does not change the wiki."** A command
+needs this setup unless it is one of the dozen `tools/CONTRACT.md` marks exempt in its command
+table (`search`, `doctor`, `links show`, `cite id`, `budget status`, the read-only forms of
+`eval`, `version`, `migrate` and `upstream verify`) - that table, not a rule of thumb here, is
+the single list.
+
+`lint` is the case that breaks the "changes the wiki" reading: it only writes to `reports/`,
+which is gitignored, so it looks side-effect-free - but it is not on the allowlist and is counted
+like any mutating command. A skill that calls only exempt commands needs no session id; a skill
+that calls `lint` alone still does.
 
 The limits themselves, and what to do when one trips, are in [gates.md](gates.md).