Rename gerbil_ MCP tool references to jerboa_ in CLAUDE.md

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+# jerboa-code — Project Instructions
+
+## MANDATORY: Editing .ss Files
+
+**ALWAYS use `jerboa_balanced_replace` (MCP tool) instead of `Edit` when modifying `.ss` Scheme source files.**
+
+It validates parenthesis balance before AND after the change, rejecting edits that break balance. This prevents the most common class of bug in this project.
+
+```
+# Workflow for every .ss edit:
+1. jerboa_balanced_replace (dry_run: true)  — preview
+2. jerboa_balanced_replace (dry_run: false) — apply
+3. jerboa_check_balance                     — confirm file is clean
+```
+
+If you need to add a new top-level `def`/`def`/`defstruct` form, prefer appending with `jerboa_balanced_replace` on a known anchor string rather than writing free-form code with `Edit`.
+
+After ALL edits to .ss files, run `jerboa_check_balance` on every modified file before attempting `make build`.
+
+## NEVER COMMIT THESE FILES
+
+**`jcode.json` contains live API keys. It is in `.gitignore`. NEVER stage or commit it.**
+
+Do not commit any file matching: `*.json` in the project root, `.env`, `*secret*`, `*key*`, `*token*` unless you have read its full contents and confirmed it has no credentials.
+
+When committing, always run `git diff --cached` and scan for key-shaped strings (`sk-`, `AIza`, `Bearer `) before confirming.
+
+## Build
+
+```bash
+make build   # compiles src/ → lib/  via jerbuild
+make test    # runs test/run.ss
+make run     # interactive agent REPL
+```
+
+Entry point: `main.ss`. Source lives under `src/jcode/`.
+
+## Architecture
+
+```
+src/jcode/
+  core/     agent.ss  config.ss  log.ss  message.ss  session.ss
+  provider/ provider.ss
+  tool/     registry.ss  file.ss  bash.ss  web.ss  batch.ss
+  ui/       cli.ss
+```
+
+## Language
+
+This is Jerboa Scheme compiled by jerbuild. Files are `.ss`. Never write `.sls` — those are generated output in `lib/`. See `~/.claude/CLAUDE.md` for the full Jerboa language reference.