docs(readme): round-3 review fixes (21063f28)

About a third of the tests use the sandbox HOME fixtures (fewer the mock
herdr); generate-env.sh creates .mam.env only when missing, --force
overwrites with a .bak.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VCgu9Fa9iT7TbJUSzdq4Ff

README.md

@@ -38,7 +38,7 @@ bash deploy/install.sh
 - writes a starter `.mam.env` with `MQTT_BROKER=localhost`. An existing `.mam.env` is kept. If only a legacy `.env` exists, it is copied to `.mam.env` and the original stays;
 - adds `.venv`, `.mam/` and `.mam.env` to `.gitignore`.
 
-Point `MQTT_BROKER` in `.mam.env` at a broker you run (see [MESSAGING.md](MESSAGING.md) for a private broker). If `MQTT_BROKER` is not set at all, the code falls back to the public `broker.hivemq.com`. That is fine for a trial, but not for real work. `deploy/generate-env.sh` recreates `.mam.env` from `.mam.env.example`. `deploy/update.sh` and `deploy/remove.sh` update and uninstall. `deploy/install_mam.sh` is a separate installer that copies from a local clone into another directory.
+Point `MQTT_BROKER` in `.mam.env` at a broker you run (see [MESSAGING.md](MESSAGING.md) for a private broker). If `MQTT_BROKER` is not set at all, the code falls back to the public `broker.hivemq.com`. That is fine for a trial, but not for real work. `deploy/generate-env.sh` creates `.mam.env` from `.mam.env.example` when it is missing (`--force` overwrites it, keeping a `.mam.env.bak`). `deploy/update.sh` and `deploy/remove.sh` update and uninstall. `deploy/install_mam.sh` is a separate installer that copies from a local clone into another directory.
 
 ---
 
@@ -172,7 +172,7 @@ sequenceDiagram
 
 - The suite has about 1,900 tests, and a full run takes over an hour.
 - It runs its own in-process MQTT broker, so it never needs `.mam.env`. Don't export `.mam.env` for tests.
-- Every test gets a temporary job registry and audit-log directory. Most tests also use the sandbox fixtures, which set a temporary HOME and a mock herdr:
+- Every test gets a temporary job registry and audit-log directory. About a third also use the sandbox fixtures, which set a temporary HOME (and, for fewer, a mock herdr):
   - the tests that drive a real herdr start their own throwaway herdr server;
   - after the run, session-level guards check the real control plane and your agent homes (`~/.claude/projects`, `~/.codex`, `~/.gemini`, …) and fail the run if a test left entries there.
 - Some tests are platform-specific. A few need Python 3.11+ (`tomllib`), Linux (`/proc`) or the `nats-docker` submodule; elsewhere they are skipped.