fix(issue-21): PR #29 delta review follow-up - prepare installs the delegate-job requirements, removes a half-made venv on install failure; prompt dirty flag sees untracked files

- worktree_prepare.sh installs the same files deploy/install.sh does
  (.agents/skills/multi-agent-mux-delegate-job/requirements.txt: paho-mqtt,
  PyYAML) plus requirements*.txt. Without paho the loop wrapper, stop_session
  and the subscriber tests fail in the worktree - seen as 4 suite failures
  in a worktree without its own venv, all passing with one.
- review D1: a failed pip install removes the venv it half made, so the next
  run recreates it instead of reporting VENV=kept (test w1c).
- review D3: the [worktree context] block's uncommitted-changes flag uses
  --untracked-files=all like the guards.
- review D2: the create skill doc says the install needs the package index.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VCgu9Fa9iT7TbJUSzdq4Ff

.agents/skills/multi-agent-mux-create/SKILL.md

@@ -243,7 +243,7 @@ bash .agents/skills/multi-agent-mux-create/scripts/worktree_prepare.sh \
   [--creator-agent claude [--session <name>] [--role creator] [--herdr-session <s>] [--herdr-workspace <w>] [--onboard]] [--dry-run]
 ```
 
-- Creates the worktree next to the control root (a path **inside** it is refused), idempotently; creates the worktree's **own** `.venv` from the control root's `.venv/bin/python` and installs `requirements.txt` / `requirements-dev.txt` when present (never a link - a leftover link is refused with exit 1; no control-root interpreter is a warning and `VENV=skipped`); adds `/.venv` and `.pytest_cache/` to the shared `info/exclude` (a linked worktree's exclude file is `$GIT_COMMON_DIR/info/exclude`, so it applies to the main checkout too).
+- Creates the worktree next to the control root (a path **inside** it is refused), idempotently; creates the worktree's **own** `.venv` from the control root's `.venv/bin/python` and installs the delegate-job skill's `requirements.txt` (paho-mqtt, PyYAML - what `deploy/install.sh` installs) plus `requirements.txt` / `requirements-dev.txt` when present (needs network access to the package index; a failed install removes the half-made venv and exits 1 so a re-run starts over; never a link - a leftover link is refused with exit 1; no control-root interpreter is a warning and `VENV=skipped`); adds `/.venv` and `.pytest_cache/` to the shared `info/exclude` (a linked worktree's exclude file is `$GIT_COMMON_DIR/info/exclude`, so it applies to the main checkout too).
 - **Submodules are opt-in** (`--submodules`). Initialisation writes `submodule.<name>.url` to the shared `.git/config`, and any attempt - even a failed one - leaves a `modules/` directory that makes a plain `git worktree remove` refuse. A failed `--submodules` undoes only what that attempt created - new submodule checkouts are deinitialised before their git dirs are deleted, so the worktree stays a usable checkout; submodules initialised earlier and pre-existing `submodule.*` values are kept - and exits 1; re-run without `--submodules` to finish.
 - `--creator-agent` creates the creator through this skill with the control root's binding and `MAM_NO_SUBSCRIBER_DAEMON=1`; the row's `pane.cwd` is the worktree.
 - Prints `BASE=<sha>`: record it **before** delegating the implementation, then review with `run_loop.sh --worktree <WT> --base "$BASE" --review-only`.