Merge a Gate-Met Feature Pull Request Through pr_review.py and Own the Kit's autoMode Entries - #3704

…ishes (#3707)

When PyYAML is not importable, the repo gate's `composite-actions` check
resolves an interpreter through `uvx --with pyyaml python` and then runs
its reader on that interpreter. Under `UV_NO_CACHE` or uv's `no-cache =
true`, uv deletes that environment when uvx exits, so the launch failed
with a bare "No such file or directory: '<temp path>'".

Design: name the cause and the remedy in the existing single host
finding, rather than falling back to running the reader inside `uvx` per
file. The naming is a few lines and adds no second read path. A per-file
fallback would add a path that re-resolves the environment for every
action file and is only reachable on this host shape. The finding now
reads: "the interpreter uvx provided could not start: [Errno 2] ...:
'/gone', because uv deletes the environment when uvx exits under
UV_NO_CACHE or uv's no-cache = true (unset UV_NO_CACHE, turn off uv's
no-cache setting, or make PyYAML importable), so no run body was
shellchecked". Only `FileNotFoundError` gets the explanation (it is also
what Windows reports as WinError 2); other start failures keep the plain
message. The `load_action` docstring notes the exception.
`scripts/repo_gate.py` is a runpy wrapper, so only the action file
changed.

Tests pin the full rendered sentence with a stubbed `subprocess.run`,
and a PermissionError case that must not blame the uv cache.

Closes on promotion: #2358

Remaining findings:
- #3705: `scripts/README.md` lines 3 and 127 still promise that `uvx`
alone suffices; held by open PR #3704, filed for follow-up.

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Co-authored-by: Claude Sonnet 5.5 <noreply@anthropic.com>

Fixes a finding raised on promotion #3715, against the change #3709
made.

## What was wrong

`_launch` in `host-setup/agent-safety/claude/gh-write-guard.py` read
past an `env` launcher without applying it. Constructed scratch
repositories reproduced each shape, two checkouts whose origins name
different owners, one with a pull-request rule on `main`:

- `env -C <dir>`, `env --chdir=<dir>`, and `env --chdir <dir>` left the
push judged in the caller's repository. So `env --chdir=/srv/other
GIT_DIR=.git git push origin main` read the wrong remote and allowed.
- `GIT_DIR=<mine>/.git env -i git -C <other> push origin main` and the
same with `env -u GIT_DIR` read the cleared `GIT_DIR`, so the check
again ran against the wrong repository.
- `env -S '<command>'` and `env -S'<command>'` were never read at all,
so every requirement missed the command, including requirements 1, 3,
and 6.

## What changed

- `_launch` now returns a `_Launch` carrying what an `env` changes.
`-C`/`--chdir` moves the directory the command runs in, composed before
a git `-C`. A run-time directory leaves it undetermined, which fails
closed for `main`, `master`, and `develop` under requirement 4, as #3709
treats an unresolved `GIT_DIR`. `-i`/`-` and `-u`/`--unset` clear what
the command inherits, and `-S`/`--split-string` is split into the words
it runs. A short cluster such as `-iC dir`, an unambiguous long prefix,
and the value-taking `-a` and `-P` read the way `env` reads them.
- `_read` applies those to each command's environment, its own
assignments, and its directory, and passes the moved directory into an
`sh -c` body.
- Self-test cases cover each shape, against the real two-owner checkouts
for requirement 4's repository and branch, and against the fixtures for
requirements 3 and 6.
- A push naming no refspec now resolves an absolute `git -C` from an
unnamed directory, after a `cd "$X"` or an `env -C "$D"`, as the push's
remote already did. Raised in review here, and it was already reachable
through `cd "$X"`.
- `host-setup/agent-safety/README.md` states how an `env` is read, and
that an `env -C` moves the directory requirement 6 tests.

## Local strict review

Three recorded passes at the `frontier` tier, the last over the final
content with no findings. The first pass's findings on an `env -S`
comment, a repeated `-C`, and long-option prefix matching are fixed
here, and the second pass's README wording finding is fixed here too.

Two more recorded passes covered the review fix on the second push. The
first of them caught a signature change that broke `test_install.py`,
which is held by #3704, so the signature was restored.

### Pre-existing findings, filed

- `host-setup/agent-safety/claude/gh-write-guard.py` `_push_targets`,
`pre-existing`: an all-letter word after `-o` is read as a flag cluster,
so `git push -ofoo origin develop` is misread. Filed as #3720.

### Deferred

- `host-setup/agent-safety/claude/gh-write-guard.py`
`_bare_push_branch`, `introduced`, design: its `leading_cd` and `moved`
parameters are now reached only from `test_install.py`. Removing them
needs that file, so it is filed as #3723.

### Dropped findings

- `host-setup/agent-safety/claude/gh-write-guard.py` `_env_option`,
`_skips_hooks`, `_push_targets`, consolidation: one shared short-option
cluster reader. The other two are untouched code with different value
letters, so merging them is a change of its own.
- `scripts/docker_lint.py` `shell_shebang_interpreter`, consolidation:
it also walks `env` options. Declined because the hook installs as one
standalone file and cannot import it.

Closes on promotion: #3716

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---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

…nd Add a backlog-burndown Away Mode (#3736)

Promotes the changes merged into `develop` since promotion #3715 to
`main`.

- [#3704](#3704):
squash-merges a gate-met feature pull request through `pr_review.py
merge`, and the host-safety kit now owns its `autoMode` entries.
- [#3735](#3735) adds an
away mode to `backlog-burndown`:
- Parallel file-claimed rounds with no maintainer present, run by a lean
orchestrator.
- A group meeting a question parks behind a `decision` issue instead of
asking.
- Merges go only as far as the `develop`, `main` or `release` scope
named at invocation.
  - The end report names each held-back issue's real reason.

It also adds the attended `decision-triage` skill, which researches and
asks every open question at once, and retires `unattended-handoff`.
- [#3737](#3737) reads a
pull request that reads back closed after `pr_review.py merge`'s merge
call as a refusal that merged nothing, rather than as an unconfirmed
merge. It answers this promotion's first review round.

After the release, the host-safety installer re-run that #3704 needs is
still the maintainer's, per its handoff #3734. That handoff's step 3
names an `unattended-handoff` worker. That skill is retired here, so the
verification runs from a `backlog-burndown` worker instead.

Fixes #3375

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