feat(rust): port stack reorder + stack move to native Rust

[jd]

The Rust binary now serves mergify stack reorder <COMMIT>... [--dry-run] and mergify stack move <COMMIT> <POSITION> [<TARGET>] [--dry-run] natively. The Python implementations
(mergify_cli/stack/reorder.py::stack_reorder,
mergify_cli/stack/move.py, their click registrations, and
mergify_cli/tests/stack/test_{reorder,move}.py) are removed.

Both commands reduce to the same rebase-todo transformation —
they only differ in how they compute the desired pick order —
so this slice ships both behind a single new
Action::Reorder { ordered_shas } variant on
mergify_stack::rebase_todo. The transformer rebuilds the
todo with picks in the requested order and appends every
non-pick line (comments, blanks, exec annotations) at the
end, mirroring Python's run_action_rebase bucketing.

mergify stack reorder: the <COMMIT>... arguments list
every stack commit in the desired new order. Validation rejects
duplicate prefixes, prefixes that don't resolve, and length
mismatches. When the requested order already matches the
current order, we short-circuit with
Stack is already in the requested order and don't spawn a
rebase.

mergify stack move: a thin wrapper that computes the new
order from <COMMIT> <POSITION> [<TARGET>] and then delegates
to the same Action::Reorder path. POSITION is one of
first, last, before, after; before and
after require a <TARGET>, first and last reject
one.

The Python stack_reorder/stack_move functions are gone,
but mergify_cli/stack/reorder.py itself is kept as a
header file: it still hosts the get_stack_commits,
match_commit, run_scripted_rebase,
run_action_rebase and display_* helpers that the
remaining Python stack_squash (the next slice) still depends
on. When stack squash follows, the whole file goes.

Also fixes a parallel-test flake in
crates/mergify-cli/tests/stack_*.rs: each integration test
file now spawns git through a local isolated_git()
helper that sets GIT_CONFIG_GLOBAL=/dev/null and
GIT_CONFIG_NOSYSTEM=1, matching the lib-test fixture
behavior. Symptom was sporadic git failures when many test
binaries ran their per-test fixtures concurrently.

End-to-end coverage in
crates/mergify-cli/tests/stack_reorder.rs (7 cases): reorder
to explicit sequence, already-in-order is a no-op, count
mismatch errors, move to first, move before target, move
before without target errors, move first with target
errors. The pure transformer adds 3 new rebase_todo unit
tests (happy path, count mismatch, unknown SHA).

Co-Authored-By: Claude Opus 4.7 noreply@anthropic.com

Depends-On: #1519

[jd]

This pull request is part of a Mergify stack:

#	Pull Request	Link
1	feat(rust): port stack note to native Rust	#1515
2	feat(rust): port stack edit + add rebase-todo machinery	#1516
3	feat(rust): port stack drop to native Rust	#1517
4	feat(rust): port stack fixup to native Rust	#1518
5	feat(rust): port stack reword to native Rust	#1519
6	feat(rust): port stack reorder + stack move to native Rust	#1520	👈
7	feat(rust): port stack squash to native Rust	#1521
8	feat(rust): port stack checkout to native Rust	#1522
9	feat(rust): port stack sync to native Rust	#1523
10	feat(rust): port stack list + stack open to native Rust	#1524

[mergify]

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• depends-on=Mergifyio/mergify-cli#1515 [⛓️ feat(rust): port stack note to native Rust #1515 [stack]]
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• depends-on=Mergifyio/mergify-cli#1517 [⛓️ feat(rust): port stack drop to native Rust #1517 [stack]]
• depends-on=Mergifyio/mergify-cli#1518 [⛓️ feat(rust): port stack fixup to native Rust #1518 [stack]]
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• depends-on=Mergifyio/mergify-cli#1516 [⛓️ feat(rust): port stack edit + add rebase-todo machinery #1516 [stack]]
• depends-on=Mergifyio/mergify-cli#1517 [⛓️ feat(rust): port stack drop to native Rust #1517 [stack]]
• depends-on=Mergifyio/mergify-cli#1518 [⛓️ feat(rust): port stack fixup to native Rust #1518 [stack]]
• depends-on=Mergifyio/mergify-cli#1519 [⛓️ feat(rust): port stack reword to native Rust #1519 [stack]]

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[jd]

Revision history

#	Type	Changes	Reason	Date
1	initial	0b09239		2026-06-03 21:01 UTC
2	rebase	0b09239 → 3e2b895 (rebase only)		2026-06-03 21:01 UTC