also retain their CLI contracts. A broken installed extension is reported as

an import error; only an absent top-level `gix` selects CLI mode.

Native repository reuse remains future work. The fixture optimizations below

are implemented as separate commits, each validated with GixPython before CLI.

The original local measurements use official GixPython 0.1.0 and existing

CPython 3.12.14 on macOS arm64 at `89c609cf92335e75652d7725682e215a9ea080e5`.

The full suite with coverage took 757.85 seconds wall-clock (757.04 seconds

reported by pytest): 1,649 tests and 38 subtests passed, 79 skipped, and one

explicit ownership, `close()` behavior, thread semantics, and invalidation for

CLI/native mutations, configuration changes, and environment overrides.

Preserve the current safety checks and diagnostics. Establish those contracts

before replacing the current fresh-open policy.

A 19-case submodule rejection sample without coverage took 15.62 seconds:

1,258 `Git.execute()` calls accounted for 11.86 seconds, while 1,995 native

repository-open/validation attempts accounted for 0.84 seconds. Most work was

fixture setup. This sample supports prioritizing repeated setup subprocesses;

it is not a profile of the entire suite.

The original collection found 1,729 parameterized cases from 703 distinct source bodies.

Source inspection identified the following conservative set of 422 cases whose

assertions do not require changing repository state after preparation. The

remaining cases have not been exhaustively classified; these are reuse

candidates, not proof that a shared fixture is safe in every execution order.

| Original cases | Repeated setup | Implemented change |

| --- | --- | --- |

| 166 | `TExc` (157) and `TestActor` (9) inherit repository-building `TestBase`. | Use the existing `TestCase` base without repository setup. |

| 182 | Three submodule rejection bodies repeatedly build `movable_submodule`, then check snapshots for no mutation. | Prepare logical-name baselines once and copy the parent per case, retaining fresh wrappers and independent writable files. |

| 51 | Six submodule rejection bodies prepare nested metadata, separate metadata, intermediate/leaf symlinks, or retained metadata before checking rejection. | Cache ten prepared layouts and restore complete copies at their original paths, preserving absolute Git links and symlinks. Cleanup removes the active copy even after failure. |

| 15 | Eight revision-query bodies rebuild the same four-commit graph, refs, index, and reflogs through `rev_parse_repo`. | Prepare the graph once and copy it for every consumer, including mutating cases; recreate repository, branch and commit wrappers. |

| 8 | Tree lookup bodies clone and check out `0.3.2.1` through `with_rw_repo`. | Read the historical tree directly through the existing class repository, removing clones and checkouts. |

The `movable_submodule` baseline also serves mutating cases: all writable

refs, index, config, objects, worktree and module metadata are filesystem copies,

while the local clone source remains shared and immutable. The original 322

consumers no longer repeat repository initialization and submodule cloning.

The original 68 `local_submodule` cases copy both source and parent from one

prepared two-commit layout because these tests also mutate the source. The

fixture relocates all source URLs and records the private URL in parent history

for `RootModule` comparisons. No mutable Git metadata is hard-linked.

Historical dependency sources are now lazy session fixtures. Originally all

25 `TestBase` classes reconstructed both sources (50 builds), although only four

classes called the URL helpers. The suite now prepares each needed source once,

with consuming tests retaining independent writable clones.

Four additional checks exercise isolation: edits and refs in movable copies,

restoration after deliberate mutation with an absolute symlink, private source

commits, and revision-graph changes. Existing security no-side-effect snapshots

remain in place. Native repository ownership, invalidation and thread semantics

remain deferred as described above.

Per-change affected tests on existing CPython 3.12.14/macOS arm64 with official

GixPython 0.1.0, without coverage (wall-clock seconds including runner setup):

| Change | Passed cases | GixPython first | CLI second |

| --- | --- | --- | --- |

| Repository-free actor/exception tests | 166 | 0.47 s | 0.49 s |

| Lazy historical sources, all consumers | 206, plus 14 subtests; 6 skipped, 1 xfailed | 90.89 s | 160.82 s |

| Movable baseline, top-level submodule tests | 333 | 88.63 s | 178.75 s |

| Prepared rejection variants | 51 | 12.34 s | 26.23 s |

| Layout restoration check | 1 | 1.33 s | 1.62 s |

| Prepared revision graph | 23 | 4.39 s | 7.57 s |

| Historical tree lookups, whole tree module | 22 | 1.66 s | 3.86 s |

| Prepared no-fetch source and parent | 69 | 56.27 s | 117.52 s |

These selections overlap, and their timings are validation records rather than

isolated before/after benchmarks. The full-suite measurements below provide the

broader comparison. Only the existing interpreter was used.

At `c8ee26c7da373e28cc7ede17ef2eaadd763fcdfc`, the full GixPython suite

with coverage passed in **404.61 seconds wall-clock (6m45s)**, with pytest

reporting 404.12 seconds: 1,653 passed, 79 skipped, one expected failure,

and 38 subtests passed. Coverage remains 90%. Compared with the original

757.85-second run, this saved 353.24 seconds (46.6%, about 1.87 times faster).

This is one local before/after run per revision, not a statistical benchmark.

The same operation counters now record 102,581 native operations and 21,402

CLI fallback decisions, down from 114,800 and 39,002 respectively. Raw Git

calls and child processes remain outside those counters.

The subsequent full CLI run with coverage passed in **755.78 seconds

wall-clock (12m36s)**, with pytest reporting 755.30 seconds: 1,617 passed,

80 skipped, one expected failure, and 38 subtests passed. CLI coverage is 82%;

backend-specific tests account for different collection and coverage. This CLI

run validates the optimized suite; there is no matching pre-change CLI full-run

measurement here. Repository-wide Ruff lint/format, mypy and pyright passed.