3. 保存提案，探索另一条分支¶
workspace checkpoint 保存文件提案与冲突 preimage。它适合重构方案、人工审查和并行尝试。fork 启动新命令，不会继续旧进程的内存；完整 VM 恢复在第五章另行说明。
S-USE-009：重复请求只保存一次¶
自动化调用方可能重试请求。固定 --request-id，再用 list/show 查同一个保存点。
语义：相同请求返回同一 checkpoint，第二次 reused=true，list 只有一条。
违反示例：重试产生重复 checkpoint 或不同 ID。
journey_setup
pvisor run --stage "$CASE_ROOT/source" -- /bin/sh -c 'printf proposal > report.txt'
pvisor checkpoint create "$CASE_ROOT/source" --request-id before-refactor --json > "$CASE_ROOT/first.json"
pvisor checkpoint create "$CASE_ROOT/source" --request-id before-refactor --json > "$CASE_ROOT/retry.json"
checkpoint=$(journey_json "$CASE_ROOT/first.json" /checkpoint_id)
json_expect "$CASE_ROOT/retry.json" /checkpoint_id "\"$checkpoint\""
json_expect "$CASE_ROOT/retry.json" /reused true
pvisor checkpoint list "$CASE_ROOT/source" --json > "$CASE_ROOT/list.json"
json_expect "$CASE_ROOT/list.json" /checkpoints/0/checkpoint_id "\"$checkpoint\""
json_length "$CASE_ROOT/list.json" /checkpoints 1
pvisor checkpoint show "$CASE_ROOT/source" "$checkpoint" --json > "$CASE_ROOT/show.json"
json_expect "$CASE_ROOT/show.json" /branch_references 0
S-USE-010：接受文件后仍能审查保存点¶
对当前提案做决定之前保存 checkpoint，接受后仍可以审查原提案。
语义：apply 后当前改动为空；checkpoint review 仍列出 report.txt，已全部 apply 的 Job 拒绝 drop，checkpoint 保持。
违反示例：apply/drop 改写不可变保存点。
journey_setup
pvisor run --stage "$CASE_ROOT/source" -- /bin/sh -c 'printf proposal > report.txt'
pvisor checkpoint create "$CASE_ROOT/source" --json > "$CASE_ROOT/checkpoint.json"
checkpoint=$(journey_json "$CASE_ROOT/checkpoint.json" /checkpoint_id)
pvisor apply "$CASE_ROOT/source" --all
assert_content report.txt proposal
pvisor review "$CASE_ROOT/source" --json > "$CASE_ROOT/current.json"
json_paths "$CASE_ROOT/current.json"
pvisor review "$CASE_ROOT/source" --checkpoint "$checkpoint" --json > "$CASE_ROOT/saved.json"
json_paths "$CASE_ROOT/saved.json" report.txt
expect_refused pvisor drop "$CASE_ROOT/source"
assert_content report.txt proposal
pvisor checkpoint show "$CASE_ROOT/source" "$checkpoint" --json > "$CASE_ROOT/show.json"
S-USE-011：从同一提案启动两个分支¶
比较两种实现方案时，从相同 checkpoint 启动两次 fork。源提案和每个子 Job 都各自保留。
语义：两个分支都读到 seed，分别写成 branch-a/branch-b，源仍为 seed，宿主仍无 report.txt；删除被引用 checkpoint 明确失败。
违反示例：分支互相污染、修改源提案或删除仍被引用的保存点。
journey_setup
pvisor run --stage "$CASE_ROOT/source" -- /bin/sh -c 'printf seed > report.txt'
pvisor checkpoint create "$CASE_ROOT/source" --json > "$CASE_ROOT/checkpoint.json"
checkpoint=$(journey_json "$CASE_ROOT/checkpoint.json" /checkpoint_id)
pvisor fork "$CASE_ROOT/source" --checkpoint "$checkpoint" --stage "$CASE_ROOT/branch-a" -- /bin/sh -c 'test "$(cat report.txt)" = seed; printf branch-a > report.txt'
pvisor fork "$CASE_ROOT/source" --checkpoint "$checkpoint" --stage "$CASE_ROOT/branch-b" -- /bin/sh -c 'test "$(cat report.txt)" = seed; printf branch-b > report.txt'
for branch in source branch-a branch-b; do
pvisor inspect "$CASE_ROOT/$branch" -- /bin/cat report.txt > "$CASE_ROOT/$branch.txt"
done
assert_content "$CASE_ROOT/source.txt" seed
assert_content "$CASE_ROOT/branch-a.txt" branch-a
assert_content "$CASE_ROOT/branch-b.txt" branch-b
assert_absent report.txt
pvisor checkpoint show "$CASE_ROOT/source" "$checkpoint" --json > "$CASE_ROOT/show.json"
json_expect "$CASE_ROOT/show.json" /branch_references 2
expect_refused pvisor checkpoint delete "$CASE_ROOT/source" "$checkpoint"