Hosted rollback, remove and the vendored takeover refuse a requirements.txt whose only requirements are hosted pins (six==1.16.0 alone can be patched but never unpatched) #410

[agent] Found by the scheduled pip / requirements.txt bug-hunt routine (ledger #309).

Summary

v5 hosted rollback, remove and the hosted → vendored takeover (scan --mode vendored over a hosted pin) all refuse a requirements.txt when every requirement line in it is a hosted pin. The simplest project shape, a single six==1.16.0 line, can be patched by socket-patch scan but can't be un-patched or vendored afterwards.

The refusal comes from the upstream restore. It tries to infer pip's hash-checking mode from the other requirement lines, and when there are none it gives up:

cannot restore pkg:pypi/[email protected] to its upstream registry entry: every requirement in requirements.txt is a hosted pin, so whether the original used pip's hash-checking mode (`--hash`) is not derivable; restore it from version control instead (`git checkout -- requirements.txt`)

The same refusal fires when the only other lines are options or editables. For example, -e . plus a pin is refused, even though -e lines are incompatible with hash-checking mode, so the original must have been unhashed.

Impact

• socket-patch rollback and socket-patch remove <purl> exit 1 (partial_failure / hosted_revert_failed) on single-dependency projects, on projects where every pin is patched, and on -e . + pin projects.
• socket-patch scan --mode vendored on such a hosted project can't take over: Vendored 0 packages; 1 failed., exit 1, and the project stays hosted. The documented mode-takeover path (CLI_CONTRACT.md, "Takeover reconciliation (every hosted ecosystem, v5.0)") is unusable for these projects.
• v5 keeps no hosted ledger, so the CLI can't undo the rewrite at all. The only remedy is version control.

Repro

Uses a local mock of the patch API that serves a patched six-1.16.0 wheel. It's the same shape as tests/vex_pypi_real_common::RealApi: POST /v0/orgs/test-org/patches/batch, /patches/package grant, /patches/view/<uuid>, and the wheel route. Linux, pip 24.0, CPython 3.11, main 2463257.

A="--api-url http://127.0.0.1:8765 --api-token fake --org test-org --patch-server-url http://127.0.0.1:8765"
mkdir p && cd p && printf 'six==1.16.0\n' > requirements.txt
socket-patch scan $A                      # Switched 1 package to hosted patches; rewrote 1 file.
socket-patch rollback --yes $A; echo $?   # Error: Cannot restore … not derivable …   → 1
socket-patch remove pkg:pypi/[email protected] --yes $A; echo $?   # same error → 1
socket-patch scan --mode vendored $A; echo $?               # Cannot vendor … not derivable … Vendored 0 packages; 1 failed. → 1

Variants I checked (scan, then rollback):

Expected vs actual

• Expected: CLI_CONTRACT.md, "Hosted unwind coverage", says every file wiring a pin is rewritten back to the default upstream entry. The pypi bullet lists what gets refused: pdm.lock without cross_platform, non-pure uv / pylock wheels, uv option filters, and uv 0.2 locks. An all-hosted requirements.txt isn't in that list. When no other requirement constrains the mode, either restored form, six==1.16.0 or six==1.16.0 --hash=… for every release file, installs with every pip, because there is no other line it could conflict with. A -e line also settles the mode as unhashed.
• Actual: the pin is refused in rollback, remove and the takeover.

OS × version

The refusal is decided before any pip runs, so it doesn't depend on the pip version.

First bad

The code is new in 2463257 (#277), which replaced v4's ledger replay with the upstream restore. I didn't get a clean comparison: on v4.0.0, rollback of the same hosted project stopped at Manifest not found even though .socket/vendor/redirect-state.json existed.

Suspect code

• crates/socket-patch-core/src/patch/redirect/upstream/pypi.rs:597-603: the (false, false) arm of hash_mode. --prefixed lines, -e included, are skipped before the mode tally (if code.starts_with('-') { continue; }).
• Related: Hosted and vendored requirements.txt rewrites add a --hash to one line, which turns on pip's hash-checking mode and breaks pip install -r for every other unhashed line #376. The hosted writer always emits --hash, so the line itself never records the original mode. Once Hosted and vendored requirements.txt rewrites add a --hash to one line, which turns on pip's hash-checking mode and breaks pip install -r for every other unhashed line #376 / Fix requirements.txt writers ignoring pip hash mode (#376) #383 switch unhashed files to a #sha256= fragment, the hosted line's own shape (--hash vs fragment) would say which mode to restore.

Probe run: https://github.com/SocketDev/socket-patch/actions/runs/36806309982