fleet_release_bins wet witness: clear the runner's credential env; pin the temp root

[gunbai-bot]

Part of the wet-witness host-premise census (docs/plans/wet-witness-host-premise-census.md, #12652), the latent batch deep-ferret-305 chose.

test.claim.long.fleet_release_bins_key_witness fixture_env depended on two things about the runner. First, that it exports no credential-shaped variable (release_bins_credential_pattern). Second, that no ancestor of mktemp -d (which follows TMPDIR) holds .cargo/config*. If either failed, release_bins_environment_statements refused with CredentialInBuildEnvironment, or release_bins_ancestor_statements refused with AncestorCargoConfigPresent, and the positive claims went red.

The fixture now:

• unsets every name matching release_bins_credential_pattern, the same authority the guard reads;
• creates its temp root at /tmp/gunbc_release_bins.XXXXXX.

The RED claims export a credential or plant an ancestor config after the fixture runs, so they still discriminate.

Local wet receipt: claim_batch --wet --source-root dag --source-root src/v2 --entry dag/test/claim/long/fleet_release_bins_key_witness_test.dag --functions <all 26>, uid 1000, with a hostile runner environment: CARGO_REGISTRY_TOKEN=runner-leak and TMPDIR=<dir>/t, where <dir>/.cargo/config.toml exists.

• this head 58969ecec589a4ad2ce4b7a83b50a590d274991a (the working tree, committed unchanged): exit 0, 26/26 PASS.
• control: main at 584c07d in the same environment: exit 1, 5 FAIL: release_bins_unchanged_inputs_key_equally, release_bins_release_opt_level_override_changes_the_key, release_bins_multiline_rustflags_keys_apart_from_its_first_line, release_bins_RED_compiler_override_refuses, release_bins_RED_ancestor_cargo_config_refuses. The two REDs fail because the credential refusal fires ahead of the refusal each one expects.

🤖 Generated with Claude Code

[gunbai-bot]

Addressed review 73025 in 96ce6d4a8b2d0fa785a078c48c52afd65cbdf5ae. The eval of a concatenated loop is gone. The step is now unset $(env | grep -oE <release_bins_credential_pattern> | cut -d= -f1), built entirely from grammar nodes: cmd/cmdl/lit, bash_build_pipe twice, and bash_build_word_cmdsubst. The command substitution emits unquoted (bash_word_cmdsubst_source_text), so its output word-splits into the names and no loop is needed. The pattern is still the single gunbc.fleet_release_bins_key authority, and the grep is spelled the same way release_bins_environment_statements spells its own.

Local wet receipt at 96ce6d4a8b2d0fa785a078c48c52afd65cbdf5ae (working tree committed unchanged): same command and same hostile environment as the PR body (CARGO_REGISTRY_TOKEN=runner-leak, TMPDIR under a .cargo/config.toml), exit 0, 26/26 PASS. The run was on 8c710f4 plus this change, which is exactly this head.

— sent from neat-moth-20