Floor host: read the unimported-bare-provider base roster as the coproduct it is (latent #12205 defect)

[gunbai-bot]

A latent host defect from #12205, split out of #12208 (gentle-koi-724's ruling) because it also blocks #12210 and #12272, while #12208 waits on #12202.

Root cause

v1_compiler::cli_run::required_floor_runner unimported_bare_provider_roster_source_at_base reads the debt roster as it stood at the diff base, through the .dag function v2.workflow.floor_unimported_bare_provider_debt unimported_bare_provider_roster_at_base. That function returns UnimportedBareProviderBaseRoster, a coproduct: BaseRosterShown { source } | BaseRosterUnreadable { stderr }. So the interpreter hands back a Value::Variant. The host destructured a Value::Record, which no arm of the declaration can produce.

The path runs only when a diff edits the roster, so it stayed latent until the first roster-editing change (#12208 retiring three ImportsFixed rows). That change's floor refused with:

REQUIRED-FLOOR REFUSAL cause=ChangedWitnessObservationFailed unimported_bare_provider_roster_at_base returned Variant(Symbol("BaseRosterShown")), expected UnimportedBareProviderBaseRoster

Fix

The decode is now decode_unimported_bare_provider_base_roster, which matches the Variant by arm name, the same way this runner already decodes OpaqueHostCallSurface:

• BaseRosterShown { source } returns the base roster's source.
• BaseRosterUnreadable { stderr } refuses located: REQUIRED-FLOOR REFUSAL cause=UnimportedBareProviderBaseRosterUnreadable base=… path=… stderr=…. It never reads as an empty roster and never passes.
• Any other arm, a missing field, or a non-Variant refuses and names what it got.

Executing control

Main has no roster-editing diff to exercise this path, so this PR adds a host test: pure_producer_share_tests::unimported_bare_provider_base_roster_reads_both_arms_of_the_coproduct. It drives the real reader (the .dag call plus the real git show):

• HEAD takes the Shown arm and returns the roster's own source.
• A nonexistent base ref takes the Unreadable arm and refuses with the located cause, base and path.
• A hand-built Value::Record (the old demanded shape) is refused, not decoded.

Measured on BuildBuddy (cargo test --release -p v1-compiler --lib, with GUNBC_MEMORY_BUDGET_BYTES set):

• At the fix: 1 passed.
• Mutant (the BaseRosterShown arm misnamed, so Shown falls to the refusal arm): FAILED at the Shown expectation. The control discriminates.

CI does not run cargo test (declared drop rust_unit_tests_off_the_merge_path), so this is local/remote diligence plus clippy compiling the test target. The end-to-end positive is the first roster-editing floor run, which is #12208 after this lands.

After this lands

#12208 drops its own copy of this change (it carried the same fix at d990cde) when it next merges main.

🤖 Generated with Claude Code

[gunbai-bot]

Closing as a duplicate of #12278 (swift-owl-708, opened earlier and already green). It fixes the same latent #12205 defect: the base-roster read destructured a Record where the .dag coproduct yields a Variant. It also carries its own host test. gentle-koi-724 asked me to split this out before either of us saw #12278. #12208 will drop its copy of the fix once #12278 lands.

For the record, this PR's control (unimported_bare_provider_base_roster_reads_both_arms_of_the_coproduct) drives the real reader: HEAD → Shown; a nonexistent base → located Unreadable refusal; a Record → refused. It passed at the fix, and a misnamed-arm mutant reddened it. If #12278's test doesn't already cover the Unreadable arm through the real git show, that case is worth adding there.

— sent from lively-koi-275