explicate-feature-flag

name	explicate-feature-flag
description	Use when a proof/module verifies in baseline mode but reproving under a prover-affecting feature flag fails. Add explicit proof detail based on the working baseline proof until `cargo run --features <feature> -- verify ...` succeeds.

This is the feature-flag version of explicate.

Use it when:

• default/baseline reproving works
• a feature flag changes prover behavior
• feature-mode reproving fails or times out
• the right response is to add explicit proof steps to acornlib source, not to debug prover internals yet

This skill is for the acorn repo. Use cargo run, not the installed acorn binary. Edit proofs only in the sibling library repo at ../acornlib/src. Do not edit the bundled copy under vscode/extension/acornlib.

Scope

The goal is:

• baseline proof remains valid
• feature-mode reproving succeeds

The non-goal is:

• proving that feature+validate is fast

During the edit loop, do not use validate. Use feature-only reproving for speed. Add only one proof line per iteration. Only explicate at the location where the feature-flag prover is having trouble. Do not inline a large proof body. The point is to make the local proof easier for the flagged prover to rediscover, not to copy an entire theorem proof into the file.

Prerequisite

First confirm the baseline module is actually good:

cargo run --profile release -- verify MODULENAME --ignore-hash --read-only --fail-fast

If baseline fails, this is not an explication task.

Then confirm the feature-mode failure:

cargo run --profile release --features FEATURE -- verify MODULENAME --ignore-hash --read-only --fail-fast

If feature mode panics or crashes, stop. That is a prover/feature bug, not an explication task.

Explicating One Module

Find the first failing line in feature mode:

cargo run --profile release --features FEATURE -- verify MODULENAME --ignore-hash --read-only --fail-fast

If this succeeds, the module is done.

If it fails, note the failing line and move to line-level proof inspection.

Explicating One Line

Inspect the working baseline proof, not the failing feature-mode proof:

cargo run --profile release -- select MODULENAME LINENUMBER

If select is too compressed, use:

cargo run --profile release -- verify MODULENAME:LINENUMBER --ignore-hash --read-only --print-proof

Use baseline proof steps whose reasons are:

• definitions
• theorems
• boolean reduction
• simplification

Add those statements to ../acornlib/src/...:

• before the target line, or
• at the end of the target line’s by block, if it has one

Do not delete statements. Only add detail. Add a single line at a time. After you add one line, test immediately before adding another.

Iteration Loop

After each edit:

1. Check the module in baseline mode, without --read-only:

cargo run --profile release -- verify MODULENAME --ignore-hash --fail-fast

2. Then check the module in feature mode:

cargo run --profile release --features FEATURE -- verify MODULENAME --ignore-hash --read-only --fail-fast

If baseline fails, the explication is wrong. Fix the proof shape first.

If feature mode still fails, use the new failure location to decide where the next single line goes:

• if the failing point is still the same target, add the next line immediately around that target
• if the failure moves earlier, the next added line should go before the previous insertion point
• if the failure moves later, the next added line should go after the previous insertion point

If feature mode now fails on a later line, move to that new line.

Writing Cache

During this skill, every edit should be followed by baseline verify without --read-only. That is the normal workflow, not a special case.

Stopping Conditions

Keep explicating as long as the baseline proof still contains harvestable proof steps.

Only stop and report a feature bug when both are true:

1. the baseline version of the target line has been fully explicated, meaning select/--print-proof no longer gives you any useful proof steps to harvest for that line, and
2. feature-mode reproving of that same line still fails

In practice, "fully explicated" usually means the baseline target is trivial or nearly trivial and there are no remaining definition/theorem/boolean-reduction/simplification steps worth materializing.

Also stop and report a feature bug if:

• feature-mode verify panics
• the proof only fails under validate, while plain feature-mode reproving succeeds

That last case is not an explication target. It is a performance/debugging issue in validation mode.

Final Check

When the module seems fixed, rerun:

cargo run --profile release --features FEATURE -- verify MODULENAME --ignore-hash --read-only --fail-fast

If it succeeds, the explication work for that module is done.