I've read all seven source-relevant files (`Core.hs`, `Properties.hs`, `ContractChecks.hs`, `Main.hs`, `Makefile`, `README.md`) plus confirmed the directory listing. Here is my round-2 review.

## Recompilation (mental, `-Wall -Wextra -Werror -O0`)

- **Imports**: `Data.Maybe (isNothing)` used in `Core`; `Core`, `Properties (validProgram)`, `System.Exit (exitFailure, exitSuccess)` all consumed. No unused-import warnings.
- **Top-level signatures**: every top-level binding in all four modules is signed. Every non-exported helper in `Properties.hs` (`assemblyArrows`, all `replace*`, all `bad*`/`*Program`, `onlyError`, `arrowPairsOf`) and `ContractChecks.hs` (`canonicalPairs`, `orientedCharge`, `twistedCharge`, `establishedEquivalence`) is reachable from an exported value — no `-Wunused-top-binds`.
- **Totality**: no partial functions (`head`/`fromJust`/incomplete matches). The only `case` — `thomDegree charge` at `Core.hs:189` — covers both `Nothing`/`Just`. `zip`/`drop` in `adjacentPairs` are total.
- **Defaulting/shadowing**: numeric literals are pinned to `Int` record fields (no `-Wtype-defaults`); the `\arrow ->` lambda and `arrow <-` generators are sibling scopes, no shadowing.
- Compiles clean; `make test` runs all 20 checks and exits on `and results`.

## Round-1 items — verified fixed

1. **Duplicate arrows** — `validateProgram` now does an exact ordered comparison `arrowPairs /= expectedPairs` (`Core.hs:132-135`). A duplicate lengthens the list → `ArrowListMismatch`. Isolated test at `Properties.hs:265-270` asserts exactly `[ArrowListMismatch …]` via `onlyError`.
2. **Isolated negative arrow tests** — all four are present and each isolates a single defect while keeping the arrow pair-sequence otherwise correct so the intended rule is the sole error:
   - missing → `Properties.hs:259-264`
   - duplicate → `265-270`
   - providerless (`missingProviderProgram` keeps correct pairs, `Nothing` provider) → `271-279`
   - established (`establishedArrowProgram` keeps correct pairs, `Established` status) → `280-288`

   I traced each: `missingProviderProgram`/`establishedArrowProgram` reproduce `expectedPairs` exactly, so `ArrowMissingProvider`/`EstablishedAssemblyArrow` are the only errors — `onlyError` holds.
3. **Comparison & relative-charge rules isolated** — `validateComparison` / `validateRelativeCharge` are separate exported functions; `onlyError` tests confirm exact single-error output for `EquivalenceMissingTheorem`, `EquivalenceHasUnsupportedStatus`, `RelativeDegreeMismatch 3 2`, `ThomDegreeMismatch 2 99`, `NegativeCodimension (-1)`. Note the deliberate `thomDegree` adjustments in `badDegreeCharge` (`Just 1`) and `negativeCodimensionCharge` (`Nothing`) correctly prevent a second spurious `ThomDegreeMismatch`, which is what makes `onlyError` valid.
4. **Naming honesty** — `Proofs` → `ContractChecks`; module header and README (`README.md:15-17`) explicitly state these verify a finite data contract, not the analytic/homotopical statements. No stale `Proofs.hs` remains.
5. **Orientation semantics** — `Core.hs:190-191` comment plus `README.md:12-13` document that orientation is checked only when a `Thom` target is asserted (`Just`); `twistedCharge`/`orientedCharge` in `ContractChecks.hs:23-41` exercise both oriented and twisted acceptance paths.

## Remaining observations (non-blocking)

- **Assertion strength is uneven, but each case is still isolated.** `Properties.hs:242-248` (orientation), `249-255` (physical charge), and `256-258` (dimension) use `not (isValid …)` rather than `onlyError`, unlike the arrow/comparison/degree tests. Because each target program carries exactly one defect, the rule under test is still isolated; `onlyError` would additionally guard against a future spurious second error. The task's explicit requirement (isolated expected-error tests for the four *arrow* cases) is met, so this is a strengthening opportunity, not a defect.
- **`Properties`/`PropertyCheck` naming** (`Properties.hs:1-13`) — these are fixed-input example assertions, not property-based tests. This does not overstate the way "Proofs" did (the README is careful about scope), so I don't consider it actionable, but flagging for awareness given round 1's naming concern.

No correctness, type-safety, totality, or scope-honesty regressions found. The four required negative tests are exact (`onlyError`), the arrow comparison is order-exact, and scope claims match the code.

VERDICT: PASS