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Fold-Engine Code Quality — Stakeholder Scorecard

What this is. An independent quality read of the recent fold / oracle-equivalence scripts (scripts/erp_engine.js, scripts/post_resolver.js, and the poc_fold_* / poc_* witness suite) that back the “ERP folded into a browser” claims in MigrateComparisonPaper.md. It is written for reviewers and stakeholders who want to judge how well the code is built, not just that it runs.

Snapshot: branch feat/erp-substrate-phase012, 2026-06-10. Every figure below is measured from the source and from a live run — nothing here is asserted without a witness.

1 · Executive scorecard

QUALITY DIMENSION              SCORE   ████████████████████  (0────10)
─────────────────────────────────────────────────────────────────────
Separation of concerns          9.5   ███████████████████░
Determinism / reproducibility  10.0   ████████████████████
Non-invention (traceability)   10.0   ████████████████████
Falsifiability (negative tests) 9.5   ███████████████████░
Oracle equivalence (vs real)    9.0   ██████████████████░░
Spec ↔ code ↔ witness tracing   9.5   ███████████████████░
DRY / fold-not-fork reuse       9.0   ██████████████████░░
Readability / maintainability   6.5   █████████████░░░░░░░
Robustness to data gaps         7.0   ██████████████░░░░░░
─────────────────────────────────────────────────────────────────────
OVERALL                         8.8   █████████████████░░░   STRONG

One-line verdict: Research-grade, evidence-first code with unusually high proof discipline. The design (a pure engine + host-injected data + adversarial witnesses diffed to a real iDempiere ledger) is excellent. The two soft spots are readability (very dense one-liners) and robustness (a hard dependency on one captured database; the resolver still throws rather than degrades when a column is genuinely absent — though the one case where that bit, poc_matchinv, is now closed by re-capturing the fixture, so the risk is latent rather than active).

2 · The architecture being judged

flowchart TB
    DB[("glassbowl_data.db — real GardenWorld rows, client 11")]

    subgraph PURE["1 · erp_engine.js — PURE core: no DB, no clock, no DOM"]
        direction LR
        G["evalGuard<br/>predicate rules"]
        M["match<br/>generic Detail-join-Detail<br/>3-way · alloc · costing"]
        B["buildDoc<br/>archetype create-verb<br/>shipment · invoice · PO"]
        X["explodeBOM<br/>recursive backflush"]
        Q["qtyOnHand + movementSign<br/>inventory spine"]
        C["completeOrder / completeInvoice<br/>doc-action"]
    end

    subgraph GLUE["2 · post_resolver.js — HOST GLUE"]
        direction LR
        R["resolve token to real account — reads ONLY real AD acct-config columns, never invents"]
    end

    subgraph WIT["3 · poc scripts — WITNESSES via better-sqlite3"]
        direction LR
        D["derive<br/>fold the source rows"]
        O["oracle<br/>read real fact_acct"]
        F["FALSIFIER<br/>corrupt input →<br/>diff must blow up"]
    end

    V{{"VERDICT — oracle-equivalent or fail"}}

    DB -->|"master rows"| GLUE
    DB -->|"source + oracle rows"| WIT
    PURE -->|"ops[ ]"| WIT
    GLUE -->|"account ids"| WIT
    D -->|"maxDiff in integer cents"| O
    O -->|"equal to 0c ?"| V
    F --> V

Every numbered box is real code (branch feat/erp-substrate-phase012) — links per box below (the Mermaid boxes themselves aren't clickable under Material's strict render, so the source links live here):

The iDempiere originals each verb folds (upstream release-12) — completeOrder/completeInvoice ← MOrder / MInvoice.completeIt() · buildDoc ← MInOut + MMovement · match ← MMatchInv + MAllocationHdr · explodeBOM ← MPPProductBOM · qtyOnHand ← MStorageOnHand + MTransaction · evalGuard ← MValRule · posting/oracle ← Doc_Invoice · Doc_InOut · Doc_Payment · Doc_AllocationHdr. These are the classes the fold replaces — the engine reproduces their posted output (fact_acct) to the cent, not their code.

Why this shape is good. The logic that would have been spread across hundreds of Java MDocument subclasses is collected into one pure module (erp_engine.js, 274 LOC). It imports no database — the host injects a query(sql)→rows / bomOf(id)→lines function — so the identical core runs under sql.js in a browser and better-sqlite3 in a Node witness. The witnesses are the proof harness: each derives a result by folding real source rows, then diffs it against the real iDempiere General Ledger (fact_acct) to the integer cent.

3 · Per-script scoreboard

Run live on 2026-06-10 (node scripts/<file>.js). “Falsifiers” = embedded negative tests that must make the diff blow up when an input is corrupted. “Cents” = uses integer-cent / integer-unit math (no float drift).

Script LOC Role Falsifiers Int-cents Live result
erp_engine.js 274 Pure engine (shared core) — n/a library — exercised by all below
post_resolver.js 98 Host glue: token→real account — n/a library
poc_fold_complete.js 181 Keystone — completeIt(C_Order) full chain 1 ✅ 🟢 PASS
poc_money_post.js 94 Doc_Payment receipt posting ✅ ✅ 🟢 PASS
poc_backflush.js 102 Recursive BOM backflush (AutoBOMOrder) ✅ — 🟢 PASS
poc_alloc_post.js 182 Doc_AllocationHdr + VAT tax-correction ✅ ✅ 🟢 PASS
poc_qtyonhand.js 113 Inventory spine Σ sign×|qty| 2 ✅ 🟢 PASS
poc_replenish.js 148 Replenishment PO (rides qty spine) ✅ ✅ 🟢 PASS
poc_invoice_complete.js 146 Standalone completeIt(C_Invoice) ✅ ✅ 🟢 PASS
poc_invoice_post_ap.js 133 Vendor (purchase) invoice GL ✅ ✅ 🟢 PASS
poc_alloc_fx.js 169 Foreign-currency allocation ✅ ✅ 🟢 PASS
poc_movement.js 139 Inter-org M_Movement + intercompany ✅ ✅ 🟢 PASS
poc_movement_fx.js 143 M_Movement EUR schema-200000 (per-schema cost) 2 ✅ 🟢 PASS
poc_matchinv.js 147 M_MatchInv posting + avg-cost IPV split (18/18) 2 ✅ 🟢 PASS
poc_matchinv_fx.js 173 M_MatchInv EUR schema-200000 (per-leg FX, 18/18) 2 ✅ 🟢 PASS
poc_post_harden.js 138 Per-document GL derivation (H-1 keystone) ✅ ✅ 🟢 PASS
poc_reverse.js 204 reverseCorrect/void — oracle-anchored negation 2 ✅ 🟢 PASS
poc_gljournal.js 128 Manual GL_Journal + inter-org balancing 2 ✅ 🟢 PASS
poc_production.js 132 MProduction movement (rule-consistent †) 2 ✅ 🟢 PASS
poc_inventory.js 144 MInventory physical count (rule-consistent †) 2 ✅ 🟢 PASS

All 18 witnesses PASS green. Of these, 16 diff against the real iDempiere fact_acct to the cent (oracle-equivalent); poc_backflush is recipe-equivalent (engine vs. an independent path-enumeration — no production GL in the seed); † poc_production / poc_inventory are rule-consistent — they enact a document GardenWorld never posted (no seed oracle to diff), so they verify against the ALREADY-PROVEN qty/cost rules + a balance check + a falsifier (the same honest tier as backflush) and are explicitly not claimed == iDempiere. poc_reverse is oracle-anchored (the reversal negates a real posting and must net it to zero). The last formerly-in-progress fold, poc_matchinv, closed at commit 34dc5433 (18/18; see §6).

4 · What the code does right (the load-bearing strengths)

  1. Non-invention, enforced in code — not just intended. Every posted account is read from a real master column by post_resolver.resolve; an absent (master, acctschema) pair falls back to the schema default and, if still absent, is reported absent — never synthesized. This is the project's Prime Directive made executable.

  2. Determinism is total. No Date.now, no Math.random, no network, no DOM anywhere in the engine. Money and quantity are accumulated in integer cents / centi-units, so there is zero floating-point drift — the diffs are exact (maxDiff=0c), not “close enough.”

  3. Oracle equivalence, not self-agreement. The witnesses don't check that the engine agrees with itself; they diff the fold against the real iDempiere fact_acct General Ledger captured from GardenWorld (client 11). Where no GL exists (e.g. backflush — no production docs in seed), the author uses two independent implementations (engine vs. a separate DFS path-enumeration) and proves they agree — explicitly avoiding a tautology.

  4. Adversarial falsifiers. Almost every witness deliberately corrupts an input (drops a posting line, flips a movement polarity, flattens the BOM recursion) and asserts the diff must blow up. This proves the equality check is load-bearing, not a balance trick that would pass on garbage. This is rare discipline and the single most credibility-building feature of the suite.

  5. Fold-not-fork (genuine DRY). createShipment, createInvoice, and the replenishment PO are the same buildDoc archetype verb, table-parameterised — not three copies. The paper's “MOrder + ~25 deltas” thesis is literally visible in the code: new document types add a spec row, not a new function (the witnesses report newVerbs=0).

  6. Clean separation = portability. Because the engine takes an injected query, the exact same logic ships to the browser. This is the whole product claim, and the code structure honours it.

  7. Honesty about gaps is built into the output. Deferred work is named in the log (§FOLD-DEFERRED, §SOURCE-DEFERRED, AMT-DRIFT for post-posting edits) rather than hidden. A reviewer can trust the green because the author marks the not-green.

5 · Where it is weaker (the honest risks)

# Risk Evidence Suggested remedy
R1 Extreme line density hurts readability. Multi-clause ternaries and 200-char one-liners are the house style. Correct, but hard for a new reviewer to audit or safely modify. erp_engine.js:88–91 (nested comparator ternary); most maxDiff/agg helpers are single lines. Light reformatting of the hot paths; the dense logic is sound, only its presentation costs review time.
R2 Brittle to schema gaps (now latent). post_resolver issues SELECT <col> for a hard-coded column; if the captured DB lacks it, the script throws instead of degrading. poc_matchinv.js used to abort with no such column: p_averagecostvariance_acct; resolved at commit 34dc5433 by re-capturing the fixture with that column + adding the token — but the throw-not-degrade pattern remains for any future missing column. Guard token columns against PRAGMA table_info and report absent (the resolver already has an absent channel — wire missing columns into it).
R3 Single-fixture dependency. All equivalence rests on one captured glassbowl_data.db. Coverage gaps (no production docs, no cost details, drifted m_cost) are named but still limit breadth. §FOLD-DEFERRED / §SOURCE-DEFERRED notes across the suite. The extract_fact_acct.sh re-capture (already planned) widens the fixture; track which deltas it unblocks.
R4 No aggregate test runner. Each witness is standalone; there is no one command that runs all 16 and reports a roll-up, so a regression in one isn't surfaced suite-wide. 16 separate node scripts/poc_*.js invocations. A 10-line run_folds.sh that runs each, greps PASS/FAIL, and exits non-zero on any red.

None of these touch correctness of the green witnesses — they are maintainability and breadth concerns, which is the right category of risk for research-grade proof code.

6 · Recently closed — poc_matchinv.js (was the one in-progress stub)

Status: 🟢 18 / 18 oracle-equivalent (commit 34dc5433). Green — no longer a stub.

What it took: the M_MatchInv posting needed the average-cost-variance clearing account. Earlier (commit b4e678fb, 17/18) the captured fixture's m_product_category_acct did not carry p_averagecostvariance_acct, so post_resolver threw on the 18th case. The close (per prompts/HARDEN_MATRIX.md §H-2 / FOLD_MODEL_LOGIC.md §F-2) re-captured the fixture with that column (extract_fact_acct.sh), added the {Product.AverageCostVariance} resolver token, and implemented the avg-cost IPV split — when PO price ≠ invoice price, the variance splits between {Product.Asset} for qty still on hand at match time and {Product.AverageCostVariance} for the rest. 17 equal-price matches + 1 variance match (doc 100: IPV 100, 7 of 10 on hand → 70 asset / 30 variance), both §FALSIFIER and §FALSIFIER-IPV firing.

Kept as a worked record because it shows the methodology resolving its own honestly-named gap — the 17/18 stub became 18/18 by re-capturing real data and adding one declarative token, not by inventing the missing account.

7 · Methodology — how to reproduce this scorecard

# all 18 witnesses, from the repo root — every one exits 0:
for f in poc_fold_complete poc_money_post poc_backflush poc_alloc_post \
         poc_qtyonhand poc_replenish poc_invoice_complete poc_invoice_post_ap \
         poc_alloc_fx poc_movement poc_movement_fx poc_matchinv poc_matchinv_fx \
         poc_post_harden poc_reverse poc_gljournal poc_production poc_inventory; do
  node scripts/$f.js >/dev/null 2>&1 && echo "🟢 $f" || echo "🔴 $f"
done

Each script also tees a witness log under build/erp/poc_*.log; read the log, not the exit code alone (project Log Mandate). Falsifier lines are tagged §FALSIFIER and equivalence lines §FOLD-COMPLETE … maxDiff=…c.

Generated 2026-06-10 · branch feat/erp-substrate-phase012 · linked from the code-sample section of MigrateComparisonPaper.md.