SCRIP-COMPARE-004: reader-side local-only comparison with Python contract parity #280

User outcome

Provide a working browser-based local JSON comparison reachable from the canonical Reader without uploads, using the same versioned contract as #279. Do not fork a second incompatible analyzer.

Reusable pending artifacts

Scriptorium-Reader-Private-Browser-Compare-20261021.zip, Scriptorium-Browser-Number-Fidelity-20261021.zip, Scriptorium-Reader-Consolidated-RC-20261021.zip, Scriptorium-Private-Browser-Comparison-20261018.zip. These are local handoffs; prior local test counts are not canonical CI.

Acceptance

• Explicit upload controls for two local Reader JSON files; no remote network requests/telemetry or source prose retention; imports remain in-page.
• Reject oversized, duplicate-key, non-finite, impossible-count and algorithm/unit/status-tampered JSON, including lexical 3.0/3e0 on integer counters when canonical Python requires exact integers.
• Exact table with 29 metric IDs, readable labels, units and missing/incomparable states; accessible keyboard/focus/mobile flows and defensible errors/empty states.
• JSON/CSV export with formula-neutralized untrusted text; 234-case differential fixture re-run against installed Python CLI and explicit cross-runtime equality.
• Build actual Reader and test with real Analyzer-produced JSON; browser visual screenshots if permitted, else explicit VISUAL_NOT_VERIFIED. Depends on SCRIP-COMPARE-003: integrate strict private report comparison in installed Python CLI #279's canonical contract rather than duplicating it.

Reconciled local browser handoff — 2026-10-23

The existing branch scrip-compare-004-browser currently has no browser-comparator implementation: it matches the 3-commit Reader 0.4 content of PR #288. Do not treat the branch name as delivery evidence.

Local handoff: Scriptorium_Browser_Compare_Decimal_Parity_Fix_20261022.zip (SHA-256 472bb4f7f9f3724820e5ec2b1f55c13b81d4310097856ccde13378db9a662297), incorporating the earlier async race and strict numeric-lexeme fixes. Previous local JS checks reported 24/24 PASS; these are not canonical installed-Reader contract parity or 234-case differential acceptance. Revalidate all files against the current 29-metric Python contract and current head before integration.

Still required: reject lexical integer spoofs and invalid metrics, verify exact cross-runtime exports on real Analyzer-produced JSON with installed Reader, real desktop/mobile/keyboard flow, no network/cookies, canonical site build and CI. Direct browser route remains VISUAL_NOT_VERIFIED. Do not close #280 on preview-only evidence; FantLab M2 stays 0/5.