docs: add master TODO index tracking all ecosystem work

Author: ronaldtse

TODO.MASTER.md

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+# ISC Migration — Master TODO Index
+
+## Status: 247/289 deep equivalent, 289/289 parseable, 100% transliteration parity
+
+This index tracks ALL remaining work across the interscript ecosystem.
+Each item links to its detailed TODO in the respective repo.
+
+---
+
+## P0 — Blocks adoption
+
+### [ISC Runtime Integration](rababa/00-isc-runtime-integration.md) ✅ DONE
+`NodeAdapter` bridges ISC document hash → `Interscript::Node::Document`.
+ISC files can now be used for actual transliteration.
+
+### [Commit .isc files to maps repo](rababa/01-commit-isc-to-maps-repo.md)
+289 .isc files generated but not committed to `interscript/maps`.
+
+### [E2E Tests for Website](https://github.com/interscript/interscript.org/blob/astro-migration/TODO.complete/01-e2e-tests.md) ✅ DONE
+27/27 Playwright tests passing. Full-map validation: 37/37.
+
+---
+
+## P1 — Ecosystem health
+
+### [Fix Deep Equivalence Diffs](rababa/02-fix-deep-equivalence-diffs.md)
+247/289 equivalent. 40 remain (codemod edge cases + description whitespace).
+Transliteration output is 100% identical — differences are metadata-only.
+
+### [Fix ISC Spec Failures](rababa/03-fix-isc-specs.md)
+73 specs written, ~50 pass. Remaining are syntax issues (system wrappers).
+
+### [TS ISC Parser](https://github.com/interscript/interscript-ts/blob/main/TODO.complete/01-isc-parser-typescript.md)
+Port ISC grammar to Peggy for direct .isc loading in browser/Node.
+
+### [Full Parity Fixtures](https://github.com/interscript/interscript-ts/blob/main/TODO.complete/02-generate-full-parity.md)
+Commit full-parity.json (7502 samples, 0 diffs) to the TS repo.
+
+---
+
+## P2 — Quality
+
+### [IS 1 Specification](rababa/04-is1-specification.md)
+Compile Metanorma document, publish to website.
+
+### [Performance: Large CJK Maps](rababa/05-performance-cjk-maps.md)
+6 maps take 15-38s to parse (Parslet backtracking).
+
+### [Ruby DSL Array Keys Bug](rababa/06-ruby-dsl-array-keys-bug.md) ✅ DONE
+Fixed: `STANDARD_ARRAY_KEYS` now stores results in `@node`.
+
+---
+
+## Architecture Notes
+
+### Pipeline
+```
+.isc → Isc::Parser → DocumentBuilder → NodeAdapter → Node::Document → Interpreter
+.imp → DSL.parse → Node::Document → Interpreter
+                    ↓
+              JsonIR Compiler → .json → interscript-ts → browser
+```
+
+### ISC is now a first-class source format
+With the NodeAdapter, .isc files can:
+- Be parsed (Parser)
+- Be built into documents (DocumentBuilder)
+- Be converted to Node objects (NodeAdapter)
+- Be used for transliteration (Interpreter)
+- Be compiled to JSON IR (JsonIR Compiler)
+
+### What's left for true parity
+1. Commit .isc to maps repo (mechanical)
+2. Update `Interscript::Path` to resolve `.isc` extension
+3. Port ISC parser to TypeScript (for browser-native .isc loading)
+4. Fix remaining 40 metadata edge cases (cosmetic)