Answer the architecture pass: the config that owns the contract, and what each runtime leg buys

AGENTS.md

@@ -65,8 +65,8 @@ they never reach a consumer.
   `tsconfig.build.json` is that gate, typechecking the shipped files alone with `types: []` and
   `lib: ES2022`, so `node:fs`, `process` and an ES2024 method are compile errors here rather than a
   consumer's crash there. Node's test runner, the corpus reads and the build are the repo's own,
-  never the library's, and `engines.node` states the floor the shipped JavaScript needs — `>=18`,
-  the lowest line carrying ES2022 — never the higher one those repo-only tools want.
+  never the library's, and `engines.node` states the floor the shipped JavaScript needs — `>=18` —
+  never the higher one those repo-only tools want.
 - ESM only — no CommonJS build, no dual-package hazard.
 - One entrypoint: built JavaScript, `.d.ts` beside it. Do not add a TypeScript-source entrypoint —
   Node refuses to type-strip under `node_modules` (`ERR_UNSUPPORTED_NODE_MODULES_TYPE_STRIPPING`),
@@ -120,9 +120,12 @@ Test for the behaviour wanted first, then implement until green. `node --test`,
 Node, tsc and npm never run on the host — only via the pinned images (§9). Tests are independent,
 coverage does not decline, containers are torn down after a run.
 
-The gate runs that same suite under Deno and Bun as well as Node, the three images pinned alike:
-§6's compile gate proves no host API is named, and only running proves those engines execute what
-is written. Both refuse a run that matches no test, so Node's is the only vacuous-green guard.
+The gate runs that same suite under Deno and Bun as well as Node, the three images pinned alike,
+and neither extra leg is Node's proof twice. Deno refuses an extensionless or directory specifier,
+so it holds the module graph to the fully-spelled form a browser can load; Bun runs
+JavaScriptCore, the one engine of the three that is not V8, where the Unicode property escapes
+emphasis matching leans on can disagree. Both refuse a run matching no test, so Node's is the only
+vacuous-green guard.
 
 The floors live in the `test` script, so `npm test` and the gate are one path: 100% of lines and
 functions, and a branch floor that only ever moves upward. It sits below 100 because the guards

ci.sh

@@ -5,7 +5,11 @@ cd "$(dirname "$0")"
 bun_image=oven/bun:1.4.0-alpine
 deno_image=denoland/deno:2.9.6
 node_image=node:24.19.0-alpine3.24
-in_image() { docker run --rm -u "$(id -u):$(id -g)" -e HOME=/tmp -v "$PWD:/app" -w /app --entrypoint "$2" "$1" "${@:3}"; }
+in_image() {
+  local image=$1 entrypoint=$2
+  shift 2
+  docker run --rm -u "$(id -u):$(id -g)" -e HOME=/tmp -v "$PWD:/app" -w /app --entrypoint "$entrypoint" "$image" "$@"
+}
 
 in_image "$node_image" npm ci
 in_image "$node_image" npm run typecheck
@@ -21,4 +25,4 @@ if printf '%s' "$test_output" | grep -q 'ℹ tests 0'; then
 fi
 
 in_image "$deno_image" deno test --allow-read --no-check src/
-in_image "$bun_image" bun test
+in_image "$bun_image" bun test src/

todo.md

@@ -139,13 +139,16 @@ numbering is the order the work was planned in, not the order it ships.
       additions are read here as one list before that freeze — nine sessions mint them
       independently, and one cause wearing two codes is breaking to undo after `0.1.0`. `0.1.0`
       is the markdown round-trip: both markdown directions, the types, `isAdfDocument`. The build
-      lands here: `tsconfig.build.json` gains emit of JS and `.d.ts` to `dist/` (the dev config's
-      `allowImportingTsExtensions` forces `noEmit`, so the build config needs
-      `rewriteRelativeImportExtensions`), plus `exports`/`files` in `package.json`. The
+      lands here: `tsconfig.build.json` gains emit of JS and `.d.ts` to `dist/` (its own
+      `allowImportingTsExtensions` forces `noEmit`, so `rewriteRelativeImportExtensions` lands
+      beside it), plus `exports`/`files` in `package.json`. The
       maintainer's bump PR also removes `private: true`, the guard against any earlier publish.
       §6's browser half is first checkable here, on the emitted `dist/index.js` a browser can
       load — the compile gate names no host API, and a real page converting a document is the
-      other half.
+      other half; name the engines that page covers, since Bun's JavaScriptCore is not Safari's
+      and none of the three legs is SpiderMonkey. `engines.node` gets its one-line proof here
+      too — `import('./dist/index.js')` under a pinned `node:18` image, which cannot run the
+      suite that type stripping wants 22+ for, but proves exactly what the field claims.
       **Settled** (the maintainer, 2026-09-01): the round-trip proved over the checked-in corpus
       is what `0.1.0` ships on, and the open-ended proof work follows it rather than gating it —
       3k's spec suite and 4's generators and maintainer-supplied payloads are `0.2.0`, 4b's retry

tsconfig.build.json

@@ -1,9 +1,29 @@
 {
-  "extends": "./tsconfig.json",
   "compilerOptions": {
     "lib": ["ES2022"],
+    "module": "NodeNext",
+    "moduleResolution": "NodeNext",
     "target": "ES2022",
-    "types": []
+    "types": [],
+
+    "allowImportingTsExtensions": true,
+    "erasableSyntaxOnly": true,
+    "isolatedModules": true,
+    "noEmit": true,
+    "verbatimModuleSyntax": true,
+
+    "strict": true,
+    "exactOptionalPropertyTypes": true,
+    "noFallthroughCasesInSwitch": true,
+    "noImplicitOverride": true,
+    "noImplicitReturns": true,
+    "noUncheckedIndexedAccess": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
+
+    "forceConsistentCasingInFileNames": true,
+    "skipLibCheck": true
   },
-  "exclude": ["src/**/*.test.ts"]
+  "exclude": ["src/**/*.test.ts"],
+  "include": ["src"]
 }

tsconfig.json

@@ -1,28 +1,9 @@
 {
+  "extends": "./tsconfig.build.json",
   "compilerOptions": {
     "lib": ["ESNext"],
-    "module": "NodeNext",
-    "moduleResolution": "NodeNext",
     "target": "ESNext",
-    "types": ["node"],
-
-    "allowImportingTsExtensions": true,
-    "erasableSyntaxOnly": true,
-    "isolatedModules": true,
-    "noEmit": true,
-    "verbatimModuleSyntax": true,
-
-    "strict": true,
-    "exactOptionalPropertyTypes": true,
-    "noFallthroughCasesInSwitch": true,
-    "noImplicitOverride": true,
-    "noImplicitReturns": true,
-    "noUncheckedIndexedAccess": true,
-    "noUnusedLocals": true,
-    "noUnusedParameters": true,
-
-    "forceConsistentCasingInFileNames": true,
-    "skipLibCheck": true
+    "types": ["node"]
   },
-  "include": ["src"]
+  "exclude": []
 }