diff --git a/fjs/asn.1/proof.f.ts b/fjs/asn.1/proof.f.ts
index 4456c5f353..8b05fd7145 100644
--- a/fjs/asn.1/proof.f.ts
+++ b/fjs/asn.1/proof.f.ts
@@ -17,7 +17,7 @@ import {
     decodeObjectIdentifier,
     type ObjectIdentifier,
 } from "./module.f.ts"
-import { assert, assertEq } from '../asserts/module.f.ts'
+import { assert, assertEq } from '../asserts/module.f.mjs'
 
 const { concat, popFront: pop, listToVec } = msb
 const pop8 = pop(8n)
diff --git a/fjs/asserts/module.f.ts b/fjs/asserts/module.f.mjs
similarity index 72%
rename from fjs/asserts/module.f.ts
rename to fjs/asserts/module.f.mjs
index adf9948122..2e2ec4f81c 100644
--- a/fjs/asserts/module.f.ts
+++ b/fjs/asserts/module.f.mjs
@@ -6,24 +6,29 @@
 
 /**
  * Marks a code path as unimplemented. Always throws.
+ * @type {() => never}
  */
-export const todo = (): never => { throw 'not implemented' }
+export const todo = () => { throw 'not implemented' }
 
 /**
  * Throws `msg` (default `'assertion failed'`) if `v` is `false`.
  *
  * Narrows `v` to `true` via `asserts v`, so callers can rely on the
  * condition holding for the rest of the enclosing scope.
+ *
+ * @type {(v: boolean, msg?: unknown) => asserts v}
  */
-export const assert: (v: boolean, msg?: unknown) => asserts v = (v, msg = 'assertion failed') => {
+export const assert = (v, msg = 'assertion failed') => {
     if (!v) throw msg
 }
 
 /**
  * Asserts that `a` and `b` are `===`, throwing `x` (the `[a, b]` pair, plus
  * an optional third element used as an extra message) if they differ.
+ *
+ * @type {<T>(...x: readonly[T, T, unknown?]) => void}
  */
-export const assertEq = <T>(...x: readonly[T, T, unknown?]): void => {
+export const assertEq = (...x) => {
     const [a, b] = x
     assert(a === b, x)
 }
@@ -32,8 +37,10 @@ export const assertEq = <T>(...x: readonly[T, T, unknown?]): void => {
  * Compile-time-only check: a type resolves only if it is exactly `true`.
  * Used to assert type-level properties without any runtime cost, e.g.
  * `type _ = Assert<Equal<A, B>>`.
+ *
+ * @template {true} T
+ * @typedef {T} Assert
  */
-export type Assert<T extends true> = T
 
 /**
  * Asserts that `a` is neither `null` nor `undefined` and returns it,
@@ -42,8 +49,10 @@ export type Assert<T extends true> = T
  * Use this to chain directly off a call that may return a nullish value,
  * e.g. `const r = assertNotNullish(f(x))`. For a variable that already
  * exists, prefer `assert(a !== null && a !== undefined)` instead.
+ *
+ * @type {<T>(a: T|null|undefined, msg?: unknown) => T}
  */
-export const assertNotNullish = <T>(a: T|null|undefined, msg?: unknown): T => {
+export const assertNotNullish = (a, msg) => {
     assert(a !== null && a !== undefined, msg)
     return a
 }
diff --git a/fjs/asserts/proof.f.ts b/fjs/asserts/proof.f.ts
index 303b996abf..f6eb2bf3b9 100644
--- a/fjs/asserts/proof.f.ts
+++ b/fjs/asserts/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq, todo } from './module.f.ts'
+import { assert, assertEq, todo } from './module.f.mjs'
 
 export const proof = {
     assertPassesOnTrue: () => {
diff --git a/fjs/base_n/proof.f.ts b/fjs/base_n/proof.f.ts
index 4b194c7e27..1a371e7fc3 100644
--- a/fjs/base_n/proof.f.ts
+++ b/fjs/base_n/proof.f.ts
@@ -1,4 +1,4 @@
-import { assertEq } from '../asserts/module.f.ts'
+import { assertEq } from '../asserts/module.f.mjs'
 import { empty, maxLength, vec, length } from '../types/bit_vec/module.f.ts'
 import { baseN } from './module.f.ts'
 
diff --git a/fjs/basen/base64/proof.f.ts b/fjs/basen/base64/proof.f.ts
index 7c00935d78..0e151562b0 100644
--- a/fjs/basen/base64/proof.f.ts
+++ b/fjs/basen/base64/proof.f.ts
@@ -1,4 +1,4 @@
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 import { empty, vec, repeat, vec8, maxLength, type Vec } from "../../types/bit_vec/module.f.ts"
 import { encode, decode } from "./module.f.ts"
 
diff --git a/fjs/basen/cbase32/proof.f.ts b/fjs/basen/cbase32/proof.f.ts
index ff5c1ad3f0..1dbf403251 100644
--- a/fjs/basen/cbase32/proof.f.ts
+++ b/fjs/basen/cbase32/proof.f.ts
@@ -1,6 +1,6 @@
 import { empty, vec, type Vec } from "../../types/bit_vec/module.f.ts"
 import { cBase32ToVec, cBase32ToVec5x, vec5xToCBase32, vecToCBase32 } from "./module.f.ts"
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 const check5x = (s: string, v: Vec) => {
     const sr = vec5xToCBase32(v)
diff --git a/fjs/bnf/data/proof.f.ts b/fjs/bnf/data/proof.f.ts
index 9243564ab4..9358683a4b 100644
--- a/fjs/bnf/data/proof.f.ts
+++ b/fjs/bnf/data/proof.f.ts
@@ -4,7 +4,7 @@ import { sort } from '../../types/object/module.f.ts'
 import { oneEncode, option, range, rangeDecode, repeat0Plus, set } from '../module.f.ts'
 import { classic, deterministic } from '../testlib.f.ts'
 import { emptyTagMap, type RuleSet, toData } from './module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 export const proof = {
     rangeDecode: () => {
diff --git a/fjs/bnf/descent/proof.f.ts b/fjs/bnf/descent/proof.f.ts
index 95f21e28e7..ccef21888e 100644
--- a/fjs/bnf/descent/proof.f.ts
+++ b/fjs/bnf/descent/proof.f.ts
@@ -4,7 +4,7 @@ import { commaJoin0Plus, option, range, repeat0Plus, set } from '../module.f.ts'
 import { deterministic } from '../testlib.f.ts'
 import { emptyTagMap, toData } from '../data/module.f.ts'
 import { descentParser, type DescentMatch, type CodePointMeta, type DescentMatchResult } from './module.f.ts'
-import { assertEq, assertNotNullish } from '../../asserts/module.f.ts'
+import { assertEq, assertNotNullish } from '../../asserts/module.f.mjs'
 
 const mapCodePoint = (cp: CodePoint): CodePointMeta<unknown> => [cp, undefined]
 
diff --git a/fjs/bnf/ll1/proof.f.ts b/fjs/bnf/ll1/proof.f.ts
index a6b07c1864..ba352dd23f 100644
--- a/fjs/bnf/ll1/proof.f.ts
+++ b/fjs/bnf/ll1/proof.f.ts
@@ -4,7 +4,7 @@ import { commaJoin0Plus, option, range, repeat0Plus, set } from '../module.f.ts'
 import { deterministic } from '../testlib.f.ts'
 import { type RuleSet, toData } from '../data/module.f.ts'
 import { dispatchMap, type MatchResult, parser, parserRuleSet } from './module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 export const proof = {
     dispatch: [
diff --git a/fjs/bnf/module.f.ts b/fjs/bnf/module.f.ts
index 9a3885d141..d15e25c8a8 100644
--- a/fjs/bnf/module.f.ts
+++ b/fjs/bnf/module.f.ts
@@ -11,7 +11,7 @@ import { definedValues, type StringMap } from '../types/object/module.f.ts'
 import { type Array2, isArray2 } from '../types/array/module.f.ts'
 import { map, toArray, repeat as listRepeat } from '../types/list/module.f.ts'
 import { contains } from '../types/range/module.f.ts'
-import { assert } from '../asserts/module.f.ts'
+import { assert } from '../asserts/module.f.mjs'
 
 // Types
 
diff --git a/fjs/bnf/proof.f.ts b/fjs/bnf/proof.f.ts
index 67911a7d75..8657486fbc 100644
--- a/fjs/bnf/proof.f.ts
+++ b/fjs/bnf/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq } from '../asserts/module.f.ts'
+import { assert, assertEq } from '../asserts/module.f.mjs'
 import { classic, deterministic } from './testlib.f.ts'
 import {
     rangeEncode,
diff --git a/fjs/bnf/token_symbol/module.f.ts b/fjs/bnf/token_symbol/module.f.ts
index 10a0b5326f..c0f92b388b 100644
--- a/fjs/bnf/token_symbol/module.f.ts
+++ b/fjs/bnf/token_symbol/module.f.ts
@@ -8,7 +8,7 @@
  *
  * @module
  */
-import { assert } from '../../asserts/module.f.ts'
+import { assert } from '../../asserts/module.f.mjs'
 import { fromUndefined, type Nullable } from '../../types/nullable/module.f.ts'
 import { eof, rangeDecode, unicodeRange } from '../module.f.ts'
 
diff --git a/fjs/bnf/token_symbol/proof.f.ts b/fjs/bnf/token_symbol/proof.f.ts
index eb8b60a233..7a018bb811 100644
--- a/fjs/bnf/token_symbol/proof.f.ts
+++ b/fjs/bnf/token_symbol/proof.f.ts
@@ -1,4 +1,4 @@
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 import { capacity, encoding } from './module.f.ts'
 
 const names = ['>>', '>>>=', 'instanceof'] as const
diff --git a/fjs/cas/cli/proof.f.ts b/fjs/cas/cli/proof.f.ts
index 2e9a4f4f03..68dae2f8c4 100644
--- a/fjs/cas/cli/proof.f.ts
+++ b/fjs/cas/cli/proof.f.ts
@@ -5,7 +5,7 @@ import { defaultNodeProgramOptions, emptyState, virtual } from '../../effects/no
 import { type NodeProgramOptions } from '../../effects/node/module.f.ts'
 import { dispatch } from '../../cli/module.f.ts'
 import { vecToCBase32 } from '../../basen/cbase32/module.f.ts'
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 
 const makeOptions = (args: readonly string[]): NodeProgramOptions =>
     ({ ...defaultNodeProgramOptions, args })
diff --git a/fjs/cas/evo/proof.f.ts b/fjs/cas/evo/proof.f.ts
index e0dc19adad..2e78a4b0b2 100644
--- a/fjs/cas/evo/proof.f.ts
+++ b/fjs/cas/evo/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 import { pure } from '../../effects/module.f.ts'
 import { fileCas, type Cas } from '../module.f.ts'
 import { sha256 } from '../../crypto/sha2/module.f.ts'
diff --git a/fjs/cas/proof.f.ts b/fjs/cas/proof.f.ts
index d02f44623e..6d34445e1e 100644
--- a/fjs/cas/proof.f.ts
+++ b/fjs/cas/proof.f.ts
@@ -8,7 +8,7 @@ import { error, ok, type Ok } from '../types/result/module.f.ts'
 import { emptyState, virtual } from '../effects/node/virtual/module.f.ts'
 import { join } from '../path/module.f.ts'
 import { nonEmpty, empty, type List } from '../effects/list/module.f.ts'
-import { assert, assertEq, assertNotNullish } from '../asserts/module.f.ts'
+import { assert, assertEq, assertNotNullish } from '../asserts/module.f.mjs'
 
 const testDir = './test-cas-cli'
 
diff --git a/fjs/ci/deno/proof.f.ts b/fjs/ci/deno/proof.f.ts
index 890d008026..43cbfe909f 100644
--- a/fjs/ci/deno/proof.f.ts
+++ b/fjs/ci/deno/proof.f.ts
@@ -1,6 +1,6 @@
 import { coverageInclude, denoSteps } from './module.f.ts'
 import { toSteps } from '../common/module.f.ts'
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 
 const coverageRuns = (version: string): readonly string[] =>
     toSteps(denoSteps(version))
diff --git a/fjs/ci/nix/proof.f.ts b/fjs/ci/nix/proof.f.ts
index 8bbc55d45d..1a5702e8db 100644
--- a/fjs/ci/nix/proof.f.ts
+++ b/fjs/ci/nix/proof.f.ts
@@ -3,7 +3,7 @@
  *
  * @module
  */
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 import { step } from '../../effects/module.f.ts'
 import { readUtf8File } from '../../effects/node/module.f.ts'
 import { emptyState, virtual } from '../../effects/node/virtual/module.f.ts'
diff --git a/fjs/ci/node/proof.f.ts b/fjs/ci/node/proof.f.ts
index bb42d2f15d..26b56b8a50 100644
--- a/fjs/ci/node/proof.f.ts
+++ b/fjs/ci/node/proof.f.ts
@@ -1,6 +1,6 @@
 import { basicNode } from './module.f.ts'
 import { test } from '../common/module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 export const proof = {
     basicNode: () => {
diff --git a/fjs/ci/proof.f.ts b/fjs/ci/proof.f.ts
index 839fb09a85..65fd19586e 100644
--- a/fjs/ci/proof.f.ts
+++ b/fjs/ci/proof.f.ts
@@ -5,7 +5,7 @@ import { coverageInclude } from './deno/module.f.ts'
 import { utf8, utf8ToString } from '../text/module.f.ts'
 import { empty as emptyVec, isVec } from '../types/bit_vec/module.f.ts'
 import { type MetaStep, type Os, test, ubuntu, type GitHubAction, parseGitHubAction } from './common/module.f.ts'
-import { assert, assertEq } from '../asserts/module.f.ts'
+import { assert, assertEq } from '../asserts/module.f.mjs'
 import type { State } from '../effects/node/virtual/module.f.ts'
 import { emptyState, virtual, type Dir } from '../effects/node/virtual/module.f.ts'
 import { parse as jsonParse } from '../media/json/module.f.ts'
diff --git a/fjs/cli/proof.f.ts b/fjs/cli/proof.f.ts
index 61204bbe41..ce2c3b8f15 100644
--- a/fjs/cli/proof.f.ts
+++ b/fjs/cli/proof.f.ts
@@ -2,7 +2,7 @@ import { pure } from '../effects/module.f.ts'
 import type { NodeOp, NodeProgramOptions } from '../effects/node/module.f.ts'
 import { defaultNodeProgramOptions, emptyState, virtual } from '../effects/node/virtual/module.f.ts'
 import { dispatch, type Commands } from './module.f.ts'
-import { assert, assertEq } from '../asserts/module.f.ts'
+import { assert, assertEq } from '../asserts/module.f.mjs'
 
 const makeOptions = (args: readonly string[]): NodeProgramOptions =>
     ({ ...defaultNodeProgramOptions, args })
diff --git a/fjs/common/monoid/proof.f.ts b/fjs/common/monoid/proof.f.ts
index 284bb41d48..96f17924a1 100644
--- a/fjs/common/monoid/proof.f.ts
+++ b/fjs/common/monoid/proof.f.ts
@@ -1,5 +1,5 @@
 import { repeat, fold, type Monoid } from "./module.f.ts";
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 export const proof = {
     numberAdd: () => {
diff --git a/fjs/crypto/hmac/proof.f.ts b/fjs/crypto/hmac/proof.f.ts
index 9a3f3df7d4..be620c3db2 100644
--- a/fjs/crypto/hmac/proof.f.ts
+++ b/fjs/crypto/hmac/proof.f.ts
@@ -1,4 +1,4 @@
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 import { utf8 } from '../../text/module.f.ts'
 import { uint, vec } from '../../types/bit_vec/module.f.ts'
 import { sha256, sha384, sha512 } from '../sha2/module.f.ts'
diff --git a/fjs/crypto/pow/proof.f.ts b/fjs/crypto/pow/proof.f.ts
index e83a5cefd1..b21454b50a 100644
--- a/fjs/crypto/pow/proof.f.ts
+++ b/fjs/crypto/pow/proof.f.ts
@@ -2,7 +2,7 @@ import { utf8 } from '../../text/module.f.ts'
 import { empty, uint } from '../../types/bit_vec/module.f.ts'
 import { computeSync, sha224, sha256 } from '../sha2/module.f.ts'
 import { bitcoinPow, genesisNBits, genesisTarget, pow, sha256Pow, targetFromNBits } from './module.f.ts'
-import { assert, assertEq, assertNotNullish } from '../../asserts/module.f.ts'
+import { assert, assertEq, assertNotNullish } from '../../asserts/module.f.mjs'
 
 const p256 = sha256Pow
 const p224 = pow(sha224)
diff --git a/fjs/crypto/secp/proof.f.ts b/fjs/crypto/secp/proof.f.ts
index c3be1c9522..9e0e812155 100644
--- a/fjs/crypto/secp/proof.f.ts
+++ b/fjs/crypto/secp/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq, assertNotNullish } from '../../asserts/module.f.ts'
+import { assert, assertEq, assertNotNullish } from '../../asserts/module.f.mjs'
 import { prime_field } from '../../types/prime_field/module.f.ts'
 import { curve, secp256k1, secp192r1, secp256r1, eq, type Point, secp384r1, secp521r1, type Curve, type Init } from './module.f.ts'
 
diff --git a/fjs/crypto/sha2/proof.f.ts b/fjs/crypto/sha2/proof.f.ts
index d098d5fabd..e6ea4939ec 100644
--- a/fjs/crypto/sha2/proof.f.ts
+++ b/fjs/crypto/sha2/proof.f.ts
@@ -1,7 +1,7 @@
 import { utf8 } from '../../text/module.f.ts'
 import { repeat, uint, vec } from '../../types/bit_vec/module.f.ts'
 import { flip } from '../../types/function/module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 import { map } from '../../types/list/module.f.ts'
 import {
     base32,
diff --git a/fjs/crypto/sign/module.f.ts b/fjs/crypto/sign/module.f.ts
index 21770e165d..4e124f0c79 100644
--- a/fjs/crypto/sign/module.f.ts
+++ b/fjs/crypto/sign/module.f.ts
@@ -3,7 +3,7 @@
  *
  * @module
  */
-import { assertNotNullish } from '../../asserts/module.f.ts'
+import { assertNotNullish } from '../../asserts/module.f.mjs'
 import type { Array2 } from '../../types/array/module.f.ts'
 import { bitLength, divUp8, roundUp8 } from '../../types/bigint/module.f.ts'
 import { empty, length, msb, repeat, unpack, vec, vec8, type Vec } from '../../types/bit_vec/module.f.ts'
diff --git a/fjs/crypto/sign/proof.f.ts b/fjs/crypto/sign/proof.f.ts
index b93655071d..9242d968f0 100644
--- a/fjs/crypto/sign/proof.f.ts
+++ b/fjs/crypto/sign/proof.f.ts
@@ -5,7 +5,7 @@ import { hmac } from "../hmac/module.f.ts"
 import { secp192r1, secp256r1, secp384r1, secp521r1, type Curve } from "../secp/module.f.ts"
 import { computeSync, sha224, sha256, sha384, sha512, type Sha2 } from "../sha2/module.f.ts"
 import { all, concat, computeK, fromCurve, sign } from "./module.f.ts"
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 const sample = utf8("sample")
 const test = utf8("test")
diff --git a/fjs/crypto/vdf/proof.f.ts b/fjs/crypto/vdf/proof.f.ts
index 8271a49a77..516fdf9eab 100644
--- a/fjs/crypto/vdf/proof.f.ts
+++ b/fjs/crypto/vdf/proof.f.ts
@@ -1,5 +1,5 @@
 import { sloth, p } from './module.f.ts'
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 
 const { eval: evalVdf, verify, modSqrt, quadRes } = sloth
 
diff --git a/fjs/dev/module.f.ts b/fjs/dev/module.f.ts
index cffcb1b200..c7662cee11 100644
--- a/fjs/dev/module.f.ts
+++ b/fjs/dev/module.f.ts
@@ -18,7 +18,7 @@ import type { StringMap } from '../types/object/module.f.ts'
 import { unwrap } from '../types/result/module.f.ts'
 import { pure, step, type Effect } from '../effects/module.f.ts'
 import { join, relativize, toPosix } from '../path/module.f.ts'
-import { assert, assertEq } from '../asserts/module.f.ts'
+import { assert, assertEq } from '../asserts/module.f.mjs'
 import { emptyState, virtual, type Dir } from '../effects/node/virtual/module.f.ts'
 
 export type Module = {
diff --git a/fjs/dev/package_json/proof.f.ts b/fjs/dev/package_json/proof.f.ts
index 972c69e462..e056c5ad86 100644
--- a/fjs/dev/package_json/proof.f.ts
+++ b/fjs/dev/package_json/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 import { unwrap } from '../../types/result/module.f.ts'
 import {
     validatePackageJson,
diff --git a/fjs/dev/proof.f.ts b/fjs/dev/proof.f.ts
index 2bbb2eff13..62f9f490bc 100644
--- a/fjs/dev/proof.f.ts
+++ b/fjs/dev/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq, todo } from '../asserts/module.f.ts'
+import { assert, assertEq, todo } from '../asserts/module.f.mjs'
 import { shouldLoad } from './module.f.ts'
 
 export const proof = {
diff --git a/fjs/dev/update/proof.f.ts b/fjs/dev/update/proof.f.ts
index 0153b55547..5572ca7288 100644
--- a/fjs/dev/update/proof.f.ts
+++ b/fjs/dev/update/proof.f.ts
@@ -3,7 +3,7 @@
  *
  * @module
  */
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 import { utf8 } from '../../text/module.f.ts'
 import { readUtf8File } from '../../effects/node/module.f.ts'
 import { defaultNodeProgramOptions, emptyState, virtual } from '../../effects/node/virtual/module.f.ts'
diff --git a/fjs/djs/ast/proof.f.ts b/fjs/djs/ast/proof.f.ts
index 6cfff5257e..0fea209c81 100644
--- a/fjs/djs/ast/proof.f.ts
+++ b/fjs/djs/ast/proof.f.ts
@@ -1,7 +1,7 @@
 import { sort } from '../../types/object/module.f.ts'
 import { run } from './module.f.ts'
 import { stringifyAsTree } from '../serializer/module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 export const proof = {
     test: () => {
diff --git a/fjs/djs/parser/module.f.ts b/fjs/djs/parser/module.f.ts
index 8121bb5431..6921664bab 100644
--- a/fjs/djs/parser/module.f.ts
+++ b/fjs/djs/parser/module.f.ts
@@ -11,7 +11,7 @@ import { setReplace, at, type OrderedMap } from '../../types/ordered_map/module.
 import { fromMap } from '../../types/object/module.f.ts'
 import type { AstArray, AstConst, AstModule, AstModuleRef } from '../ast/module.f.ts'
 import type { TokenMetadata } from '../../js/tokenizer/module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 export type ParseError = {
     readonly message: string,
diff --git a/fjs/djs/parser/proof.f.ts b/fjs/djs/parser/proof.f.ts
index b4f3b73744..a113713dda 100644
--- a/fjs/djs/parser/proof.f.ts
+++ b/fjs/djs/parser/proof.f.ts
@@ -5,7 +5,7 @@ import { sort } from '../../types/object/module.f.ts'
 import { stringToList } from '../../text/utf16/module.f.ts'
 import { stringifyAsTree } from '../serializer/module.f.ts'
 import { stringify } from '../../media/json/module.f.ts'
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 
 const tokenizeString
     : (s: string) => readonly DjsTokenWithMetadata[]
diff --git a/fjs/djs/proof.f.ts b/fjs/djs/proof.f.ts
index 7ac73e6464..e13f11e823 100644
--- a/fjs/djs/proof.f.ts
+++ b/fjs/djs/proof.f.ts
@@ -2,7 +2,7 @@ import { compile } from './module.f.ts'
 import { virtual, emptyState } from '../effects/node/virtual/module.f.ts'
 import { utf8, utf8ToString } from '../text/module.f.ts'
 import type { Vec } from '../types/bit_vec/module.f.ts'
-import { assert, assertEq } from '../asserts/module.f.ts'
+import { assert, assertEq } from '../asserts/module.f.mjs'
 
 const readOutput = (root: typeof emptyState.root, path: string): string => {
     const file = root[path]
diff --git a/fjs/djs/serializer/proof.f.ts b/fjs/djs/serializer/proof.f.ts
index 91d33b5ed9..8dc1781270 100644
--- a/fjs/djs/serializer/proof.f.ts
+++ b/fjs/djs/serializer/proof.f.ts
@@ -2,7 +2,7 @@ import { countRefs, stringify, stringifyAsTree } from './module.f.ts'
 import { sort } from '../../types/object/module.f.ts'
 import { identity } from '../../types/function/module.f.ts'
 import { setProperty } from '../../media/json/module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 export const proof = {
     stringify: [
diff --git a/fjs/djs/tokenizer/proof.f.ts b/fjs/djs/tokenizer/proof.f.ts
index 71ad92c8fd..391418803e 100644
--- a/fjs/djs/tokenizer/proof.f.ts
+++ b/fjs/djs/tokenizer/proof.f.ts
@@ -2,7 +2,7 @@ import { descentParser } from '../../bnf/descent/module.f.ts'
 import { stringToCodePointList, stringToList } from '../../text/utf16/module.f.ts'
 import { toArray } from '../../types/list/module.f.ts'
 import { jsGrammar, tokenizeString, descentParserCpOnly, tokenizeJs, tokenize } from './module.f.ts'
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 import { stringifyAsTree } from '../serializer/module.f.ts'
 import { sort } from '../../types/object/module.f.ts'
 import type { Unknown } from '../module.f.ts'
diff --git a/fjs/djs/transpiler/proof.f.ts b/fjs/djs/transpiler/proof.f.ts
index c21fa6aeb3..d1f913e0f7 100644
--- a/fjs/djs/transpiler/proof.f.ts
+++ b/fjs/djs/transpiler/proof.f.ts
@@ -3,7 +3,7 @@ import { transpile } from './module.f.ts'
 import { stringifyAsTree } from '../serializer/module.f.ts'
 import { virtual, emptyState, type Dir } from '../../effects/node/virtual/module.f.ts'
 import { utf8 } from '../../text/module.f.ts'
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 
 const run = (root: Dir) => (path: string) => {
     const [_, result] = virtual({ ...emptyState, root })(transpile(path))
diff --git a/fjs/effects/eff/proof.f.ts b/fjs/effects/eff/proof.f.ts
index a2c3bc8c6b..ad75f43f85 100644
--- a/fjs/effects/eff/proof.f.ts
+++ b/fjs/effects/eff/proof.f.ts
@@ -1,5 +1,5 @@
 import { do_, match, pure } from '../module.f.ts'
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 import { assertPure } from '../proof.f.ts'
 import { eff } from './module.f.ts'
 
diff --git a/fjs/effects/memory/proof.f.ts b/fjs/effects/memory/proof.f.ts
index 914a64c016..786263e0b0 100644
--- a/fjs/effects/memory/proof.f.ts
+++ b/fjs/effects/memory/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 import { run, type MemOperationMap } from '../mock/module.f.ts'
 import { pure, step } from '../module.f.ts'
 import {
diff --git a/fjs/effects/module.f.ts b/fjs/effects/module.f.ts
index 4fd20aedf9..4f5311add2 100644
--- a/fjs/effects/module.f.ts
+++ b/fjs/effects/module.f.ts
@@ -95,7 +95,7 @@
  * @module
  */
 
-import { assert } from '../asserts/module.f.ts'
+import { assert } from '../asserts/module.f.mjs'
 import { fold, type List } from '../types/list/module.f.ts'
 import { at } from '../types/object/module.f.ts'
 import type { Option } from '../types/option/module.f.ts'
diff --git a/fjs/effects/node/memory/proof.ts b/fjs/effects/node/memory/proof.ts
index 00a3e353fb..821b861b5a 100644
--- a/fjs/effects/node/memory/proof.ts
+++ b/fjs/effects/node/memory/proof.ts
@@ -11,7 +11,7 @@ import {
     type Key, type MemOp,
 } from '../../memory/module.f.ts'
 import { memoryOperationMap, run } from './module.ts'
-import { assert, assertEq } from '../../../asserts/module.f.ts'
+import { assert, assertEq } from '../../../asserts/module.f.mjs'
 import { step } from '../../module.f.ts'
 
 export const proof = {
diff --git a/fjs/effects/node/proof.f.ts b/fjs/effects/node/proof.f.ts
index 1c17bdd82f..d873e3122d 100644
--- a/fjs/effects/node/proof.f.ts
+++ b/fjs/effects/node/proof.f.ts
@@ -5,7 +5,7 @@ import { both, fetch, mkdir, now, readdir, readFile, readUtf8File, rm, sandbox,
 import { create as memCreate, read as memRead, write as memWrite } from "../memory/module.f.ts"
 import { empty as listEmpty, nonEmpty as listNonEmpty } from "../list/module.f.ts"
 import { emptyState, virtual, type Dir } from "./virtual/module.f.ts"
-import { assert, assertEq, assertNotNullish } from '../../asserts/module.f.ts'
+import { assert, assertEq, assertNotNullish } from '../../asserts/module.f.mjs'
 import { ok } from '../../types/result/module.f.ts'
 
 // Answers the one command the `map` proof below drives. Routing the loop
diff --git a/fjs/effects/node/virtual/module.f.ts b/fjs/effects/node/virtual/module.f.ts
index 64d4248870..0c2da21fc0 100644
--- a/fjs/effects/node/virtual/module.f.ts
+++ b/fjs/effects/node/virtual/module.f.ts
@@ -3,7 +3,7 @@
  *
  * @module
  */
-import { todo } from '../../../asserts/module.f.ts'
+import { todo } from '../../../asserts/module.f.mjs'
 import { isProperPrefix, join, parse } from '../../../path/module.f.ts'
 import { utf8ToString } from '../../../text/module.f.ts'
 import { empty, length, maxLengthBytes, msb, vec, type Vec } from '../../../types/bit_vec/module.f.ts'
diff --git a/fjs/effects/node/virtual/proof.f.ts b/fjs/effects/node/virtual/proof.f.ts
index 9d5db6be34..6fb8c0afbc 100644
--- a/fjs/effects/node/virtual/proof.f.ts
+++ b/fjs/effects/node/virtual/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq } from '../../../asserts/module.f.ts'
+import { assert, assertEq } from '../../../asserts/module.f.mjs'
 import { access, awaitIfPromise, fetch, rm, writeFile, readFile, readdir, import_, rename, readBytes, writeBytes } from '../module.f.ts'
 import { maxLengthBytes, vec, vec8 } from '../../../types/bit_vec/module.f.ts'
 import { emptyState, virtual, type Dir, type JsModule } from './module.f.ts'
diff --git a/fjs/effects/proof.f.ts b/fjs/effects/proof.f.ts
index a35c175e8c..8148de50a2 100644
--- a/fjs/effects/proof.f.ts
+++ b/fjs/effects/proof.f.ts
@@ -1,6 +1,6 @@
 import { step, do_, foldStep, forEachStep, mapStep, match, okStep, history, pure, runPure, type Effect, type Operation, historyStep } from './module.f.ts'
 import { error, ok } from '../types/result/module.f.ts'
-import { assert, assertEq } from '../asserts/module.f.ts'
+import { assert, assertEq } from '../asserts/module.f.mjs'
 
 /**
  * Asserts that `e` yields `expected` without performing a command. Exported so
diff --git a/fjs/emergent_testing/proof.f.ts b/fjs/emergent_testing/proof.f.ts
index 8a22897772..2093a8d9a5 100644
--- a/fjs/emergent_testing/proof.f.ts
+++ b/fjs/emergent_testing/proof.f.ts
@@ -2,7 +2,7 @@ import type { Effect } from '../effects/module.f.ts'
 import { log, type NodeProgramOptions, type Sandbox, type Write } from '../effects/node/module.f.ts'
 import { defaultNodeProgramOptions, emptyState, type JsModule } from '../effects/node/virtual/module.f.ts'
 import { virtual } from '../effects/node/virtual/module.f.ts'
-import { assert, assertEq } from '../asserts/module.f.ts'
+import { assert, assertEq } from '../asserts/module.f.mjs'
 import {
     testAll, defaultReporter, fmtPath, fmtTerm, fmtImport, ghEscape, isInteger, isIdentifier,
     registerModule, parseTestSet,
diff --git a/fjs/fsc/module.f.ts b/fjs/fsc/module.f.ts
index 44ea1d75d2..0a062468bc 100644
--- a/fjs/fsc/module.f.ts
+++ b/fjs/fsc/module.f.ts
@@ -15,7 +15,7 @@ import { reduce as listReduce, toArray, map, type List } from '../types/list/mod
 import { range as asciiRange } from '../text/ascii/module.f.ts'
 import { flip, fn } from '../types/function/module.f.ts'
 import { one, type Range } from '../types/range/module.f.ts'
-import { assertEq } from '../asserts/module.f.ts'
+import { assertEq } from '../asserts/module.f.mjs'
 
 const fromCharCode = String.fromCharCode
 
diff --git a/fjs/fsc/proof.f.ts b/fjs/fsc/proof.f.ts
index ed849f5f85..bb2213f3bc 100644
--- a/fjs/fsc/proof.f.ts
+++ b/fjs/fsc/proof.f.ts
@@ -1,7 +1,7 @@
 import { init, terminal } from './module.f.ts'
 import { one } from '../text/ascii/module.f.ts'
 import { stringify } from '../media/json/module.f.ts'
-import { assertEq } from '../asserts/module.f.ts'
+import { assertEq } from '../asserts/module.f.mjs'
 
 const s = stringify(i => i)
 
diff --git a/fjs/fsm/proof.f.ts b/fjs/fsm/proof.f.ts
index e7984e7747..f37b776387 100644
--- a/fjs/fsm/proof.f.ts
+++ b/fjs/fsm/proof.f.ts
@@ -5,7 +5,7 @@ import { stringify } from '../media/json/module.f.ts'
 import { identity } from '../types/function/module.f.ts'
 import { toArray } from '../types/list/module.f.ts'
 import { stringToList } from '../text/utf16/module.f.ts'
-import { assertEq } from '../asserts/module.f.ts'
+import { assertEq } from '../asserts/module.f.mjs'
 
 const stringifyIdentity = stringify(identity)
 
diff --git a/fjs/js/tokenizer/module.f.ts b/fjs/js/tokenizer/module.f.ts
index 008be995d3..f36522d082 100644
--- a/fjs/js/tokenizer/module.f.ts
+++ b/fjs/js/tokenizer/module.f.ts
@@ -69,7 +69,7 @@ import {
     rightCurlyBracket,
     dollarSign
 }  from '../../text/ascii/module.f.ts'
-import { todo, assertEq } from '../../asserts/module.f.ts'
+import { todo, assertEq } from '../../asserts/module.f.mjs'
 
 const { fromCharCode } = String
 
diff --git a/fjs/mcp/evo/proof.f.ts b/fjs/mcp/evo/proof.f.ts
index ce4bfe73ef..b661809f08 100644
--- a/fjs/mcp/evo/proof.f.ts
+++ b/fjs/mcp/evo/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 import { fileCas } from '../../cas/module.f.ts'
 import { sha256 } from '../../crypto/sha2/module.f.ts'
 import { emptyState, virtual } from '../../effects/node/virtual/module.f.ts'
diff --git a/fjs/mcp/proof.f.ts b/fjs/mcp/proof.f.ts
index b0d0357d51..fbb0cde4c1 100644
--- a/fjs/mcp/proof.f.ts
+++ b/fjs/mcp/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq } from '../asserts/module.f.ts'
+import { assert, assertEq } from '../asserts/module.f.mjs'
 import { pure, step, type Effect, type Operation } from '../effects/module.f.ts'
 import { create } from '../effects/memory/module.f.ts'
 import { parse as parseJson, type Unknown } from '../media/json/module.f.ts'
diff --git a/fjs/media/html/proof.f.ts b/fjs/media/html/proof.f.ts
index 29c45a2949..de86df4f29 100644
--- a/fjs/media/html/proof.f.ts
+++ b/fjs/media/html/proof.f.ts
@@ -1,5 +1,5 @@
 import { htmlToString, type Element } from "./module.f.ts"
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 export const proof = {
     empty: () => {
diff --git a/fjs/media/json/module.f.ts b/fjs/media/json/module.f.ts
index d4c38776e5..66a85f1949 100644
--- a/fjs/media/json/module.f.ts
+++ b/fjs/media/json/module.f.ts
@@ -22,7 +22,7 @@ import { compose, fn } from '../../types/function/module.f.ts'
 import { objectWrap, arrayWrap, stringSerialize, numberSerialize, nullSerialize, boolSerialize } from './serializer/module.f.ts'
 import { boolean as rttiBoolean, number as rttiNumber, string as rttiString, or, record, array as rttiArray } from '../../types/rtti/module.f.ts'
 import type { Ts } from '../../types/rtti/ts/module.f.ts'
-import type { Assert } from '../../asserts/module.f.ts'
+import type { Assert } from '../../asserts/module.f.mjs'
 import type { Equal } from '../../types/ts/module.f.ts'
 
 // ── rtti schemas ──────────────────────────────────────────────────────────────
diff --git a/fjs/media/json/parser/module.f.ts b/fjs/media/json/parser/module.f.ts
index 4b56db028a..5ecc47fc99 100644
--- a/fjs/media/json/parser/module.f.ts
+++ b/fjs/media/json/parser/module.f.ts
@@ -10,7 +10,7 @@ import { type JsonToken } from '../tokenizer/module.f.ts'
 import { setReplace, type OrderedMap } from '../../../types/ordered_map/module.f.ts'
 import { type Unknown } from '../module.f.ts'
 import { fromMap } from '../../../types/object/module.f.ts'
-import { assertEq } from '../../../asserts/module.f.ts'
+import { assertEq } from '../../../asserts/module.f.mjs'
 
 type JsonObject = {
     readonly kind: 'object'
diff --git a/fjs/media/json/parser/proof.f.ts b/fjs/media/json/parser/proof.f.ts
index 5a172f56ee..f7cc0c784b 100644
--- a/fjs/media/json/parser/proof.f.ts
+++ b/fjs/media/json/parser/proof.f.ts
@@ -4,7 +4,7 @@ import { toArray } from '../../../types/list/module.f.ts'
 import { stringify as jsonStringify } from '../module.f.ts'
 import { sort } from '../../../types/object/module.f.ts'
 import { stringToList } from '../../../text/utf16/module.f.ts'
-import { assertEq } from '../../../asserts/module.f.ts'
+import { assertEq } from '../../../asserts/module.f.mjs'
 
 const tokenizeString
     : (s: string) => readonly JsonToken[]
diff --git a/fjs/media/json/proof.f.ts b/fjs/media/json/proof.f.ts
index 560d845661..17f18126fc 100644
--- a/fjs/media/json/proof.f.ts
+++ b/fjs/media/json/proof.f.ts
@@ -1,7 +1,7 @@
 import { parse, setProperty, stringify } from './module.f.ts'
 import { sort } from '../../types/object/module.f.ts'
 import { identity } from '../../types/function/module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 export const proof = {
     setProperty: [
diff --git a/fjs/media/json/schema/proof.f.ts b/fjs/media/json/schema/proof.f.ts
index 7325691a7e..6b19e888ac 100644
--- a/fjs/media/json/schema/proof.f.ts
+++ b/fjs/media/json/schema/proof.f.ts
@@ -1,7 +1,7 @@
 import { boolean, number, string, bigint, unknown, array, record, or, option } from '../../../types/rtti/module.f.ts'
 import { stringify, type Unknown as JsonValue } from '../module.f.ts'
 import { toJsonSchema, type Unknown, unknown as schemaUnknown } from './module.f.ts'
-import { assert, assertEq } from '../../../asserts/module.f.ts'
+import { assert, assertEq } from '../../../asserts/module.f.mjs'
 
 const serialize = (v: Unknown) => stringify(e => e)(v as unknown as JsonValue)
 
diff --git a/fjs/media/json/serializer/proof.f.ts b/fjs/media/json/serializer/proof.f.ts
index a2ec799141..fba5bd57c4 100644
--- a/fjs/media/json/serializer/proof.f.ts
+++ b/fjs/media/json/serializer/proof.f.ts
@@ -1,7 +1,7 @@
 import { arrayWrap, boolSerialize, numberSerialize, objectWrap, stringSerialize } from './module.f.ts'
 import * as list from '../../../types/list/module.f.ts'
 import { concat } from '../../../types/string/module.f.ts'
-import { assertEq } from '../../../asserts/module.f.ts'
+import { assertEq } from '../../../asserts/module.f.mjs'
 
 const { toArray } = list
 
diff --git a/fjs/media/module.f.ts b/fjs/media/module.f.ts
index 4453efacdc..b50c588a0e 100644
--- a/fjs/media/module.f.ts
+++ b/fjs/media/module.f.ts
@@ -45,7 +45,7 @@ import type { Vec } from '../types/bit_vec/module.f.ts'
 import { fromVec } from '../text/utf8/module.f.ts'
 import { detectVec, type DetectMeta } from './type/module.f.ts'
 import { parse } from './json/module.f.ts'
-import { assert, assertNotNullish } from '../asserts/module.f.ts'
+import { assert, assertNotNullish } from '../asserts/module.f.mjs'
 import type { Struct } from '../types/rtti/module.f.ts'
 import type { Ts, Unknown } from '../types/rtti/ts/module.f.ts'
 import { validate, type Validate } from '../types/rtti/validate/module.f.ts'
diff --git a/fjs/media/nix/proof.f.ts b/fjs/media/nix/proof.f.ts
index 4aeb7eaf2f..a540d5ec97 100644
--- a/fjs/media/nix/proof.f.ts
+++ b/fjs/media/nix/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 import { toArray } from '../../types/list/module.f.ts'
 import { nix, nixToString, type Expression } from './module.f.ts'
 
diff --git a/fjs/media/proof.f.ts b/fjs/media/proof.f.ts
index f1c0d5537a..17b8f3cd2b 100644
--- a/fjs/media/proof.f.ts
+++ b/fjs/media/proof.f.ts
@@ -1,4 +1,4 @@
-import { assertEq } from '../asserts/module.f.ts'
+import { assertEq } from '../asserts/module.f.mjs'
 import { msb, u8ListToVec, repeat, vec8, type Vec } from '../types/bit_vec/module.f.ts'
 import { detect, dialectEntry, type DialectEntry } from './module.f.ts'
 import { dialect, revisionDialect } from './revision/module.f.ts'
diff --git a/fjs/media/revision/proof.f.ts b/fjs/media/revision/proof.f.ts
index c631ab10c0..e3b67794e1 100644
--- a/fjs/media/revision/proof.f.ts
+++ b/fjs/media/revision/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 import type { Object as JsonObject } from '../json/module.f.ts'
 import { dialect, mediaType, isHash, validate, decodeText, encodeText, type LockMap } from './module.f.ts'
 
diff --git a/fjs/media/type/proof.f.ts b/fjs/media/type/proof.f.ts
index c200e1b6d0..3da246f1fe 100644
--- a/fjs/media/type/proof.f.ts
+++ b/fjs/media/type/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 import { msb, u8ListToVec, vec8, repeat, empty, type Vec } from '../../types/bit_vec/module.f.ts'
 import { runPure } from '../../effects/module.f.ts'
 import { nonEmpty, empty as emptyList, type List } from '../../effects/list/module.f.ts'
diff --git a/fjs/path/proof.f.ts b/fjs/path/proof.f.ts
index e85444c13e..77379c113d 100644
--- a/fjs/path/proof.f.ts
+++ b/fjs/path/proof.f.ts
@@ -1,5 +1,5 @@
 import { concat, isProperPrefix, join, normalize, relativize, toPosix } from "./module.f.ts"
-import { assertEq } from '../asserts/module.f.ts'
+import { assertEq } from '../asserts/module.f.mjs'
 
 const normalizeTest = [
     () => {
diff --git a/fjs/proof.f.ts b/fjs/proof.f.ts
index c2b448cb09..c76e195ad6 100644
--- a/fjs/proof.f.ts
+++ b/fjs/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq } from './asserts/module.f.ts'
+import { assert, assertEq } from './asserts/module.f.mjs'
 import { pure } from './effects/module.f.ts'
 import type { NodeProgram, NodeProgramOptions } from './effects/node/module.f.ts'
 import { defaultNodeProgramOptions, emptyState, virtual, type Dir } from './effects/node/virtual/module.f.ts'
diff --git a/fjs/protocol/json_rpc/proof.f.ts b/fjs/protocol/json_rpc/proof.f.ts
index ad41e97567..c6c6785627 100644
--- a/fjs/protocol/json_rpc/proof.f.ts
+++ b/fjs/protocol/json_rpc/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 import { ok, error } from '../../types/result/module.f.ts'
 import { validate } from '../../types/rtti/validate/module.f.ts'
 import {
diff --git a/fjs/protocol/mcp/proof.f.ts b/fjs/protocol/mcp/proof.f.ts
index a15ac20df5..dac6a344f1 100644
--- a/fjs/protocol/mcp/proof.f.ts
+++ b/fjs/protocol/mcp/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 import { pure, step, type Operation } from '../../effects/module.f.ts'
 import { eff } from '../../effects/eff/module.f.ts'
 import type { Effect } from '../../effects/module.f.ts'
diff --git a/fjs/protocol/mcp/stdio/proof.f.ts b/fjs/protocol/mcp/stdio/proof.f.ts
index 90bc071e66..8c0035fa84 100644
--- a/fjs/protocol/mcp/stdio/proof.f.ts
+++ b/fjs/protocol/mcp/stdio/proof.f.ts
@@ -1,4 +1,4 @@
-import { assertEq } from '../../../asserts/module.f.ts'
+import { assertEq } from '../../../asserts/module.f.mjs'
 import { pure, type Effect } from '../../../effects/module.f.ts'
 import { emptyState, virtual, type State } from '../../../effects/node/virtual/module.f.ts'
 import type { Unknown } from '../../../media/json/module.f.ts'
diff --git a/fjs/sul/id/module.f.ts b/fjs/sul/id/module.f.ts
index 46bf76209f..94bd9f7ea7 100644
--- a/fjs/sul/id/module.f.ts
+++ b/fjs/sul/id/module.f.ts
@@ -16,7 +16,7 @@ import {
     vec,
     type Vec
 } from '../../types/bit_vec/module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 import { utf8 } from '../../text/module.f.ts'
 import { secp256r1, type Point2D } from '../../crypto/secp/module.f.ts'
 import { base32, type V8 } from '../../crypto/sha2/module.f.ts'
diff --git a/fjs/sul/id/proof.f.ts b/fjs/sul/id/proof.f.ts
index a7374add5c..2d96a580d6 100644
--- a/fjs/sul/id/proof.f.ts
+++ b/fjs/sul/id/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 import { mask } from '../../types/bigint/module.f.ts'
 import { vec } from '../../types/bit_vec/module.f.ts'
 import { compress, hashId, isHash, isRaw, level3Id, rawId } from './module.f.ts'
diff --git a/fjs/sul/level/hash/proof.f.ts b/fjs/sul/level/hash/proof.f.ts
index c404d4bd04..4d6261b2da 100644
--- a/fjs/sul/level/hash/proof.f.ts
+++ b/fjs/sul/level/hash/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq } from '../../../asserts/module.f.ts'
+import { assert, assertEq } from '../../../asserts/module.f.mjs'
 import { compress, level3Id, type Id } from '../../id/module.f.ts'
 import { emptyEncodeState, encode, type EncodeState } from './module.f.ts'
 
diff --git a/fjs/sul/level/literal/proof.f.ts b/fjs/sul/level/literal/proof.f.ts
index a8ddb6b07c..bf6a4dd888 100644
--- a/fjs/sul/level/literal/proof.f.ts
+++ b/fjs/sul/level/literal/proof.f.ts
@@ -1,5 +1,5 @@
 import { chunkList, msb, vec, type Vec } from '../../../types/bit_vec/module.f.ts'
-import { assert, assertEq } from '../../../asserts/module.f.ts'
+import { assert, assertEq } from '../../../asserts/module.f.mjs'
 import { map, stateScan, toArray } from '../../../types/list/module.f.ts'
 import {
     emptyEncodeState,
diff --git a/fjs/sul/proof.f.ts b/fjs/sul/proof.f.ts
index ea580cef51..00dd76bf63 100644
--- a/fjs/sul/proof.f.ts
+++ b/fjs/sul/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq } from '../asserts/module.f.ts'
+import { assert, assertEq } from '../asserts/module.f.mjs'
 import { compress, type Id } from './id/module.f.ts'
 import { encode, emptyEncodeState } from './module.f.ts'
 import type { Add } from './level/hash/module.f.ts'
diff --git a/fjs/text/ascii/proof.f.ts b/fjs/text/ascii/proof.f.ts
index fe1cfa0550..5a1cfdd74e 100644
--- a/fjs/text/ascii/proof.f.ts
+++ b/fjs/text/ascii/proof.f.ts
@@ -1,7 +1,7 @@
 import { one, range } from './module.f.ts'
 import { stringify as jsonStringify } from '../../media/json/module.f.ts'
 import { sort } from '../../types/object/module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 const stringify = jsonStringify(sort)
 
diff --git a/fjs/text/proof.f.ts b/fjs/text/proof.f.ts
index 1269efea6d..665b7304cc 100644
--- a/fjs/text/proof.f.ts
+++ b/fjs/text/proof.f.ts
@@ -1,4 +1,4 @@
-import { assertEq, assertNotNullish } from '../asserts/module.f.ts'
+import { assertEq, assertNotNullish } from '../asserts/module.f.mjs'
 import { flat, utf8, utf8ToString, tryUtf8, type Block } from './module.f.ts'
 import { join } from '../types/string/module.f.ts'
 import { empty, maxLengthBytes } from '../types/bit_vec/module.f.ts'
diff --git a/fjs/text/sgr/proof.f.ts b/fjs/text/sgr/proof.f.ts
index 04079858aa..d6deaf2d4d 100644
--- a/fjs/text/sgr/proof.f.ts
+++ b/fjs/text/sgr/proof.f.ts
@@ -1,7 +1,7 @@
 import { fgRed, reset, createConsoleText, backspace, csiWrite } from './module.f.ts'
 import { virtual, emptyState, defaultNodeProgramOptions } from '../../effects/node/virtual/module.f.ts'
 import type { NodeProgramOptions } from '../../effects/node/module.f.ts'
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 
 const makeOptions = (isTTY: boolean): NodeProgramOptions =>
     ({ ...defaultNodeProgramOptions, std: { stdout: { isTTY }, stderr: { isTTY } } })
diff --git a/fjs/text/utf16/proof.f.ts b/fjs/text/utf16/proof.f.ts
index 39379fa206..7f4c7b6c32 100644
--- a/fjs/text/utf16/proof.f.ts
+++ b/fjs/text/utf16/proof.f.ts
@@ -10,7 +10,7 @@ import {
 import { stringify as jsonStringify, type Unknown } from '../../media/json/module.f.ts'
 import { sort } from '../../types/object/module.f.ts'
 import { toArray } from '../../types/list/module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 const stringify = (a: readonly Unknown[]) =>
     jsonStringify(sort)(a)
diff --git a/fjs/text/utf8/proof.f.ts b/fjs/text/utf8/proof.f.ts
index 44136209a5..26c6632696 100644
--- a/fjs/text/utf8/proof.f.ts
+++ b/fjs/text/utf8/proof.f.ts
@@ -3,7 +3,7 @@ import { stringify as jsonStringify } from '../../media/json/module.f.ts'
 import { sort } from '../../types/object/module.f.ts'
 import { toArray } from '../../types/list/module.f.ts'
 import { msb, u8ListToVec, vec } from '../../types/bit_vec/module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 const stringify = jsonStringify(sort)
 
diff --git a/fjs/types/array/proof.f.ts b/fjs/types/array/proof.f.ts
index f310d635e6..1293753d81 100644
--- a/fjs/types/array/proof.f.ts
+++ b/fjs/types/array/proof.f.ts
@@ -1,7 +1,7 @@
 import { at, first, last, head, tail, splitFirst, splitLast, empty } from './module.f.ts'
 import { stringify as jsonStringify } from '../../media/json/module.f.ts'
 import { sort } from '../object/module.f.ts'
-import { assertEq, assertNotNullish } from '../../asserts/module.f.ts'
+import { assertEq, assertNotNullish } from '../../asserts/module.f.mjs'
 
 const stringify = jsonStringify(sort)
 
diff --git a/fjs/types/bigfloat/proof.f.ts b/fjs/types/bigfloat/proof.f.ts
index 887a383612..8354d1ffee 100644
--- a/fjs/types/bigfloat/proof.f.ts
+++ b/fjs/types/bigfloat/proof.f.ts
@@ -1,5 +1,5 @@
 import { decToBin } from './module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 export const proof = {
     decToBin: [
diff --git a/fjs/types/bigint/proof.f.ts b/fjs/types/bigint/proof.f.ts
index 5816d328f0..d99cb9bd97 100644
--- a/fjs/types/bigint/proof.f.ts
+++ b/fjs/types/bigint/proof.f.ts
@@ -15,7 +15,7 @@ import {
     divUp8,
     roundUp8
 } from './module.f.ts'
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 import { min } from '../function/compare/module.f.ts'
 
 const oldLog2 = (v: bigint): bigint => {
diff --git a/fjs/types/bit_vec/proof.f.ts b/fjs/types/bit_vec/proof.f.ts
index a1503f4cd2..3d81fa69b8 100644
--- a/fjs/types/bit_vec/proof.f.ts
+++ b/fjs/types/bit_vec/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 import { mask } from '../bigint/module.f.ts'
 import type { Sign } from '../function/compare/module.f.ts'
 import { asBase, asNominal } from '../nominal/module.f.ts'
diff --git a/fjs/types/btree/find/proof.f.ts b/fjs/types/btree/find/proof.f.ts
index 63c035acd9..9623d6734c 100644
--- a/fjs/types/btree/find/proof.f.ts
+++ b/fjs/types/btree/find/proof.f.ts
@@ -5,7 +5,7 @@ import { sort } from '../../object/module.f.ts'
 import { type TNode } from '../types/module.f.ts'
 import { cmp } from '../../string/module.f.ts'
 import { set as setSet } from '../set/module.f.ts'
-import { assertEq } from '../../../asserts/module.f.ts'
+import { assertEq } from '../../../asserts/module.f.mjs'
 
 const jsonStr = stringify(sort)
 
diff --git a/fjs/types/btree/proof.f.ts b/fjs/types/btree/proof.f.ts
index c0afa03d20..c068e81da0 100644
--- a/fjs/types/btree/proof.f.ts
+++ b/fjs/types/btree/proof.f.ts
@@ -6,7 +6,7 @@ import { cmp } from '../string/module.f.ts'
 import { next, toArray, type List, type Result } from '../list/module.f.ts'
 import { set as setSet } from './set/module.f.ts'
 import { value, find as findFind } from './find/module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 const jsonStr = jsonStringify(sort)
 
diff --git a/fjs/types/btree/remove/proof.f.ts b/fjs/types/btree/remove/proof.f.ts
index 415e628166..7238822506 100644
--- a/fjs/types/btree/remove/proof.f.ts
+++ b/fjs/types/btree/remove/proof.f.ts
@@ -4,7 +4,7 @@ import { set as setSet } from '../set/module.f.ts'
 import { cmp } from '../../string/module.f.ts'
 import { stringify } from '../../../media/json/module.f.ts'
 import { sort } from '../../object/module.f.ts'
-import { assertEq, assertNotNullish } from '../../../asserts/module.f.ts'
+import { assertEq, assertNotNullish } from '../../../asserts/module.f.mjs'
 
 const set = (node: TNode<string>) => (value: string) =>
     setSet(cmp(value))(() => value)(node)
diff --git a/fjs/types/btree/set/proof.f.ts b/fjs/types/btree/set/proof.f.ts
index 5a307f7079..4801dd4338 100644
--- a/fjs/types/btree/set/proof.f.ts
+++ b/fjs/types/btree/set/proof.f.ts
@@ -3,7 +3,7 @@ import type { TNode } from '../types/module.f.ts'
 import { cmp } from '../../string/module.f.ts'
 import { stringify } from '../../../media/json/module.f.ts'
 import { sort } from '../../object/module.f.ts'
-import { assertEq } from '../../../asserts/module.f.ts'
+import { assertEq } from '../../../asserts/module.f.mjs'
 
 const set = (node: TNode<string>) => (value: string): TNode<string> =>
     setSet(cmp(value))(() => value)(node)
diff --git a/fjs/types/byte_set/proof.f.ts b/fjs/types/byte_set/proof.f.ts
index 94fc8f5ce2..a4f1147809 100644
--- a/fjs/types/byte_set/proof.f.ts
+++ b/fjs/types/byte_set/proof.f.ts
@@ -2,7 +2,7 @@ import { has, empty, set, setRange, unset, universe, complement, toRangeMap } fr
 import { every, countdown, map, toArray } from '../list/module.f.ts'
 import { stringify as jsonStringify, type Unknown } from '../../media/json/module.f.ts'
 import { sort } from '../object/module.f.ts'
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 
 const stringify: (a: readonly Unknown[]) => string
     = jsonStringify(sort)
diff --git a/fjs/types/function/compare/proof.f.ts b/fjs/types/function/compare/proof.f.ts
index 3a823447d5..184e617a38 100644
--- a/fjs/types/function/compare/proof.f.ts
+++ b/fjs/types/function/compare/proof.f.ts
@@ -1,5 +1,5 @@
 import { cmp, min, max } from './module.f.ts'
-import { assertEq } from '../../../asserts/module.f.ts'
+import { assertEq } from '../../../asserts/module.f.mjs'
 
 export const proof = () => {
     {
diff --git a/fjs/types/function/operator/proof.f.ts b/fjs/types/function/operator/proof.f.ts
index e0edb3f44c..7494ae2bef 100644
--- a/fjs/types/function/operator/proof.f.ts
+++ b/fjs/types/function/operator/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq } from '../../../asserts/module.f.ts'
+import { assert, assertEq } from '../../../asserts/module.f.mjs'
 import {
     join,
     concat,
diff --git a/fjs/types/function/proof.f.ts b/fjs/types/function/proof.f.ts
index f760e9c604..0f08e48f72 100644
--- a/fjs/types/function/proof.f.ts
+++ b/fjs/types/function/proof.f.ts
@@ -1,5 +1,5 @@
 import { fn } from './module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 export const proof = () => {
     const f: (x: string) => readonly[string]
diff --git a/fjs/types/list/proof.f.ts b/fjs/types/list/proof.f.ts
index d4e88ff5a0..d68f2c4daa 100644
--- a/fjs/types/list/proof.f.ts
+++ b/fjs/types/list/proof.f.ts
@@ -31,7 +31,7 @@ import {
 import { stringify, type Unknown } from '../../media/json/module.f.ts'
 import { sort } from '../object/module.f.ts'
 import { addition, strictEqual, reduceToScan } from '../function/operator/module.f.ts'
-import { assert, assertEq, assertNotNullish } from '../../asserts/module.f.ts'
+import { assert, assertEq, assertNotNullish } from '../../asserts/module.f.mjs'
 
 const str
     : (sequence: List<Unknown>) => string
diff --git a/fjs/types/map/proof.f.ts b/fjs/types/map/proof.f.ts
index 13b59742d0..6b171815b4 100644
--- a/fjs/types/map/proof.f.ts
+++ b/fjs/types/map/proof.f.ts
@@ -1,5 +1,5 @@
 import { mapSet, mapDelete } from './module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 export const proof = {
     set: () => {
diff --git a/fjs/types/nibble_set/proof.f.ts b/fjs/types/nibble_set/proof.f.ts
index a7f2ce0c2f..ce73734081 100644
--- a/fjs/types/nibble_set/proof.f.ts
+++ b/fjs/types/nibble_set/proof.f.ts
@@ -1,6 +1,6 @@
 import { every, map, countdown } from '../list/module.f.ts'
 import { empty, has, set, setRange, unset, universe, complement } from './module.f.ts'
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 
 export const proof = {
     has: () => {
diff --git a/fjs/types/nominal/proof.f.ts b/fjs/types/nominal/proof.f.ts
index 938dc42b63..2cd82e4b8e 100644
--- a/fjs/types/nominal/proof.f.ts
+++ b/fjs/types/nominal/proof.f.ts
@@ -1,5 +1,5 @@
 import { asBase, asNominal, type Nominal } from "./module.f.ts"
-import { assert } from '../../asserts/module.f.ts'
+import { assert } from '../../asserts/module.f.mjs'
 
 declare const noCompareBrand: unique symbol
 
diff --git a/fjs/types/nullable/module.f.ts b/fjs/types/nullable/module.f.ts
index 62e1f1aa25..869e42a15c 100644
--- a/fjs/types/nullable/module.f.ts
+++ b/fjs/types/nullable/module.f.ts
@@ -3,7 +3,7 @@
  *
  * @module
  */
-import { assert } from '../../asserts/module.f.ts'
+import { assert } from '../../asserts/module.f.mjs'
 import { fn } from '../function/module.f.ts'
 import type { Option } from '../option/module.f.ts'
 
diff --git a/fjs/types/nullable/proof.f.ts b/fjs/types/nullable/proof.f.ts
index 42635250aa..499069c932 100644
--- a/fjs/types/nullable/proof.f.ts
+++ b/fjs/types/nullable/proof.f.ts
@@ -1,5 +1,5 @@
 import { fromUndefined, map, match, toOption } from './module.f.ts'
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 
 export const proof = [
     () => {
diff --git a/fjs/types/number/proof.f.ts b/fjs/types/number/proof.f.ts
index 8e09b93ae8..7fce7eeec3 100644
--- a/fjs/types/number/proof.f.ts
+++ b/fjs/types/number/proof.f.ts
@@ -1,5 +1,5 @@
 import { sum, min, max, cmp, countOnes } from './module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 export const proof = {
     sum: () => {
diff --git a/fjs/types/object/proof.f.ts b/fjs/types/object/proof.f.ts
index c4584c9665..b90b657136 100644
--- a/fjs/types/object/proof.f.ts
+++ b/fjs/types/object/proof.f.ts
@@ -1,6 +1,6 @@
 import { at } from './module.f.ts'
 import type { OptionalMap, RequiredMap, StringMap } from './module.f.ts'
-import { assertEq, type Assert } from '../../asserts/module.f.ts'
+import { assertEq, type Assert } from '../../asserts/module.f.mjs'
 import type { Equal } from '../ts/module.f.ts'
 
 type _StringMapIsOptional = Assert<Equal<
diff --git a/fjs/types/ordered_map/proof.f.ts b/fjs/types/ordered_map/proof.f.ts
index 3bee873cbe..0a0fa10562 100644
--- a/fjs/types/ordered_map/proof.f.ts
+++ b/fjs/types/ordered_map/proof.f.ts
@@ -1,6 +1,6 @@
 import { at, setReplace, setReduce, empty, entries, remove, fromEntries, type OrderedMap } from './module.f.ts'
 import { toArray } from '../list/module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 export const proof = {
     main: [
diff --git a/fjs/types/patricia_trie/proof.f.ts b/fjs/types/patricia_trie/proof.f.ts
index f41edaeb39..319d2976c0 100644
--- a/fjs/types/patricia_trie/proof.f.ts
+++ b/fjs/types/patricia_trie/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 import { emptyState, patriciaTrie, type State } from './module.f.ts'
 
 type NodeList = readonly [bigint, bigint, bigint][]
diff --git a/fjs/types/prime_field/module.f.ts b/fjs/types/prime_field/module.f.ts
index a408f46d0e..caa414fc54 100644
--- a/fjs/types/prime_field/module.f.ts
+++ b/fjs/types/prime_field/module.f.ts
@@ -8,7 +8,7 @@
  */
 import type { Unary, Reduce } from '../bigint/module.f.ts'
 import { repeat } from '../../common/monoid/module.f.ts'
-import { assertNotNullish } from '../../asserts/module.f.ts'
+import { assertNotNullish } from '../../asserts/module.f.mjs'
 
 /**
  * A type representing a prime field and its associated operations.
diff --git a/fjs/types/prime_field/proof.f.ts b/fjs/types/prime_field/proof.f.ts
index f82c43b629..f7e60a1f05 100644
--- a/fjs/types/prime_field/proof.f.ts
+++ b/fjs/types/prime_field/proof.f.ts
@@ -1,5 +1,5 @@
 import { modSqrt, prime_field, sqrt } from './module.f.ts'
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 
 export const proof = {
     throw: {
diff --git a/fjs/types/range/proof.f.ts b/fjs/types/range/proof.f.ts
index 5dc3c558f4..556511fd44 100644
--- a/fjs/types/range/proof.f.ts
+++ b/fjs/types/range/proof.f.ts
@@ -1,5 +1,5 @@
 import { contains } from './module.f.ts'
-import { assert } from '../../asserts/module.f.ts'
+import { assert } from '../../asserts/module.f.mjs'
 
 export const proof = () => {
     assert(contains(0, 5)(1), 1)
diff --git a/fjs/types/range_map/proof.f.ts b/fjs/types/range_map/proof.f.ts
index 7b374d865d..970ef6c090 100644
--- a/fjs/types/range_map/proof.f.ts
+++ b/fjs/types/range_map/proof.f.ts
@@ -5,7 +5,7 @@ import { union, type SortedSet } from '../sorted_set/module.f.ts'
 import { equal, toArray } from '../list/module.f.ts'
 import { strictEqual } from '../function/operator/module.f.ts'
 import { cmp } from '../string/module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 const str
     : (a: readonly Unknown[]) => string
diff --git a/fjs/types/range_set/proof.f.ts b/fjs/types/range_set/proof.f.ts
index 45812e459e..56149becf9 100644
--- a/fjs/types/range_set/proof.f.ts
+++ b/fjs/types/range_set/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert } from "../../asserts/module.f.ts"
+import { assert } from "../../asserts/module.f.mjs"
 import { toArray } from "../list/module.f.ts"
 import { fromRange, merge, get } from "./module.f.ts"
 import { type Range } from '../range/module.f.ts'
diff --git a/fjs/types/result/proof.f.ts b/fjs/types/result/proof.f.ts
index 6ae51466c2..0362d2e7ad 100644
--- a/fjs/types/result/proof.f.ts
+++ b/fjs/types/result/proof.f.ts
@@ -1,5 +1,5 @@
 import { error, ok, unwrap, invert, mapOk, type Result } from "./module.f.ts"
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 
 const example = () => {
     const success: Result<number, string> = ok(42)
diff --git a/fjs/types/rtti/common/proof.f.ts b/fjs/types/rtti/common/proof.f.ts
index 191e1e5865..ed262ae86d 100644
--- a/fjs/types/rtti/common/proof.f.ts
+++ b/fjs/types/rtti/common/proof.f.ts
@@ -1,7 +1,7 @@
 import { eachEntry } from './module.f.ts'
 import { error, ok, type Result } from '../../result/module.f.ts'
 import type { ValidationError } from './module.f.ts'
-import { assert, assertEq } from '../../../asserts/module.f.ts'
+import { assert, assertEq } from '../../../asserts/module.f.mjs'
 
 type Entries = ReadonlyArray<readonly [string, number]>
 
diff --git a/fjs/types/rtti/module.f.ts b/fjs/types/rtti/module.f.ts
index a37c341a0e..54bbb58633 100644
--- a/fjs/types/rtti/module.f.ts
+++ b/fjs/types/rtti/module.f.ts
@@ -36,7 +36,7 @@
  *
  * See `./ts/module.f.ts` for `Ts<T>` and the `*Ts` transformer types.
  */
-import type { Assert } from '../../asserts/module.f.ts'
+import type { Assert } from '../../asserts/module.f.mjs'
 import { includes, type Includes } from '../array/module.f.ts'
 import type { Equal } from '../ts/module.f.ts'
 import type { StringMap } from '../object/module.f.ts'
diff --git a/fjs/types/rtti/parse/proof.f.ts b/fjs/types/rtti/parse/proof.f.ts
index 688ee18e6e..a1eea37f18 100644
--- a/fjs/types/rtti/parse/proof.f.ts
+++ b/fjs/types/rtti/parse/proof.f.ts
@@ -3,8 +3,8 @@ import { boolean, number, string, bigint, unknown, array, record, or, option } f
 import type { Equal } from '../../ts/module.f.ts'
 import type { Ts } from '../ts/module.f.ts'
 import type { Unknown as DjsUnknown } from '../../../djs/module.f.ts'
-import type { Assert } from '../../../asserts/module.f.ts'
-import { assert, assertEq } from '../../../asserts/module.f.ts'
+import type { Assert } from '../../../asserts/module.f.mjs'
+import { assert, assertEq } from '../../../asserts/module.f.mjs'
 
 const assertOk = ([k]: readonly [string, unknown]) => { assertEq(k, 'ok', 'expected ok') }
 const assertError = ([k]: readonly [string, unknown]) => { assertEq(k, 'error', 'expected error') }
diff --git a/fjs/types/rtti/ts/module.f.ts b/fjs/types/rtti/ts/module.f.ts
index 354a33e10b..5682fa1f87 100644
--- a/fjs/types/rtti/ts/module.f.ts
+++ b/fjs/types/rtti/ts/module.f.ts
@@ -9,7 +9,7 @@
  */
 import { type Equal, primitive, union, printer as tsPrinter } from '../../ts/module.f.ts'
 import type { Tag0, Tag1, Const, Or, String as RttiString, Struct, Tuple, Type, ConstObject } from '../module.f.ts'
-import type { Assert } from '../../../asserts/module.f.ts'
+import type { Assert } from '../../../asserts/module.f.mjs'
 import type { phantomKey } from '../../phantom/module.f.ts'
 import type { StringMap } from '../../object/module.f.ts'
 
diff --git a/fjs/types/rtti/validate/proof.f.ts b/fjs/types/rtti/validate/proof.f.ts
index a3482d9778..c0fffd818f 100644
--- a/fjs/types/rtti/validate/proof.f.ts
+++ b/fjs/types/rtti/validate/proof.f.ts
@@ -3,8 +3,8 @@ import { boolean, number, string, bigint, unknown, array, record, or, option } f
 import type { Equal } from '../../ts/module.f.ts'
 import type { Ts } from '../ts/module.f.ts'
 import type { Unknown as DjsUnknown } from '../../../djs/module.f.ts'
-import type { Assert } from '../../../asserts/module.f.ts'
-import { assert, assertEq } from '../../../asserts/module.f.ts'
+import type { Assert } from '../../../asserts/module.f.mjs'
+import { assert, assertEq } from '../../../asserts/module.f.mjs'
 
 const assertOk = ([k]: readonly [string, unknown]) => { assertEq(k, 'ok', 'expected ok') }
 const assertError = ([k]: readonly [string, unknown]) => { assertEq(k, 'error', 'expected error') }
diff --git a/fjs/types/sorted_list/proof.f.ts b/fjs/types/sorted_list/proof.f.ts
index fc8f40f52d..20dfc40a6c 100644
--- a/fjs/types/sorted_list/proof.f.ts
+++ b/fjs/types/sorted_list/proof.f.ts
@@ -4,7 +4,7 @@ import { sort } from '../object/module.f.ts'
 import { toArray, countdown, length } from '../list/module.f.ts'
 import { flip } from '../function/module.f.ts'
 import { cmp } from '../number/module.f.ts'
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 
 const str: (a: readonly Unknown[]) => string
     = stringify(sort)
diff --git a/fjs/types/sorted_set/proof.f.ts b/fjs/types/sorted_set/proof.f.ts
index 0b074733b6..c3812e7e8a 100644
--- a/fjs/types/sorted_set/proof.f.ts
+++ b/fjs/types/sorted_set/proof.f.ts
@@ -4,7 +4,7 @@ import { sort } from '../object/module.f.ts'
 import { toArray, countdown, length } from '../list/module.f.ts'
 import { flip } from '../function/module.f.ts'
 import { cmp } from '../number/module.f.ts'
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 
 const str: (a: readonly Unknown[]) => string
     = a => stringify(sort)(a)
diff --git a/fjs/types/string/proof.f.ts b/fjs/types/string/proof.f.ts
index c747436a47..2e46e75506 100644
--- a/fjs/types/string/proof.f.ts
+++ b/fjs/types/string/proof.f.ts
@@ -1,6 +1,6 @@
 import { join, concat, repeat, cmp, splitAt } from './module.f.ts'
 import { repeat as repeatList } from '../list/module.f.ts'
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 
 export const proof = {
     example: () => {
diff --git a/fjs/types/string_set/proof.f.ts b/fjs/types/string_set/proof.f.ts
index 1482d369b1..155a1f5cdf 100644
--- a/fjs/types/string_set/proof.f.ts
+++ b/fjs/types/string_set/proof.f.ts
@@ -1,5 +1,5 @@
 import { contains, fromValues, remove, set } from './module.f.ts'
-import { assert, assertEq } from '../../asserts/module.f.ts'
+import { assert, assertEq } from '../../asserts/module.f.mjs'
 
 export const proof = {
     example: () => {
diff --git a/fjs/types/ts/proof.f.ts b/fjs/types/ts/proof.f.ts
index e7ac754c9c..75eb60b58c 100644
--- a/fjs/types/ts/proof.f.ts
+++ b/fjs/types/ts/proof.f.ts
@@ -1,6 +1,6 @@
-import type { Assert } from '../../asserts/module.f.ts'
+import type { Assert } from '../../asserts/module.f.mjs'
 import { printer, primitive, union, type Equal } from './module.f.ts'
-import { assertEq } from '../../asserts/module.f.ts'
+import { assertEq } from '../../asserts/module.f.mjs'
 
 const ro = printer()
 const mut = printer(true)
diff --git a/fjs/types/uint8array/module.f.ts b/fjs/types/uint8array/module.f.ts
index 7c254caff5..ccdeefb5a2 100644
--- a/fjs/types/uint8array/module.f.ts
+++ b/fjs/types/uint8array/module.f.ts
@@ -9,7 +9,7 @@
  *
  * @module
  */
-import { assert, assertNotNullish } from '../../asserts/module.f.ts'
+import { assert, assertNotNullish } from '../../asserts/module.f.mjs'
 import { utf8, utf8ToString } from '../../text/module.f.ts'
 import { maxLengthBytes, msb, tryU8ListToVec, u8List, u8ListToVec, type Vec } from '../bit_vec/module.f.ts'
 import { compose } from '../function/module.f.ts'
@@ -29,7 +29,7 @@ export const toVec = (input: Uint8Array): Vec => {
 
 const m = map(fromArrayLike)
 
-export const listToVec = (input: List<Uint8Array>): Vec => 
+export const listToVec = (input: List<Uint8Array>): Vec =>
     assertNotNullish(tryU8ListToVecMsb(flat(m(input))), "the array is too big")
 
 /**
diff --git a/fjs/types/uint8array/proof.f.ts b/fjs/types/uint8array/proof.f.ts
index 967bf079b3..e17aca76e2 100644
--- a/fjs/types/uint8array/proof.f.ts
+++ b/fjs/types/uint8array/proof.f.ts
@@ -2,7 +2,7 @@ import { maxLength, maxLengthBytes, vec } from '../bit_vec/module.f.ts'
 import { toVec, fromVec, listToVec, decodeUtf8, encodeUtf8 } from './module.f.ts'
 import { strictEqual } from '../function/operator/module.f.ts'
 import { equal, fromArrayLike } from '../list/module.f.ts'
-import { assert } from '../../asserts/module.f.ts'
+import { assert } from '../../asserts/module.f.mjs'
 
 const assertEq = <T>(a: T, b: T) => {
     assert(a === b, [a, b])
diff --git a/fjs/website/proof.f.ts b/fjs/website/proof.f.ts
index f43d29896c..8346e01cd6 100644
--- a/fjs/website/proof.f.ts
+++ b/fjs/website/proof.f.ts
@@ -1,6 +1,6 @@
 import { main } from './module.f.ts'
 import { emptyState, virtual } from '../effects/node/virtual/module.f.ts'
-import { assertEq, assertNotNullish } from '../asserts/module.f.ts'
+import { assertEq, assertNotNullish } from '../asserts/module.f.mjs'
 
 export const proof = {
     main: () => {
diff --git a/nanvm-lib/tests/proof.f.ts b/nanvm-lib/tests/proof.f.ts
index 978f0ae2e7..5ae7fc9a58 100644
--- a/nanvm-lib/tests/proof.f.ts
+++ b/nanvm-lib/tests/proof.f.ts
@@ -1,4 +1,4 @@
-import { assert } from '../../fjs/asserts/module.f.ts'
+import { assert } from '../../fjs/asserts/module.f.mjs'
 
 const { is } = Object;