Flake: typeless_package_ts_with_cjs_syntax_loads_as_cjs on Node 20.11 (ERR_INTERNAL_ASSERTION)

[colinhacks]

Failed on Test (ubuntu-latest, node 20.11) in https://github.com/nubjs/nub/actions/runs/31321866733/job/93266014376, green on re-run. Node raises ERR_INTERNAL_ASSERTION from its own ModuleJob.runSync loading tests/fixtures/module-format/notype/cjs.ts.

feature_matrix.rs:320 injects --experimental-detect-module on [20.10.0, 20.19.0) and the preload rides --import. That pair is nodejs/node#54577 and nodejs/node#55500, which fire depending on module load order.

The fixture ran 10/10 green locally on Node 20.11.0. Found while landing #705; not caused by it.

[pullfrog]

Reproduced on Node 20.11.0 — 15/60 runs of notype/cjs.ts failed with the exact ModuleJob.runSync stack. Fix in #707 (0/140 after).

The cause is not --experimental-detect-module: suppressing it still gave 17/50. The trigger is the deferred transpile-cache sweep. maybeSweepCache fires an unawaited import("./cache-evict.mjs") from a setImmediate, and that module's static node:fs / node:path imports leave pending builtin jobs in the ESM loadCache. A transpiled CJS entry's require() runs through the ESM translator's sync path (getModuleJobSync → runSync) and asserts on a job whose module is not yet a ModuleWrap.

What pins it:

Arm (Node 20.11.0)	Result
require("node:path") from a transpiled .ts	15/40 fail
require("node:fs") from a transpiled .ts	14/40 fail
require("node:os") — not imported by cache-evict.mjs	0/40
plain .js entry, require("node:path")	0/40
sweep sentinel pre-seeded, so no import() fires	0/60

Clean on 18.19.1, 20.19.0 and 22.13.0. The harness gives every invocation a fresh XDG_CACHE_HOME, so the sweep is due on every run; a real user on Node 20.10–20.18 hits the same crash once a day, which makes this a runtime bug rather than a test defect.

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