effect-basic-smoke: runtime TypeError 'undefined is not iterable' (regressed by 2026-07-02; window includes #5466)

[proggeramlug]

Summary

effect-basic-smoke fails at runtime: the fixture compiles clean (37.2MB binary, auto-optimize path) but exits with

TypeError: undefined is not iterable
    at <anonymous>

and empty stdout.

Evidence

• Run https://github.com/PerryTS/perry/actions/runs/28653042861 (PR fix(deps): pin bson to mongodb's re-exported major — restores the extended CI gate (#5872) #5886's labeled run, 2026-07-03): artifact effect-basic-smoke-logs — perry-compile.log ends with Wrote executable ... Binary size: 37.2MB; perry-run.log contains only the TypeError; perry-out.txt is empty.
• The same job also failed on PR fix(runtime): #5763 regression — setPrototypeOf cycle walk must not advance past chain end #5866's labeled run (2026-07-03, base e8e2b5240) — i.e. the failure predates transform(async): CPS async class methods, capturing-closure fns, and nested async closures #5854 (async class-method CPS), fix(runtime): promise reactions must not clobber the single handler slot (combinators + .finally) #5867 (promise reaction slots), fix(transform): #5868 — switch inside async/generator state machines miscompiled #5885 (switch state machines), and the bson episode (deps(deps): bump bson from 2.15.0 to 3.1.0 #5830/fix(deps): bson 3.x/mongodb feature mismatch broke default build #5887). On the 2026-07-03 morning runs it was masked by the bson E0308 build breakage.

Window

Last known-green effect-basic run would be the most recent tag's extended suite (extended jobs are tag/label-gated). Regression window is bounded above by 2026-07-02 ~13:00Z; the largest in-window merge is #5466 (ce0117a60, representation-aware type lowering, 2026-07-02) — prime suspect by timing and blast radius, alongside the rest of the 0.5.1213 wave.

Notes

• Effect leans heavily on generators (Effect.gen(function*(){ yield* ... })) and iterator protocol — "undefined is not iterable" smells like an iterator-returning path (e.g. [Symbol.iterator] lookup or a yield* operand) coming back undefined.
• Related standing Effect tracker: Tracking: Effect framework end-to-end compat (post-#309 / #310) #321 (end-to-end), perry-codegen: Effect — (number).slice is not a function during Schema.ts__init (#680 follow-up, ~310th init) #684 (Schema.ts ~310th-init).

[proggeramlug]

Window refinement from the v0.5.1205 tag run's artifact (run 28110573641, 2026-06-24): effect-basic failed to LINK back then — undefined reference to perry_fn_node_modules_effect_src_SchemaAST_ts__$null (the $-named-export symbol family, cf. #5431). So between 2026-06-24 and 2026-07-02 the link failure got fixed and the failure moved forward to the current runtime TypeError: undefined is not iterable. The runtime-regression window stays bounded by 2026-07-02; note the fixture wasn't green immediately before it — it went link-fail → runtime-fail, which is progress but changes what 'regressed' means here.