docs: session handoff (b) — stdlib AOT 13/19 (#135)

docs/history/SESSION-HANDOFF-2026-05-18b.md

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+<!-- SPDX-License-Identifier: PMPL-1.0-or-later -->
+<!-- SPDX-FileCopyrightText: 2026 hyperpolymath -->
+
+# Session handoff (b) — #128/#135 stdlib AOT, continued
+
+Continues `SESSION-HANDOFF-2026-05-18.md`. Single session, sole driver
+(the parallel session was stopped). Read the triage doc + this.
+
+## State
+
+stdlib **13/19 compile** `resolve→typecheck→borrow` on `main`
+(was 11). 7 PRs merged this run (#167, #170, #172, #173, #174, #184,
+plus the earlier slice-10/trunc), each gated on full suite **233/233**,
+zero regression.
+
+The import/builtin **infrastructure is now solid** (this was the bulk
+of the work — io.affine surfaced a 5-layer systemic stack, all fixed):
+
+- **#172** imported modules now get builtin-seeded resolve + typecheck
+  contexts (`seed_builtins` shared; `register_builtins` called in the
+  import path); ADR-011 `use module::{...}` works end to end.
+- **#173** `register_builtins` reconciled with the resolver seed list —
+  file-I/O / env / time / float-math family + `read_line` → `Result`.
+- **#174** imported type-schemes threaded into `check_program`
+  (`~import_types`), so cross-module *values* type-check.
+- **#184** `math.affine` green (`to_float` → `float(n)`; 8 `let mut`).
+
+ADR-011 module model is **ruled**: explicit `use module::{...}`,
+`pub` required (not flat-namespace, not prelude-hub).
+
+## Remaining to close STAGE A
+
+6 files, each a span-less typecheck/parse hunt — one PR each:
+
+| file | error | note |
+|---|---|---|
+| collections | `Unify (Array, (_ -> Bool))` | HOF/filter scheme |
+| io | `Unify (String, Array[String])` | `split` `[String]` at use-site |
+| option | parse `320:15` | slice 9 `&mut Option<T>`; hardest, do last |
+| result | `Unify ((_->_), T)` | generic instantiation |
+| testing | `Unify ((Unit->TestResult), TestResult)` | fn ref vs call |
+| traits | `Unify (ref _, Int)` | ref/borrow scheme |
+
+Then closers: **#138** (remove the `typecheck.ml` "If without else
+returns Never" debug `eprintf`) → **#136** (CI stdlib-wide AOT smoke
+gate) → **#137** (multi-module integration test).
+
+## Build
+
+```
+cd /home/hyperpolymath/dev/affinescript
+export PATH="/usr/bin:$PATH"
+eval $(opam env --switch=/home/hyperpolymath/dev/affinescript --set-switch)
+dune build && dune test            # must stay 233/233
+./_build/default/bin/main.exe check stdlib/<f>.affine
+```
+
+When sweeping, filter the stray `If without else returns Never`
+stderr line (a debug `eprintf`, not a failure — closer #138 removes it).
+
+## Method (kept)
+
+One file per PR; reproduce with `check`; errors carry no span so read
+and reason; most failures are simple **stdlib** bugs (`let`→`let mut`,
+`n+0.0`→`float(n)`, missing `use`/`pub`) not compiler bugs — prefer the
+stdlib fix. Full sweep + `dune test` before every commit; zero
+regression mandatory. `Refs #128`, squash-merge, mirror status on the
+#128 thread. Rigorous triage over a partial hack; don't guess at
+typecheck/borrow internals.