fibers B1.2: 0151 fixed → async surface callable; blocked on 0152 (Atomic(bool) i1 atomic)

issue 0151 (generic $T inference through generic-struct / pointer / UFCS-pack
params) is fixed and committed, so io.sx's async/await/cancel are now callable
in every form. Building the async examples then tripped a SEPARATE codegen bug:
Atomic(bool) emits a sub-byte (i1) atomic load/store that fails LLVM
verification (must be byte-sized). Future.canceled: Atomic(bool) hits it.

Filed issues/0152 with a standalone repro + investigation prompt (codegen fix
in src/backend/llvm/ops.zig — promote sub-byte atomics to i8 storage). Per the
STOP rule, paused B1.2's async examples (1805/1806) pending the 0152 fix.
Checkpoint updated: 0151 RESOLVED, async surface BLOCKED on 0152.

current/CHECKPOINT-FIBERS.md

@@ -4,10 +4,29 @@ Companion to [PLAN-FIBERS.md](PLAN-FIBERS.md). Update after every step (one step
 per the cadence rule). New corpus category: `18xx` concurrency.
 
 ## Last completed step
-**B1.2 (Io capability) — PARTIALLY LANDED + adversarially reviewed. Infrastructure GOOD;
-async SURFACE blocked on a generic-inference compiler bug (issue 0151, widened).**
-Commits `a1b14f0` (lock) + `45d869d` (Io capability) + `3eeb965` (issue 0151). Suite green
-**726/0**, master clean.
+**issue 0151 FIXED — generic `$T` now infers through generic-struct / pointer / UFCS-pack
+params.** `await`/`cancel`/`async` are CALLABLE again. The async SURFACE is now blocked on a
+DIFFERENT, freshly-exposed codegen bug: **issue 0152 — `Atomic(bool)` emits a sub-byte (i1)
+atomic that LLVM rejects** (the `Future.canceled: Atomic(bool)` field hits it). Suite green
+**728/0**, master clean.
+- **0151 fix (committed):** four gaps closed on the inference + UFCS-dispatch path —
+  (1) `extractTypeParam`/`matchTypeParam(Static)` got a `parameterized_type_expr` arm
+  (recover the arg instance's recorded per-param bindings via `struct_instance_bindings` +
+  the template's ordered `type_params`, recurse positionally; this also fixes `*Box($T)` —
+  it recurses into its `Box($T)` pointee); (2) the `pointer_type_expr` arm now falls through
+  to match the pointee against a non-pointer arg (auto-address-of: a `*Box($T)` param accepts
+  a by-value `Box($T)`, e.g. a UFCS receiver `b.m()`); (3) `ExprTyper.inferType` got a
+  `.lambda` arm building the closure type from the lambda's annotations (the UFCS binder types
+  args from the raw AST before they're lowered, so it can now bind `Closure(..) -> $R` from
+  the worker's declared return type); (4) a pack UFCS target routes through the SAME
+  `lowerPackFnCall` the direct call uses, with the receiver spliced in as `args[0]`.
+- Regression tests: `examples/0214-generics-ufcs-closure-return-pack.sx` (direct + UFCS
+  closure-return pack) + `examples/0215-generics-infer-through-pointer.sx` (by-value /
+  pointer / multi-param / nested / UFCS-auto-ref struct-head inference). Issue 0151 marked
+  RESOLVED; repro moved into the suite.
+
+### Earlier — B1.2 (Io capability) — LANDED + adversarially reviewed
+Commits `a1b14f0` (lock) + `45d869d` (Io capability) + `3eeb965` (issue 0151 lock).
 - **LANDED + review-confirmed correct** (commit 45d869d): `Io :: protocol #inline`
   (spawn_raw/suspend_raw/ready/poll/now_ms/arm_timer) + `io` field on `Context`
   (`{allocator; data; io}`, io LAST); BOTH `__sx_default_context` materializers
@@ -82,24 +101,27 @@ body); closed + locked. The review's `.naked`-lambda CRITICAL was a false positi
 (unparseable — `isLambda` breaks on the `abi` keyword).
 
 ## Current state
-**B1.2 is UNBLOCKED.** Master GREEN (726/0), installed `sx` clean. The earlier "blockers"
-were NOT real: issue **0151 was INVALID** (its repro used the non-idiomatic `($A)->$R`
-bare-fn-ptr form) — **removed**. The correct `async` idiom **works today with no compiler
-change** (verified live): `spawn :: (worker: Closure(..$args) -> $R, ..$args) -> Wrap($R)`
-with a **lambda worker** + the `w : Wrap($R) = ---; w.v = worker(..args);` build form —
-mirrors the canonical `examples/0543-packs-canonical-map.sx`. Ran `42 42` for homogeneous +
-heterogeneous args. Caveats (work within them, not "bugs"): lambda params must be annotated
-(`(a: i64, b: i64) -> i64 => …`); a bare *named* fn passed as the worker is non-idiomatic —
-use a lambda; build the result struct with `= ---` + field-assign, not a struct-literal in
-`return`. Issue **0150** (`void` struct field → SIGTRAP exit 133) is a **real** bug but only
-reached via `Future(void)` (void-returning worker / `timeout`) — **DEFERRED**: B1.2 supports
-non-void workers; revisit `Future(void)` in B1.4 (or fix 0150 standalone). The B1.2 *design*
-(Io protocol on Context, blocking `CBlockingIo`, `context.io.now_ms()`) was validated live;
-WIP at `.sx-tmp/b12-wip/` has the working Io/Context/materializer parts — reuse those, rewrite
-the async layer to the pack-lambda idiom above.
+**B1.2 Io capability is LANDED; the async surface is now CALLABLE but blocked on issue 0152.**
+Master GREEN (728/0), installed `sx` clean.
+- **0151 fixed (this session, committed):** the generic-inference engine now binds `$T`
+  through a generic-struct param head (`Box($T)`), through a pointer (`*Box($T)`, incl. the
+  UFCS auto-address-of receiver), and through a closure-return-via-pack on the UFCS dot-call
+  path. So `async`/`await`/`cancel` in `library/modules/std/io.sx` — all `ufcs`, with
+  `await`/`cancel` taking `*Future($R)` — are callable in every form. Details in the
+  "Last completed step" block above; regression tests `examples/0214` + `0215`.
+- **NEW blocker — issue 0152 (`Atomic(bool)` → sub-byte i1 atomic):** with the surface
+  callable, building the async examples now trips LLVM verification: `Atomic($T)` lowers a
+  `bool` element to `i1` and emits an `i1` atomic load/store, which LLVM rejects ("atomic
+  memory access' size must be byte-sized"). `Future.canceled: Atomic(bool)` hits this in
+  `async`/`cancel`/`await`. Standalone repro + investigation prompt filed at
+  `issues/0152-atomic-bool-sub-byte-atomic-llvm-reject.md`. The fix is codegen-level
+  (`src/backend/llvm/ops.zig` atomic emitters — promote sub-byte atomics to `i8` storage with
+  `trunc`/`zext` at the value boundary). A secondary `or`-merge PHI i1/i64 mismatch appeared in
+  the same probe — likely entangled with the malformed `Atomic(bool)` field; re-check after 0152.
+- Issue **0150** (`void` struct field → SIGTRAP) remains DEFERRED — only `Future(void)` /
+  `timeout`, which are B1.4.
 
-### B1.2 attempt (BLOCKED — design proven, two compiler bugs filed)
-What was built + verified WORKING (then reverted to keep master green):
+### B1.2 Io capability — what is LANDED + verified (commit 45d869d)
 - `Io :: protocol #inline { spawn_raw; suspend_raw -> !; ready; poll; now_ms; arm_timer; }`
   in `core.sx` next to `Allocator`, with `SpawnOpts{ pin: PinTarget }` + `ParkToken{ handle }`.
   Six methods, each justified by a downstream consumer (B1.3-B1.5).
@@ -124,22 +146,15 @@ What was built + verified WORKING (then reverted to keep master green):
   `!` by contract (e.g. `Io.suspend_raw`) yet never raise; the "declared `!` but never errors —
   drop the `!`" hint is a false positive for impl methods, now suppressed for them.
 
-Where it BROKE (the two blockers — both INDEPENDENT of the Io design, both repro standalone):
-- **issue 0150** — `Future(void)` (for `timeout -> Future(void)`) makes a `result: void` field;
-  a `void` struct field crashes the compiler with an unsized-type SIGTRAP in LLVM
-  `getTypeSizeInBits` (a bare `struct { v: void; }` repros it). `timeout` was DEFERRED (it is a
-  B1.4 stub needing `arm_timer` anyway) rather than routed around with a non-void shape.
-- **issue 0151** — `async(io, worker: ($A) -> $R, arg: $A) -> Future($R)`: `$R` inferred from a
-  fn-pointer parameter's RETURN type type-checks the call but is NOT bound as a usable type in
-  the body, so `Future(R)` errors `unknown type 'R'`. A direct `arg: $A` binds fine — the gap is
-  specific to type-vars nested in a fn-ptr/closure param signature. This blocks the central
-  `async`/`await` free-fns. (Manifested as the "unresolved type reached LLVM emission" panic —
-  the same one another session filed against my dirty binary as issue 0149, now moot after the
-  revert.)
+Status of the blockers that originally stopped B1.2:
+- **issue 0151 — FIXED this session** (generic `$T` through generic-struct / pointer /
+  UFCS-pack params). `async`/`await`/`cancel` are callable. See "Last completed step".
+- **issue 0152 — NEW, the current blocker** (`Atomic(bool)` → sub-byte i1 atomic; LLVM reject).
+  Blocks the async examples via `Future.canceled: Atomic(bool)`. Filed; codegen-level fix.
+- **issue 0150** — `void` struct field SIGTRAP; only `Future(void)`/`timeout` (B1.4). DEFERRED.
 
-Per the IMPASSABLE STOP rule: filed 0150 + 0151, reverted all B1.2 working changes (master
-green again, photo project unbroken), STOPPED. Resume B1.2 once 0150 + 0151 land — the WIP in
-`.sx-tmp/b12-wip/` makes it ~mechanical (the design is proven).
+Per the IMPASSABLE STOP rule: 0151 fix shipped (suite green 728/0), 0152 filed, STOPPED.
+Resume B1.2's async examples once 0152 lands.
 
 ### Earlier — B1.0 + B1.1 complete
 Stream A (atomics) is feature-complete (✅). Stream B1: **B1.0 + B1.1 complete.** The two
@@ -163,18 +178,18 @@ fibers/Io/scheduler code yet. Grounded floor facts:
   boundary; a sharper sx diagnostic for it is a candidate polish, not a blocker.
 
 ## Next step
-**Fix issue 0151 (generic inference through a pointer) so `await`/`cancel` become callable —
-then complete B1.2's async surface.** Sequence:
-1. **Fix 0151 (WIDENED):** make the generic-inference engine bind `$T` from a pointer-wrapped
-   param (`b: *Box($T)` ⇒ `unbox(@b)` infers `T`), which unblocks `await`/`cancel`
-   (`*Future($R)`). The same bug has two more faces — `$R` from a closure-return via a pack,
-   and via UFCS dot-dispatch (the original 0151 + the `f.await()` SIGTRAP). Acceptance cases
-   are in `issues/0151-...md`. This is generic-inference-engine work
-   (`src/ir/lower/generic.zig` `extractTypeParam` + the UFCS call path) — its own focused step.
-2. **Restore/add the async examples:** `examples/1805-concurrency-io-blocking-async.sx`
-   (`context.io.async((a:i64,b:i64)->i64 => a+b, 40, 2).await()` → 42) + `1806-...-io-cancel.sx`
-   (cancel → state `.canceled`). lock→green. Regen `.ir` only after green; confirm layout-only.
-3. Then B1.2 is truly done → proceed to **B1.3 (fiber runtime)**.
+**BLOCKED on issue 0152 (`Atomic(bool)` sub-byte atomic).** Once it lands, complete B1.2's
+async surface:
+1. **Add the async examples:** `examples/1805-concurrency-io-blocking-async.sx`
+   (`context.io.async((a:i64,b:i64)->i64 => a+b, 40, 2).await() or {…}` → 42; `double:`/`sum:`)
+   + `1806-...-io-cancel.sx` (cancel → `await` raises `.Canceled`). The async surface is already
+   callable (0151 fixed); a working probe lives at `.sx-tmp/async_surface.sx` — it builds the
+   Futures and dispatches `async`/`await`/`cancel` correctly, only the `Atomic(bool)` codegen
+   (0152) stops it. lock→green, then regen `.ir` (confirm layout-only).
+   - Note: `await` returns a value-failable `($R, !IoErr)`; use `f.await() or { default }` (a
+     braced `or`, not `catch <expr>`). Re-verify the `or`-merge PHI i1/i64 symptom is gone once
+     0152 lands (it was likely a cascade from the malformed `Atomic(bool)` field).
+2. Then B1.2 is truly done → proceed to **B1.3 (fiber runtime)**.
 
 **Deferred (do NOT block B1.2 on these):** issue **0150** (`void` struct field SIGTRAP) — only
 `Future(void)`/`timeout`, which are B1.4. The **`::` callable-parameter feature** (named-fn
@@ -185,16 +200,16 @@ done, inference incomplete); a dedicated effort; lambda workers are the B1.2 idi
 `call.zig:1229`, io last). Io protocol + materializers + push-inherit are LANDED + reviewed.
 
 ## Known issues / capability gaps
-- **🔴 B1.2 BLOCKERS (both filed, both standalone-reproducible, both independent of the Io
-  design):**
-  - **issue 0150** — a `void` struct field crashes the compiler (unsized-type SIGTRAP in LLVM
-    `getTypeSizeInBits`). Blocks `Future(void)` → `timeout`. Repro: `issues/0150-...`.
-  - **issue 0151** — a type-var inferred from a fn-pointer parameter's RETURN type is not bound
-    in the function body (`unknown type 'R'`). Blocks `async(io, worker: ($A)->$R, arg)`'s
-    `Future(R)`. Repro: `issues/0151-...`.
-  - (Note: **issue 0149**, filed by another session against the dirty in-progress binary, was a
-    manifestation of 0151 — "unresolved type reached LLVM emission". Moot after the revert; its
-    real root cause is 0151.)
+- **🔴 B1.2 BLOCKER — issue 0152** (`Atomic(bool)` → sub-byte i1 atomic load/store; LLVM
+  rejects "atomic memory access' size must be byte-sized"). Blocks the async examples via
+  `Future.canceled: Atomic(bool)`. Standalone repro + fix prompt: `issues/0152-...`. Codegen-
+  level (`src/backend/llvm/ops.zig` atomic emitters; promote sub-byte → i8 storage).
+- **✅ issue 0151 — FIXED this session** (generic `$T` through generic-struct / pointer /
+  UFCS-pack params). Regression: `examples/0214` + `0215`. Was the original B1.2 surface blocker.
+- **issue 0150** (deferred) — a `void` struct field crashes the compiler (unsized-type SIGTRAP
+  in LLVM `getTypeSizeInBits`). Blocks `Future(void)` → `timeout` (B1.4). Repro: `issues/0150-...`.
+  - (Note: **issue 0149**, filed by another session against an earlier dirty binary, was a
+    manifestation of the pre-fix 0151 — now moot.)
 - **Orthogonal (not a B1 blocker):** default VALUES for comptime params don't bind on
   generic-struct methods (free-fn defaults DO work) — inherited from Stream A. Only matters
   if a B2 lib type wants a defaulted comptime param; atomics/fibers require explicit, so
@@ -291,3 +306,16 @@ done, inference incomplete); a dedicated effort; lambda workers are the B1.2 idi
   filed with standalone repros + investigation prompts. Per the STOP rule: reverted ALL B1.2
   working changes (master green again, 726/0; the dirty binary had broken the photo project —
   see the now-moot 0149), saved WIP to `.sx-tmp/b12-wip/`, STOPPED. Resume after 0150 + 0151.
+- **0151 FIXED** — generic inference now binds `$T` through a generic-struct param head, a
+  pointer (`*Box($T)`, incl. UFCS auto-ref), and a closure-return-via-pack on the UFCS path.
+  Four gaps closed: `parameterized_type_expr` arm in `extractTypeParam`/`matchTypeParam(Static)`
+  (recovers the arg instance's recorded per-param bindings, recurses positionally); pointer arm
+  falls through to match a value arg (auto-address-of); `ExprTyper.inferType` `.lambda` arm
+  (closure type from annotations — UFCS types args from raw AST pre-lowering); pack UFCS target
+  routes through `lowerPackFnCall` with the receiver spliced in as `args[0]`. Issue 0151 marked
+  RESOLVED; repro → `examples/0214-generics-ufcs-closure-return-pack.sx`; widened cases →
+  `examples/0215-generics-infer-through-pointer.sx`. Suite green 728/0. The now-callable async
+  surface immediately exposed a SEPARATE codegen bug — **issue 0152** (`Atomic(bool)` → sub-byte
+  i1 atomic, LLVM reject; `Future.canceled` hits it). Filed with standalone repro + fix prompt.
+  Per the STOP rule: shipped the 0151 fix, filed 0152, STOPPED. Resume the async examples
+  (1805/1806) after 0152.

issues/0152-atomic-bool-sub-byte-atomic-llvm-reject.md

@@ -0,0 +1,79 @@
+# 0152 — `Atomic(bool)` emits a sub-byte (i1) atomic load/store that LLVM rejects
+
+## Symptom
+
+`Atomic(bool)` lowers `bool` to LLVM `i1` and emits the atomic load/store
+at that type. LLVM requires atomic memory accesses to be byte-sized, so
+codegen fails verification:
+
+```
+LLVM verification failed: atomic memory access' size must be byte-sized
+ i1  store atomic i1 %load5, ptr %gep release, align 1
+ i1  %atomic_load = load atomic i1, ptr %gep11 acquire, align 1
+```
+
+- `Atomic(i64)`, `Atomic(i32)`, … → fine (byte-sized).
+- `Atomic(bool)` → LLVM verifier error (i1 is 1 *bit*, not byte-sized).
+
+## Reproduction
+
+Standalone — depends on no project symbols beyond `modules/std.sx` +
+`modules/std/atomic.sx`:
+
+```sx
+#import "modules/std.sx";
+#import "modules/std/atomic.sx";
+
+main :: () -> i32 {
+    a := Atomic(bool).init(false);
+    a.store(true, .release);
+    if a.load(.acquire) { print("yes\n"); } else { print("no\n"); }
+    return 0;
+}
+```
+
+Expected: prints `yes`. Actual: LLVM verification failure (i1 atomic).
+
+## Impact
+
+Blocks the B1.2 async surface. `library/modules/std/io.sx`'s
+`Future($R)` carries a `canceled: Atomic(bool)` cancellation flag (atomic
+so a future scheduler thread can flip it). `async`/`cancel`/`await` all
+touch it (`Atomic(bool).init`, `.store(true, .release)`,
+`.load(.acquire)`), so the async examples (`1805`/`1806`) cannot build.
+This is independent of issue 0151 (generic inference) — that is now fixed,
+which is what newly exposed this codegen path.
+
+## Investigation prompt
+
+The atomic load/store emitters in `src/backend/llvm/ops.zig`
+(`emitAtomicLoad` ~line 387, `emitAtomicStore`, `emitAtomicRmw`,
+`emitAtomicCmpxchg`) use `toLLVMType(instruction.ty)` directly as the
+atomic access type. For a `bool` element that is `i1`, which LLVM rejects
+for atomics (must be a byte-multiple).
+
+The fix should promote a sub-byte atomic to its byte-sized storage type:
+load/store as `i8` (the ABI storage type for `bool`) and `trunc`/`zext`
+between `i1` and `i8` at the value boundary — mirroring how a non-atomic
+`bool` field is already stored as a byte. Apply consistently across
+load / store / rmw / cmpxchg so an `Atomic(bool)` round-trips. Confirm the
+alignment (`LLVMSetAlignment`) uses the promoted byte size.
+
+Possible alternative: have `Atomic($T)` (in `library/modules/std/atomic.sx`)
+constrain / widen a `bool` element to a byte-sized integer in the type
+itself — but the codegen-level promotion is more robust (any i1-typed
+atomic, however it arises, becomes legal).
+
+Verification: run the repro above; expect `yes`. Then restore
+`examples/1805-concurrency-io-blocking-async.sx` (+ add `1806` cancel) per
+Stream B1 / CHECKPOINT-FIBERS and confirm the async surface builds and runs
+(`sum: 42` / `double: 42`, cancel → `.canceled`).
+
+### Possibly-related secondary symptom (verify after the i1 fix)
+
+The same async probe also tripped an `or`-merge PHI type mismatch
+(`%bp = phi i1 [ true, … ], [ 0, … ]`) when `f.await() or { <i64> }` was
+lowered. A minimal `(i64, !E)` + `or { -1 }` does NOT reproduce it, so this
+may be entangled with the malformed `Atomic(bool)` field in the `Future`
+struct rather than a second bug. Re-check once the i1 atomic is fixed; if it
+persists, file separately.