GREEN: io/print_str byte-faithful via @fputs(@stdout) — closes #29

The runtime print path now writes exactly the bytes of its
argument with no implicit trailing newline. `io/print_str` is
byte-faithful; authors who want a newline emit `(do io/print_str
"\n")` themselves.

## Codegen

`crates/ailang-codegen/src/lib.rs`:
- Module preamble: `@puts(ptr)` → `@fputs(ptr, ptr)` plus
  `@stdout = external global ptr` (libc's `FILE *stdout`).
- Effect-op lowering for `io/print_str`: emit
  `getelementptr +8` then `load ptr, ptr @stdout` then
  `call/tail call i32 @fputs(ptr bytes, ptr fp)`. Identical
  bytes-pointer GEP, distinct sink.
- The pinned IR-shape test renames from
  `print_str_calls_puts_with_bytes_pointer` to
  `print_str_calls_fputs_with_bytes_pointer_and_stdout` and now
  asserts: bytes-GEP present, stdout-load present, both module-
  preamble declarations present, and no `@puts(` call anywhere
  in the emitted IR.

## Why this shape, and not the alternatives

- *Rename `io/print_str` to `io/println_str` (issue #29 option 2)*
  — kept the auto-newline, just relabelled it. AILang's design
  bias is explicit-over-implicit (CLAUDE.md: implicit conversions
  cut). Auto-newline is a hidden runtime augmentation; the rename
  would have preserved it. Rejected.
- *Append `\n` inside the polymorphic `print` (Show-mediated)
  function in `examples/prelude.ail`* — would have been a one-line
  fix. Rejected: `print` is the Show-mediated formatter, not a
  newline emitter; baking a newline into it would have re-imposed
  the same implicit-augmentation problem one layer up, breaking
  callers that legitimately want pure-bytes output.

## Fixture / test sweep

30 `.ail` fixtures whose owning tests asserted line-separated
stdout now emit explicit `(do io/print_str "\n")` after each
print. Tests that asserted on multi-line stdout (`show_print_e2e`,
`floats_e2e`, `str_concat_e2e`, `eq_ord_e2e`, several `print_*`
smoke tests) had their fixtures sweetened the same way; assertions
themselves remain the canonical observable output. Fixtures that
never relied on the newline (no test ever read the absence of one)
were left untouched.

## Migrated metadata

- `crates/ailang-core/tests/hash_pin.rs`: the `ordering_match::main`
  canonical hash is refreshed (`b65a7f834703ffb4` →
  `8ed47b4062ce00f5`). The comment now names both successive
  corpus migrations honestly: the per-type-print-retirement (which
  moved `(do io/print_int x)` to `(app print x)`) AND this
  fputs swap (which wrapped that with `(seq ... (do io/print_str
  "\n"))`).
- `design/contracts/str-abi.md`: the consumer-ABI table now lists
  `@fputs` as the print sink. A prose paragraph documents the
  byte-faithful semantics and references this issue.
- `examples/ordering_match.prose.txt`: regenerated from the
  updated `ordering_match.ail`.
- `crates/ail/tests/snapshots/{hello,sum,max3,list,ws_main}.ll`:
  IR snapshots regenerated via `UPDATE_SNAPSHOTS=1`.
- Stale `@puts` comments in `runtime/str.c`,
  `crates/ail/tests/{e2e,show_print_e2e,print_no_leak_pin}.rs`
  replaced with `@fputs`.

## Verification

- `cargo test -p ail --test print_str_no_auto_newline_e2e` — both
  RED tests from commit c8ecfa3 now pass.
- `cargo test --workspace` — 90 test groups GREEN, 0 failures.
- `cargo build --workspace` — GREEN.
- No new clippy lints (24 warnings pre-existing in
  `crates/ailang-core/src/lib.rs:129`).
- Stats: `bench/orchestrator-stats/2026-05-21-iter-bugfix-print-
  str-fputs.json` — 1/1 tasks, 0 re-loops, 0 review loops.

## Empirical evidence cited

Caught in the 2026-05-21 Qwen3-Coder naming-A/B run
(`experiments/2026-05-21-naming-ab/runs/r1/`): every cohort wrote
`(do io/print_str "...\n")` with explicit `\n` and got doubled
newlines, failing the `t3_main_prints` stdout match across all
three cohorts. The empirical LLM-natural form already assumes the
new (post-this-commit) semantics — confirming the
feature-acceptance test in CLAUDE.md.

closes #29

crates/ail/tests/e2e.rs

@@ -2580,7 +2580,8 @@ fn ail_run_accepts_ail_source_with_same_stdout_as_ail_json() {
 /// wired in hs.4 — exercises checker (signature install), codegen
 /// (lower_app arm + IR-header declare + is_static_callee whitelist),
 /// runtime (str.c's `ailang_int_to_str` allocates a heap-Str slab,
-/// @puts reads from the bytes pointer at offset 8), and the
+/// @fputs reads from the bytes pointer at offset 8 with @stdout as
+/// the FILE*), and the
 /// unconditional `runtime/rc.c` link (str.c's weak extern of
 /// `ailang_rc_alloc` resolves to the strong rc.c definition under
 /// every alloc strategy after the hs.4 hoist).

crates/ail/tests/print_no_leak_pin.rs

@@ -16,7 +16,7 @@
 //! `ailang_rc_stats: allocs=1 frees=0 live=1`. The IR for the post-
 //! mono `ail_prelude_print__Int` body contains a `call ptr
 //! @ail_prelude_show__Int(...)` followed by `getelementptr +8` +
-//! `@puts` + `ret i8 0` — there is no `ailang_rc_dec` on the
+//! `@fputs` + `ret i8 0` — there is no `ailang_rc_dec` on the
 //! show-result before return. Root cause sits at codegen's
 //! `is_rc_heap_allocated` App-arm: it reads the callee's
 //! `Type::Fn.ret_mode` via `synth_callee_ret_mode` and requires

crates/ail/tests/show_print_e2e.rs

@@ -56,12 +56,15 @@ fn build_and_run(fixture: &str) -> String {
 #[test]
 fn print_primitives_smoke_runs_end_to_end() {
     let stdout = build_and_run("show_print_smoke.ail");
-    // print 42        → "42\n"   (int_to_str + puts)
-    // print true      → "true\n" (bool_to_str + puts)
-    // print "hello"   → "hello\n" (str_clone + puts)
-    // print 3.14      → "3.14\n" (float_to_str / libc %g + puts)
-    // puts emits each Str + a trailing newline; trimmed output is
-    // "42\ntrue\nhello\n3.14".
+    // Post Gitea #29 (io/print_str → @fputs), the print path no
+    // longer appends an implicit newline. The fixture now emits
+    // each value with an explicit `(do io/print_str "\n")` after
+    // the print, so the raw stdout is "42\ntrue\nhello\n3.14\n"
+    // and `.trim()` lands at "42\ntrue\nhello\n3.14".
+    // print 42        → "42"   (int_to_str), then explicit "\n"
+    // print true      → "true" (bool_to_str), then explicit "\n"
+    // print "hello"   → "hello" (str_clone), then explicit "\n"
+    // print 3.14      → "3.14" (float_to_str / libc %g)
     assert_eq!(stdout, "42\ntrue\nhello\n3.14", "got: {stdout:?}");
 }
 

crates/ail/tests/snapshots/hello.ll

@@ -5,7 +5,8 @@ target triple = "<NORMALIZED>"
 @.str_hello_str_0 = private unnamed_addr constant <{ i64, [15 x i8] }> <{ i64 14, [15 x i8] c"Hello, AILang.\00" }>, align 8
 
 declare i32 @printf(ptr, ...)
-declare i32 @puts(ptr)
+declare i32 @fputs(ptr, ptr)
+@stdout = external global ptr
 declare ptr @ailang_rc_alloc(i64)
 declare void @ailang_rc_inc(ptr)
 declare void @ailang_rc_dec(ptr)
@@ -33,7 +34,8 @@ declare i64 @llvm.fptosi.sat.i64.f64(double)
 define i8 @ail_hello_main() {
 entry:
   %v1 = getelementptr inbounds i8, ptr getelementptr inbounds (<{ i64, [15 x i8] }>, ptr @.str_hello_str_0, i32 0, i32 0), i64 8
-  call i32 @puts(ptr %v1)
+  %v2 = load ptr, ptr @stdout, align 8
+  call i32 @fputs(ptr %v1, ptr %v2)
   ret i8 0
 }
 

crates/ail/tests/snapshots/list.ll

@@ -3,7 +3,8 @@ source_filename = "list.ail"
 target triple = "<NORMALIZED>"
 
 declare i32 @printf(ptr, ...)
-declare i32 @puts(ptr)
+declare i32 @fputs(ptr, ptr)
+@stdout = external global ptr
 declare ptr @ailang_rc_alloc(i64)
 declare void @ailang_rc_inc(ptr)
 declare void @ailang_rc_dec(ptr)
@@ -240,7 +241,8 @@ define i8 @ail_prelude_print__Int(i64 %arg_x) {
 entry:
   %v1 = call ptr @ail_prelude_show__Int(i64 %arg_x)
   %v2 = getelementptr inbounds i8, ptr %v1, i64 8
-  call i32 @puts(ptr %v2)
+  %v3 = load ptr, ptr @stdout, align 8
+  call i32 @fputs(ptr %v2, ptr %v3)
   call void @ailang_rc_dec(ptr %v1)
   ret i8 0
 }

crates/ail/tests/snapshots/max3.ll

@@ -3,7 +3,8 @@ source_filename = "max3.ail"
 target triple = "<NORMALIZED>"
 
 declare i32 @printf(ptr, ...)
-declare i32 @puts(ptr)
+declare i32 @fputs(ptr, ptr)
+@stdout = external global ptr
 declare ptr @ailang_rc_alloc(i64)
 declare void @ailang_rc_inc(ptr)
 declare void @ailang_rc_dec(ptr)
@@ -228,7 +229,8 @@ define i8 @ail_prelude_print__Int(i64 %arg_x) {
 entry:
   %v1 = call ptr @ail_prelude_show__Int(i64 %arg_x)
   %v2 = getelementptr inbounds i8, ptr %v1, i64 8
-  call i32 @puts(ptr %v2)
+  %v3 = load ptr, ptr @stdout, align 8
+  call i32 @fputs(ptr %v2, ptr %v3)
   call void @ailang_rc_dec(ptr %v1)
   ret i8 0
 }

crates/ail/tests/snapshots/sum.ll

@@ -3,7 +3,8 @@ source_filename = "sum.ail"
 target triple = "<NORMALIZED>"
 
 declare i32 @printf(ptr, ...)
-declare i32 @puts(ptr)
+declare i32 @fputs(ptr, ptr)
+@stdout = external global ptr
 declare ptr @ailang_rc_alloc(i64)
 declare void @ailang_rc_inc(ptr)
 declare void @ailang_rc_dec(ptr)
@@ -132,7 +133,8 @@ define i8 @ail_prelude_print__Int(i64 %arg_x) {
 entry:
   %v1 = call ptr @ail_prelude_show__Int(i64 %arg_x)
   %v2 = getelementptr inbounds i8, ptr %v1, i64 8
-  call i32 @puts(ptr %v2)
+  %v3 = load ptr, ptr @stdout, align 8
+  call i32 @fputs(ptr %v2, ptr %v3)
   call void @ailang_rc_dec(ptr %v1)
   ret i8 0
 }

crates/ail/tests/snapshots/ws_main.ll

@@ -3,7 +3,8 @@ source_filename = "ws_main.ail"
 target triple = "<NORMALIZED>"
 
 declare i32 @printf(ptr, ...)
-declare i32 @puts(ptr)
+declare i32 @fputs(ptr, ptr)
+@stdout = external global ptr
 declare ptr @ailang_rc_alloc(i64)
 declare void @ailang_rc_inc(ptr)
 declare void @ailang_rc_dec(ptr)
@@ -119,7 +120,8 @@ define i8 @ail_prelude_print__Int(i64 %arg_x) {
 entry:
   %v1 = call ptr @ail_prelude_show__Int(i64 %arg_x)
   %v2 = getelementptr inbounds i8, ptr %v1, i64 8
-  call i32 @puts(ptr %v2)
+  %v3 = load ptr, ptr @stdout, align 8
+  call i32 @fputs(ptr %v2, ptr %v3)
   call void @ailang_rc_dec(ptr %v1)
   ret i8 0
 }