diff --git a/bench/orchestrator-stats/2026-05-20-iter-bugfix-float-to-str-dot-zero.json b/bench/orchestrator-stats/2026-05-20-iter-bugfix-float-to-str-dot-zero.json
new file mode 100644
index 0000000..de8f495
--- /dev/null
+++ b/bench/orchestrator-stats/2026-05-20-iter-bugfix-float-to-str-dot-zero.json
@@ -0,0 +1,12 @@
+{
+  "iter_id": "bugfix-float-to-str-dot-zero",
+  "date": "2026-05-20",
+  "mode": "mini",
+  "outcome": "DONE",
+  "tasks_total": 1,
+  "tasks_completed": 1,
+  "reloops_per_task": { "1": 0 },
+  "review_loops_spec": 0,
+  "review_loops_quality": 0,
+  "blocked_reason": null
+}
diff --git a/crates/ail/tests/e2e.rs b/crates/ail/tests/e2e.rs
index d687241..6d45def 100644
--- a/crates/ail/tests/e2e.rs
+++ b/crates/ail/tests/e2e.rs
@@ -2702,7 +2702,12 @@ fn int_to_str_smoke() {
 /// default applies and the dev target's glibc produces the three
 /// bytes `3.5` (no trailing zeros). If a future target's libc or
 /// locale produces a different rendering, this assertion is the
-/// trip-wire that surfaces it.
+/// trip-wire that surfaces it. Note: post-Gitea-#7 the runtime
+/// also applies a `.0`-fallback when `%g`'s output for a finite
+/// double contains neither `.` nor `e`/`E` (mirroring the surface
+/// printer's `write_float_lit`); `3.5` already contains `.`, so
+/// the fallback does not fire here and the golden stays at the
+/// three bytes `3.5`.
 #[test]
 fn float_to_str_smoke() {
     let out = build_and_run("float_to_str_smoke.ail");
@@ -2866,12 +2871,13 @@ fn mut_counter_prints_55() {
 
 /// Float twin of `mut_counter_prints_55`: `sum_helper` returns the
 /// sum 1.0+...+10.0 = 55.0. The polymorphic `print` routes through
-/// `Show Float.show` → `float_to_str`'s libc `%g` formatter, which
-/// strips the trailing `.0` — so the canonical stdout for Float
-/// 55.0 is `"55"` (matches `examples/floats.ail`'s output of
-/// `4` for `1.5 + 2.5`).
+/// `Show Float.show` → `float_to_str`'s libc `%g` formatter plus
+/// the runtime `.0`-fallback for finite whole-valued doubles whose
+/// `%g` output lacks `.`/`e`/`E` (Gitea #7), so the canonical
+/// stdout for Float 55.0 is `"55.0"` (matches `examples/floats.ail`'s
+/// output of `4.0` for `1.5 + 2.5`).
 #[test]
 fn mut_sum_floats_prints_55() {
     let stdout = build_and_run("mut_sum_floats.ail");
-    assert_eq!(stdout.trim(), "55", "mut_sum_floats must print 55, got {stdout:?}");
+    assert_eq!(stdout.trim(), "55.0", "mut_sum_floats must print 55.0, got {stdout:?}");
 }
diff --git a/crates/ail/tests/floats_e2e.rs b/crates/ail/tests/floats_e2e.rs
index c6a6522..c9e02b5 100644
--- a/crates/ail/tests/floats_e2e.rs
+++ b/crates/ail/tests/floats_e2e.rs
@@ -2,11 +2,12 @@
 //!
 //! `examples/floats.ail.json` is built via the public `ail build`
 //! CLI and run; stdout is matched against the expected three
-//! lines (`4`, `42`, `-1.5`). This test exercises the full
+//! lines (`4.0`, `42.0`, `-1.5`). This test exercises the full
 //! pipeline — Float literal lowering, polymorphic `+` Float arm,
 //! `int_to_float` (sitofp), `neg` Float (fneg), and the polymorphic
 //! `print` for Float (routes through `Show Float.show` →
-//! `float_to_str`, libc `%g`).
+//! `float_to_str`, libc `%g` plus the runtime `.0`-fallback for
+//! whole-valued Float results, per Gitea #7).
 
 use std::path::PathBuf;
 use std::process::Command;
@@ -59,7 +60,7 @@ fn floats_example_prints_expected_stdout() {
     );
 
     let stdout = String::from_utf8_lossy(&run.stdout);
-    let expected = "4\n42\n-1.5\n";
+    let expected = "4.0\n42.0\n-1.5\n";
     assert_eq!(
         stdout, expected,
         "stdout mismatch.\nGot:\n{}\nExpected:\n{}",
diff --git a/examples/float_to_str_smoke.ail b/examples/float_to_str_smoke.ail
index c4127a0..33aecdc 100644
--- a/examples/float_to_str_smoke.ail
+++ b/examples/float_to_str_smoke.ail
@@ -1,6 +1,6 @@
 (module float_to_str_smoke
   (fn main
-    (doc "Iter hs.4: smoke pin for the float_to_str heap-Str builtin. `do io/print_str(float_to_str(3.5))` builds through the whole pipeline (checker resolves float_to_str:(Float)->Str, codegen lowers to call ptr @ailang_float_to_str(double 3.5), runtime/str.c's ailang_float_to_str snprintfs into a heap-Str slab via libc %g, io/print_str's @puts prints from the bytes pointer at offset 8). The exact rendering of 3.5 is libc-target-dependent; on the dev target's clang+glibc with default C locale it is the three bytes `3.5`. Single-value smoke; NaN / +Inf / -Inf edge cases are deferred per the hs.4 plan.")
+    (doc "Iter hs.4: smoke pin for the float_to_str heap-Str builtin. `do io/print_str(float_to_str(3.5))` builds through the whole pipeline (checker resolves float_to_str:(Float)->Str, codegen lowers to call ptr @ailang_float_to_str(double 3.5), runtime/str.c's ailang_float_to_str snprintfs into a heap-Str slab via libc %g plus a `.0`-fallback for finite whole-valued doubles whose %g output lacks `.`/`e`/`E` (Gitea #7), io/print_str's @puts prints from the bytes pointer at offset 8). The exact rendering of 3.5 is libc-target-dependent; on the dev target's clang+glibc with default C locale it is the three bytes `3.5` (the fallback does not fire because `.` is already present). Single-value smoke; NaN / +Inf / -Inf edge cases are deferred per the hs.4 plan.")
     (type (fn-type (params) (ret (con Unit)) (effects IO)))
     (params)
     (body (do io/print_str (app float_to_str 3.5)))))
diff --git a/examples/mut_sum_floats.ail b/examples/mut_sum_floats.ail
index 607e4aa..056ad8c 100644
--- a/examples/mut_sum_floats.ail
+++ b/examples/mut_sum_floats.ail
@@ -1,7 +1,7 @@
 (module mut_sum_floats
 
   (fn main
-    (doc "Float twin of mut_counter via a tail-recursive helper. Expected stdout: 55 (Float-55.0 via %g).")
+    (doc "Float twin of mut_counter via a tail-recursive helper. Expected stdout: 55.0 (Float 55.0 via %g plus the runtime `.0`-fallback for finite whole-valued doubles, Gitea #7).")
     (type (fn-type (params) (ret (con Unit)) (effects IO)))
     (params)
     (body
diff --git a/runtime/str.c b/runtime/str.c
index 8230d3c..cba0666 100644
--- a/runtime/str.c
+++ b/runtime/str.c
@@ -18,6 +18,7 @@
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <math.h>
 
 /* Defined in runtime/rc.c — exposed with default external linkage.
  * Returns a zero-initialised payload whose `rc_header` sits at
@@ -125,6 +126,16 @@ char *ailang_int_to_str(int64_t n) {
  * oversized. Defensive `abort()` on truncation, same shape as
  * `ailang_int_to_str`.
  *
+ * `.0`-fallback (Gitea #7): if `x` is finite and `%g`'s output
+ * contains neither `.` nor `e`/`E`, append `.0` so a whole-valued
+ * Float renders with a Float-shaped suffix instead of Int-shaped
+ * text. Mirrors the surface printer's `write_float_lit` fallback
+ * at `crates/ailang-surface/src/print.rs` lines 624-637, keeping
+ * the surface/runtime round-trip-on-lex symmetry intact. The
+ * `isfinite(x)` fence skips the fallback for `nan`/`inf`/`-inf`,
+ * which would otherwise match the no-`.`-no-`e` predicate and
+ * render as `nan.0`/`inf.0`.
+ *
  * Returns the payload pointer of a fresh heap-Str slab.
  */
 char *ailang_float_to_str(double x) {
@@ -138,6 +149,24 @@ char *ailang_float_to_str(double x) {
         abort();
     }
     uint64_t len = (uint64_t)written;
+    /* `.0`-fallback — see block comment above and the surface
+     * counterpart at crates/ailang-surface/src/print.rs lines
+     * 624-637. `%g` output is ASCII, so plain `memchr` suffices. */
+    if (isfinite(x)
+        && memchr(buf, '.', len) == NULL
+        && memchr(buf, 'e', len) == NULL
+        && memchr(buf, 'E', len) == NULL) {
+        if (len + 2 >= sizeof(buf)) {
+            fprintf(stderr,
+                    "ailang_float_to_str: .0-fallback would overflow buffer "
+                    "(len=%llu, buffer=%zu) — should be unreachable for any finite double; aborting\n",
+                    (unsigned long long)len, sizeof(buf));
+            abort();
+        }
+        buf[len] = '.';
+        buf[len + 1] = '0';
+        len += 2;
+    }
     char *payload = str_alloc(len);
     memcpy(payload + 8, buf, len);
     payload[8 + len] = '\0';