diff --git a/.github/scripts/interrupt-install.sh b/.github/scripts/interrupt-install.sh
index e805b11d90..c6cfe9b0f8 100755
--- a/.github/scripts/interrupt-install.sh
+++ b/.github/scripts/interrupt-install.sh
@@ -86,14 +86,31 @@ if [ "$killed" = "true" ]; then
     kill -0 "$PID" 2>/dev/null || break
     sleep 1
   done
-  if kill -0 "$PID" 2>/dev/null; then
-    echo "[interrupt] group survived SIGTERM; SIGKILL"
-    kill -KILL -- -"$PID" 2>/dev/null || kill -KILL "$PID" 2>/dev/null || true
-  fi
+  # Unconditional, and to the GROUP. The leader can exit on SIGTERM while a uv or
+  # python descendant ignores it or is mid-shutdown; `kill -0 "$PID"` then reported
+  # the leader gone, this escalation was skipped, and `wait` reaped only the leader,
+  # leaving that descendant free to finish the dependency pass while the probe ran.
+  # Signalling an already-empty group is a no-op.
+  echo "[interrupt] SIGKILL to process group -$PID"
+  kill -KILL -- -"$PID" 2>/dev/null || kill -KILL "$PID" 2>/dev/null || true
 fi
 
 wait "$PID" 2>/dev/null
 rc=$?
+
+# Only after the reap: an unreaped leader is still a member of its own group, so
+# polling the group before `wait` would report it alive forever. Do not let the
+# probe start while an installer process is still running.
+if [ "$killed" = "true" ]; then
+  for _ in $(seq 1 "$KILL_GRACE"); do
+    kill -0 -- -"$PID" 2>/dev/null || break
+    kill -KILL -- -"$PID" 2>/dev/null || true
+    sleep 1
+  done
+  if kill -0 -- -"$PID" 2>/dev/null; then
+    echo "::warning::processes from installer group -$PID outlived SIGKILL"
+  fi
+fi
 echo "[interrupt] installer exit=$rc reason=$reason killed=$killed"
 echo "[interrupt] last log lines:"
 tail -15 "$LOG" || true
diff --git a/.github/scripts/interrupted_install_probe.py b/.github/scripts/interrupted_install_probe.py
index dd5a9c2254..e7a27c98b9 100644
--- a/.github/scripts/interrupted_install_probe.py
+++ b/.github/scripts/interrupted_install_probe.py
@@ -135,9 +135,16 @@ def main(argv: list[str]) -> int:
         popen_kw["start_new_session"] = True
     else:
         popen_kw["creationflags"] = getattr(subprocess, "CREATE_NEW_PROCESS_GROUP", 0)
+    # Straight to the artefact file, never a PIPE: nothing reads that pipe until after
+    # the polling loop, so a backend whose imports emit more than the OS pipe buffer
+    # (64 KiB on Linux and macOS, a single page by default on Windows) blocks on write
+    # BEFORE it binds the port. backend_ok, which this whole verdict pivots on, would
+    # then be false for a perfectly good install.
+    blog_path = out / "backend.log"
+    blog_fh = blog_path.open("w", encoding = "utf-8", errors = "replace")
     proc = subprocess.Popen(
         [binp, "studio", "--api-only", "-H", "127.0.0.1", "-p", str(port)],
-        stdout = subprocess.PIPE,
+        stdout = blog_fh,
         stderr = subprocess.STDOUT,
         text = True,
         **popen_kw,
@@ -180,12 +187,8 @@ def main(argv: list[str]) -> int:
                 proc.kill()
 
     reap()
-    try:
-        blog = proc.communicate(timeout = 30)[0] or ""
-    except subprocess.TimeoutExpired:
-        proc.kill()
-        blog = proc.communicate()[0] or ""
-    (out / "backend.log").write_text(blog, encoding = "utf-8", errors = "replace")
+    blog_fh.close()
+    blog = blog_path.read_text(encoding = "utf-8", errors = "replace")
     say("backend_ok", backend_ok)
 
     missing = ""
diff --git a/.github/workflows/interrupted-install-ci.yml b/.github/workflows/interrupted-install-ci.yml
index 319cf4ba4e..358141f456 100644
--- a/.github/workflows/interrupted-install-ci.yml
+++ b/.github/workflows/interrupted-install-ci.yml
@@ -37,6 +37,11 @@ on:
       # without a single leg running.
       - 'unsloth_cli/_studio_deps.py'
       - 'studio/install_manifest.py'
+      # The requirement files are the phases. studio.txt is where structlog is
+      # declared, the package whose absence IS the reported false-ready bug, and
+      # the single-env files drive the later steps, so moving a package between
+      # them changes what every interrupted state looks like.
+      - 'studio/backend/requirements/**'
       # `*` never matches `/`, and it is a literal `-install` that follows, so
       # `interrupt*-install*` matches interrupt-install.sh / .ps1 but NOT the
       # underscored probe. List the probe explicitly rather than rely on a glob.