Fix the first build on a fresh clone

AGENTS.md

@@ -68,7 +68,10 @@ src/                      # gitignored — cloned upstream trees live here
 - **`.build-status.json`** is written atomically (`tmp` → `mv`) so a reader
   never sees a half-written file. Phases: `init → clone → venv → prebuild →
   build_start → building → build_done → wheel → done`, or `failed`. Anything
-  interpolated into it goes through `json_escape`.
+  interpolated into it goes through `json_escape`. It lives inside the source
+  tree, so on a first build nothing is written until the clone lands — `init`
+  and `clone` only show up on a re-run. Emitting it is best-effort by design:
+  a status write must never take down a build that has been running for hours.
 - **Every env var takes the form `${VAR:-default}`**, so any single value can be
   overridden without editing a file. Keep it that way.
 - **Paths derive from the repo root**, computed from the script's own location.

CHANGELOG.md

@@ -7,6 +7,23 @@ and the project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Fixed
+
+- **The first build on a fresh clone always failed.** `emit_status` writes
+  `.build-status.json` into the target's source tree, but the `init` phase fires
+  before the clone has created that directory — so `make build-pytorch` died
+  instantly with `src/pytorch/.build-status.json.tmp: No such file or directory`
+  on any checkout that had never been built. Status emission now skips until the
+  tree is a git repo, and never fails the build if the write does not land. This
+  also unbreaks the case where the destination directory exists but is empty:
+  the old code seeded a status file into it, and `git clone` then refused the
+  now-non-empty directory.
+- **The pytorch preset was missing two build requirements.** Upstream builds
+  through `scikit-build-core` now, and `--no-build-isolation` installs nothing on
+  our behalf, so `numpy` and `scikit-build-core` have to be seeded into the venv
+  alongside the rest of `[build-system] requires`. Without them the build fails
+  at backend import, before a single file compiles.
+
 ## [0.1.0] - 2026-08-03
 
 First public release. conceit began as the private build orchestration behind a

scripts/build-upstream.sh

@@ -59,11 +59,23 @@ json_escape() {
 
 emit_status() {
   local phase=$1 step=${2:-null} jobs=${3:-0} detail=${4:-}
-  [[ -z "$_status_file" ]] && return
-  printf '{"phase":"%s","ts":"%s","step":"%s","jobs":%s,"detail":"%s"}\n' \
+  [[ -z "$_status_file" ]] && return 0
+
+  # The status file lives inside the source tree, which does not exist yet on a
+  # fresh checkout — and must stay empty until the clone lands, because git
+  # refuses to clone into a directory that already has files in it. So skip the
+  # write until the tree is a repo: the init/clone phases have nowhere to go.
+  # Never fail here either; a status write must not kill a three-hour build.
+  [[ -d "${_status_file%/*}/.git" ]] || return 0
+
+  if printf '{"phase":"%s","ts":"%s","step":"%s","jobs":%s,"detail":"%s"}\n' \
     "$(json_escape "$phase")" "$(ts_iso)" "$(json_escape "$step")" \
     "$jobs" "$(json_escape "$detail")" \
-    > "${_status_file}.tmp" && mv "${_status_file}.tmp" "$_status_file"
+    > "${_status_file}.tmp" 2>/dev/null
+  then
+    mv -f "${_status_file}.tmp" "$_status_file" 2>/dev/null || true
+  fi
+  return 0
 }
 
 # Count all descendants of a PID (not just direct children).
@@ -219,7 +231,11 @@ case "$preset" in
   pytorch)
     build_cmd=${BUILD_CMD:-"MAX_JOBS=${MAX_JOBS} NVCC_THREADS=${NVCC_THREADS} python -m pip install -e . -v --no-build-isolation"}
     build_dist_cmd=${BUILD_DIST_CMD:-"python -m pip wheel --no-build-isolation --no-deps -w dist ."}
-    extra_pip_deps=${EXTRA_PIP_DEPS:-"cmake ninja packaging pyyaml typing_extensions six"}
+    # --no-build-isolation means pip installs nothing on our behalf: every entry
+    # in pytorch's [build-system] requires has to already be in the venv. numpy
+    # and scikit-build-core (the build backend since the setup.py retirement)
+    # are load-bearing — without them the build dies before the first compile.
+    extra_pip_deps=${EXTRA_PIP_DEPS:-"cmake ninja packaging pyyaml typing_extensions six numpy scikit-build-core"}
     ;;
   vllm)
     # vllm uses uv (per AGENTS.md). We override the torch==2.11.0 pin with our