diff --git a/Makefile b/Makefile
index f9d5504..9cbffb3 100644
--- a/Makefile
+++ b/Makefile
@@ -15,6 +15,31 @@ CC      ?= cc
 CFLAGS  ?= -O2 -std=gnu11 -Wall -Wextra
 LDLIBS  := -lm -lpthread
 
+# The interpreter for the three Python recipes below, resolved by RUNNING a
+# candidate rather than by looking one up. On Windows the name `python3` on
+# PATH is usually the Microsoft Store App Execution Alias: a zero-byte
+# reparse point that exists, exits 49, and prints an advert for the Store
+# instead of running anything, so a recipe reports its own tool broken. Same
+# finding as tests/run.sh, which shims PATH because it has 49 call sites and
+# subprocesses to cover; three recipes want a name instead. PATH set inside
+# run.sh does not reach a recipe make runs itself, which is why this is here
+# and not there.
+#
+# Windows installs the versionless `python`, and `py` besides, so a working
+# interpreter is normally there under another name. If none answers this
+# stays `python3` and the recipe fails loudly at first use, which is right
+# for a build target: unlike the suite, there is nothing here to skip.
+#
+# Recursive rather than `:=` so the probe runs only when a recipe actually
+# expands $(PY). Immediate assignment costs every `make` invocation two
+# process spawns, `make clean` and a no-op build included, and on the box
+# this was found the first spawn is the Store alias itself: measured 196 ms
+# added per invocation, which nearly triples a no-op make. The fallback
+# lives inside the shell for the same reason, since an `ifeq` on $(PY)
+# would force the expansion at parse time and undo it.
+PY = $(shell for p in python3 python py; do \
+         "$$p" -c '' >/dev/null 2>&1 && { echo "$$p"; exit 0; }; done; echo python3)
+
 # The target triple rather than `uname -m`, because those differ the moment
 # anyone cross-compiles: building for Windows from this ARM laptop, uname
 # says arm64 and would put the NEON translation unit into an x86 binary
@@ -299,7 +324,7 @@ check: test
 # libwaste as a shared object rather than the archive the CLI links, and
 # because it is the one part of this repo that is not C.
 serve-check: libwaste.$(SOEXT)
-	@python3 -m unittest discover -s tests/serve -t . -p "test_*.py"
+	@$(PY) -m unittest discover -s tests/serve -t . -p "test_*.py"
 
 # Sanitizers. Separate targets rather than a flag on `make`, because they
 # need a full rebuild: mixing instrumented and uninstrumented objects
@@ -320,7 +345,7 @@ asan:
 	 $(MAKE) --no-print-directory clean; exit $$rc
 
 fuzz: test
-	@python3 tools/fuzz_container.py --runs $(FUZZ_RUNS)
+	@$(PY) tools/fuzz_container.py --runs $(FUZZ_RUNS)
 
 FUZZ_RUNS ?= 200
 
@@ -332,7 +357,7 @@ fuzz-asan:
 	    CFLAGS="-std=gnu11 -Wall -Wextra -DVQ_SUPER=$(VQ_SUPER) -MMD -MP $(SAN_FLAGS)" \
 	    LDLIBS="-lm -lpthread $(SAN_FLAGS)"
 	@rc=0; ASAN_OPTIONS=detect_leaks=0 UBSAN_OPTIONS=print_stacktrace=1 \
-	    python3 tools/fuzz_container.py --runs $(FUZZ_RUNS) || rc=$$?; \
+	    $(PY) tools/fuzz_container.py --runs $(FUZZ_RUNS) || rc=$$?; \
 	 $(MAKE) --no-print-directory clean; exit $$rc
 
 .PHONY: all test check serve-check clean asan fuzz fuzz-asan
diff --git a/tools/fetch_weights.sh b/tools/fetch_weights.sh
index 798b583..1df54e9 100755
--- a/tools/fetch_weights.sh
+++ b/tools/fetch_weights.sh
@@ -30,6 +30,26 @@
 
 set -uo pipefail
 
+# python3, resolved by RUNNING a candidate rather than by looking one up.
+# On Windows the name on PATH is usually the Microsoft Store App Execution
+# Alias: a zero-byte reparse point that exists, exits 49, and prints an
+# advert for the Store instead of running anything. Same finding as
+# tests/run.sh, which shims PATH because it has 49 call sites and
+# subprocesses to cover; the handful here get a name and pass it down.
+#
+# Windows installs the versionless `python`, and `py` besides, so a working
+# interpreter is normally there under another name. If none answers, this
+# stays `python3` and the script fails loudly at first use, which is right
+# here: unlike the suite there is nothing to skip, and a run that cannot
+# read its own index must stop rather than carry on.
+if [ -z "${PY:-}" ]; then
+    for _cand in python3 python py; do
+        "$_cand" -c '' >/dev/null 2>&1 && { PY="$_cand"; break; }
+    done
+    : "${PY:=python3}"
+fi
+export PY
+
 REPO="${REPO:-moonshotai/Kimi-K3}"
 DEST="${DEST:-/Volumes/WasteDisk/k3}"
 JOBS="${JOBS:-3}"
@@ -185,7 +205,7 @@ if [ "$DRY" = 0 ] && [ "$CHECK_ONLY" = 0 ]; then
     # missed preprocessor_config.json, so the image normalization was the
     # CLIP convention for a day when the release states mean = std = 0.5.
     # A whitelist cannot report what it never knew to ask for.
-    SMALL=$(hcurl -sfL --max-time 60 "$API" 2>/dev/null | python3 -c '
+    SMALL=$(hcurl -sfL --max-time 60 "$API" 2>/dev/null | "$PY" -c '
 import json, sys
 try:
     d = json.load(sys.stdin)
@@ -247,14 +267,14 @@ fi
 # build that cannot be tested from here, and deleting a byte that must never
 # appear in a safetensors filename is checkable by reading. It is a no-op
 # everywhere else.
-python3 - "$DEST/model.safetensors.index.json" <<'PY' | tr -d '\r' > "$DEST/.shards"
+"$PY" - "$DEST/model.safetensors.index.json" <<'PY' | tr -d '\r' > "$DEST/.shards"
 import json, sys
 idx = json.load(open(sys.argv[1]))
 for s in sorted(set(idx["weight_map"].values())):
     print(s)
 PY
 TOTAL=$(wc -l < "$DEST/.shards" | tr -d ' ')
-TOTAL_BYTES=$(python3 - "$DEST/model.safetensors.index.json" <<'PY' | tr -d '\r'
+TOTAL_BYTES=$("$PY" - "$DEST/model.safetensors.index.json" <<'PY' | tr -d '\r'
 import json, sys
 print(json.load(open(sys.argv[1])).get("metadata", {}).get("total_size", 0))
 PY
@@ -272,7 +292,7 @@ while read -r f; do
 done < "$DEST/.shards"
 
 log "repo $REPO -> $DEST  (stat: $STAT_MODE)"
-python3 - "$TOTAL_BYTES" "$have_bytes" "$(free_kb)" "$TOTAL" "$have" <<'PY'
+"$PY" - "$TOTAL_BYTES" "$have_bytes" "$(free_kb)" "$TOTAL" "$have" <<'PY'
 import sys
 tot, got, availkb, n, nhave = (int(x) for x in sys.argv[1:6])
 g = 1 << 30
diff --git a/tools/pipeline.sh b/tools/pipeline.sh
index c58889a..310766c 100755
--- a/tools/pipeline.sh
+++ b/tools/pipeline.sh
@@ -39,6 +39,28 @@
 # be downloaded again — so it stays something the caller asks for.
 
 set -uo pipefail
+
+# python3, resolved by RUNNING a candidate rather than by looking one up.
+# On Windows the name on PATH is usually the Microsoft Store App Execution
+# Alias: a zero-byte reparse point that exists, exits 49, and prints an
+# advert for the Store instead of running anything. Same finding as
+# tests/run.sh, which shims PATH because it has 49 call sites and
+# subprocesses to cover; the handful here get a name and pass it down.
+#
+# Windows installs the versionless `python`, and `py` besides, so a working
+# interpreter is normally there under another name. If none answers, this
+# stays `python3` and the script fails loudly at first use, which is right
+# here: unlike the suite there is nothing to skip, and a run that cannot
+# read its own index must stop rather than carry on.
+# Exported rather than local, so the fetch_weights.sh this drives inherits
+# the same answer instead of resolving it again per stage.
+if [ -z "${PY:-}" ]; then
+    for _cand in python3 python py; do
+        "$_cand" -c '' >/dev/null 2>&1 && { PY="$_cand"; break; }
+    done
+    : "${PY:=python3}"
+fi
+export PY
 cd "$(dirname "$0")/.."
 
 SRC="${SRC:-/Volumes/WasteDisk/k3}"
@@ -61,7 +83,7 @@ say "=== pipeline start ==="
 say "src $SRC -> out $OUT, $JOBS conversion processes"
 
 # ---- 1. download ---------------------------------------------------------
-NEED=$(python3 -c "
+NEED=$("$PY" -c "
 import json;print(len(set(json.load(open('$SRC/model.safetensors.index.json'))['weight_map'].values())))" 2>/dev/null || echo 0)
 [ "$NEED" -gt 0 ] || die "download (no index at $SRC)"
 
@@ -83,7 +105,7 @@ say "stage 2: probe — ${FREE} GB free on the target volume"
 
 # The first MoE layer. K3 nests the text model, and the dense prefix has no
 # experts to round-trip, so neither is a detail this can guess at.
-PROBE=$(python3 -c "
+PROBE=$("$PY" -c "
 import json
 c = json.load(open('$SRC/config.json'))
 c = c.get('text_config', c)
@@ -91,7 +113,7 @@ print(c.get('first_k_dense_replace', 0))" 2>/dev/null || echo "")
 [ -n "$PROBE" ] || die "probe (no config.json at $SRC)"
 
 probe_done() {
-    python3 -c "
+    "$PY" -c "
 import json, sys
 try:
     m = json.load(open('$OUT/manifest.json'))
@@ -156,7 +178,7 @@ say "  prompt ids: $IDS"
 $UV tools/kimi_ref.py --container "$OUT" --tokens 0 --prompt-ids "$IDS" \
     --dump "$RUN/logits_ref.bin" >>"$LOG" 2>&1 || die "oracle"
 
-python3 - "$RUN/logits_c.bin" "$RUN/logits_ref.bin" > "$RUN/diff.txt" <<'PY'
+"$PY" - "$RUN/logits_c.bin" "$RUN/logits_ref.bin" > "$RUN/diff.txt" <<'PY'
 import struct, sys
 def L(p):
     b = open(p, "rb").read()