family Makefile: siblings, park and resume refuse by name when scripts/siblings.py is absent, and update-shape.py says the Makefile it copies calls it, so a holder updated without --add no longer fails on can't open file (#489)

AGENTS.md

@@ -413,10 +413,10 @@ python3 scripts/family.py siblings --family-root <path>
    different repository is reported and skipped; the exit is the human's
    hand, not an overwrite.
 6. `update-shape.py` updates a family root exactly as it updates a project,
-   and the same four refusals apply. It mirrors into `family.yaml`. An
-   existing holder receives `scripts/siblings.py` that way: `check` reports
-   it as `upstream-added` and `apply --add scripts/siblings.py` takes it, on
-   the human's word, per file.
+   with the same four refusals, and mirrors into `family.yaml`. An existing
+   holder receives `scripts/siblings.py` that way: `check` reports it as
+   `upstream-added`, `apply --add scripts/siblings.py` takes it on the human's
+   word, per file, and without it `make siblings`, `park` and `resume` refuse.
 
 ## Parking and resuming
 

templates/family-root/Makefile

@@ -24,7 +24,36 @@
 # refuses is reported too; either way the holder carries on to the next
 # member and exits non-zero at the end. A skip is not a pass, and a refusal
 # is never hidden. The dispatch clones nothing and fetches nothing.
+#
+# A HOLDER CUT BEFORE `scripts/siblings.py` EXISTED (2026-09-09, #76) may hold
+# this Makefile without it (#489). `update-shape.py` copies a changed Makefile
+# on `apply`, but takes an added file only on the human's word, per file
+# (`--add`), so a holder updated exactly as AGENTS.md prescribes can have
+# `siblings`, `park` and `resume` and not the script they run. Each of the
+# three asks first and, when the script is not there, REFUSES BY NAME instead
+# of dying on `can't open file`: it says what is missing and which command
+# takes it, and stops with make's own exit 2. The question is make's
+# `$(wildcard)` and the refusal is `$(error)`, so neither needs a shell
+# `test` or an `echo` and the answer is the same wherever make runs.
 PYTHON ?= python3
+# One message, three targets, so the three refusals cannot drift apart. It
+# names the file, why it can be missing, and the two commands that take it:
+# `check` to read the verdict, then `apply --add` once the human has said so.
+# A holder that took the file and then DELETED it is the one case `check` does
+# not call upstream-added (`copy-missing`: the pin has a row, and `--add`
+# refuses a pinned path), so the message ends with that exit.
+SIBLINGS_SCRIPT := scripts/siblings.py
+SIBLINGS_MISSING = $(SIBLINGS_SCRIPT), which this holder does not have. \
+    update-shape.py copies a changed Makefile but adds a new file only on the \
+    human's word, so a holder updated without --add $(SIBLINGS_SCRIPT) lands \
+    here. From a checkout of openRepoShape run `python3 update-shape.py check \
+    --root "$(CURDIR)"`, which reports $(SIBLINGS_SCRIPT) as upstream-added. \
+    When the human says to take it, run the apply command it prints with \
+    --add $(SIBLINGS_SCRIPT) added. If it reports copy-missing instead, a \
+    pinned copy was deleted: restore it from this holder's history rather \
+    than with --add
+SIBLINGS_GUARD = $(if $(wildcard $(SIBLINGS_SCRIPT)),,$(error make $(1) \
+    needs $(SIBLINGS_MISSING)))
 .DEFAULT_GOAL := help
 
 .PHONY: help bootstrap siblings validate pins park resume
@@ -46,6 +75,7 @@ bootstrap:
 	$(PYTHON) scripts/bootstrap.py
 
 siblings:
+	$(call SIBLINGS_GUARD,siblings)
 	$(PYTHON) scripts/siblings.py
 
 validate:
@@ -56,7 +86,9 @@ pins:
 	$(PYTHON) scripts/validate-family.py --pins
 
 park:
+	$(call SIBLINGS_GUARD,park)
 	$(PYTHON) scripts/siblings.py --make park --make-arg 'ARGS=$(ARGS)'
 
 resume:
+	$(call SIBLINGS_GUARD,resume)
 	$(PYTHON) scripts/siblings.py --make resume --make-arg 'ARGS=$(ARGS)'