fix(test): stop the Antigravity cases failing on a host without jq

main has been red since e9ad692. The gate passed; the shell suite failed on
three Antigravity cases.

Not a bug in the wiring. install.sh treats jq as optional by design — every
other target is dependency-free, so wire_antigravity warns and skips when jq is
missing. It did exactly that on the runner:

  [skills] Antigravity: jq not found — skipping

The tests were the problem: they inherited whatever jq the host happened to
have. koala has it and reported 12/12; the runner does not and reported 3
failures on the same commit. Works-on-my-machine, caught by CI doing its job.

Two changes:

- The three merge-behaviour cases now run only where jq exists, and print a SKIP
  naming what is not covered. A case that fails because the host lacks an
  optional dependency is a false red, and false reds are how a suite stops being
  read.
- The skip path gets a real test of its own, because it is a contract rather than
  a fallback. install.sh gains SKILLS_JQ so the jq-absent branch is exercisable
  on a host that has jq — the same seam pattern as DOCTOR_LATEST_TAG_CMD. It
  asserts no skills.json is written, the skip is reported, and the other
  harnesses still wire.

Verified both ways on koala by building a jq-free PATH:
  with jq:    install: 13 passed, 0 failed, 0 skipped
  without jq: install: 10 passed, 0 failed, 3 skipped

Consequence worth naming: CI now SKIPS the merge assertions rather than running
them, so idempotency and entry-preservation are untested there until the runner
gets jq. Filed as #42.

Refs #41
Bump-Type: patch

install.sh

@@ -62,6 +62,10 @@ CRUSH_DIR="${CRUSH_SKILLS_DIR:-$HOME/.config/crush/skills}"
 OPENCODE_DIR="${OPENCODE_SKILLS_DIR:-$HOME/.config/opencode/skills}"
 ANTIGRAVITY_SKILLS_JSON="${ANTIGRAVITY_SKILLS_JSON:-$HOME/.gemini/config/skills.json}"
 EXTRA_SOURCES="${SKILLS_EXTRA_SOURCES:-}"
+# Overridable so the jq-absent branch is testable on a host that has jq. That
+# branch is a contract, not a fallback: jq is optional here while every other
+# target in this script is dependency-free.
+JQ="${SKILLS_JQ:-jq}"
 # Recorded beside the managed directory rather than inside it: a stray file in
 # there would look like a skill to every harness reading the dir.
 SOURCES_MANIFEST="$(dirname "$AGENTS_DIR")/$(basename "$AGENTS_DIR")-sources"
@@ -226,7 +230,7 @@ link_dir() {
 # config (json_configs.md), so a hand-added entry (e.g. a personal skills
 # dir) must survive a re-run untouched.
 wire_antigravity() {
-  if ! command -v jq >/dev/null 2>&1; then
+  if ! command -v "$JQ" >/dev/null 2>&1; then
     log "Antigravity: jq not found — skipping (needed to merge $ANTIGRAVITY_SKILLS_JSON safely)"
     return
   fi
@@ -240,7 +244,7 @@ wire_antigravity() {
     existing='{}'
   fi
 
-  already="$(printf '%s' "$existing" | jq --arg p "$AGENTS_DIR" \
+  already="$(printf '%s' "$existing" | "$JQ" --arg p "$AGENTS_DIR" \
     '[.entries // [] | .[] | select(.path == $p)] | length' 2>/dev/null)" || {
     log "Antigravity: $ANTIGRAVITY_SKILLS_JSON is not valid JSON — leaving it untouched"
     return 1
@@ -251,7 +255,7 @@ wire_antigravity() {
     return
   fi
 
-  updated="$(printf '%s' "$existing" | jq --arg p "$AGENTS_DIR" \
+  updated="$(printf '%s' "$existing" | "$JQ" --arg p "$AGENTS_DIR" \
     '.entries = ((.entries // []) + [{path: $p}])')"
   printf '%s\n' "$updated" > "$ANTIGRAVITY_SKILLS_JSON"
   log "Antigravity: registered $AGENTS_DIR in $ANTIGRAVITY_SKILLS_JSON"

tests/install_test.sh

@@ -17,6 +17,7 @@ SUT="$ROOT/install.sh"
 
 pass=0
 fail=0
+skipped=0
 WORK=${TMPDIR:-/tmp}/install_test.$$
 
 if [ ! -f "$SUT" ]; then
@@ -157,6 +158,40 @@ else
   no 'configured sources are recorded for doctor' "$out"
 fi
 
+# --- Antigravity: jq is optional, so BOTH branches must be tested -----------
+# These three cases inherited whatever jq the host happened to have. koala has
+# it, the CI runner does not, so they passed locally and failed in CI — the
+# classic works-on-my-machine gate. install.sh treats jq as optional by design,
+# which means the skip is a contract and needs a test of its own.
+
+# run_install_nojq <fixture> — same as run_install, with the jq lookup pointed
+# at a binary that does not exist. Deterministic regardless of the host.
+run_install_nojq() {
+  _f=$1
+  _out=$(HOME="$_f/home" \
+    SKILLS_SKIP_FETCH=1 \
+    SKILLS_CHECKOUT_DIR="$_f/ck" \
+    AGENTS_SKILLS_DIR="$_f/home/.agents/skills" \
+    CRUSH_SKILLS_DIR="$_f/home/.config/crush/skills" \
+    OPENCODE_SKILLS_DIR="$_f/home/.config/opencode/skills" \
+    SKILLS_JQ="definitely-not-jq-$$" \
+    bash "$SUT" 2>&1)
+  rc=$?
+  printf '%s' "$_out"
+}
+
+f=$(new_fixture antigravity_nojq)
+out=$(run_install_nojq "$f")
+if [ -e "$f/home/.gemini/config/skills.json" ]; then
+  no 'without jq, no skills.json is written' "$out"
+elif ! printf '%s' "$out" | grep -qi 'jq not found'; then
+  no 'without jq, the skip is reported' "$out"
+elif [ ! -L "$f/home/.agents/skills/alpha" ]; then
+  no 'without jq, the other harnesses are still wired' "$out"
+else
+  ok 'without jq, Antigravity is skipped and the rest still wires'
+fi
+
 # --- 8. surfaces: the library link set is not "every skill" -----------------
 # claude.ai has no shell, no cluster and no checkout, so a chat-only skill
 # linked into Crush is a skill that can never fire, competing for selection
@@ -184,18 +219,25 @@ else
   no 'a source with no surfaces convention is linked as-is' "$out"
 fi
 
-# --- 9. Antigravity: the managed agents dir is registered, not the raw checkout
-# skills.json entries must point at $AGENTS_DIR — that's what already carries
+# --- 9-11. Antigravity's merge behaviour, only where jq exists ---------------
+# These three assert what jq DOES. install.sh treats jq as optional, so on a
+# host without it there is nothing to assert — and failing there is what turned
+# main red: they passed on koala (jq present) and failed on the runner (absent).
+# A skipped case is honest; a case that fails because the host lacks an optional
+# dependency is a false red, and false reds are how a suite stops being read.
+if ! command -v jq >/dev/null 2>&1; then
+  skipped=$((skipped + 3))
+  printf '  SKIP jq absent — Antigravity merge behaviour not covered on this host (3 cases)\n'
+else
+  # skills.json entries must point at $AGENTS_DIR — that carries the
   # surfaces-filtering, collision handling and multi-source merge. Pointing at
-# the checkout directly would bypass all of it and give Antigravity a
-# different skill set than every other harness.
+  # the checkout directly would give Antigravity a different skill set than
+  # every other harness.
   f=$(new_fixture antigravity)
   out=$(run_install "$f")
   AG="$f/home/.gemini/config/skills.json"
   if [ ! -f "$AG" ]; then
     no 'Antigravity skills.json is created' "$out"
-elif ! command -v jq >/dev/null 2>&1; then
-  no 'jq available to verify Antigravity wiring' "(jq missing on test host)"
   else
     registered=$(jq -r --arg p "$f/home/.agents/skills" '[.entries[]? | select(.path == $p)] | length' "$AG")
     if [ "$registered" = "1" ]; then
@@ -205,7 +247,6 @@ else
     fi
   fi
 
-# --- 10. Antigravity wiring is idempotent ------------------------------------
   f=$(new_fixture antigravity_idempotent)
   run_install "$f" >/dev/null
   out=$(run_install "$f")
@@ -217,7 +258,6 @@ else
     no 'Antigravity wiring is idempotent (no duplicate entries)' "entries=$count"$'\n'"$out"
   fi
 
-# --- 11. Antigravity wiring preserves entries it doesn't own -----------------
   # A user may hand-edit skills.json to point at their own personal skills dir
   # (json_configs.md documents this). Our merge must not clobber it.
   f=$(new_fixture antigravity_preserve)
@@ -231,6 +271,7 @@ if [ "$personal" = "1" ]; then
   else
     no 'Antigravity wiring preserves pre-existing hand-authored entries' "$(cat "$AG")"$'\n'"$out"
   fi
+fi
 
-printf '\ninstall: %d passed, %d failed\n' "$pass" "$fail"
+printf '\ninstall: %d passed, %d failed, %d skipped\n' "$pass" "$fail" "$skipped"
 [ "$fail" -eq 0 ]