fix(adr): template emitted invalid YAML frontmatter

The frontmatter exists to be machine-read. Two shapes this template
suggested do not parse, so any ADR that copied them dropped silently out of
every "what is still open?" query while looking correct:

  supersedes:    -                 a bare dash is a YAML sequence entry
  deciders:      pending: Mathias  the unquoted second colon reads as a
                                   nested mapping

Both were found live during an estate-wide ADR survey on 2026-09-05:
openbanking-api ADR-0001 (the one genuinely open decision in the estate --
invisible to the survey until fixed) and infra ADR-0019, each copied
verbatim from here.

Template corrected to `null` and a quoted `"pending: <name>"`, plus a short
section after the fence explaining why and giving a one-line yaml.safe_load
check to run before committing. The explanation is deliberately OUTSIDE the
fenced block so it is not copied into the ADR being written.

.claude-plugin/plugin.json

@@ -1,7 +1,7 @@
 {
   "name": "skills",
   "description": "Mathias's engineering skills library, plus the hooks and MCP servers that make it enforceable: TDD, clean code, debugging, specs, discovery, CI, and secret hygiene.",
-  "version": "0.17.1",
+  "version": "0.18.1",
   "author": {
     "name": "Mathias",
     "url": "https://git.d-ma.be/mathias"

README.md

@@ -100,9 +100,11 @@ default to point into `~/dev`.
 | `AGENTS_SKILLS_DIR` | `$HOME/.agents/skills` |
 | `CRUSH_SKILLS_DIR` | `$HOME/.config/crush/skills` |
 | `OPENCODE_SKILLS_DIR` | `$HOME/.config/opencode/skills` |
+| `ANTIGRAVITY_SKILLS_JSON` | `$HOME/.gemini/config/skills.json` (registers `AGENTS_SKILLS_DIR` as a path entry; needs `jq`) |
 | `SKILLS_EXTRA_SOURCES` | unset (colon-separated extra source directories) |
 
-Antigravity and Mistral Vibe targets were removed — unused.
+The Mistral Vibe target was removed — unused. Antigravity's was removed for
+the same reason and re-added once it came back into use.
 
 ## Checking a host
 

install.sh

@@ -17,8 +17,8 @@
 #   /plugin install skills@mathias
 #
 # That path carries the hooks and MCP server definitions too, which symlinks
-# cannot. This script covers the harnesses with no plugin system: Crush, Pi
+# cannot. This script covers the harnesses with no plugin system: Crush, Pi,
-# and OpenCode.
+# OpenCode, and Antigravity.
 #
 # Wiring model — one managed directory, one link per harness:
 #
@@ -27,6 +27,13 @@
 #   ~/.config/crush/skills      -> ~/.agents/skills
 #   ~/.config/opencode/skills   -> ~/.agents/skills
 #
+# Antigravity has no symlink-directory discovery — it reads a path-entries
+# JSON instead (~/.gemini/config/skills.json:
+# {"entries":[{"path":"..."}]}). One entry points at ~/.agents/skills, so it
+# sees exactly the same surfaces-filtered, collision-resolved set every other
+# harness does. Requires jq; skipped with a warning if jq is unavailable —
+# every other target in this script stays dependency-free on purpose.
+#
 # ~/.agents/skills was itself a link to this checkout until #27. That encoded
 # an assumption nobody had stated — that this checkout is the ONLY source of
 # skills on the host — and on flamingo the only way to install this library
@@ -53,7 +60,12 @@ CHECKOUT_DIR="${SKILLS_CHECKOUT_DIR:-$HOME/.local/share/skills}"
 AGENTS_DIR="${AGENTS_SKILLS_DIR:-$HOME/.agents/skills}"
 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"
@@ -213,6 +225,42 @@ link_dir() {
   log "linked $link → $target"
 }
 
+# wire_antigravity — register $AGENTS_DIR in Antigravity's skills.json.
+# Merges rather than overwrites: skills.json is a documented user-editable
+# config (json_configs.md), so a hand-added entry (e.g. a personal skills
+# dir) must survive a re-run untouched.
+wire_antigravity() {
+  if ! command -v "$JQ" >/dev/null 2>&1; then
+    log "Antigravity: jq not found — skipping (needed to merge $ANTIGRAVITY_SKILLS_JSON safely)"
+    return
+  fi
+
+  local existing already updated
+  mkdir -p "$(dirname "$ANTIGRAVITY_SKILLS_JSON")"
+
+  if [ -s "$ANTIGRAVITY_SKILLS_JSON" ]; then
+    existing="$(cat "$ANTIGRAVITY_SKILLS_JSON")"
+  else
+    existing='{}'
+  fi
+
+  already="$(printf '%s' "$existing" | "$JQ" --arg p "$AGENTS_DIR" \
+    '[.entries // [] | .[] | select(.path == $p)] | length' 2>/dev/null)" || {
+    log "Antigravity: $ANTIGRAVITY_SKILLS_JSON is not valid JSON — leaving it untouched"
+    return 1
+  }
+
+  if [ "$already" -gt 0 ]; then
+    log "Antigravity: $AGENTS_DIR already registered in $ANTIGRAVITY_SKILLS_JSON"
+    return
+  fi
+
+  updated="$(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"
+}
+
 main() {
   ensure_checkout
 
@@ -224,6 +272,7 @@ main() {
 
   link_dir "$CRUSH_DIR" "$AGENTS_DIR"
   link_dir "$OPENCODE_DIR" "$AGENTS_DIR"
+  wire_antigravity
 
   log "done — $LINKED_COUNT skill(s) linked from $(sources | wc -l | tr -d ' ') source(s), ref=$REF"
   log "Claude Code: install the plugin instead — /plugin marketplace add $REPO_URL"

skills/adr/SKILL.md

@@ -58,8 +58,8 @@ adr:           0004
 title:         <the decision, as a sentence — not "database choice">
 status:        proposed | accepted | superseded | amended
 date:          2026-08-29
-deciders:      <who accepted it, by name — or "pending: <name>" while proposed>
+deciders:      <who accepted it, by name — or "pending: <name>" (QUOTED) while proposed>
-supersedes:    <adr number, or ->
+supersedes:    <adr number, or null>
 ---
 
 # ADR-0004 — <same title>
@@ -97,6 +97,25 @@ the condition that fires a revisit. An ADR with no validation section is a prefe
 with a template around it.
 ```
 
+### The frontmatter must actually parse
+
+It exists to be machine-read, so a block that does not load is worse than no block at
+all: it drops that ADR silently out of every "what is still open?" query, while looking
+correct. Two shapes this template used to suggest are invalid YAML, and both were found
+live in the estate on 2026-09-05 — `openbanking-api` ADR-0001 and `infra` ADR-0019, each
+copied verbatim from here:
+
+| Wrong | Why | Right |
+|---|---|---|
+| `supersedes:    -` | a bare dash is a YAML *sequence entry*, not a string | `supersedes:    null` |
+| `deciders:      pending: Mathias` | the second, unquoted colon reads as a nested mapping | `deciders:      "pending: Mathias"` |
+
+Check before committing:
+
+```sh
+python3 -c "import yaml,sys;yaml.safe_load(open(sys.argv[1]).read().split('---')[1]);print('ok')" docs/adr/0004-*.md
+```
+
 ## Preserving a productive tension
 
 Some tradeoffs are not unresolved because nobody thought hard enough. They are

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 "$SUT" ]; then
@@ -55,6 +56,7 @@ run_install() {
     AGENTS_SKILLS_DIR="$_f/home/.agents/skills" \
     CRUSH_SKILLS_DIR="$_f/home/.config/crush/skills" \
     OPENCODE_SKILLS_DIR="$_f/home/.config/opencode/skills" \
+    ANTIGRAVITY_SKILLS_JSON="$_f/home/.gemini/config/skills.json" \
     SKILLS_EXTRA_SOURCES="$_extra" \
     bash "$SUT" 2>&1)
   rc=$?
@@ -156,6 +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
@@ -183,5 +219,59 @@ else
   no 'a source with no surfaces convention is linked as-is' "$out"
 fi
 
-printf '\ninstall: %d passed, %d failed\n' "$pass" "$fail"
+# --- 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 $AGENTS_DIR — that carries the
+  # surfaces-filtering, collision handling and multi-source merge. Pointing at
+  # the checkout directly would give Antigravity a different skill set than
+  # every other harness.
+  f=$(new_fixture antigravity)
+  out=$(run_install "$f")
+  AG="$f/home/.gemini/config/skills.json"
+  if [ ! -f "$AG" ]; then
+    no 'Antigravity skills.json is created' "$out"
+  else
+    registered=$(jq -r --arg p "$f/home/.agents/skills" '[.entries[]? | select(.path == $p)] | length' "$AG")
+    if [ "$registered" = "1" ]; then
+      ok 'Antigravity registers the managed agents dir, not the raw checkout'
+    else
+      no 'Antigravity registers the managed agents dir, not the raw checkout' "$(cat "$AG")"
+    fi
+  fi
+
+  f=$(new_fixture antigravity_idempotent)
+  run_install "$f" >/dev/null
+  out=$(run_install "$f")
+  AG="$f/home/.gemini/config/skills.json"
+  count=$(jq '.entries | length' "$AG" 2>/dev/null || echo "?")
+  if [ "$count" = "1" ]; then
+    ok 'Antigravity wiring is idempotent (no duplicate entries)'
+  else
+    no 'Antigravity wiring is idempotent (no duplicate entries)' "entries=$count"$'\n'"$out"
+  fi
+
+  # 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=$(new_fixture antigravity_preserve)
+  mkdir -p "$f/home/.gemini/config"
+  printf '{"entries":[{"path":"/Users/mathias/personal-skills"}]}' > "$f/home/.gemini/config/skills.json"
+  out=$(run_install "$f")
+  AG="$f/home/.gemini/config/skills.json"
+  personal=$(jq -r '[.entries[]? | select(.path == "/Users/mathias/personal-skills")] | length' "$AG" 2>/dev/null || echo 0)
+  if [ "$personal" = "1" ]; then
+    ok 'Antigravity wiring preserves pre-existing hand-authored entries'
+  else
+    no 'Antigravity wiring preserves pre-existing hand-authored entries' "$(cat "$AG")"$'\n'"$out"
+  fi
+fi
+
+printf '\ninstall: %d passed, %d failed, %d skipped\n' "$pass" "$fail" "$skipped"
 [ "$fail" -eq 0 ]