feat: wire Crush + Antigravity harnesses

Phase 2 of mathias/skills extraction. Adds two new per-tool wirers
alongside Claude Code:

- Crush — ~/.config/crush/skills/<name>/SKILL.md (charmbracelet/crush,
  successor to opencode-ai/opencode which is archived)
- Antigravity — ~/.gemini/antigravity/skills/<name>/SKILL.md (Google
  VS Code extension). Our SKILL.md frontmatter (name + description)
  is already in the format Antigravity expects — no manifest
  translation step needed.

Both wirers added to Taskfile.yml (install:crush + install:antigravity)
and install.sh (wire_crush + wire_antigravity). The aggregate `install`
target now calls all four targets (claude:global, claude:repo, crush,
antigravity). Idempotent symlinks, same shape as the Claude Code wirer.

Per-host env overrides documented in README: SKILLS_REF for tag pinning,
CRUSH_SKILLS_DIR + ANTIGRAVITY_SKILLS_DIR for non-default paths.

Skipped:
- opencode (opencode-ai/opencode): archived, succeeded by Crush; its
  Custom Commands surface is user prompt templates, not system skills
- gitea-resident agents: consume via per-repo .claude/skills or brain
  MCP, no special target needed

Bump-Type: minor

README.md

@@ -44,15 +44,37 @@ changes. CI tags every change as a `vX.Y.Z` release (see
 
 ## Wired harnesses
 
-Phase 1 (current) wires **Claude Code** only:
+| Harness | Target path | Notes |
+|---|---|---|
+| **Claude Code (global)** | `~/.claude/skills/<name>` | Visible in every Claude Code session on the host. |
+| **Claude Code (per-repo)** | `<repo>/.claude/skills/<name>` | Created when `install` is invoked inside a git repo (not the skills repo itself). Gitignored globally via `**/.claude/skills/`. |
+| **Crush** | `~/.config/crush/skills/<name>` | Charmbracelet Crush — successor to `opencode-ai/opencode` (archived). |
+| **Antigravity** | `~/.gemini/antigravity/skills/<name>` | Google Antigravity (VS Code extension). Our `SKILL.md` frontmatter (`name` + `description`) is already in the format Antigravity expects, so symlinks suffice — no manifest translation. |
 
-- Global: `~/.claude/skills/<name>` → `~/.local/share/skills/<name>`
-- Per-repo: `<repo>/.claude/skills/<name>` (when invoked from a git
-  repo) → same
+### Not wired (and why)
 
-Phase 2 will add: Crush, opencode, antigravity, gitea-resident agents
-(cobalt-dingo, agentsquad). See `mathias/infra` issue `infra#62`
-addendum for the roadmap.
+- **opencode** (`opencode-ai/opencode`): archive notice; succeeded by Crush.
+  Its only "skill"-like surface — Custom Commands at `~/.config/opencode/commands/` —
+  is for user-facing prompt templates, not system-level instructions.
+  Misaligned with how we use skills. Skipped.
+- **gitea-resident agents** (cobalt-dingo, agentsquad): they consume
+  skills via their containing project's `.claude/skills` directory
+  (populated by the per-repo wirer when run from the host), or via the
+  brain MCP. No special target needed.
+
+### Per-host env-var overrides
+
+Each target path can be overridden by setting the matching env var before
+running `install.sh`:
+
+| Env var | Default |
+|---|---|
+| `SKILLS_REPO_URL` | `https://gitea.d-ma.be/mathias/skills.git` |
+| `SKILLS_REF` | `main` (set to e.g. `v0.1.0` to pin a release) |
+| `SKILLS_CHECKOUT_DIR` | `$HOME/.local/share/skills` |
+| `CLAUDE_SKILLS_DIR` | `$HOME/.claude/skills` |
+| `CRUSH_SKILLS_DIR` | `$HOME/.config/crush/skills` |
+| `ANTIGRAVITY_SKILLS_DIR` | `$HOME/.gemini/antigravity/skills` |
 
 ## Versioning
 

Taskfile.yml

@@ -12,6 +12,11 @@ vars:
   REPO_URL: 'https://gitea.d-ma.be/mathias/skills.git'
   CHECKOUT_DIR: '{{.HOME}}/.local/share/skills'
   CLAUDE_GLOBAL_DIR: '{{.HOME}}/.claude/skills'
+  CRUSH_DIR: '{{.HOME}}/.config/crush/skills'
+  ANTIGRAVITY_DIR: '{{.HOME}}/.gemini/antigravity/skills'
+  # Anything at the repo root that is NOT a skill directory. Both
+  # Taskfile + install.sh share this exclusion regex.
+  NON_SKILL_ENTRIES: '^(Taskfile.yml|install.sh|README.md|SKILLS_INDEX.md|.gitea|.git$)$'
 
 tasks:
 
@@ -26,17 +31,19 @@ tasks:
     silent: true
 
   install:
-    desc: 'Wire skills into every harness detected on this host (Claude Code today, more in phase 2).'
+    desc: 'Wire skills into every supported harness (Claude Code, Crush, Antigravity).'
     cmds:
       - task: install:claude:global
       - task: install:claude:repo
+      - task: install:crush
+      - task: install:antigravity
 
   install:claude:global:
     desc: 'Per-skill symlinks under ~/.claude/skills/<name> — visible in every Claude Code project on this host.'
     cmds:
       - mkdir -p {{.CLAUDE_GLOBAL_DIR}}
       - |
-        for skill in $(ls -1 "{{.TASKFILE_DIR}}" | grep -Ev "^(Taskfile.yml|install.sh|README.md|SKILLS_INDEX.md|.gitea|.git$)$"); do
+        for skill in $(ls -1 "{{.TASKFILE_DIR}}" | grep -Ev "{{.NON_SKILL_ENTRIES}}"); do
           target="{{.TASKFILE_DIR}}/${skill}"
           link="{{.CLAUDE_GLOBAL_DIR}}/${skill}"
           if [ -L "$link" ] || [ -e "$link" ]; then
@@ -63,7 +70,7 @@ tasks:
         fi
         target_dir="$repo/.claude/skills"
         mkdir -p "$target_dir"
-        for skill in $(ls -1 "{{.TASKFILE_DIR}}" | grep -Ev "^(Taskfile.yml|install.sh|README.md|SKILLS_INDEX.md|.gitea|.git$)$"); do
+        for skill in $(ls -1 "{{.TASKFILE_DIR}}" | grep -Ev "{{.NON_SKILL_ENTRIES}}"); do
           target="{{.TASKFILE_DIR}}/${skill}"
           link="${target_dir}/${skill}"
           if [ -L "$link" ] || [ -e "$link" ]; then
@@ -77,6 +84,44 @@ tasks:
           echo "linked $link → $target"
         done
 
+  install:crush:
+    desc: 'Per-skill symlinks under ~/.config/crush/skills/<name> — visible in every Crush session on this host.'
+    cmds:
+      - mkdir -p {{.CRUSH_DIR}}
+      - |
+        for skill in $(ls -1 "{{.TASKFILE_DIR}}" | grep -Ev "{{.NON_SKILL_ENTRIES}}"); do
+          target="{{.TASKFILE_DIR}}/${skill}"
+          link="{{.CRUSH_DIR}}/${skill}"
+          if [ -L "$link" ] || [ -e "$link" ]; then
+            current=$(readlink "$link" 2>/dev/null || true)
+            if [ "$current" = "$target" ]; then
+              continue
+            fi
+            rm -rf "$link"
+          fi
+          ln -s "$target" "$link"
+          echo "linked $link → $target"
+        done
+
+  install:antigravity:
+    desc: 'Per-skill symlinks under ~/.gemini/antigravity/skills/<name>. SKILL.md frontmatter (name + description) is already antigravity-compatible.'
+    cmds:
+      - mkdir -p {{.ANTIGRAVITY_DIR}}
+      - |
+        for skill in $(ls -1 "{{.TASKFILE_DIR}}" | grep -Ev "{{.NON_SKILL_ENTRIES}}"); do
+          target="{{.TASKFILE_DIR}}/${skill}"
+          link="{{.ANTIGRAVITY_DIR}}/${skill}"
+          if [ -L "$link" ] || [ -e "$link" ]; then
+            current=$(readlink "$link" 2>/dev/null || true)
+            if [ "$current" = "$target" ]; then
+              continue
+            fi
+            rm -rf "$link"
+          fi
+          ln -s "$target" "$link"
+          echo "linked $link → $target"
+        done
+
   update:
     desc: 'git pull the canonical checkout then re-run install.'
     cmds:

install.sh

@@ -17,6 +17,8 @@ REPO_URL="${SKILLS_REPO_URL:-https://gitea.d-ma.be/mathias/skills.git}"
 REF="${SKILLS_REF:-main}"
 CHECKOUT_DIR="${SKILLS_CHECKOUT_DIR:-$HOME/.local/share/skills}"
 CLAUDE_GLOBAL_DIR="${CLAUDE_SKILLS_DIR:-$HOME/.claude/skills}"
+CRUSH_DIR="${CRUSH_SKILLS_DIR:-$HOME/.config/crush/skills}"
+ANTIGRAVITY_DIR="${ANTIGRAVITY_SKILLS_DIR:-$HOME/.gemini/antigravity/skills}"
 
 log() { printf '[skills] %s\n' "$*"; }
 
@@ -69,6 +71,28 @@ wire_claude_global() {
   done < <(list_skills)
 }
 
+wire_crush() {
+  # Crush reads skills from ~/.config/crush/skills/<name>/SKILL.md.
+  # Pre-creating the dir is cheap even when Crush isn't installed.
+  mkdir -p "$CRUSH_DIR"
+  while IFS= read -r skill; do
+    [ -n "$skill" ] || continue
+    link_skill "$CRUSH_DIR" "$skill"
+  done < <(list_skills)
+}
+
+wire_antigravity() {
+  # Antigravity (Google's VS Code extension) reads global skills from
+  # ~/.gemini/antigravity/skills/<name>/SKILL.md. Our SKILL.md files
+  # already carry the required `name` + `description` YAML frontmatter,
+  # so symlinks are sufficient — no manifest translation step.
+  mkdir -p "$ANTIGRAVITY_DIR"
+  while IFS= read -r skill; do
+    [ -n "$skill" ] || continue
+    link_skill "$ANTIGRAVITY_DIR" "$skill"
+  done < <(list_skills)
+}
+
 wire_claude_repo() {
   # Only wire per-repo when invoked from inside a git repo and it isn't
   # the skills repo itself.
@@ -92,6 +116,8 @@ main() {
   ensure_checkout
   wire_claude_global
   wire_claude_repo
+  wire_crush
+  wire_antigravity
   log "done — $(list_skills | wc -l | tr -d ' ') skill(s) wired at ref=$REF"
 }