This is the third sibling of the Claude Code and Codex integrations (see hooks/mempal_save_hook.sh and .codex-plugin/hooks/). The overall shape is the same — a Stop event triggers a background save, a startup-time event injects memory into the agent — but the wire format and STDOUT contract are Antigravity-specific (see STDIN_SHAPE.md).

Quick start

From the repo root:

bash hooks/antigravity/install.sh

This installs the plugin to ~/.gemini/config/plugins/mempalace/. Restart Antigravity and the MCP server, skill, and hooks all register automatically.

To dry-run first:

bash hooks/antigravity/install.sh --dry-run

To uninstall:

bash hooks/antigravity/install.sh --uninstall

What gets installed

~/.gemini/config/plugins/mempalace/
├── plugin.json                              # marker manifest
├── mcp_config.json                          # registers mempalace-mcp
├── hooks.json                               # rendered from hooks.json.tmpl
├── README.md
├── skills/
│   └── mempalace/
│       └── SKILL.md
└── hooks/
    ├── lib/
    │   └── common.sh
    ├── mempal_save_hook_antigravity.sh      # Stop event handler
    └── mempal_wake_hook_antigravity.sh      # PreInvocation handler

hooks.json carries absolute paths to the two hook scripts (resolved from __PLUGIN_DIR__ at install time).

What the hooks do

`mempal_save_hook_antigravity.sh` (Stop event)

Fires every time the agent's execution loop terminates. Increments a per-conversation counter; every MEMPAL_SAVE_INTERVAL fires (default 15), spawns mempalace mine <transcript-dir> --mode convos --wing <inferred> in the background. The hook itself returns {} to stdout in under a few milliseconds — the actual mining runs detached and does not block the user.

Defers when:

fullyIdle == false (background tasks still running)
terminationReason == "error" (transcript may be corrupt)
A previous save for this conversation is still running
Any kill switch is set

`mempal_wake_hook_antigravity.sh` (PreInvocation event, gated)

Fires before every model invocation. Gated to invocationNum == 1 (first invocation of the conversation only) — beyond that we'd be re-injecting on every turn. Calls mempalace wake-up --wing <inferred> with a 500ms hard timeout and emits the verbatim output as an ephemeralMessage so the agent sees relevant memory on its first response without polluting the persistent transcript.

Skips when:

invocationNum != 1
Already woke this conversation (atomic mkdir loop guard)
mempalace wake-up exits non-zero, times out, or produces empty output
Any kill switch is set

Kill switches

Any one of these disables both hooks (silent passthrough, exit 0):

Knob	Value
`MEMPAL_DISABLE_HOOK`	`1`, `true`, `yes`
`MEMPALACE_HOOKS_AUTO_SAVE`	`false`, `0`, `no`
`~/.mempalace/config.json`	`{"hooks": {"auto_save": false}}`
Removing `~/.mempalace/` entirely	(palace nuke)

Workspace-scoped install (advanced)

If you want MemPalace to load only inside a specific workspace, manually copy the rendered plugin into your workspace's .agents/plugins/:

bash hooks/antigravity/install.sh --install-dir /tmp/render-stage
mkdir -p <workspace>/.agents/plugins/
cp -r /tmp/render-stage <workspace>/.agents/plugins/mempalace
rm -rf /tmp/render-stage

The global install at ~/.gemini/config/plugins/mempalace/ is the canonical UX and what we recommend.

Troubleshooting

Hooks aren't firing

Confirm Antigravity sees the plugin: open the IDE, navigate to the Customizations page; mempalace should appear in the global plugins list.
Check ~/.mempalace/hook_state/antigravity_hook.log — every fire logs a line. No log lines = the hook is not being invoked.
Verify mempalace-mcp is on $PATH: mempalace-mcp --version.
Inspect the rendered hooks.json paths point at executable files: bash -n ~/.gemini/config/plugins/mempalace/hooks/*.sh.

Save fires but no mining happens

Look for the most recent [event=stop] lines in antigravity_hook.log — count and interval should both be visible. Mining only triggers when count % interval == 0.
Ensure a Python that can import mempalace is reachable. The hook runs "$MEMPAL_PYTHON_BIN" -m mempalace, where MEMPAL_PYTHON_BIN is resolved (in order) from $MEMPAL_PYTHON, the mempalace-mcp / mempalace console-script shebang on $PATH, then python3. A failed probe logs:
```
ERROR: mempalace is not runnable via <python> -m mempalace; install mempalace or set MEMPAL_PYTHON
```
On a GUI-launched Antigravity the harness PATH may differ from your shell PATH; if the shebang heuristic can't find the right interpreter, export MEMPAL_PYTHON=/abs/path/python (e.g. "$(uv tool dir)/mempalace/bin/python") and restart.

Wake injection isn't appearing

The wake hook only injects on invocationNum == 1. Subsequent invocations are gated.
The atomic mkdir marker ~/.mempalace/hook_state/antigravity_woke_<conversationId> exists after a successful injection. Remove it to re-inject (rare).
mempalace wake-up --wing <inferred> may be returning empty output if the wing doesn't exist yet. Run mempalace status to verify wing presence.

README.md

MemPalace — Antigravity hook scripts