feat(antigravity): add recall skill, optional rule, shared protocol

[undeadindustries]

Summary

Adds the recall layer to the Antigravity plugin, mirroring the three-layer wiring from feat/cursor-hooks-support, adapted for Antigravity's native plugin and hook surfaces. Follows on from #1633.

• integrations/shared/recall-protocol.md — canonical "search before answering" protocol, single source of truth shared across Cursor, Antigravity, Claude Code, Codex, OpenClaw. Skills and rules link here rather than restating the protocol, so they can never drift from each other.
• .antigravity-plugin/skills/mempalace-recall/SKILL.md — recall-only skill (Protocol, Tool selection, Unhappy paths, Anti-patterns). Complements the ops mempalace skill. Protocol cross-reference uses a GitHub URL rather than a relative file path, so the link works in the installed copy at ~/.gemini/config/plugins/mempalace/ as well as in the repo.
• .antigravity-plugin/rules/mempalace-recall.md — plain .md recall rule (no .mdc, no YAML frontmatter per Antigravity's rules/<name>.md format). Body mirrors the Cursor rule.
• hooks/antigravity/install.sh — creates skills/mempalace-recall/ and rules/ in the install directory; copies both new files (cmp-gated, idempotent). Verified: first run writes, second run is silent.
• .antigravity-plugin/README.md — updated layout tree + "Three recall layers" section (wake hook eager layer → recall skill on-demand layer → optional rule).
• 11 new tests in tests/test_antigravity_plugin_manifest.py covering: shared protocol presence, recall skill structure (YAML frontmatter, required sections, GitHub URL reference), rule format (plain .md, no frontmatter), and installer lines.

Why the wake hook is unchanged

The Antigravity wake hook (PreInvocation, invocationNum==1) already injects actual palace content via injectSteps[].ephemeralMessage. This is strictly better than Cursor's sessionStart approach of emitting a static "please call these tools" directive — it delivers the memory itself rather than asking the agent to go fetch it. No change needed.

Test plan

• uv run pytest tests/test_antigravity_plugin_manifest.py — 22 tests (11 new), all pass
• uv run pytest tests/ --ignore=tests/benchmarks — 2349 passed, 3 skipped
• bash hooks/antigravity/install.sh --dry-run — shows correct mkdir + copy_file entries for recall skill and rule
• bash hooks/antigravity/install.sh then re-run — idempotent (no second-run writes)
• uv run ruff check . — clean

Made with Cursor

[gemini-code-assist]

Code Review

This pull request introduces a three-layer recall system for the MemPalace Antigravity plugin, which includes a wake hook, a recall-only skill, and an optional recall rule, all anchored to a new canonical recall protocol (integrations/shared/recall-protocol.md). It also updates the installer script and adds comprehensive manifest tests to validate these new files. The review feedback correctly notes that the protocol steps in the newly added SKILL.md have already slightly drifted from the canonical protocol definition, and recommends keeping them synchronized to ensure consistent agent behavior.

Important

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[gemini-code-assist]

The protocol steps described here have already drifted from the canonical protocol defined in integrations/shared/recall-protocol.md. For example:

• Step 3: The canonical protocol includes specific examples (name, age, relationship, preference) and the phrase "Wrong is worse than slow." which are missing here.
• Step 4: The canonical protocol uses "Return verbatim. Quote the drawer's exact stored words. Never summarize, paraphrase, or lossy-compress..." whereas this skill uses "Return the drawer's verbatim text. Never summarize or paraphrase...".
• Step 5: The canonical protocol has different phrasing regarding background hooks and double-filing.

While some platform-specific details (like Antigravity's PreInvocation hook in Step 1) are appropriate here, the core instructions, unhappy paths, and anti-patterns should be kept synchronized with the canonical source of truth to ensure consistent agent behavior across all integrations.