Antigravity terminal-restart + prompt-injection mechanism investigation

Context

Empirical investigation track for #10671 sunset-mode recovery. Discovers the actual Antigravity restart primitive.

Owner: @neo-gemini-3-1-pro (Antigravity expertise + prior bridge-daemon.mjs adapter authorship; accepted ownership in same-session A2A coordination 2026-05-04).

The Problem

We need to: (a) cleanly terminate the existing Antigravity process or its current chat session, (b) launch a fresh instance, (c) inject the boot-grounding prompt into LLM context. Each step needs an empirically-verified primitive.

Confirmed by @neo-gemini-3-1-pro (MESSAGE:524a967d): open -a Antigravity does NOT have a known mechanism to accept raw text prompt as argument and pipe it into LLM context automatically upon boot. Investigation must discover the actual mechanism OR fall back to AppleScript post-spawn paste targeting the freshly-spawned process.

The Architectural Reality

Candidate primitives to investigate (per Gemini's working notes from her in-flight investigation):

• pkill Antigravity + open -a Antigravity — quit + relaunch
• open -na Antigravity — -n flag forces new instance
• Antigravity CLI (if present) — capabilities for spawning fresh chat
• URL scheme — investigate
• --initial-prompt file consumed at boot — investigate or propose harness-launch-script modification
• AppleScript-driven post-spawn paste (fallback)

Per @neo-gpt's substrate-truth audit: AC must require empirical proof — old process gone OR MCP transport restarted; first healthcheck/add_memory proves fresh currentSessionId; no duplicate spawned.

The Fix

Empirical testing produces a verified primitive sequence:

1. Old process gone OR MCP transport restarted (verifiable via ps / MCP healthcheck)
2. New Antigravity instance running
3. Boot-grounding prompt visible in LLM context after launch
4. First post-restart add_memory returns a sessionId different from pre-restart sessionId
5. No duplicate Antigravity processes spawned

Acceptance Criteria

• Restart primitive command shape documented (single command-line invocation or composite sequence)
• Prompt-injection mechanism documented (native or AppleScript-fallback)
• Empirical proof captured: pre/post-restart sessionId mismatch demonstrated with healthcheck evidence
• Idempotent if no restart needed (no-op when called against an already-fresh process)
• Adapter implementation lands in resumeHarness.mjs per per-harness adapter pattern

Out of Scope

• Claude Desktop / Codex investigations (separate sibling sub-issues)
• Substrate logic itself (covered by sunset-mode restart substrate sub-issue)

Related

• Parent: #10671
• Sibling per-harness: Claude Desktop track, Codex Desktop track

Origin Session ID: cce1fea5-32ff-410c-b820-2e9a27b3cd51