feat: add Antigravity CLI adapter and session parser

[shreem26]

Purpose

Add full IDE adapter for Google Antigravity CLI (agy), enabling Observal to scan, detect, and capture sessions from Antigravity installations. This brings Antigravity to first-class IDE status with session parsing support.

Approach

Follows the existing adapter pattern (one adapter per IDE on both CLI and server sides):

CLI side:

• observal_cli/ide/antigravity.py — scan home/project for MCPs, skills, hooks, agents
• observal_cli/ide_specs/antigravity_hooks_spec.py — hook spec using hooks.json format with PreInvocation + Stop events
• observal_cli/sessions/antigravity.py — session file helpers with WSL path resolution
• observal_cli/hooks/antigravity_session_push.py — hook-based session push (for when agy hook execution works)
• observal_cli/cmd_reconcile_cli.py — observal reconcile --ide antigravity for manual session push
• observal_cli/cmd_doctor.py — _patch_antigravity() writes hooks to ~/.gemini/config/hooks.json

Server side:

• observal-server/services/ide/antigravity.py — config file generation for agent installs
• observal-server/services/session_parsers/antigravity.py — parses brain/<id>/.system_generated/logs/transcript.jsonl into normalized trace events

Shared:

• observal_cli/shared/utils.py — resolve_wsl_windows_home(), resolve_antigravity_dir(), resolve_antigravity_config_dir() for cross-platform path resolution
• IDE registry entries on both server and CLI sides with session_parser: "antigravity"

Key paths:

• Config: ~/.gemini/antigravity-cli/ (sessions, MCPs, settings)
• Hooks: ~/.gemini/config/hooks.json (separate from settings.json)
• Sessions: ~/.gemini/antigravity-cli/brain/<conversation-id>/.system_generated/logs/transcript.jsonl
• MCP config: ~/.gemini/config/mcp_config.json

How has this been tested

• 19 new tests in tests/test_antigravity_adapter.py covering:
  • Registry entry validation
  • Adapter registration and protocol compliance
  • MCP scanning (global + project, including serverUrl for remote MCPs)
  • Skill discovery
  • Hook detection from hooks.json
  • Hook config generation
  • Shim status
• Existing test suites pass (156 total across adapter, registry, and sync tests)
• Manual testing on WSL:
  • observal scan --ide antigravity detects the IDE and shows hook status
  • observal doctor patch --hook --ide antigravity writes correct hooks.json
  • observal reconcile --ide antigravity --dry-run discovers sessions with transcript data

Learnings

• agy (Go binary) ≠ Gemini CLI (TypeScript): The closed-source agy binary has a different hook implementation from the open-source Gemini CLI. It logs "executing command" for hooks but does not actually spawn child processes in v1.0.3. The open-source Gemini CLI hooks are synchronous and functional.
• Session transcripts are incremental JSONL: Written to brain/<id>/.system_generated/logs/transcript.jsonl in real-time during sessions. Format includes step_index, source, type, status, created_at, content, and tool_calls.
• WSL path resolution needs 3 fallbacks: (1) native ~/.gemini/, (2) cmd.exe + wslpath, (3) scan /mnt/c/Users/ for username match.
• observal reconcile is the reliable path: Until agy fixes hook execution, manual reconcile is the only way to push sessions. The hook infrastructure is ready for when it works.

Known limitations

• Hook-based real-time capture does not work with agy v1.0.3 (hooks fire but commands are not executed)
• observal reconcile --ide antigravity requires the server ingest endpoint to accept the payload (needs server rebuild)
• Token counts are not available in the transcript format
• Transcript files may be empty for very short sessions or if agy is killed ungracefully