Standalone LS for Proxy Isolation

Goal

Route ALL proxy traffic through a standalone LS instance instead of the real one, so development/testing/proxying never interferes with active coding sessions.

Current State

The proxy currently talks to the real LS spawned by Antigravity. This is risky — a bad cascade or proxy bug can disrupt the coding conversation.

What Works

Standalone LS starts fine with custom init metadata via stdin protobuf
Connects to the main extension server (-extension_server_port)
Accepts cascade requests (returns cascadeId)
With detect_and_use_proxy = ENABLED (field 34 = 2), honors HTTPS_PROXY

What Doesn't Work

Cascades silently fail — the LS accepts the request but never processes it
- No planner invocation, no upstream API call, no logs beyond startup
- 9 lines of log after 40s wait
- Main LS logs show zero trace of the standalone's cascade

Suspected Blockers (investigate in order)

Auth context — standalone may not receive OAuth token from extension server
- Check: does the standalone's GetUserStatus return valid auth?
- The extension server might only share tokens with the "primary" LS
Unleash feature flags — cascade processing gated by flags the standalone doesn't fetch
- The standalone connects to Unleash via the proxy, but might not get the right flags
- Check: compare Unleash responses between main and standalone
Workspace indexing — planner might require indexed workspace state
- The standalone's workspace (/tmp/antigravity-standalone) is empty
- Try: point it at a real workspace with actual files
Extension server coupling — cascade might need the extension to "drive" it
- The chat panel in the extension might send additional RPCs to progress the cascade
- Check: trace what RPCs the extension sends after StartCascade

Investigation Plan

# 1. Launch with max verbosity
echo "$METADATA" | base64 -d | \
    timeout 90 "$LS_BIN" \
    -v 5 \
    -server_port 42200 \
    ... > /tmp/standalone-verbose.log 2>&1 &

# 2. Check auth status
curl -sk "https://127.0.0.1:42200/exa.language_server_pb.LanguageServerService/GetUserStatus" \
    -H "Content-Type: application/json" \
    -H "x-codeium-csrf-token: $CSRF" \
    -d '{}'

# 3. Send cascade and watch logs in real-time
tail -f /tmp/standalone-verbose.log &
curl -sk "https://127.0.0.1:42200/.../StartCascade" ...

# 4. Compare Unleash flags
# Main LS unleash vs standalone unleash

Key Technical Details

Init metadata protobuf field 34 = detect_and_use_proxy (enum: 0=UNSPECIFIED, 1=ENABLED, 2=DISABLED)
Model IDs: M18=Flash, M8=Pro-High, M7=Pro-Low, M26=Opus4.6, M12=Opus4.5
LS binary: /usr/share/antigravity/resources/app/extensions/antigravity/bin/language_server_linux_x64
API endpoint: daily-cloudcode-pa.googleapis.com/v1internal:streamGenerateContent?alt=sse

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