# Helper Page Lifecycle Fix & Hidden Domain Support

**Date:** 2026-04-14
**Status:** Approved

## Problem Statement

Two bugs in the browser-helper.html page management:

1. **Duplicate helper pages**: Every WebSocket client reconnection triggers a new `serve_client()` call, which creates a new `LiveBrowserCallbackHost` and opens a new helper page via `sgBrowerserOpenPage`. The old helper page tab is never closed, causing accumulation of orphaned tabs.

2. **Helper page is visible**: The bootstrap uses `sgBrowerserOpenPage` (visible tab API) instead of `sgHideBrowerserOpenPage` (hidden domain API). The helper page should not be visible to the user.

## Root Cause Analysis

### Duplicate pages

Call chain:
- `src/service/mod.rs:72` — outer `loop` accepts new WebSocket connections
- `src/service/mod.rs:79` — each connection calls `serve_client()`
- `src/service/server.rs:241` — `cached_host` declared as local variable, re-initialized to `None` each call
- `src/service/server.rs:288` → `callback_host.rs:241` — `bootstrap_helper_page()` opens a new helper tab

`Drop for LiveBrowserCallbackHost` (`callback_host.rs:321-328`) only shuts down the HTTP server thread. It does not send a browser close command for the helper tab.

### Visible page

`callback_host.rs:28`: `HELPER_BOOTSTRAP_ACTION = "sgBrowerserOpenPage"` — this is the visible-domain open API (API #7). The hidden-domain equivalent is `sgHideBrowerserOpenPage` (API #6).

## Solution: Approach C — Incremental Fix

### Step 1: Fix lifecycle (immediate, deterministic fix)

#### 1a. Lift `cached_host` to outer loop

Move `cached_host: Option<Arc<LiveBrowserCallbackHost>>` from inside `serve_client()` to before the `loop` in `run_service()` (`mod.rs`). Change `serve_client()` signature to accept `&mut Option<Arc<LiveBrowserCallbackHost>>` instead of creating its own.

Effect: Multiple WebSocket reconnections share the same host. Helper page opens once per process lifetime.

#### 1b. Close helper page on Drop

Enhance `Drop for LiveBrowserCallbackHost`:
- Add `browser_ws_url: String` field to `LiveBrowserCallbackHost` (stored at construction time)
- Add `use_hidden_domain: bool` field (stored at construction time)
- In `Drop::drop`, before shutting down the server thread:
  1. Connect to `browser_ws_url` with 100ms connection timeout
  2. Send register message
  3. Send close command: `[helper_url, close_api, helper_url]`
     - `close_api` = `"sgBrowserClosePage"` when `use_hidden_domain == false`
     - `close_api` = `"sgHideBrowerserClosePage"` when `use_hidden_domain == true`
  4. All steps are best-effort: failures are silently ignored
  5. Total timeout cap: 500ms

### Step 2: Hidden domain config switch (for testing/gradual rollout)

#### 2a. Parameter plumbing

- `LiveBrowserCallbackHost::start_with_browser_ws_url` gains parameter `use_hidden_domain: bool`
- `bootstrap_helper_page` selects API based on this flag:
  - `true` → `"sgHideBrowerserOpenPage"`
  - `false` → `"sgBrowerserOpenPage"` (current behavior, default)
- `LiveBrowserCallbackHost` stores the flag for Drop close-command selection

#### 2b. Caller changes

- `mod.rs` / `server.rs` pass `false` as default
- To enable hidden domain, change the call site to pass `true`

## What Does NOT Change

- `callback_backend.rs` `SHOW_AREA = "show"` — JS injection targets visible business pages, not the helper itself
- `sgBrowserExcuteJsCodeByDomain` area parameter — stays `"show"` regardless of helper domain
- Helper page HTML content — WebSocket connection and command polling JS remain the same
- `collect_lineloss.js` — not affected

## Affected Files

| File | Change |
|------|--------|
| `src/browser/callback_host.rs` | New fields on `LiveBrowserCallbackHost`, `start_with_browser_ws_url` signature change, `Drop` enhancement, new `close_helper_page` helper fn |
| `src/service/mod.rs` | `cached_host` lifted to outer loop, passed to `serve_client` |
| `src/service/server.rs` | `serve_client` signature change to accept `&mut Option<Arc<LiveBrowserCallbackHost>>` |
| Existing test files | Adapt `start_with_browser_ws_url` calls with new `use_hidden_domain` parameter |

## Testing

- Existing `callback_host` tests: adapt to new signature (add `false` parameter)
- New unit test: `use_hidden_domain = true` → bootstrap sends `sgHideBrowerserOpenPage`
- New unit test: `use_hidden_domain = false` → bootstrap sends `sgBrowerserOpenPage` (regression)
- `cargo build` + `cargo test` full verification

## Browser API Reference

| API | Wire format | Effect |
|-----|------------|--------|
| `sgBrowerserOpenPage` (API #7) | `[requesturl, "sgBrowerserOpenPage", url]` | Opens visible tab |
| `sgHideBrowerserOpenPage` (API #6) | `[requesturl, "sgHideBrowerserOpenPage", url]` | Opens in hidden domain |
| `sgBrowserClosePage` (API #64) | `[requesturl, "sgBrowserClosePage", url]` | Closes visible tab |
| `sgHideBrowerserClosePage` (API #68) | `[requesturl, "sgHideBrowerserClosePage", url]` | Closes hidden domain page |
