## v6.2 — Full Chrome TLS Impersonation (BoringSSL)

### Critical Fix: Complete Browser Fingerprint Impersonation

The v6.1 fixes (Chrome headers, HTTP/2, cookies) were necessary but **not sufficient**.
Cloudflare uses **three fingerprinting layers simultaneously**, and v6.1 only addressed one:

| Layer | What CF Checks | v6.1 Status | v6.2 Status |
|-------|---------------|-------------|-------------|
| **HTTP Headers** | UA, Sec-CH-UA, Sec-Fetch-* | ✅ Fixed | ✅ (now via rquest) |
| **TLS Fingerprint (JA3/JA4)** | Cipher suites, extensions, GREASE | ❌ FAILED (rustls) | ✅ Fixed (BoringSSL) |
| **HTTP/2 Fingerprint (Akamai)** | SETTINGS frame values, window size | ❌ FAILED (hyper defaults) | ✅ Fixed (Chrome H2) |

### Root Cause

`reqwest` + `rustls` generates a TLS ClientHello that is **nothing like Chrome's**:
- `rustls` sends ~6 cipher suites in wrong order. Chrome sends 16 with GREASE.
- `rustls` doesn't support `compress_certificate` (brotli). Chrome does.
- `rustls` doesn't inject GREASE values. Chrome uses RFC 8701 GREASE.
- `hyper`'s HTTP/2 sends `INITIAL_WINDOW_SIZE=65535`. Chrome sends `6291456` (6MB).
- `hyper` sends SETTINGS that produce a different Akamai H2 fingerprint.

Cloudflare detects this mismatch **at the TLS handshake level** — before any HTTP headers are even sent. No amount of header faking can fix a wrong JA3.

### Solution: `rquest` with BoringSSL

Replaced `reqwest` (rustls) with `rquest` (BoringSSL-backed Chrome impersonation):

```toml
# OLD (v6.1):
reqwest = { version = "0.12", features = ["rustls-tls", "gzip", "brotli", "cookies", "http2"] }

# NEW (v6.2):
rquest = { version = "1.0", features = ["full"] }
```

**`rquest`** uses a patched BoringSSL (Chrome's actual TLS library) that emits a **byte-for-byte identical** TLS ClientHello to Chrome 137. It also configures HTTP/2 SETTINGS to match Chrome's exact values.

One-line initialization:
```rust
let client = Client::builder()
    .impersonate(Impersonate::Chrome137)
    .cookie_store(true)
    .build()?;
```

This single call configures:
- ✅ TLS cipher suite order (16 ciphers + GREASE, exact Chrome order)
- ✅ TLS extension ordering (with compress_certificate, ALPS, GREASE)
- ✅ HTTP/2 SETTINGS frame (INITIAL_WINDOW_SIZE=6291456, etc.)
- ✅ Header ordering (sec-ch-ua before accept, as Chrome does)
- ✅ User-Agent (Chrome 137)
- ✅ GREASE values (random per-connection, as Chrome does)
- ✅ Certificate compression (brotli, zlib)
- ✅ ALPN (h2, http/1.1)

### What This Means in Practice

| Site | v6.1 (rustls) | v6.2 (BoringSSL) |
|------|---------------|-------------------|
| Cloudflare Basic | ⚠️ Sometimes | ✅ Always passes |
| Cloudflare JS Challenge | ❌ Blocked | ✅ Cookie-based pass |
| DataDome | ❌ Blocked | ✅ Passes (JA3 matches) |
| PerimeterX/HUMAN | ❌ Blocked | ✅ Passes (JA3+H2 match) |
| Akamai Bot Manager | ❌ Blocked | ✅ Passes (H2 FP match) |
| Cloudflare Turnstile | ❌ Needs WebView | ❌ Still needs WebView |

### Changes

**`crates/bex-core/Cargo.toml`**:
- Removed `reqwest` with `rustls-tls` feature
- Added `rquest = { version = "1.0", features = ["full"] }`
- Version bumped to 2.1.0

**`crates/bex-core/src/http_service.rs`**: Complete rewrite:
- Uses `rquest::Client` with `Impersonate::Chrome137`
- Removed all manual header construction (`browser_default_headers()` deleted)
- Headers are now managed by the impersonation layer automatically
- Plugin headers still override when explicitly set (for custom Referer, etc.)
- Auto-Referer from URL origin still works
- Cache logic unchanged

### Build Requirements

`rquest` bundles BoringSSL which requires:
```bash
# Linux:
apt-get install cmake clang

# macOS:
brew install cmake llvm
```

The build handles BoringSSL compilation automatically via the `boring` crate.

### Migration Notes for Plugin Authors

**No changes needed.** The WIT interface (`http::send-request`) is unchanged.
Plugins still set their own headers via `Request.headers` — these override
the Chrome defaults when explicitly provided.

The only behavioral difference: requests that previously got CF-challenged
or blocked will now succeed transparently. No code changes needed in plugins.

### Known Limitation

Cloudflare Turnstile (interactive CAPTCHA) still requires actual human interaction.
This is by design — Turnstile uses browser fingerprinting + proof-of-work that
cannot be solved programmatically without a full WebView.