[loop cycle 3] feat(calls): expose minimal window.chrome so WhatsApp enables call buttons

[karem505]

What

Targets "calls are not supported." WhatsApp Web disables the voice/video call buttons unless it judges the environment an eligible Chrome/Edge browser. The UA and navigator.userAgentData already report Chrome 131, but the calling-eligibility check also probes window.chrome, which WebKitGTK doesn't expose — so the buttons stay greyed.

Crucially, this is a detection gate, not a capability one: it was verified that this WebKitGTK build (2.52.3) ships WebRTC (libwebrtc codec symbols + enable-webrtc present), and the app already enables it and auto-grants mic/camera (enable_webview_media in window.rs). So the engine can do calls once WhatsApp considers it eligible.

How

bridge.js section 1b adds a minimal, idempotent stand-in:

if (!window.chrome) {
  Object.defineProperty(window, "chrome", {
    configurable: true, enumerable: true, writable: true,
    value: { app: { isInstalled: false }, runtime: {} },
  });
}

• app.isInstalled:false is exactly what a normal web page in real Chrome sees — it steers WhatsApp away from the Chrome-Apps path, not into it.
• runtime:{} satisfies a typeof chrome.runtime probe without exposing callable extension APIs.
• Origin-guarded, own try/catch, never clobbers a genuine window.chrome.

Verification

Gate 1 — cargo build --locked + cargo test: PASS (51 tests).

Gate 2 — real WebKitGTK engine harness (origin spoofed), two cases: PASS

• absent → window.chrome becomes an object with runtime + app.isInstalled===false; userAgentData (3 brands) + Notification shim intact.
• preset ({__sentinel:"real"}) → sentinel preserved (no clobber); existing shims intact.

Gate 3 — generation-blind code review: APPROVE, severity none, no must-fix. Confirmed the no-clobber guard, descriptor flags matching real Chrome, low regression risk (minimal stub avoids triggering extension/Chrome-App code paths), isolation, and idempotency.

⚠ Human-test gate (please confirm before merging)

The call button can't be exercised headlessly — it needs a logged-in WhatsApp. Before merging, please:

1. Build/run this branch, open a chat, and check whether the voice/video call icons are now enabled (no longer greyed).
2. Optionally start a call to confirm mic/camera negotiate.

If the buttons are still disabled, this wasn't the (only) gate — the next lever is WebRTC codec availability (H264/VP8) in this WebKitGTK build, tracked as backlog C2. Either way this change is safe and reversible (it only adds a Chrome marker).

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🤖 PR-ONLY — do not auto-merge. Releasing whatRust is manual via a v* tag; this loop never merges, bumps the version, or tags a release. Opened by the whatrust-fix-loop (cycle 3/6).