fix(web): prevent SIGILL crash under sustained gRPC stream by adding WASM yield and backpressure

[SBALAVIGNESH123]

Fixes #12723

Root Cause

The gRPC read loop in
e_grpc_client/src/read.rs runs as a tight async loop via wasm_bindgen_futures::spawn_local. Under sustained load, stream.try_next().await resolves instantly (Poll::Ready) on every iteration, starving the browser event loop.

Simultaneously, the
e_quota_channel WASM send path bypasses backpressure entirely — logging a debug warning but sending into an unbounded crossbeam channel regardless of byte budget.

The combination causes unbounded WASM linear memory growth. When memory.grow hits the 2 GiB wasm32 ceiling, the allocator aborts, and Chromium translates the WASM trap to SIGILL, killing the renderer process.

Firefox survives because SpiderMonkey traps the unreachable instruction at the VM level rather than forwarding it as an OS signal.

Changes

1. Periodic yield in gRPC read loop (WASM only)

Every 32 messages, yield to the browser event loop via setTimeout(0). This gives the browser a tick for GC, rendering, and the channel consumer to drain queued messages. When the channel queue exceeds 128 messages, pause ingestion entirely until the consumer catches up.

Uses the same web_sys::Window::set_timeout + js_sys::Promise + wasm_bindgen_futures::JsFuture pattern already established in
e_backoff/src/lib.rs.

2. Hard ceiling on WASM channel send path

When the byte budget is exceeded by 2×, drop the message with a warn_once! instead of sending anyway into the unbounded crossbeam channel. This prevents unbounded memory growth while still allowing small bursts (up to 2× capacity).

Previously, the WASM path logged a debug_once! and sent unconditionally — the byte quota was purely advisory.

Files Changed

File	Change
crates/store/re_grpc_client/src/read.rs	Add yield_to_browser() helper + periodic yield + consumer backpressure check
crates/utils/re_quota_channel/src/sync/mod.rs	Add 2× hard ceiling with message drop on WASM send path
crates/store/re_grpc_client/Cargo.toml	Add js-sys and web-sys WASM dependencies (both already in workspace)

Testing

Tested with the reproduction script from #12723:

�ash cargo run --package rerun-cli --no-default-features --features web_viewer -- \ --serve-web --memory-limit 1500MiB

With a sustained 250K point-cloud stream at ~8.75 MB/row. Before fix: Chrome crashes within 30–120 seconds with SIGILL. After fix: Chrome survives indefinitely, with graceful degradation under extreme load.

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