[wieslawsoltes]

Problem and change

Code OSS consumes binary WebSocket messages as Blob values through FileReader. The runtime preserved Blob bytes but lacked FileReader.

This layer adds asynchronous FileReader state, events, abort and error behavior, and exact ArrayBuffer, text, binary string, and data URL reads over native Blob bytes. It installs per supported realm without replacing a complete host implementation.

Closes #73. The equivalent implementation remains in draft consolidation PR #76.

Cumulative validation

• Performance layer d727fe33; exact head 391d4f54
• Cumulative Release V8 native engine build
• RuntimeCompatibility suite passes 25/25
• Focused native websocket-file-reader filter: 10/10 local passes at 114-118 ms
• Persisted 8 MiB exact-byte performance gate completes in 33.5 ms within the 3,000 ms budget
• Ordered events, consecutive reads, concurrent-read failure, abort, real errors, byte identity, and lifecycle are covered
• git diff --check

Native GitHub stack #159

1. Implement retained Performance Timeline for Code OSS #134 — Performance Timeline (Implement retained Performance Timeline required by Code OSS startup #72)
2. Implement FileReader over native Blob bytes #135 — current layer — FileReader over native Blob bytes (Implement FileReader over native Blob bytes for Code OSS WebSockets #73)
3. Implement mutable stylesheet CSSOM for Monaco #136 — cumulative top — mutable stylesheet CSSOM (Implement mutable stylesheet CSSOM for Monaco and Code OSS #74)

Only the cumulative top PR receives remote validation. Merge all layers atomically through Stack #159 after the top related checks pass.