## What changed
Advertise `fileWriteStreaming` and support `fs/open` with `mode: "replace"` to create or truncate a file for writing. Implement `fs/writeBlock` with explicit offsets and nonempty chunks of up to 1 MiB, rejecting ranges beyond the signed 64-bit file offset limit.
Apply write sandbox permissions when opening writable handles, including when full-disk reads are allowed. Keep `read` as the default open mode.
## Testing
Add integration coverage for positional writes, chunk and offset bounds, replacement truncation, read/write handle permissions, and sandbox write restrictions. Verify that duplicate handle IDs and exhausted handle capacity reject replacement opens without creating or truncating files.
GitOrigin-RevId: 696ee6437dd5f5b69d5a7667dddea0ff44472094
## What changed
Run direct `read_file` operations in a blocking task with bounded read chunks and cancellation checks. Dropping the async caller cancels further reads between chunks. Preserve the 512 MiB size limit, symlink-following options, and regular-file validation.
## Testing
Add regression coverage for 4 MiB reads and oversized-file rejection with both symlink-following options, cancellation after the first chunk, and FIFO rejection without waiting for a writer.
GitOrigin-RevId: 19f2816de15a03bd89b463de6b002367e6a692a9
Adam Perry @ OpenAI