## 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
## Why
The per-connection limit of 128 file read handles was checked only after opening the file, leaving pending opens outside the limit.
## What changed
Reserve a semaphore permit before polling the file-open future, counting pending opens and registered handles against the same limit. Release capacity when an open fails or is cancelled, or when a handle closes, even if a read still retains the file.
Use synchronous handle-table locks that never cross an await, and recheck duplicate IDs after opening to preserve the winning handle during concurrent opens.
## Testing
Add tests for stalled-open progress, pending-open admission limits, permit cleanup after failure or cancellation, capacity reuse while a file remains in use, and concurrent duplicate IDs.
GitOrigin-RevId: caabf38c74dda5951f2fc75234a7149daaa01263
## What changed
Rename `file_read` to `file_handle` and `FileReadHandleManager` to `FileHandleManager`. Update the filesystem handler field, handle ID validation helper, and related constants to use file handle terminology. File operations, limits, and error messages remain unchanged.
GitOrigin-RevId: 25ad81a917386da23fd42ecff79bd47a482ce430
Adam Perry @ OpenAI