Gracefully fall back when fs.watch is unsupported on SMB/network filesystems

Finding: In an external report on openai/codex#36961 (https://github.com/openai/codex/issues/36961), the Codex VS Code extension repeatedly logs a Git repo watcher failure, "UNKNOWN: unknown error, watch", when the workspace is on a Samba SMB share. The reporter's environment was Windows 11, Node.js v24.18.0 and Git for Windows; the extension version was not captured. This is an external report only and was not reproduced by KFA. Reported evidence: The reporter says a minimal standalone Node.js script calling fs.watch() on the directory prints that the watch was established, then emits the same UNKNOWN error from node:internal/fs/watchers. The same script reportedly succeeds on a local NTFS directory. The failure also reportedly occurs on newly created SMB directories, which points away from Git metadata. Setting core.filemode=false cleaned the Git working tree but did not change the fs.watch() failure (https://github.com/openai/codex/issues/36961). The reporter labels this an enhancement request, not a bug, and attributes the limitation to Node.js fs.watch() on Windows network filesystems. That attribution is the reporter's hypothesis and is not maintainer-confirmed. Second report: On 2026-10-09 another user described what they believe is the same issue across about 100 university Windows machines with SMB-hosted files. They see a VS Code launch dialog, "A JavaScript error occurred in the main process", with the same UNKNOWN watch error (https://github.com/openai/codex/issues/36961#issuecomment-6087111335). That is a main-process exception. The supplied content does not show whether Codex triggers it, so treat it as possibly the same underlying fs.watch behavior but unattributed. Proposed mitigation, not implemented: An earlier non-maintainer comment suggests probing fs.watch() once at watcher init. On the first failure it would disable the watcher for that workspace, log one warning, and fall back to bounded polling for repository status refresh (https://github.com/openai/codex/issues/36961#issuecomment-5183982500). This is a design suggestion only. Status: The issue is OPEN with no maintainer response, fix commit or released fix in the supplied material. A confirmed workaround is UNKNOWN. Limitations: Reports are unverified by KFA and the version is unknown. Comment coverage may omit middle comments.