fix(safe-bash): explain typed curl output failures

[kamilio]

When curl cannot write a downloaded file, it currently replaces the filesystem's typed refusal with a generic error 23. An agent trying to overwrite a loaded read-only file cannot see why the download failed.

Preserve the message of a typed FsError in curl's output diagnostic. Keep error 23 and preserve the generic message for arbitrary exceptions. Nested error causes are not exposed.

The network regression verifies the typed read-only reason, generic handling of an untyped exception even when it carries a filesystem-like code, and the absence of a private nested cause. Existing partial-write failure expectations now include the typed filesystem reason.

Validation: 59 focused network tests pass. Owning source/test typecheck and all 26 public consumer groups pass. The maintained root build and guarded ESLint pass (10,527 files, zero diagnostics, 25 boundary receipts). A separate Poe2 consumer change supplies actionable new-path guidance while retaining loaded-file immutability.

Screenshots

Recorded downstream controlled Poe2 integration with the consumer guidance change: actual execute_shell/API/native storage results and deterministic image responses rendered in Chat. Immutable overwrite retains exit 23; writing a new path succeeds and original bytes were verified unchanged. No model run or production service; not standalone upstream proof.

[kamilio]

Cherry-picked typed curl output diagnostics as ee7d98f.

Verified on remote main at 4da2a66 after local validation and final installed-package qualification. Closing after cherry-pick/reconciliation rather than merging obsolete branch history.

Release is in progress: https://github.com/poe-platform/poe-code/actions/runs/34500155547 ; scoped packages: https://github.com/poe-platform/poe-code/actions/runs/34500155125 .