Optimistic concurrency

content_hash is FNV-1a, 8 hex digits, of the full file bytes. Range, head, tail, and base64 reads still return that full-file hash. Pass it as expected_hash on the next edit_file, multi_edit, or single-file apply_patch.

If the file changed, the edit is rejected. The envelope code is OCC_MISMATCH. retryable is true. recovery is read_and_rebase. The body includes expected_hash, current_hash, and a conflict report (changed_ranges). A bounded diff is included only when include_diff:true or detail:"full".

write_file records the post-write hash from the reopened host file. Chain write_file to edit_file(expected_hash: <hash from write>). That does not look like an external change.

--auto-occ

Applies when the edit omits expected_hash. The session stores the hash of each read and of its own writes. It flags external changes, not the session’s own edits.

Value	Effect
off	No automatic check.
warn	Default. Edit proceeds. A non-blocking notice is appended.
block	Edit is rejected. Code HASH_REQUIRED. retryable is true. Read the file and resend with expected_hash.

dry_run does not write and does not update the undo chain.

git(action:"review") and paged git diff use a separate token, status_hash. A mismatch is STALE_GIT (retryable true, recovery read_and_rebase) and returns no diff body.