Read an Unrecognized env Option as an Undetermined Repository in the Write Guard #3725

Raised by the second review round of promotion #3715 (P1 thread) on the change #3722 made.

_env_option in host-setup/agent-safety/claude/gh-write-guard.py looks a long option up in _ENV_LONG by its exact name and maps any name it does not know to an empty letter, which the launcher reader then ignores. GNU env accepts a unique abbreviation of a long option, so a constructed command such as

env --ch=/srv/other GIT_DIR=.git git push origin main

runs git in /srv/other while the guard reads --ch as a no-op and resolves GIT_DIR and the remote from the working directory, the shape #3716 closed for the full spelling.

Fix: read an env option the guard does not recognize, long or short, as leaving the repository undetermined, which blocks main, master and develop the way #3709 and #3722 treat a shape they cannot resolve, rather than matching prefixes. That also covers an option a future env adds.

Backlog burndown claim. Branch: feature/burndown-guard-env-abbrev. Predicted file set: host-setup/agent-safety/claude/gh-write-guard.py, host-setup/agent-safety/README.md.