Three lower-severity core-tool robustness fixes from a targeted audit, each
reproduced live:
1. terminal_tool did not validate non-positive timeouts. 'timeout or default'
silently coerced 0 to the config default (0 can't mean 'no timeout'), and a
negative value is truthy so it flowed into 'deadline = now + timeout' and
fired an immediate '-Ns' timeout. Reject timeout <= 0 with a clear message.
2. fuzzy_find_and_replace accepted a whitespace-only old_string, which matches
trivially (blank line / run of spaces) and mass-replaces under replace_all
or raises an opaque ambiguity error. Reject it alongside the empty check.
3. The '/private/var/' sensitive-path prefix over-blocked ALL macOS temp-file
writes: , /tmp, and /var/folders realpath into /private/var/folders
on macOS (and paths are resolved through symlinks), and /private/var/tmp is
a normal temp dir. Narrowed to the genuinely-sensitive subtrees
(/private/var/db, /private/var/root); /etc and /private/etc stay blocked.
All verified with sabotage-checked regression tests. 85 terminal/fuzzy/file
tests pass; normal timeouts, legit replacements, and /var + /boot + /etc
blocking are unaffected.
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