fix(secret-guard): treat env as a dump only when no command follows

`env -u VAR cmd` and `env FOO=bar cmd` exec a command with a modified
environment and print nothing themselves. The old rule matched any `env`
token followed anywhere later by a pipe into a filter, so it blocked the
documented 1Password write path and forced a `(unset VAR; cmd)` workaround.
False positives only — never a leak — but a guard people route around is a
guard on its way out.

The rule now denies only when everything after `env` is exhausted by options
and VAR=value assignments. That is strictly the dumping shape, and it also
closes a hole the two previous rules left open: `env FOO=bar` with no command
word prints the whole environment and was allowed.

Three new deny/allow pairs pin it, including the 1Password write shape that
motivated the report. 20 cases now, up from 14, all passing.

Closes #25
Bump-Type: patch

tests/secret_guard_test.sh

@@ -61,6 +61,17 @@ expect deny 'op read "op://vault/item/field"' 'op read'
 expect deny 'env | grep -i gitea' 'env piped to grep'
 expect deny 'env' 'bare env'
 expect deny 'printenv' 'printenv'
+expect deny 'env -i | grep -i token' 'env -i with no command is still a dump'
+expect deny 'env FOO=bar' 'env with only assignments and no command is a dump'
+
+# --- allow: `env VAR=x cmd` / `env -u VAR cmd` RUN a command (#25) ---
+# These print nothing themselves; a pipe into grep filters the command's own
+# output, not the environment. Blocking them cost a documented workaround
+# ((unset VAR; cmd)) on the 1Password write path, which is the shape below.
+expect allow 'env -u ANTHROPIC_API_KEY claude --debug -p "ok" 2>&1 | grep -i plugin' 'env -u VAR runs a command'
+expect allow 'env FOO=bar ./script.sh | grep x' 'env VAR=x runs a command'
+expect allow 'env -u OP_SERVICE_ACCOUNT_TOKEN op item create - < item.json' 'env -u on the 1P write path'
+expect deny 'env -u FOO ./run.sh; env | grep -i secret' 'a real dump later in the same line still denies'
 
 # --- deny: kubernetes secret material ---
 expect deny 'kubectl get secret brain-app -o yaml' 'kubectl get secret -o yaml'