framework tools/git: pr-review validates --action before provider contact (codex blocker on PR #1464)

An unsupported --action previously reached platform detection (and
could touch the provider) before failing with a provider-class status;
comment-without-body exited 1 mid-switch. Both now fail fast with
usage_error (rc 2, stderr) immediately after argument parsing. Test
arms added including the zero-provider-contact assertion for
invalid-action runs.

packages/mosaic/framework/tools/git/test-pr-review-usage-contract.sh

@@ -97,6 +97,15 @@ expect_rc 2 "missing -a exits 2" -n 5
 expect_stderr "Action is required" "missing -a message on stderr"
 expect_rc 2 "request-changes without comment exits 2" -n 5 -a request-changes
 expect_stderr "comment required for request-changes" "request-changes message on stderr"
+expect_rc 2 "invalid action exits 2 pre-detection" -n 5 -a bogus
+expect_stderr "unknown action" "invalid action message on stderr"
+# Invalid-action arms must not contact any provider (validation precedes
+# detect_platform): probe log empty at this point.
+if [[ -s "$PROBE_LOG" ]]; then
+    echo "FAIL: an invalid-action arm contacted a provider:" >&2
+    cat "$PROBE_LOG" >&2
+    exit 1
+fi
 
 # 4. Value-less flags: rc 2 with "requires a value" on stderr.
 for flag in -n -a -b -c -l -r --number --action --body --comment --login --repo; do