fix(fkill): stop when initial signal fails

[ALX99]

Problem and impact

fkill schedules its delayed escalation even when the initial signal command fails. An invalid signal can therefore return an error from the first attempt yet still terminate the selected process five seconds later.

Reproduction and observed result

Revalidated against current master 50d7c989c6603c0d5d274be2a6539b39c8db6f47 using exact production blobs (dfd3e31b12d439e894cc0128a7583bd877c9fa05 parent, f47c3ea992328a9d6690811b1b8492da974a2f40 fixed). A temporary fzf stub selected a disposable sleep 30; real system process tools handled signaling.

• Invalid BADSIGNAL: parent status 0 and target dead after 6s; fixed status 123 and target alive after 6s.
• Valid TERM: parent and fixed status 0; target terminated.
• Picker cancellation: parent and fixed status 0; no action.

Root cause and fix

The initial signaling pipeline's failure status was ignored. The fix exits when that pipeline fails, before scheduling delayed escalation.

Validation commands and results

GNU Bash 5.2.37, GNU findutils 4.10.0, procps-ng 4.0.4:

• Exact parent/fixed blob hashes matched GitHub.
• bash -n passed for both.
• Focused before/after reproduction passed before and after rebase.
• An isolated Git repository constructed from the exact blobs passed git diff --check.
• GitHub compare reports 1 commit ahead, 0 behind, and only .local/bin/fkill changed.
• GitHub Linter / ShellCheck passed on head 6b262f2cc5eaca3a245e1438ea77858d49c1a030.

A fresh HTTPS clone was attempted first, but this runtime could not resolve github.com. The branch was rebuilt from the exact current GitHub master tree plus the validated fixed blob. Literal full-tree local git status and git diff --check origin/master...HEAD were unavailable and are not claimed.

Scope and risk

Only .local/bin/fkill changes by one failure guard. Successful signaling, the five-second grace period, escalation, multi-selection, and cancellation behavior are unchanged.

[ALX99]

Revalidated and rebased this draft onto current master 50d7c989c6603c0d5d274be2a6539b39c8db6f47. The branch is now exactly one commit ahead and zero behind, with only .local/bin/fkill changed. The focused exact-blob reproduction still distinguishes the parent and fixed behavior, bash -n passed, and the newly triggered Linter / ShellCheck workflow passed on head 6b262f2cc5eaca3a245e1438ea77858d49c1a030. Direct HTTPS cloning remains unavailable in this runtime because github.com cannot be resolved, so no full-tree local git status claim is made.