Why: two recurring papercuts from 2026-09-30 sessions — (1) task-start treated a zero-exit submodule update as complete, but a worktree could still carry 12 drifted/uninitialized nested submodules that only surfaced at build time; (2) close ran a single git push, so a tunnel hiccup left the card-close branch unpushed and the auto-PR never created (hand-patched twice that day).
Evidence: bash -n clean; smoke start of a throwaway task measured nested drift count explicitly and abandon-path finish recycled worktree and branch cleanly (both PASS); fresh-clone commit identity probe also PASS after setting the global identity outside this repo.
Impact: scripts/task.sh cmd_start (+3-line status check) and cmd_close (one retry on push); no interface change.
Refs: .task/fix-followup-hardening.md
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