fix: merge-todo treats ## Removed as a deletion

[hkwuks]

Summary

hooks/merge-todo could not treat a ## Removed tombstone as a deletion of the same live entry. key_of took the whole - ID: TF-x (removed …) suffix, and split_todo gave the entire Removed blob a single key (the first tombstone’s ID). The driver’s “only one side has it → keep it” rule therefore kept the other side’s live copy and resurrected it.

This was observed live: rebasing the housekeeping commit onto PR #49 invoked the driver and restored three already-removed todos, leaving four duplicated - ID: lines on main.

• key_of uses the first whitespace token; ## Removed is always head:Removed.
• A live entry whose ID is in the other side’s Removed set is not emitted (deletion wins).
• Two changed Removed bodies union by tombstone ID instead of conflicting.

Data cleanup: resurrected live sections for 4d8ae2 / 76e7fb / 2877ca dropped (tombstones remain); live 985164 kept (this task) and its false v1.0.7 tombstone dropped. uniq -d on - ID: is empty.

TaskFlow traceability

• Task: TaskFlowDocs/2026-09-22-merge-todo-removed/
• Todo item: TF-20260918-985164
• Scope: hooks/merge-todo, hooks/smoke-test, TaskFlowDocs/todo.md, task documents
• Base branch: main
• Target repository: hkwuks/TaskFlow (origin)

Verification

• bash hooks/smoke-test — ALL SMOKE PASSED
• git diff --check — clean
• Relevant Skill/plugin validation — quick_validate.py skills/taskflow → Skill is valid!; no skill file is touched
• Results recorded in the TaskFlow Plan — TaskFlowDocs/2026-09-22-merge-todo-removed/plan.md, ## Verification / Review

Beyond the suite: bash -n on both changed hooks; delete/keep fixtures in both directions and a dual-tombstone union are covered by the new smoke section; existing merge-driver sections (disjoint adds, one-sided edit, double-edit conflict, install idempotence) stay green.

Review boundaries

• No secrets or opaque remote payloads included
• No unrelated task or user files changed — only the merge driver, its smoke section, this task’s documents, and the duplicate-ID cleanup in todo.md
• Remote/base assumptions are stated — pushed to origin (hkwuks/TaskFlow), targeting main
• Known limitations and follow-ups are documented below

Known limitations

• task remove’s Task: gate can still be bypassed by rewriting Task: to Not promoted. first (Notes: gate-only is the wrong fix; left out of this PR).
• If one side deletes an entry and the other also edits the live body, deletion wins and the edit is dropped rather than conflicted. Not observed; preferable to resurrection.
• Two ## Removed bodies that both change still take the union path by design (parallel removes are ordinary).