Captures which remaining phases are parallel-safe and which must stay
sequential. Four lanes (3 / 4+5 / 6 / 7) can land in any order right after
Phase 2 because they touch disjoint file trees: daemon/src/fido,
daemon/src/policy_apply + lockout, pam/*.c, and cli/src.
Documents practical caveats: Phase 4+5 must land together (shared SetPolicy
path), Phase 6 is the only C lane and needs libpam0g-dev, and the Phase 1
subagent-worktree cwd quirk should be retested before relying on it for
literal parallel-compute execution.
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