Determinism Phase 6 — `primer` detect, migrate, init, drift

[talgolan]

Mode detection and migration triggers (pure boolean logic over file
existence), the backlog rename migration's destructive git mv, init-mode
template copy and placeholder substitution, and the drift check with modal
test-count pinning. Largest phase, lowest per-invocation frequency, highest
blast radius — it rewrites five files; depends on Phase 3. Scope: the Phase 6
entry in the program design; needs a plan.

[talgolan]

Phase 6 is done for now. Final disposition, captured in meta/superpowers/specs/2026-09-02-determinism-program-design.md's Phase 6 entry:

• Sub-project A (Step 1 detect/dispatch) — shipped: hooks/lib/primer-detect.sh/.jq
• Sub-project B (Step 4 test-count rerun) — shipped: hooks/lib/test-count-rerun.sh/.jq
• Sub-project D (Step 2 placeholder derivation) — shipped: hooks/lib/primer-init-derive.sh/.jq
• Sub-project C (Step 3c/3d git mv/git rm migration) — deprioritized, not scoped. Zero real audience today (this repo's own BACKLOG.md is gone; no known external plugin installs; no marketplace submission yet, Submit to the Anthropic marketplace #35). Tracked separately: Phase 6 sub-project C deprioritized: no audience today + 3b/3d format mismatch #59 (also documents a real 3b/3d heading-format mismatch found while scoping this).
• Sub-project E (Step 3/3b split-mode migrations) — deprioritized, same reasoning as C: legacy-migration-only, zero audience, most judgment-heavy of the five.

Closing rather than leaving open indefinitely for two sub-projects with no real audience to build against. Revisit C/E if #35 ships and external installs old enough to hit either path start accumulating.