FIX6 07 — Writer/builder repoint (authoritative in the REAL apply path)

The recurring FIX1..FIX5 failure mode: new guards were built but the real writer/builder still used the old ones. FIX6 repoints the actual apply path so v9/v6/content-hash are AUTHORITATIVE (verified: writer uses_v9/uses_signoff_v6/uses_content_hash/uses_unclassified = all true).

fn_dot_birth_qt001_apply (writer) — EXECUTE path gates (all additive/stricter, all fail-closed today)

In order, each RAISEs (blocks) if unmet:

1. v_qt001_authoritative_legacy_dependency_guard (kept; diagnostic structural callgraph).
2. v_qt001_callgraph_unclassified_fail_guard (FIX6; native callgraph completeness — currently false → always blocks).
3. v_qt001_apply_readiness_guard_v9.overall_ready (FIX6; NULL-strict — currently false).
4. Fixed-point: CURRENT qt001_plan_content_binding.content_hash == v_qt001_plan_content_hash (signoff-independent). Satisfiable & stable (not circular).
5. tier apply_allowed (none in 2.6A).
6. fn_qt001_signoff_satisfies_v6 (FIX6; schema-valid, content-hash-bound — none today).
7. gateway integrity + Stage 0 freeze + valid OPEN execute permit (none) + expected_delta/max_rows binds + false-done prevention.

Dry-run path (NOT p_execute OR p_dry_run) is UNCHANGED and returns before the execute gates → production monitoring behaviour preserved. The execute path was already unreachable under FIX5; FIX6 makes it strictly MORE blocked.

fn_qt001_build_plan_registry (builder)

Unchanged logic + one addition: after minting the CURRENT plan it populates qt001_plan_content_binding with the stable v_qt001_plan_content_hash (forward coherence so a future rebuild keeps the fixed-point binding).

Rollback (ROLLBACK_fix6_to_fix5.sql) restores the exact FIX5 writer/builder bodies and drops all FIX6 objects/constraints/registry rows.