Retire the pre-request convergence settlement chain and land the four-case gate

[pinin4fjords]

Parent: #1745

Predecessor: #1754 and its stacked draft PR, which made convergence grant application a mechanical recipe materializer and completed Seed 77.

Prototype evidence: draft PR #1743 and checkpoint 3f11f175.

Retrieving the prototype: git fetch origin refs/pull/1743/head:pr-1743-checkpoint, then read files with git show 3f11f1758f16341ace6b1409eff53a36a36ec715:<path>. Never check that branch out into your worktree.

Outcome

Retire the pre-request legacy convergence settlement chain on main so the cohort plan is the first and only owner of the coordinates it migrates, and land the complete four-case acceptance gate: Seed 15, Seed 77, opposing bypass, and stacked collector pass together, here, once.

Estimate: 4-8 focused hours, hard maximum one working day. If any single legacy pass cannot be subsumed within budget, stop and split by pass family with a documented boundary; each split half must still transfer and delete together.

Starting evidence

On main, the legacy settlement chain runs BEFORE the request producer, so the old owner decides trunk/landing coordinates first and the cohort request reads the post-settlement value. The competing owners (all src/nf_metro/layout/routing/convergences.py): _pack_cotravelling_corridor_runs, _separate_distinct_cotravelling_trunks, _separate_distinct_counter_running_trunks, _lane_trunk_runs, _settle_shared_opening_pivots (2120), _settle_shared_source_openings (2163), _settle_opposing_landing_channels (2212), _move_trunk_flank, _move_landing_opening, _reseat_landing_opening, _reseat_landing_cross, _settle_shared_trunk_channels, and any remaining _move_trunk_axis caller left after #1754 retired the grant path. Note: _settle_reserved_trunk_axes is NOT on main (checkpoint-branch-only); nothing may create it.

These passes resolve real, gate-triage-documented conflicts, including feasibility refusals (#1712). Subsumption means the typed relations and grants from #1751/#1752/#1754 express the same conflicts constructively; the new model must refuse the same infeasible cases, not silently accept them.

Scope

• For each legacy pass above: either subsume it (its conflict resolution becomes typed relations and grants, and it is deleted in this PR) or explicitly retain it with cited evidence that it cannot write a coordinate a grant controls. Record every decision in the PR body under "Coordinates transferred / setters deleted in this PR".
• Land the four-case gate, spelled by test id, re-deriving geometric expectations against this stack's settled geometry (checkpoint coordinates are not copied blindly).
• Add the trace-independent opposing-bypass geometry lock. This is where it first becomes mandatory: on examples/topologies/opposing_bypass_corridor.mmd, the two opposite-running lines hold distinct, direction-qualified lane coordinates one pitch apart (the checkpoint content was top_crossings == {"ribo": {692.0}, "rnaseq": {696.0}}; re-derive exact values from this stack's geometry). Name it test_opposing_bypass_lines_hold_separated_direction_qualified_lanes. Materialize accepted grants once through owner frames #1756, Publish and enforce the cohort-final freeze #1757, and Run the aggregate checkpoint with the mechanical ownership audit #1758 must preserve it.

The four-case gate, spelled by test id

pytest -q -n 0 \
  "tests/test_member_geometry.py::test_seed_15_routes_split_siblings_as_independent_members" \
  "tests/test_member_geometry.py::test_seed_15_wraps_u_bypass_above_crossing_merge_trunk" \
  "tests/test_member_geometry.py::test_seed_77_shortfall_requests_one_atomic_corridor_aperture" \
  "tests/test_member_geometry.py::test_reservation_reroute_reseats_port_peeloff_after_reconciliation" \
  "tests/test_corridor_cohort_integration.py::test_opposing_bypass_lines_hold_separated_direction_qualified_lanes" \
  "tests/test_corridor_cohort_integration.py::test_no_solver_owner_contains_opposite_running_claims"

Port the seed and collector locks from the checkpoint (tests/test_member_geometry.py:222, :284, :985, :1017 at 3f11f175). Confirm the collected count matches six before believing a pass; no test name contains "opposing" or "stacked", so -k opposing and -k stacked silently select nothing. main's test_stacked_collector_reuses_three_lanes_across_twelve_claims in tests/test_route_reservations.py is unrelated.

Non-goals

• No new constraint, retry, render stage, or APERTURE cycle.
• No point-distance search, current-shape inference, or direction repair.
• No persistence, materialization, or freeze work (those are Persist the accepted cohort plan and make re-observation consume it #1755 onward).

Acceptance

• The four-case gate above passes together, including the opposing-bypass geometry lock.
• Every subsumed pass is deleted in this PR; every retained pass has cited evidence it cannot write a granted coordinate.
• No granted trunk-axis coordinate is re-set by any retained legacy pass.
• Feasibility refusals the legacy chain enforced are still refused, with typed provenance.
• Opposite-running routes remain distinct and unbundled.
• The behavior-changing stacked PR runs CI and the authoritative render diff; it remains draft and unmerged until the complete stack is green.

Verification

pytest -q -n 0 tests/test_convergence_corridor_grants.py
pytest -q -n 0 tests/test_member_geometry.py -k 'seed_15 or seed_77 or reservation_reroute_reseats'
pytest -q -n 0 tests/test_corridor_cohort_integration.py -k 'opposing_bypass or opposite_running'
pytest -q -n 0 tests/test_hash_seed_determinism.py
ruff check src/nf_metro/layout/routing/convergences.py src/nf_metro/layout/routing/planning.py
ruff format --check src/nf_metro/layout/routing/convergences.py src/nf_metro/layout/routing/planning.py
mypy

Check the collected count on every -k run; zero collected exits 5, which reads like success. Behavioral children also refresh the derived corpora (hash pins, python scripts/routing_gate_coverage.py --write, guard goldens via python tests/test_guard_registry_golden.py) and declare the churn in the PR body.

#1653 guardrail and stop condition

Deletion is part of the ownership transfer. If removing a legacy pass exposes missing coverage, stop and repair the earlier owner model (the missing relationship belongs in #1751/#1752); do not retain dual ownership, add a post-pass, or weaken a gate.