fix(router): reconcile #672 and #677 drilled-hole legality into one API

[ecto]

What

Reconciles the two independent drilled-hole (hole-to-hole) legality implementations that both added to RouteSession, keeping one API.

• fix(router): enforce via hole-to-hole spacing at probe time #672 (fix/router-via-hole-to-hole) — the broader one: SessionHole + HoleProbeResult, commit_hole, probe_hole, probe_via_hole with a per-net class via-drill map, rip-up/compaction, and wiring into auto.rs / maze.rs / pair.rs / complete.rs.
• Close the CM5 autorouting verdict's last unknowns (0 unknown, per-connection certificates) #677 (claude/close-cm5-unknowns) — the narrower one, which had already landed in main via feat(router): universal pair coupling and the SI receipt (M7) #681: DrillElement + DrillProbe, probe_drill / commit_drill, ViaClass-driven barrel probe, and the grid-pitch floor in route_window_complete_pinned, plus the cm5_verdict example driver.

This branch merges #672 into current main, resolves the session.rs / complete.rs conflicts so #672's richer API survives, deletes #677's drill index entirely, and rewires #677's already-merged consumers onto the survivor.

Key decisions

Survivor = #672's API. Removed DrillElement / DrillProbe / probe_drill / commit_drill / drill_elements. Kept SessionHole / probe_hole / commit_hole / probe_via_hole (SpanId-keyed, so a via barrel rips out with its copper; compaction preserved).

Ported #677's two extra behaviors onto it:

• Grid-pitch floor — route_window_complete_pinned still floors the WinGrid pitch at drill + hole_to_hole(), so two vias one cell apart can't violate the rule.
• ViaClass-driven barrel probe — barrel_ok probes the pinned ViaClass drill via probe_hole when the caller provides one, and falls back to each net's class drill (probe_via_hole) otherwise. The layer-independent hole check is therefore never skipped (slightly broader than either PR alone).

Same-net question — narrowed the exemption to coincident barrels only. drc::check_hole_to_hole is net-agnostic, and legalize::merge_same_net_vias dedups coincident same-net drills. So #672's blanket h.net == net skip would miss a real HoleToHole: two same-net vias at distinct spots closer than hole_to_hole. The survivor now exempts only a barrel stacked on an existing same-net one (center_dist <= COINCIDENT_HOLE_EPS, matching legalize's POS_EPS); everything else — other nets and same-net drills at distinct spots — is compared net-agnostically, exactly like the DRC.

Kept #681's M7 pair coupling (strict_pair_coupling, in_pair_breakout, pair_pads, pair_gap_between) fully intact.

Reviewer notes

• New test hole_probe_agrees_with_drc_on_same_net_barrels pins the same-net behavior directly against check_drc: the probe refuses exactly what the DRC flags.
• cm5_verdict.rs and complete.rs rewired from probe_drill/commit_drill → probe_hole/commit_hole.
• The branch carries fix(router): enforce via hole-to-hole spacing at probe time #672's full commit history (its merge-backs to an older base). The net diff vs main is only the 7 reconciliation files; the extra commits are fix(router): enforce via hole-to-hole spacing at probe time #672's originals.

Testing

• cargo test -p vcad-ecad-pcb — 263 lib tests pass (updated hole tests, the new DRC-pinning test, fix(router): enforce via hole-to-hole spacing at probe time #672's disjoint-layer-span refusal test, and the M7 pair tests).
• cargo clippy -p vcad-ecad-pcb --all-targets — clean (one pre-existing si_claims.rs warning from feat(router): universal pair coupling and the SI receipt (M7) #681, unrelated).

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4 Skipped Deployments

Project	Deployment	Actions	Updated (UTC)
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vcad-mcp	Ignored		Jul 25, 2026 1:42pm

[ecto]

Superseded by the direct merge of #672 into main (f851af1a, "fix(router): enforce via hole-to-hole spacing at probe time").

This PR was reconciling #672 and #677 into a single drilled-hole legality API. While it was in review, #672 landed on main already reconciled against #677 (which had merged via #681) — upstream kept #677's DrillElement/probe_drill/commit_drill naming and grafted #672's richer behaviors onto it: commit_drill now returns a SpanId for rip-up, probe_via_drill gives the net-class-drill convenience, and the auto/maze/pair wiring is in place.

Main now satisfies the reconciliation goal in full:

• one implementation (the drill_* API)
• both Close the CM5 autorouting verdict's last unknowns (0 unknown, per-connection certificates) #677 behaviors intact (grid-pitch floor + ViaClass barrel probe in complete.rs)
• the same-net question settled net-agnostically, which correctly catches same-net non-coincident pairs
• a DRC-pinning test (via_refused_when_drills_collide_across_disjoint_layer_spans, asserting check_drc agreement)

This PR does the identical reconciliation with hole_* naming and a coincident-only exemption. Merging it would revert a reviewed decision for no functional gain, so closing as redundant.