Detect structural no-path routes before SelectiveRerip iteration exhaustion

[0hmX]

Parent: SRJ-23 remaining completion failures.

Problem

The static reachability precheck stops after 16 seen hops and treats larger searches as provisionally reachable. It catches some small disconnected components in sample 002 but misses:

• the second sample-002 disconnected route,
• sample 100,
• both sample-101 cuts,
• sample 107.

The downstream blocker search reports no_path, performs only global rerips, and eventually fails with SelectiveReripTinyHyperGraphSolver ran out of iterations. This masks an immutable graph cut as an iteration-budget problem.

Acceptance criteria

• Exhaustively establish reachability, or return an explicit inconclusive result instead of reachable after a fixed hop threshold.
• Fail early with the connection ID and relevant start/end/cut regions when no legal path exists.
• Do not rerip repeatedly when no committed route can remove the blocker.
• Add regressions for both a small disconnected component and a large reservation-separated component.
• Do not add fallback logic that marks an unsolved route solved.