fix(tdx-hydro): derive root-successor orientation from unique evidence

[CooperBigFoot]

Summary

• derive root-successor orientation only from predecessors with exactly one in-tolerance endpoint pairing
• fail closed when root evidence is undetermined or conflicting, or when it does not select exactly one current endpoint
• preserve the non-root source-order path and all existing topology guards
• add six focused topology fixtures covering traversal order, distance-ordering discriminators, undetermined evidence, ambiguous current endpoints, and conflict handling

Verification

• cargo fmt --check
• cargo clippy --workspace --all-targets -- -D warnings
• cargo check --workspace --all-targets
• cargo test --workspace
• cargo build --workspace
• test -x target/debug/hfx
• HFX_BINARY="$(pwd -P)/target/debug/hfx" uv run --project adapters/tdx-hydro python adapters/tdx-hydro/test_build_adapter.py (118 tests passed)
• two full read-only acquired-evidence runs for processing basin 2020071190, each with a fresh scratch-capacity check and temporary scratch root

Both acquired runs progressed past root LINKNO 1104039, confirmed the pinned endpoint evidence and population counts, and then raised the exact expected later non-root refusal at native LINKNO 1307547 and downstream LINKNO 1308923. Evidence files and metadata remained unchanged, no SQLite sidecars appeared, and all temporary spools were removed.

Remaining limitation

Processing basin 2020071190 still does not compile. A later non-root source-order refusal remains at 1307547 -> 1308923; adjudicating that systematic near-degeneracy class is deliberately out of scope for this step.