Rust conditional semantic edge suppression diagnostics

[jununfly]

This was generated by AI during triage.

What to build

Add explicit diagnostics for Rust graph writes that are skipped because package/cfg/feature semantics make the target conditionally present or semantically unsafe.

This slice should preserve conservative graph behavior: prefer a missing edge plus a precise taxonomy bucket over a wrong unconditional edge. It should not introduce feature-aware graph writes.

Acceptance criteria

• Rust edge-write diagnostics include suppression reason buckets for cfg-affected or conditionally-present Rust semantics where existing write paths must fail closed.
• Suppression diagnostics are surfaced in result JSON/profile counters, consistent with existing Rust visibility and trait edge write diagnostics.
• Default graph writes remain conservative; no active cfg evaluation or feature-aware edge writing is introduced.
• Deterministic tests cover at least one skipped conditional semantic write or guard path with a precise reason bucket.
• Targeted Rust core tests pass.

Blocked by

• Rust repo-local package ownership and condition taxonomy hardening #603

[jununfly]

This was generated by AI during triage.

Closing as implemented. Rust core now exposes rustCargoConditionalSemanticSuppressionCounts for cfg-affected trait impl and trait-method suppression paths while keeping graph writes conservative.

Verification: deterministic cfg-affected trait fixture plus cargo test -p zcodegraph-core.