Date: 2026-03-01
Issue: #180
Domain: Runtime-viewer bridge precondition for egui_glow -> egui_wgpu

Capture the next bridge-spike harness slice by recording concrete path/geometry/timing fields in compositor replay samples for measurement export.

1. Extended CompositorReplaySample with bridge-spike measurement fields:
   • bridge_path
   • tile_rect_px
   • render_size_px
   • callback_us
   • presentation_us
2. Added BridgeProbeContext and wired it from register_render_to_parent_content_pass(...) into run_content_callback_with_guardrails(...).
3. Bound current bridge-path label to gl.render_to_parent_callback.
4. Included new sample fields in diagnostics JSON replay export (compositor_replay_samples).
5. Updated replay-sample fixture coverage in diagnostics/compositor tests.

• cargo test -q --lib replay_export_feedback_includes_path_and_counts
• cargo test -q --lib replay_ring_is_bounded_to_capacity
• cargo test -q --lib snapshot_json_includes_compositor_replay_samples_section
• cargo check -q

• This remains additive and backend-neutral; no egui_glow swap occurs in this slice.
• These fields are intended to support the measurement contract in follow-up #180 evidence receipts.