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Fixture 004: Dual Attractor Baseline

Purpose

Fixture 004 is the first multi-attractor characterization fixture in the repo. It preserves the simpler single-row source topology and the hardened runtime, capture, verification, ledger, and reporting pipeline established by Fixtures 002 and 003 while introducing two controlled field centers as the primary canonical spatial change.

Its role is to create a minimal competing-basin baseline. The goal is not to expand source complexity or restructure the fixture, but to keep the Fixture 003 operating style as stable as practical while moving from one attractor to two.

Why It Exists Relative To Fixture 003

  • Fixture 003 established the first off-axis single-attractor asymmetry baseline.
  • Fixture 004 keeps the same single-row five-dot source topology and general scene framing.
  • Fixture 004 changes the primary field topology from one field center to two controlled field centers.
  • This gives the repo a canonical next step for studying transport under competing local basins without changing the hardened characterization pipeline.

Current Harness

  • Harness script: scripts/run_fixture_004.sh
  • Reporter: tools/fixture_004_report.py
  • Shared report core: tools/fixture_characterization_report.py
  • Scene: res://test-grin-basic-visual-linear-dual-attractor-minimal.tscn
  • Fixture identity expected by launch audit: grin_basic_visual_linear_dual_attractor_minimal
  • Fixture id: fixture_004
  • Launcher token configured by the harness: run_fixture_004

What Changed

  • The single Fixture 003 field center is replaced by two controlled field centers.
  • The dual-center arrangement is horizontal and symmetric:
  • left attractor at X = -2.0
  • right attractor at X = +2.0
  • The controller now applies fixture-level field overrides across all FieldSource3D nodes under the same fixture root so the two attractors stay coupled under the same control surface.
  • The default Fixture 004 harness operating point requests:
  • stepLength = 0.040
  • turnThreshold = 2.4
  • errorTolerance = 0.010

What Stayed Fixed

  • Single centered source row topology from Fixtures 002 and 003
  • Same five-dot row layout
  • Same backdrop, camera framing, and overall fixture scale as Fixture 003
  • Same controller, verification, capture, ledger, and report architecture
  • Same preferred visual/capture modes
  • Same report artifact contract
  • Same ledger append behavior

Control-Validation Contract

Treat a Fixture 004 run as usable for control-surface interpretation only when all of these checks are true:

  • runtime_fingerprint_present = true
  • assembly_timestamp_present = true
  • effective_step_matches_requested = true
  • row_diagnostics_present = true
  • scheduler_clean = true

Launch Fixture 004 only through scripts/run_fixture_004.sh, and treat it as non-destructive and independent of Fixtures 001–003 histories.

Expected Capture Modes

  • Visual mode: diagnostic_flat
  • Analysis capture mode: categorical_final
  • Alternate analysis capture mode: resolved_film

Expected Artifact Set

  • summary.json
  • metrics.json
  • capture.png
  • analysis_capture.png
  • debug_capture.png
  • row_coverage.txt
  • row_coverage.json
  • radial_profile.txt
  • radial_profile.json
  • radial_sector_profile.txt
  • radial_sector_profile.json
  • field_radial_profile.txt
  • field_radial_profile.json
  • field_radial_sector_profile.txt
  • field_radial_sector_profile.json
  • nearest_attractor_profile.txt
  • nearest_attractor_profile.json
  • ledger append through tools/characterization_ledger/ledger_writer.py

Canonical Analysis Basis

  • Initial scaffold basis:
  • image-center artifacts may still be emitted for continuity
  • single-field-relative artifacts may still be emitted for continuity
  • Multi-attractor basis:
  • nearest_attractor_profile.* is the proper Fixture 004 interpretation surface for per-basin transport partitioning
  • Current continuity anchor:
  • the harness FieldPath resolves to the left / primary attractor so the shared field-relative artifact path remains intact
  • Expected future direction:
  • Fixture 004 is expected to motivate a nearest-attractor-relative analysis basis, because a single fixed attractor-relative origin is only a continuity bridge once transport begins to partition around competing local basins
  • Promotion placeholder:
  • the first promoted Fixture 004 interpretation should record how these continuity artifacts compare against the future nearest-attractor reference frame

Best Verified Operating Point

Placeholder. To be filled once the first verified Fixture 004 run is promoted.

Lower-Variance Fallback

Placeholder. To be filled once repeatable verified runs establish the first stable fallback operating point.

Topology Interpretation

Placeholder. Expected initial interpretation focus:

  • whether hit structure partitions around the left and right attractor basins
  • whether the central source row feeds one basin preferentially or splits comparably between them
  • whether rendered-no-hit and unrendered regions remain scheduler-clean under dual-center competition