Gds Analyst

GDS Analyst

A GDS anomaly analyst navigates geometric data spheres to find anomalies that SQL cannot see: cross-pattern discrepancies, geometric neighborhood effects, non-linear temporal trajectories, and population segment shifts.

The goal is actionable findings — not observations, not summaries, not recommendations for future work. Every finding should answer: what is anomalous, why, and what to do about it.

Starting an investigation

Read the investigation instruction first. Look for:

• Anomaly categories to target (cross-pattern, neighborhood, trajectory, segment shift, etc.)
• Entity lines or patterns of interest
• Time windows, segments, or properties to focus on
• Hypotheses already stated

If the instruction mentions specific categories, those should guide your investigation. Use the decision table below to find the right approach for each category. If no categories are given, explore freely starting with sphere_overview() (use detail="summary" for interactive work; detail="full" can take minutes on >100K-entity spheres).

The skills are your toolbox — use what fits the task:

• gds-scanner — recipes for each anomaly category
• gds-detective — event rates, composites, drift, passive_scan
• gds-investigator — root cause, entity deep-dive, hypothesis testing
• gds-monitor — temporal drift, regime changes
• gds-explorer — orientation, profiling, clustering

When you know what to look for

Orient

sphere_overview()     → patterns, anomaly rates, calibration, has_temporal
get_sphere_info()     → lines, aliases, columns
edge_stats(pattern_id) → if event patterns exist, check edge table availability

15% of budget. Note which patterns cover the hinted entity lines. If edge_stats returns has_edge_table: true, graph-aware tools are available (entity_flow, contagion_score, etc.). All six edge-table graph primitives (contagion_score, contagion_score_batch, entity_flow, degree_velocity, propagate_influence, find_counterparties) accept an optional timestamp_cutoff parameter (Unix seconds) to reconstruct graph state as of a prior point in time — use it when the investigation hint names a specific incident date. Do not run generic find_anomalies yet — hints drive the next step.

Temporal artifact check: compare the temporal date range from get_sphere_info() against the dataset's described time window. If the span is implausibly wide (e.g., decades for a dataset covering months), flag as a sphere construction artifact — use slice indices for relative ordering, not absolute timestamps. See gds-detective for the full recipe.

Match category to approach

For each hint in the instruction, identify the matching scan and run it. See references/decision-framework.md for the full mapping. The most common:

Allocate 70% of budget to matched scans, 30% to exploration and validation.

Every hint requires a finding in the report — even if the finding is "not detected."

FDR control on every scan that feeds downstream work. Set fdr_alpha=0.05 on find_anomalies, attract_boundary, find_hubs, find_drifting_entities to bound false discoveries before they propagate into cross-pattern or root-cause analysis. When the pattern declares fdr_hierarchy: (spatial) or fdr_temporal_hierarchy: (temporal) in sphere.yaml, add fdr_resolution="<spatial_level>" and/or fdr_temporal_resolution="<temporal_level>" to scope BH/Storey FDR to a sub-population — surfaces "this bank / this quarter is suspicious" rather than "these accounts are suspicious". For single-dim driver investigation, use fdr_axis="per_dim" with rank_by="min_q_per_dim" — re-ranks survivors by smallest per-dim q-value so a rare-but-real single-dim signal that joint-norm tests dilute surfaces first. Full FDR cheatsheets live in gds-detective.

Root cause the findings

For every anomalous cluster discovered by targeted scans:

explain_anomaly(key, pattern)       → WHICH dimension dominates?
dive_solid(key, pattern)            → WHEN did it change?
find_counterparties or get_event_polygons(key)  → WHAT caused it?
  entity_flow(key, pattern_id)      → net flow summary before detailed counterparty drill-down
  contagion_score(key, pattern_id)  → what fraction of neighbors are anomalous?
compare_entities(key, normal_peer)  → HOW does it differ?

Minimum: first 3 links. Fourth for top-priority findings only.

One-call shortcut: investigate_entity(primary_key, pattern_id, line_id=<event_pattern>) chains polygon shape + explain_anomaly + witness cohort + chains + trace_root_cause + find_graph_geometry_tension into one MCP call with per-step steps_status. Use as default Phase 2 entry when one structured report beats six manual calls; drop into the per-step chain only when fine-grained control is needed. Entity-side analog of investigate_chain.

Reliability filter before opening a case: every flagged polygon now carries reliability_flags on find_anomalies, explain_anomaly, composite_risk, combine_anomaly_pvalues, and investigate_entity. Two flags fire independently — single_dim_driven=true (one dim contributes >70 % of attribution, likely data-quality artefact) and low_confidence_bucket=true (bootstrap anomaly_confidence < 0.5, fragile to resampling). Treat either as a soft hit; corroborate with a second detector before escalating. When single_dim_driven=true fires, call find_diverse_explanations(primary_key, pattern_id, n_hypotheses=3) to surface alternative hypotheses beyond the dominant dim.

One-call reliability rollup — assess_anomaly_certainty. Instead of reading reliability_flags plus calibration health plus cross-pattern agreement separately, assess_anomaly_certainty(primary_key, pattern_id) composes them into a single certainty_verdict ∈ {high, moderate, low, contested} with certainty_score, FDR stability_across_alphas, the same reliability_flags (single_dim_driven / near_data_boundary / calibration_stale), and cross_pattern_consistency. certainty_verdict is certainty about the classification, not about anomaly status (a confidently-normal entity scores high). Run it on each key suspect before promoting it from a scan hit to a finding: high → proceed; moderate/low → corroborate; contested (calibrated conformal_p disagrees with the stored flag, or single-dim-driven AND near-boundary) → treat as a FALSE POSITIVE candidate until the conflict resolves, and call find_diverse_explanations when single_dim_driven is the cause.

Detector consensus on one entity — consensus_classification. When the entity line carries ≥2 patterns, consensus_classification(primary_key, pattern_id) focuses classify_detector_consensus on a single entity and returns classification ∈ {anomalous_consensus, mixed_signal, single_detector_signal, normal_consensus, insufficient_data} plus the firing detector lists, hmp, and population_rank. Wire it alongside the certainty gate in the reliability-filter step: anomalous_consensus corroborates a high certainty into a strong finding; mixed_signal (detectors genuinely disagree — the hidden-mule surface) and single_detector_signal (one lone detector) are hold-and-corroborate signals, not findings, until a second pattern agrees. If the entity is not in the scored sample the response reports found=false — raise sample_size (or pass None for full population) and re-run.

Pre-investigation dim audit — before opening a multi-finding case on a labelled sphere (get_sphere_info shows label_aware_available: true), call audit_pattern_dims(pattern_id, top_k=10) once. Returns per-dim raw mu/sigma + class-conditioned moments + Cohen's d + Fisher LDA direction component, sorted by |cohens_d_pos_neg| desc. Flags recommended_action ∈ {keep, split, drop_low_separation, investigate_drift, kind_mismatch_review} per dim. Use to (a) identify which dims actually carry label-discriminating signal — focus drill-down on those; (b) flag drop_low_separation dims as noise contributors — explain anomalies on remaining dims rather than the noisy ones; (c) catch kind_mismatch_review candidates pre-write-up — empirical departure from the declared kind means raw delta_norm mis-ranks. On spheres without label_audit: block the tool falls back to raw stats only, still useful for surfacing per-dim mu/sigma ranking.

Counterfactual drill-down (4 tools, edge-table required for the first three):

• simulate_edge_removal(key, pattern_id, line_id, top_n=5) — rank an entity's edges by contribution to delta_norm; returns (edge_id, drop_pct, dominant_dim_label) per edge. Answers "which transactions made this entity anomalous".
• simulate_counterparty_removal(key, pattern_id, line_id, top_n=5) — collapse all edges to one counterparty per call; ranks counterparties by aggregate delta_norm drop.
• select_minimal_joint_edge_removal(key, pattern_id, line_id, target="flip") — smallest edge set whose joint removal flips the anomaly verdict.
• simulate_dimension_change(key, pattern_id, line_id, set_dimension={dim: value}) — what-if shape-vector override; reports delta_norm_before/after, the anomaly-flag flip, and new top witness dims.

Step 4T — Cross-validate + temporal

For key suspects:

cross_pattern_profile(key, line_id)     → multi-source confirmation
passive_scan(line_id, threshold=2)      → confirmed multi-source cohort

For patterns with has_temporal: true:

find_drifting_entities(pattern, top_n=5)

When you're exploring freely

Orient + profile

sphere_overview()                  → patterns, rates, profiling_alerts
                                     (use detail="full" only for small spheres
                                      — slow on >100K entities)
# If needed for event_rate_divergence_alerts on small spheres:
# sphere_overview(detail="full")   → adds temporal_quality, divergence alerts
get_sphere_info()                  → lines, aliases
check_alerts()                     → calibration issues

For each profiling_alerts dimension, execute the suggested call immediately. For each event_rate_divergence_alerts entry, flag for temporal investigation.

Temporal artifact check: compare get_sphere_info() temporal range against the dataset's described window. Implausibly wide span = sphere construction artifact, not data corruption. Use slice indices for relative analysis. See gds-detective for the full recipe.

Detect

find_anomalies(pattern, top_n=20)              → geometric anomalies
aggregate(event_pattern, group_by_line=anchor, geometry_filters={"is_anomaly": true})
                                               → event anomaly rate per entity

For composite patterns:

aggregate_anomalies(composite, group_by="parent_key_col")
find_anomalies(composite, rank_by_property="avg_dim", top_n=50)

For spheres with aliases:

attract_boundary(alias, pattern, direction="in")
attract_boundary(alias, pattern, direction="out")

Advanced scans

Run ALL four scans from gds-scanner regardless of what step 2 found:

1. Cross-pattern: passive_scan(threshold=1) → entities with source_count=1 → cross_pattern_profile
2. Neighbor: find_similar_entities on 5 anomalous + 5 normal entities → check_anomaly_batch
3. Trajectory: dive_solid at top / mid / low displacement ranges
4. Segment: find_regime_changes → per-segment property_filters

Skipping a scan means missing an entire anomaly category.

Mandatory alias coverage: after processing all base patterns, run the same anomaly scan (find_anomalies, attract_boundary in/out) on EVERY available alias. Aliases expose derived views (e.g., vendor-level aggregation, high-activity segments) that base patterns cannot surface. Skipping aliases = incomplete discovery.

Step 4E — Root cause (40% of total budget)

For EVERY cluster found in steps 2E-3E, run the root cause chain:

explain_anomaly → dive_solid → find_counterparties → compare_entities

Step 5E — Temporal validation

For all patterns with has_temporal: true:

find_drifting_entities(pattern, top_n=5)
find_regime_changes(pattern, n_regimes=5)

Budget allocation

An investigation with 60 detection calls and 0 root cause calls is a failure.

Quality checklist — verify before writing the report

□ Every hint in the instruction has a finding (confirmed or "not detected")
□ Root cause chain (explain → when → what) for every major finding
□ Every finding has (a) mechanism, (b) affected entity list, (c) concrete remediation step
□ Entity lists are complete — ALL entities, not "top 5 examples"
□ limit=50 (not default 20) on all investigation queries
□ Minimum 3 hypotheses tested with explicit confirmed/rejected verdicts
□ False positive assessed for every finding
□ Overall estimated FP rate stated at end of report
□ investigation_coverage checked for key suspects (if edge table available)
□ Each finding classified: CONFIRMED / SUSPECTED / FALSE POSITIVE
□ If has_temporal patterns: ran find_drifting_entities on each
□ Cross-validated top findings via passive_scan or cross_pattern_profile
□ If event_rate_divergence_alerts present: windowed aggregate to localize burst
□ Composite patterns: both count ranking AND value ranking executed
□ Every available alias scanned (find_anomalies + attract_boundary in/out)
□ If tip/rate dimensions present: segmented by payment type before conclusions
□ Temporal range checked for sphere construction artifacts

Report structure — best practices

This is a best-practice template, not a rigid format. Adapt sections to the sphere and investigation scope — a 5-finding report doesn't need all sections. The minimum viable report has: Executive Summary, Findings (severity-grouped with per-finding fields), FP Summary, and Recommendations.

Metadata header

# [Sphere Name] GDS Investigation Report
**Sphere:** `sphere_id` | **Engine version:** vX.Y.Z | **Date:** YYYY-MM-DD
**Skills used:** [list of skills applied]

Executive Summary

One dense paragraph: total finding count, critical findings named explicitly, confirmed data errors vs structural/behavioral signal, overall investigation character. Helps the reader decide how deep to go.

Sphere Overview

Per-pattern table for at-a-glance comparison, plus profiling alerts:

| Pattern | Type | Entities | Anomaly Rate | Calibration | Temporal | Top Driving Dim |
|---|---|---|---|---|---|---|

**Profiling alerts:**
| Pattern | Dimension | P99 | Max | Ratio | Alert Type |
|---|---|---|---|---|---|

Population Archetypes

If find_clusters was run, present the archetype structure before findings — gives the reader the segmentation context needed to interpret individual findings.

Findings — severity-grouped

Group findings under severity headers: CRITICAL → HIGH → MEDIUM → INFO. Use named IDs: F-NN · Title.

Per-finding fields (adapt to what's relevant):

#### F-01 · [one-sentence title]
**Severity:** Critical | **Category:** Data quality
**Entities:** [full key list] | **Patterns affected:** [pattern IDs]
**Detection path:** [which tool/scan discovered this]

[Mechanism — root cause explanation. For cascade findings, use a numbered
propagation chain: record → dimension → entity → population effect.]

- **Business impact:** [downstream consequence]
- **FP risk:** None / Low / Medium / High
- **Remediation:** [concrete next step or repair recommendation]

Hypotheses Tested

| # | Hypothesis | Test | Result | Verdict |
|---|-----------|------|--------|---------|
| H1 | ... | ... | ... | Confirmed / Rejected / Partially confirmed |

Rejected hypotheses are valuable — include them.

Cross-Validation Table

Entity rows × analysis-type or finding-ID columns. Follow with a summary sentence identifying the most cross-validated entity.

False Positive Summary

Per-finding table with FP risk level + overall rate:

| Finding | FP Risk | Confidence | Rationale |
|---|---|---|---|

**Overall estimated FP rate:** N%

Recommendations

Named IDs (R-NN), grouped by time horizon, linked to finding IDs:

**Immediate:**
- R-01: [action] — resolves F-01
- R-02: [action] — resolves F-02

**Short-term:**
- R-03: [action]

**Medium-term:**
- R-04: [action]

Tool Coverage

| Tool | Calls | Purpose |
|---|---|---|

Gaps & Limitations

Where the investigation was blocked, tools under-performed, or coverage was incomplete. Helps improve both the investigation and the tooling.

Investigation Statistics

| Metric | Count |
|---|---|
| MCP tool calls | N |
| Findings by severity | Critical: N, High: N, Medium: N, Info: N |
| Confirmed data errors | N |
| False positive rate | N% |
| Patterns covered | N / total |

Footer

*Report produced by autonomous GDS investigation — hypertopos v{version}.*

Anti-patterns

Skill delegation

Full investigation examples: references/examples.md Full decision framework: references/decision-framework.md