# Session 19 — Operational Infrastructure & Fractal Aggregation
**Date**: 2026-02-28 (Legion Pro 7)
**Continuation**: From Session 18 (427/427)

## Session Score: 385/385 checks, 5 bugs fixed, 5 tracks complete

## Tracks

### Track 1: Observability & Trust Telemetry (81/81) — 2 bugs fixed
**File**: `implementation/reference/observability_trust_telemetry.py`
- Hash-chained immutable event logs with tamper detection
- Distributed span-based tracing (parent/child spans, timing)
- Trust tensor time series with velocity & volatility
- ATP flow tracing with wash trading detection (circular flow ratio)
- Federation health monitoring (node heartbeats, partition detection)
- Anomaly detection: sybil bursts, entropy drops, trust oscillation
- Alert engine with severity levels & cooldowns
- Telemetry query interface (time range, entity, metric filters)
- Dashboard aggregation (top entities, health scores)
- Retention policies with time-based expiry
- Performance: 10K events logged, queried, analyzed

**Bugs**:
1. Python falsiness: `timestamp or time.time()` — `0.0` is falsy! Fixed: `timestamp if timestamp is not None else time.time()`
2. Re-seal test: deterministic content hash means re-sealing with original data heals chain (binding property). Changed test expectation.

### Track 2: Parameter Governance & Adaptive Tuning (82/82) — 0 bugs
**File**: `implementation/reference/parameter_governance_tuning.py`
- Typed parameter schemas with validation (int/float/string/bool + range constraints)
- Federation-size auto-tuning: CFL alpha, gossip fan-out, BFT quorum, ATP per entity
- Trust dynamics config: diffusion alpha, gravity sigma, time horizon
- ATP economics: base payment, fee rate, max balance, target Gini
- Consensus config: BFT max faults, gossip fan-out, confirmation depth
- Safety bound verification (parameter sets checked against invariants)
- Parameter migration/versioning with transformation functions
- Multi-tenant isolation with inheritance (per-federation overrides)
- Sensitivity analysis via finite differences (measure parameter impact)
- Config composition: merge parameter sets with override semantics
- Performance: 1000 parameter sets validated

### Track 3: RDF Graph Query Engine (69/69) — 0 bugs
**File**: `implementation/reference/rdf_graph_query_engine.py`
- Triple store with SPO/POS/OSP indexes (O(1) lookup by any position)
- SPARQL-like pattern matching with variable binding (None = wildcard)
- Property path traversal (transitive closure via BFS)
- Graph metrics: degree centrality, betweenness centrality, clustering coefficient
- Shortest trust path (BFS + Dijkstra with trust-weighted edges)
- Delegation chain extraction along `web4:delegatesTo` edges
- MRH-filtered access control (zone computation + query filtering)
- Aggregate queries: count, average trust, group-by
- Graph diff (added/removed triples between snapshots)
- Incremental updates with snapshot/restore
- Performance: 10K triples, pattern matching, centrality computation

### Track 4: Wire Protocol & Tensor Serialization (90/90) — 1 bug fixed
**File**: `implementation/reference/wire_protocol_serialization.py`
- LEB128 varint encoding/decoding (unsigned integers)
- IEEE 754 float64 encoding (big-endian, 8 bytes)
- Length-prefixed string encoding (varint length + UTF-8 bytes)
- TLV trust tensor format (~37 bytes per tensor)
- ATP packet encoding with all fields
- Message envelope with SHA-256 integrity MAC
- Version negotiation (capability exchange, highest common version)
- zlib compression with ratio tracking
- Batch encoding (multiple messages in one frame)
- Roundtrip fuzz testing: 500 random objects all survive encode/decode
- Protocol handshake with challenge-response
- Error recovery with frame reader (sync bytes, frame boundaries)
- Performance: 10K tensors encoded/decoded

**Bug**: Tampered data crash — flipping a byte in encoded envelope caused `UnicodeDecodeError` because integrity check was computed but decode was attempted anyway. Fix: fail-fast, return empty envelope when integrity check fails (before attempting decode).

### Track 5: Fractal Trust Aggregation (63/63) — 1 bug fixed
**File**: `implementation/reference/fractal_trust_aggregation.py`
- Trust hierarchy nodes with parent/children links & weight
- Bottom-up aggregation (weighted_mean, min, geometric_mean)
- Top-down decomposition (propagate targets to leaves)
- Zoom operations (zoom_in, zoom_out, zoom_to_level)
- Level-appropriate resolution (trust_at_resolution)
- Cross-level consistency verification
- Self-similarity metrics (comparing subtree structure)
- Dynamic updates with upward propagation
- Hierarchy rebalancing (split nodes exceeding max children)
- Granularity trade-offs: information loss measurement, optimal resolution
- Multi-root federation with cross-links
- Performance: 341-node tree, aggregation + zoom in <2s

**Bug**: `federated_trust()` used `node_id.startswith(root_id)` to check federation membership — but nodes `"a_0"` don't start with `"fed_a"`. Fix: build node→root mapping by tree traversal, then check membership via the map.

## Key Insights

1. **Python falsiness continues to bite**: `0.0 or default` returns `default` because 0.0 is falsy. This is the 5th+ time this bug class has appeared. Always use `x if x is not None else default`.

2. **Hash chain binding property**: Re-sealing with original content produces original hash — chain heals automatically. This is a feature, not a bug. Content hash is deterministic.

3. **Integrity before parsing**: Never attempt to decode data before verifying integrity. Corrupted bytes can cause UnicodeDecodeError, struct.unpack failures, or worse. Fail-fast on integrity check.

4. **Federation membership ≠ naming convention**: Don't rely on string prefix matching for tree membership. Tree structure is the authority — traverse it.

5. **Three consecutive clean first runs** (Tracks 2, 3, and earlier Session 18 Track 5) — pattern knowledge from 180+ implementations reduces bug rate.

## Cumulative Stats
- Total implementations: 185
- Session 19 checks: 385/385
- Cumulative checks: ~11,933+
- Bug rate: 5 bugs in 385 checks = 1.3% (continuing downward trend)

## What's Next
- Hardware binding (TPM2) — deferred from this session due to automation fragility
- More cross-module integration tests
- Formal specification alignment checks
- Attack surface coverage for new modules
