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Determinism is optional. Use it when you need stable traces for evals, regression tests, or debugging a specific episode. You can ignore it for casual experimentation.

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Quick setup: seed-based determinism

The easiest way to get repeatable behavior is to fix a seed on your session: 
import noesis as ns
from noesis.runtime.session import SessionBuilder

session = (
    SessionBuilder.from_env()
    .with_determinism(seed=42)
    .build()
)

ep = session.run("Summarize incident INC-1234")
With a deterministic model/tooling stack, runs with the same seed will produce the same episode trajectory and metrics. The seed is recorded in summary.json.

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Stricter reproducibility (clock + RNG)

If you need fully stable timings/IDs (e.g., evals in CI), add a deterministic clock and RNG: 
import noesis as ns
from noesis.runtime.session import SessionBuilder
from noesis.runtime.determinism import DeterministicClock, DeterministicRNG

clock = DeterministicClock.from_start("2024-01-15T10:30:00Z", tick_ms=10)
rng = DeterministicRNG(seed=42)

session = (
    SessionBuilder.from_env()
    .with_determinism(clock=clock, rng=rng, episode_timestamp_ms=1705314600000)
    .build()
)

ep = session.run("Draft release notes")
This locks timestamps, random numbers, and episode timestamps; the configuration is reflected in summary.json.

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Replay and comparison

Compare two episodes to check for drift. Ignore timing fields to focus on behavior: 
import noesis as ns


def compare_episodes(ep_a: str, ep_b: str) -> dict:
    events_a = list(ns.events.read(ep_a))
    events_b = list(ns.events.read(ep_b))

    diffs = {
        "event_count_match": len(events_a) == len(events_b),
        "phase_sequence_match": True,
        "payload_diffs": [],
    }

    for e1, e2 in zip(events_a, events_b):
        if e1["phase"] != e2["phase"]:
            diffs["phase_sequence_match"] = False
            break

        # Ignore timing differences; compare payloads to catch behavioral drift
        p1 = dict(e1.get("payload", {}))
        p2 = dict(e2.get("payload", {}))

        if p1 != p2:
            diffs["payload_diffs"].append(
                {"phase": e1["phase"], "diff": {"expected": p1, "actual": p2}}
            )

    return diffs

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Golden tests (pytest)

Use deterministic sessions in tests: 
import json
from pathlib import Path
import noesis as ns
from noesis.runtime.session import SessionBuilder


def test_golden_episode():
    session = (
        SessionBuilder.from_env()
        .with_determinism(seed=42)
        .build()
    )
    episode_id = session.run("Generate test data")

    summary = ns.summary.read(episode_id)
    events = list(ns.events.read(episode_id))

    golden = json.loads(Path("tests/golden/generate_test_data.json").read_text())

    assert summary["metrics"]["success"] == golden["metrics"]["success"]
    assert summary["metrics"]["act_count"] == golden["metrics"]["act_count"]
    assert [e["phase"] for e in events] == [e["phase"] for e in golden["events"]]

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Episode ID format

Episode IDs are human-readable and sortable: 
ep_<YYYYMMDD>_<HHMMSS>_<hash>_<entropy>_s<seed>
  • Prefix ep_
  • Date + time for sortability
  • Content hash + entropy for uniqueness
  • Seed suffix (s0 if unset) for reproducibility

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Deterministic components (overview)

ComponentPurposeHow it works
Deterministic clockConsistent timestampsFixed tick intervals instead of wall clock
Deterministic RNGReproducible random valuesSeeded random number generator
Deterministic IDsStable identifiersUUIDv5 based on namespace + content
Canonical JSONByte-identical outputSorted keys, consistent formatting
Direction/governance events use deterministic UUIDv5 IDs so the same inputs produce the same identifiers, making replay comparisons reliable.

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Advanced: canonical JSON

Artifacts use canonical JSON so the same data yields the same bytes: 
from noesis.runtime.determinism import canonical_dumps

payload = {"b": 2, "a": 1, "c": [3, 1, 2]}
assert canonical_dumps(payload) == canonical_dumps(payload)
This keeps manifest hashes and diffs stable.

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When to use determinism

Use deterministic mode for:
  • Evals and golden tests
  • Debugging specific runs
  • Compliance scenarios that require reproducibility
Avoid deterministic mode for:
  • Production workloads that need real timestamps/IDs
  • Performance benchmarks
  • Security-sensitive operations where predictable IDs are a risk

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CI validation

Add deterministic tests and replay checks to CI: 
# .github/workflows/determinism.yml
name: Determinism Validation

on: [push, pull_request]

jobs:
  golden-tests:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: astral-sh/setup-uv@v4

      - name: Run golden tests
        run: uv run pytest tests/golden/ -v

      - name: Check replay stability
        run: uv run python scripts/validate_replay.py