Déjà System Specification & Architecture Reference

The Thesis: Rejection of Inference

Most incident resolution tools rely on probabilistic models (LLMs, embeddings, similarity) to guess relationships. Déjà rejects this for production infrastructure: a "high confidence guess" is still noise if an operator must manually verify it.

Promise: Déjà offers proven matches or silence. Silence is preferable to hallucination.

Trust Properties

• Zero hallucination: cannot invent a link that does not exist.
• Zero data leakage: source code is never passed to a third-party generative model.
• Auditability: every match traces to a commit hash, path identity, or error signature.

"…matching the canonical path… comprises a deterministic match that does not require real-time inference by a machine learning model."

Zero tolerance for un-hydrated code

Minified/obfuscated stack traces are rejected at the edge. Unusable payloads are "data pollution." Déjà does not guess original source paths.

• Reject minified bundles (e.g., a.js)
• Reject hashed filenames (e.g., main.8f9a21b4.chunk.js)
• Reject vendor frames (node_modules, runtime) unless whitelisted

First actionable frame

Traverse frames F0→Fn. Skip vendor/middleware and entropy-rejected frames. Anchor on first hydrated User Code frame.

"Black hole defense": if anchor appears in generic utility paths, peek to caller and use compound anchoring.

Hash composition (SHA-256)

Fingerprint collisions define identity. Dynamic message segments are sanitized prior to hashing.

Fingerprint = SHA256(AnchorFrame + CallerContext + ExceptionInvariant)

Source maps first

The Entropy Gate requires fully hydrated traces. A common CI/CD failure is reporting errors before source maps are processed.

Sentry.init({
  beforeSend(event) {
    if (event.request?.data) event.request.data = "[Redacted]";
    if (event.user) { delete event.user.email; delete event.user.ip_address; }
    return event;
  }
});

Least privilege

Tier 1 (Default): read-only metadata/diffs. Tier 2 (Optional): write scopes for patch PRs (never pushes to protected branches).

Tokens encrypted at rest (AES-256-GCM), short-lived where supported. API-first fetching: diffs processed in memory; no full repo clones.

Non-actionable paths

Prevent "black hole" incidents by skipping internal libraries to force deeper anchor selection.

normalization:
  sentinels:
    - "src/middleware/**"
    - "src/utils/http-client.ts"

Consolidate fragmentation

Merge fingerprints that should be treated as the same after refactors or identity breaks.

grouping:
  - target: "src/auth/NewLogin.ts"
    aliases:
      - "src/legacy/OldLoginController.js"

Dirty invariants

Regex rules to strip high-entropy segments that break stable grouping.

sanitizers:
  - pattern: "TX-[A-Z0-9]{4}-[A-Z]+"
    replacement: "<tx_id>"

Tenant separation

• PostgreSQL Row Level Security (RLS) scoped to vault_id
• Cache/queue namespacing with tenant-prefixed keys
• Data residency: us-east-1 default; optional single-tenant EU deployments

Contract + architecture

• No neural weights: deterministic hashing, no probabilistic inference
• Ephemeral processing: diffs processed in memory then discarded
• Store metadata, not contiguous corpora for model training

Statistical validation

Compare pre/post windows normalized by traffic. Validation pauses when traffic lacks significance.

ΔE = (Rate(W_pre) - Rate(W_post)) / Rate(W_pre) * 100
Rate(W) = fingerprinted_errors / total_traffic

-100 penalty

Reverts within 72 hours are the strongest signal of a failed solution signature.

Visibility tiers

States

Definitions

• Ingesting: awaiting normalization (<120ms) then dropped or normalized
• Candidate: merged PR touches anchor frame files
• Validating: rate gate active; pauses during low traffic
• Regressed: verified fingerprint reappears ("zombie bug")
• Immunized: patched before incident occurred

No match found

• Entropy rejection: minified trace → upload maps before deploy
• Sentinel interference: sentinels too broad → refine patterns
• Black hole: generic utility anchor + unstable message → add sentinel or sanitizer

Wrong fix shown

• Monolith problem: anchor on huge generic file → sentinel it, deepen linkage
• Generic error: invariant entropy too low → throw typed errors; improve messages

Default: fail closed on trust

• Matching: fail closed (silence) if proof cannot be established.
• Ingestion: accept telemetry, but quarantine/mark degraded if payloads are unusable.
• Validation: do not "declare verified" without statistical confidence.

Explicit degraded modes

• Git provider API unavailable: pause Lane 1 backfill; keep Lane 2 ingest; mark "INDEXING_DEGRADED: VCS_UNREACHABLE".
• Webhook ingestion delayed: maintain ordering where possible; surface "INGEST_LATENCY: ELEVATED"; avoid invalid validation windows.
• Validation insufficient traffic: pause soak until significance returns; do not treat low traffic as success.

Core objects

• Vault — tenant boundary. Owns all data + keys.
• Fingerprint — SHA-256 identity of incident signature.
• Alias — canonical path ↔ legacy path mapping (rename graph).
• ResolutionArtifact — PR/commit that claims to fix an incident.
• ValidationEvent — rate gate outcomes + revert signals.

How they connect

Vault 1—N Fingerprint
Fingerprint 0—N ResolutionArtifact (candidates)
ResolutionArtifact 0—N ValidationEvent
Fingerprint 0—N Alias (path history)
Alias N—1 CanonicalPath (by vault)

All entities are vault-scoped. Cross-vault joins are prohibited by enforcement at query and key namespaces.

Throughput per vault

• Target SLO: <120ms receipt → normalization
• Backpressure + rate limits per key/vault
• Quarantine mode when rejection ratio spikes

Time travel bounds

• Commit traversal is O(n commits) within configured horizon
• Diff parsing bounded by touched files + PR metadata
• Runs as batch lane: completeness over latency

Compaction strategy

• Metadata growth roughly proportional to unique fingerprints + aliases
• Prune raw webhooks after 7 days (replay window)
• Bound diff contexts (e.g., 30 days) then purge

Compatibility guarantees

• Fingerprint algorithm versions are immutable identifiers (e.g., fp_v1).
• New versions introduced only with documented migration notes.
• Verified matches reference the version used at time of validation.

Migration strategy

• Historical fingerprints are not silently re-written.
• Optional re-index/backfill can compute new fingerprints in parallel.
• UI can show fp_v1 vs fp_v2 collisions for review.

End-to-end incident walkthrough

Recommended: include a realistic incident timeline from ingest → match → validation → verified recall on regression.

Validation math worked example

Show Rate Gate windows with traffic normalization and the "2 AM traffic drop" pause/resume behavior.

Security questionnaire mapping

Map controls to SOC2, ISO 27001, and GDPR requirements. Provide evidence pointers (logs, configs, policies).