Here’s a compact pattern you can drop into Stella Ops to make reachability checks fast, reproducible, and audit‑friendly.

---

# Lazy, single‑use reachability cache + signed “reach‑map” artifacts

**Why:** reachability queries explode combinatorially; precomputing everything wastes RAM and goes stale. Cache results only when first asked, make them deterministic, and emit a signed artifact so the same evidence can be replayed in VEX proofs.

**Core ideas (plain English):**

* **Lazy on first call:** compute only the exact path/query requested; cache that result.
* **Deterministic key:** cache key = `algo_signature + inputs_hash + call_path_hash` so the same inputs always hit the same entry.
* **Single‑use / bounded TTL:** entries survive just long enough to serve concurrent deduped calls, then get evicted (or on TTL/size). This keeps memory tight and avoids stale proofs.
* **Reach‑map artifact:** every cache fill writes a compact, deterministic JSON “reach‑map” (edges, justifications, versions, timestamps) and signs it (DSSE). The artifact is what VEX cites, not volatile memory.
* **Replayable proofs:** later runs can skip recomputation by verifying + loading the reach‑map, yielding byte‑for‑byte identical evidence.

**Minimal shape (C#/.NET 10):**

```csharp
public readonly record struct ReachKey(
    string AlgoSig, // e.g., "RTA@sha256:…"
    string InputsHash, // SBOM slice + policy + versions
    string CallPathHash // normalized query graph (src->sink, opts)
);

public sealed class ReachCache {
    private readonly ConcurrentDictionary<ReachKey, Lazy<Task<ReachResult>>> _memo = new();

    public Task<ReachResult> GetOrComputeAsync(
        ReachKey key,
        Func<Task<ReachResult>> compute,
        CancellationToken ct)
    {
        var lazy = _memo.GetOrAdd(key, _ => new Lazy<Task<ReachResult>>(
            () => compute(), LazyThreadSafetyMode.ExecutionAndPublication));

        return lazy.Value.ContinueWith(t => {
            if (t.IsCompletedSuccessfully) return t.Result;
            _memo.TryRemove(key, out _); // don’t retain failures
            throw t.Exception ?? new Exception("reachability failed");
        }, ct);
    }

    public void Evict(ReachKey key) => _memo.TryRemove(key, out _);
}
```

**Compute path → emit DSSE reach‑map (pseudocode):**

```csharp
var result = await cache.GetOrComputeAsync(key, async () => {
    var graph = BuildSlice(inputs);             // deterministic ordering!
    var paths = FindReachable(graph, query);    // your chosen algo
    var reachMap = Canonicalize(new {
        algo = key.AlgoSig,
        inputs_hash = key.InputsHash,
        call_path = key.CallPathHash,
        edges = paths.Edges,
        witnesses = paths.Witnesses, // file:line, symbol ids, versions
        created = NowUtcIso8601()
    });
    var dsse = Dsse.Sign(reachMap, signingKey); // e.g., in‑toto/DSSE
    await ArtifactStore.PutAsync(KeyToPath(key), dsse.Bytes);
    return new ReachResult(paths, dsse.Digest);
}, ct);
```

**Operational rules:**

* **Canonical everything:** sort nodes/edges, normalize file paths, strip nondeterministic fields.
* **Cache scope:** per‑scan, per‑workspace, or per‑feed version. Evict on feed/policy changes.
* **TTL:** e.g., 15–60 minutes; or evict after pipeline completes. Guard with a max‑entries cap.
* **Concurrency:** use `Lazy<Task<…>>` (above) to coalesce duplicate in‑flight calls.
* **Validation path:** before computing, look for `reach-map.dsse` by `ReachKey`; if signature verifies and schema version matches, load and return (no compute).

**How this helps VEX in Stella Ops:**

* **Consistency:** the DSSE reach‑map is the evidence blob your VEX record links to.
* **Speed:** repeat scans and parallel microservices reuse cached or pre‑signed artifacts.
* **Memory safety:** no unbounded precompute; everything is small, query‑driven.

**Drop‑in tasks for your agents:**

1. **Define ReachKey builders** in `Scanner.WebService` (inputs hash = SBOM slice + policy + resolver versions).
2. **Add ReachCache** as a scoped service with size/TTL config (appsettings → `Scanner.Reach.Cache`).
3. **Implement Canonicalize + Dsse.Sign** in `StellaOps.Crypto` (support FIPS/eIDAS/GOST modes).
4. **ArtifactStore**: write/read `reach-map.dsse.json` under deterministic path:
   `artifacts/reach/<algo>/<inputsHash>/<callPathHash>.dsse.json`.
5. **Wire VEXer** to reference the artifact digest and include a verification note.
6. **Tests:** golden fixtures asserting stable bytes for the same inputs; mutation tests to ensure any input change invalidates the cache key.

If you want, I can turn this into a ready‑to‑commit `StellaOps.Scanner.Reach` module (interfaces, options, tests, and a stub DSSE signer).
I will split this in two parts:

1. What are Stella Ops’ concrete advantages (the “moats”).
2. How developers must build to actually realize them (guidelines and checklists).

---

## 1. Stella Ops Advantages – What We Are Optimizing For

### 1.1 Deterministic, Replayable Security Evidence

**Idea:** Any scan or VEX decision run today must be replayable bit-for-bit in 3–5 years for audits, disputes, and compliance.

**What this means:**

* Every scan has an explicit **input manifest** (feeds, rules, policies, versions, timestamps).
* Outputs (findings, reachability, VEX, attestations) are **pure functions** of that manifest.
* Evidence is stored as **immutable artifacts** (DSSE, SBOMs, reach-maps, policy snapshots), not just rows in a DB.

---

### 1.2 Reachability-First, Quiet-By-Design Triage

**Idea:** The main value is not “finding more CVEs” but **proving which ones matter** in your actual runtime and call graph – and keeping noise down.

**What this means:**

* Scoring/prioritization is dominated by **reachability + runtime context**, not just CVSS.
* Unknowns and partial evidence are surfaced **explicitly**, not hidden.
* UX is intentionally quiet: “Can I ship?” → “Yes / No, because of these N concrete, reachable issues.”

---

### 1.3 Crypto-Sovereign, Air-Gap-Ready Trust

**Idea:** The platform must run offline, support local CAs/HSMs, and switch between cryptographic regimes (FIPS, eIDAS, GOST, SM, PQC) by configuration, not by code changes.

**What this means:**

* No hard dependency on any public CA, cloud KMS, or single trust provider.
* All attestations are **locally verifiable** with bundled roots and policies.
* Crypto suites are **pluggable profiles** selected per deployment / tenant.

---

### 1.4 Policy / Lattice Engine (“Trust Algebra Studio”)

**Idea:** Vendors, customers, and regulators speak different languages. Stella Ops provides a **formal lattice** to merge and reason over:

* VEX statements
* Runtime observations
* Code provenance
* Organizational policies

…without losing provenance (“who said what”).

**What this means:**

* Clear separation between **facts** (observations) and **policies** (how we rank/merge them).
* Lattice merge operations are **explicit, testable functions**, not hidden heuristics.
* Same artifact can be interpreted differently by different tenants via different lattice policies.

---

### 1.5 Proof-Linked SBOM→VEX Chain

**Idea:** Every VEX claim must point to concrete, verifiable evidence:

* Which SBOM / version?
* Which reachability analysis?
* Which runtime signals?
* Which signer/policy?

**What this means:**

* VEX is not just a JSON document – it is a **graph of links** to attestations and analysis artifacts.
* You can click from a VEX statement to the exact DSSE reach-map / scan run that justified it.

---

### 1.6 Proof-of-Integrity Graph (Build → Image → Runtime)

**Idea:** Connect:

* Source → Build → Image → SBOM → Scan → VEX → Runtime

…into a single **cryptographically verifiable graph**.

**What this means:**

* Every step has a **signed attestation** (in-toto/DSSE style).
* Graph queries like “Show me all running pods that descend from this compromised builder” or
  “Show me all VEX statements that rely on this revoked key” are first-class.

---

### 1.7 AI Codex & Zastava Companion (Explainable by Construction)

**Idea:** AI is used only as a **narrator and planner** on top of hard evidence, not as an oracle.

**What this means:**

* Zastava never invents facts; it explains **what is already in the evidence graph**.
* Remediation plans cite **concrete artifacts** (scan IDs, attestations, policies) and affected assets.
* All AI outputs include links back to raw structured data and can be re-generated in future with the same evidence set.

---

### 1.8 Proof-Market Ledger & Adaptive Trust Economics

**Idea:** Over time, vendors publishing good SBOM/VEX evidence should **gain trust-credit**; sloppy or contradictory publishers lose it.

**What this means:**

* A ledger of **published proofs**, signatures, and revocations.
* A **trust score** per artifact / signer / vendor, derived from consistency, coverage, and historical correctness.
* This feeds into procurement and risk dashboards, not just security triage.

---

## 2. Developer Guidelines – How to Build for These Advantages

I will phrase this as rules and checklists you can directly apply in Stella Ops repos (.NET 10, C#, Postgres, MongoDB, etc.).

---

### 2.1 Determinism & Replayability

**Rules:**

1. **Pure functions, explicit manifests**

   * Any long-running or non-trivial computation (scan, reachability, lattice merge, trust score) must accept a **single, structured input manifest**, e.g.:

     ```jsonc
     {
       "scannerVersion": "1.3.0",
       "rulesetId": "stella-default-2025.11",
       "feeds": {
         "nvdDigest": "sha256:...",
         "osvDigest": "sha256:..."
       },
       "sbomDigest": "sha256:...",
       "policyDigest": "sha256:..."
     }
     ```

   * No hidden configuration from environment variables, machine-local files, or system clock inside the core algorithm.

2. **Canonicalization everywhere**

   * Before hashing or signing:

     * Sort arrays by stable keys.
     * Normalize paths (POSIX style), line endings (LF), and encodings (UTF-8).
   * Provide a shared `StellaOps.Core.Canonicalization` library used by all services.

3. **Stable IDs**

   * Every scan, reachability call, lattice evaluation, and VEX bundle gets an opaque but **stable** ID based on the input manifest hash.
   * Do not use incremental integer IDs for evidence; use digests (hashes) or ULIDs/GUIDs derived from content.

4. **Golden fixtures**

   * For each non-trivial algorithm, ship at least one **golden fixture**:

     * Input manifest JSON
     * Expected output JSON
   * CI must assert byte-for-byte equality for these fixtures (after canonicalization).

**Developer checklist (per feature):**

* [ ] Input manifest type defined and versioned.
* [ ] Canonicalization applied before hashing/signing.
* [ ] Output stored with `inputsDigest` and `algoDigest`.
* [ ] At least one golden fixture proves determinism.

---

### 2.2 Reachability-First Analysis & Quiet UX

**Rules:**

1. **Reachability lives in Scanner.WebService**

   * All lattice/graph heavy lifting for reachability must run in `Scanner.WebService` (standing architectural rule).
   * Other services (Concelier, Excitors, Feedser) only **consume** reachability artifacts and must “preserve prune source” (never rewrite paths/proofs, only annotate or filter).

2. **Lazy, query-driven computation**

   * Do not precompute reachability for entire SBOMs.
   * Compute per **exact query** (image + vulnerability or source→sink path).
   * Use an in-memory or short-lived cache keyed by:

     * Algorithm signature
     * Input manifest hash
     * Query description (call-path hash)

3. **Evidence-first, severity-second**

   * Internal ranking objects should look like:

     ```csharp
     public sealed record FindingRank(
         string FindingId,
         EvidencePointer Evidence,
         ReachabilityScore Reach,
         ExploitStatus Exploit,
         RuntimePresence Runtime,
         double FinalScore);
     ```

   * UI always has a “Show evidence” or “Explain” action that can be serialized as JSON and re-used by Zastava.

4. **Quiet-by-design UX**

   * For any list view, default sort is:

     1. Reachable, exploitable, runtime-present
     2. Reachable, exploitable
     3. Reachable, unknown exploit
     4. Unreachable
   * Show **counts by bucket**, not only total CVE count.

**Developer checklist:**

* [ ] Reachability algorithms only in Scanner.WebService.
* [ ] Cache is lazy and keyed by deterministic inputs.
* [ ] Output includes explicit evidence pointers.
* [ ] UI endpoints expose reachability state in structured form.

---

### 2.3 Crypto-Sovereign & Air-Gap Mode

**Rules:**

1. **Cryptography via “profiles”**

   * Implement a `CryptoProfile` abstraction (e.g. `FipsProfile`, `GostProfile`, `EidasProfile`, `SmProfile`, `PqcProfile`).
   * All signing/verifying APIs take a `CryptoProfile` or resolve one from tenant config; no direct calls to `RSA.Create()` etc. in business code.

2. **No hard dependency on public PKI**

   * All verification logic must accept:

     * Provided root cert bundle
     * Local CRL or OCSP-equivalent
   * Never assume internet OCSP/CRL.

3. **Offline bundles**

   * Any operation required for air-gapped mode must be satisfiable with:

     * SBOM + feeds + policy bundle + key material
   * Define explicit **“offline bundle” formats** (zip/tar + manifest) with hashes of all contents.

4. **Key rotation and algorithm agility**

   * Metadata for every signature must record:

     * Algorithm
     * Key ID
     * Profile
   * Verification code must fail safely when a profile is disabled, and error messages must be precise.

**Developer checklist:**

* [ ] No direct crypto calls in feature code; only via profile layer.
* [ ] All attestations carry algorithm + key id + profile.
* [ ] Offline bundle type exists for this workflow.
* [ ] Tests for at least 2 different crypto profiles.

---

### 2.4 Policy / Lattice Engine

**Rules:**

1. **Facts vs. Policies separation**

   * Facts:

     * SBOM components, CVEs, reachability edges, runtime signals.
   * Policies:

     * “If vendor says ‘not affected’ and reachability says unreachable, treat as Informational.”
   * Serialize facts and policies separately, with their own digests.

2. **Lattice implementation location**

   * Lattice evaluation (trust algebra) for VEX decisions happens in:

     * `Scanner.WebService` for scan-time interpretation
     * `Vexer/Excitor` for publishing and transformation into VEX documents
   * Concelier/Feedser must not recompute lattice results, only read them.

3. **Formal merge operations**

   * Each lattice merge function must be:

     * Explicitly named (e.g. `MaxSeverity`, `VendorOverridesIfStrongerEvidence`, `ConservativeIntersection`).
     * Versioned and referenced by ID in artifacts (e.g. `latticeAlgo: "trust-algebra/v1/max-severity"`).

4. **Studio-ready representation**

   * Internal data structures must align with a future “Trust Algebra Studio” UI:

     * Nodes = statements (VEX, runtime observation, reachability result)
     * Edges = “derived_from” / “overrides” / “constraints”
     * Policies = transformations over these graphs.

**Developer checklist:**

* [ ] Facts and policies are serialized separately.
* [ ] Lattice code is in allowed services only.
* [ ] Merge strategies are named and versioned.
* [ ] Artifacts record which lattice algorithm was used.

---

### 2.5 Proof-Linked SBOM→VEX Chain

**Rules:**

1. **Link, don’t merge**

   * SBOM, scan result, reachability artifact, and VEX should keep their own schemas.
   * Use **linking IDs** instead of denormalizing everything into one mega-document.

2. **Evidence pointers in VEX**

   * Every VEX statement (per vuln/component) includes:

     * `sbomDigest`
     * `scanId`
     * `reachMapDigest`
     * `policyDigest`
     * `signerKeyId`

3. **DSSE everywhere**

   * All analysis artifacts are wrapped in DSSE:

     * Payload = canonical JSON
     * Envelope = signature + key metadata + profile
   * Do not invent yet another custom envelope format.

**Developer checklist:**

* [ ] VEX schema includes pointers back to all upstream artifacts.
* [ ] No duplication of SBOM or scan content inside VEX.
* [ ] DSSE used as standard envelope type.

---

### 2.6 Proof-of-Integrity Graph

**Rules:**

1. **Graph-first storage model**

   * Model the lifecycle as a graph:

     * Nodes: source commit, build, image, SBOM, scan, VEX, runtime instance.
     * Edges: “built_from”, “scanned_as”, “deployed_as”, “derived_from”.
   * Use stable IDs and store in a graph-friendly form (e.g. adjacency collections in Postgres or document graph in Mongo).

2. **Attestations as edges**

   * Attestations represent edges, not just metadata blobs.
   * Example: a build attestation is an edge: `commit -> image`, signed by the CI builder.

3. **Queryable from APIs**

   * Expose API endpoints like:

     * `GET /graph/runtime/{podId}/lineage`
     * `GET /graph/image/{digest}/vex`
   * Zastava and the UI must use the same APIs, not private shortcuts.

**Developer checklist:**

* [ ] Graph nodes and edges modelled explicitly.
* [ ] Each edge type has an attestation schema.
* [ ] At least two graph traversal APIs implemented.

---

### 2.7 AI Codex & Zastava Companion

**Rules:**

1. **Evidence in, explanation out**

   * Zastava must receive:

     * Explicit evidence bundle (JSON) for a question.
     * The user’s question.
   * It must not be responsible for data retrieval or correlation itself – that is the platform’s job.

2. **Stable explanation contracts**

   * Define a structured response format, for example:

     ```json
     {
       "shortAnswer": "You can ship, with 1 reachable critical.",
       "findingsSummary": [...],
       "remediationPlan": [...],
       "evidencePointers": [...]
     }
     ```

   * This allows regeneration and multi-language rendering later.

3. **No silent decisions**

   * Every recommendation must include:

     * Which lattice policy was assumed.
     * Which artifacts were used (by ID).

**Developer checklist:**

* [ ] Zastava APIs accept evidence bundles, not query strings against the DB.
* [ ] Responses are structured and deterministic given the evidence.
* [ ] Explanations include policy and artifact references.

---

### 2.8 Proof-Market Ledger & Adaptive Trust

**Rules:**

1. **Ledger as append-only**

   * Treat proof-market ledger as an **append-only log**:

     * New proofs (SBOM/VEX/attestations)
     * Revocations
     * Corrections / contradictions
   * Do not delete; instead emit revocation events.

2. **Trust-score derivation**

   * Trust is not a free-form label; it is a numeric or lattice value computed from:

     * Number of consistent proofs over time.
     * Speed of publishing after CVE.
     * Rate of contradictions or revocations.

3. **Separation from security decisions**

   * Trust scores feed into:

     * Sorting and highlighting.
     * Procurement / vendor dashboards.
   * Do not hard-gate security decisions solely on trust scores.

**Developer checklist:**

* [ ] Ledger is append-only with explicit revocations.
* [ ] Trust scoring algorithm documented and versioned.
* [ ] UI uses trust scores only as a dimension, not a gate.

---

### 2.9 Quantum-Resilient Mode

**Rules:**

1. **Optional PQC**

   * PQC algorithms (e.g. Dilithium, Falcon) are an **opt-in crypto profile**.
   * Artifacts can carry multiple signatures (classical + PQC) to ease migration.

2. **No PQC assumption in core logic**

   * Core logic must treat algorithm as opaque; only crypto layer understands whether it is PQ or classical.

**Developer checklist:**

* [ ] PQC profile implemented as a first-class profile.
* [ ] Artifacts support multi-signature envelopes.

---

## 3. Definition of Done Templates

You can use this as a per-feature DoD in Stella Ops:

**For any new feature that touches scans, VEX, or evidence:**

* [ ] Deterministic: input manifest defined, canonicalization applied, golden fixture(s) added.
* [ ] Evidence: outputs are DSSE-wrapped and linked (not merged) into existing artifacts.
* [ ] Reachability / Lattice: if applicable, runs only in allowed services and records algorithm IDs.
* [ ] Crypto: crypto calls go through profile abstraction; tests for at least 2 profiles if security-sensitive.
* [ ] Graph: lineage edges added where appropriate; node/edge IDs stable and queryable.
* [ ] UX/API: at least one API to retrieve structured evidence for Zastava and UI.
* [ ] Tests: unit + golden + at least one integration test with a full SBOM → scan → VEX chain.

If you want, next step can be to pick one module (e.g. Scanner.WebService or Vexer) and turn these high-level rules into a concrete CONTRIBUTING.md / ARCHITECTURE.md for that service.