Here’s a practical way to make a cross‑platform, hash‑stable JSON “fingerprint” for things like a `graph_revision_id`, so your hashes don’t change between OS/locale settings.

---

### What “canonical JSON” means (in plain terms)

* **Deterministic order:** Always write object properties in a fixed order (e.g., lexicographic).
* **Stable numbers:** Serialize numbers the same way everywhere (no locale, no extra zeros).
* **Normalized text:** Normalize all strings to Unicode **NFC** so accented/combined characters don’t vary.
* **Consistent bytes:** Encode as **UTF‑8** with **LF** (`\n`) newlines only.

These ideas match the JSON Canonicalization Scheme (RFC 8785)—use it as your north star for stable hashing.

---

### Drop‑in C# helper (targets .NET 8/10)

This gives you a canonical UTF‑8 byte[] and a SHA‑256 hex hash. It:

* Recursively sorts object properties,
* Emits numbers with invariant formatting,
* Normalizes all string values to **NFC**,
* Uses `\n` endings,
* Produces a SHA‑256 for `graph_revision_id`.

```csharp
using System;
using System.Buffers.Text;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Text.Json;
using System.Text.Json.Nodes;
using System.Text.Unicode;

public static class CanonJson
{
    // Entry point: produce canonical UTF-8 bytes
    public static byte[] ToCanonicalUtf8(object? value)
    {
        // 1) Serialize once to JsonNode to work with types safely
        var initialJson = JsonSerializer.SerializeToNode(
            value,
            new JsonSerializerOptions
            {
                NumberHandling = JsonNumberHandling.AllowReadingFromString,
                Encoder = System.Text.Encodings.Web.JavaScriptEncoder.UnsafeRelaxedJsonEscaping // we will control escaping
            });

        // 2) Canonicalize (sort keys, normalize strings, normalize numbers)
        var canonNode = CanonicalizeNode(initialJson);

        // 3) Write in a deterministic manner
        var sb = new StringBuilder(4096);
        WriteCanonical(canonNode!, sb);

        // 4) Ensure LF only
        var lf = sb.ToString().Replace("\r\n", "\n").Replace("\r", "\n");

        // 5) UTF-8 bytes
        return Encoding.UTF8.GetBytes(lf);
    }

    // Convenience: compute SHA-256 hex for graph_revision_id
    public static string ComputeGraphRevisionId(object? value)
    {
        var bytes = ToCanonicalUtf8(value);
        using var sha = SHA256.Create();
        var hash = sha.ComputeHash(bytes);
        var sb = new StringBuilder(hash.Length * 2);
        foreach (var b in hash) sb.Append(b.ToString("x2"));
        return sb.ToString();
    }

    // --- Internals ---

    private static JsonNode? CanonicalizeNode(JsonNode? node)
    {
        if (node is null) return null;

        switch (node)
        {
            case JsonValue v:
                if (v.TryGetValue<string>(out var s))
                {
                    // Normalize strings to NFC
                    var nfc = s.Normalize(NormalizationForm.FormC);
                    return JsonValue.Create(nfc);
                }
                if (v.TryGetValue<double>(out var d))
                {
                    // RFC-like minimal form: Invariant, no thousand sep; handle -0 => 0
                    if (d == 0) d = 0; // squash -0
                    return JsonValue.Create(d);
                }
                if (v.TryGetValue<long>(out var l))
                {
                    return JsonValue.Create(l);
                }
                // Fallback keep as-is
                return v;

            case JsonArray arr:
                var outArr = new JsonArray();
                foreach (var elem in arr)
                    outArr.Add(CanonicalizeNode(elem));
                return outArr;

            case JsonObject obj:
                // Sort keys lexicographically (RFC 8785 uses code unit order)
                var sorted = new JsonObject();
                foreach (var kvp in obj.OrderBy(k => k.Key, StringComparer.Ordinal))
                    sorted[kvp.Key] = CanonicalizeNode(kvp.Value);
                return sorted;

            default:
                return node;
        }
    }

    // Deterministic writer matching our canonical rules
    private static void WriteCanonical(JsonNode node, StringBuilder sb)
    {
        switch (node)
        {
            case JsonObject obj:
                sb.Append('{');
                bool first = true;
                foreach (var kvp in obj)
                {
                    if (!first) sb.Append(',');
                    first = false;
                    WriteString(kvp.Key, sb); // property name
                    sb.Append(':');
                    WriteCanonical(kvp.Value!, sb);
                }
                sb.Append('}');
                break;

            case JsonArray arr:
                sb.Append('[');
                for (int i = 0; i < arr.Count; i++)
                {
                    if (i > 0) sb.Append(',');
                    WriteCanonical(arr[i]!, sb);
                }
                sb.Append(']');
                break;

            case JsonValue val:
                if (val.TryGetValue<string>(out var s))
                {
                    WriteString(s, sb);
                }
                else if (val.TryGetValue<long>(out var l))
                {
                    sb.Append(l.ToString(CultureInfo.InvariantCulture));
                }
                else if (val.TryGetValue<double>(out var d))
                {
                    // Minimal form close to RFC 8785 guidance:
                    // - No NaN/Infinity in JSON
                    // - Invariant culture, trim trailing zeros and dot
                    if (double.IsNaN(d) || double.IsInfinity(d))
                        throw new InvalidOperationException("Non-finite numbers are not valid in canonical JSON.");
                    if (d == 0) d = 0; // squash -0
                    var sNum = d.ToString("G17", CultureInfo.InvariantCulture);
                    // Trim redundant zeros in exponentless decimals
                    if (sNum.Contains('.') && !sNum.Contains("e") && !sNum.Contains("E"))
                    {
                        sNum = sNum.TrimEnd('0').TrimEnd('.');
                    }
                    sb.Append(sNum);
                }
                else
                {
                    // bool / null
                    if (val.TryGetValue<bool>(out var b))
                        sb.Append(b ? "true" : "false");
                    else
                        sb.Append("null");
                }
                break;

            default:
                sb.Append("null");
                break;
        }
    }

    private static void WriteString(string s, StringBuilder sb)
    {
        sb.Append('"');
        foreach (var ch in s)
        {
            switch (ch)
            {
                case '\"': sb.Append("\\\""); break;
                case '\\': sb.Append("\\\\"); break;
                case '\b': sb.Append("\\b"); break;
                case '\f': sb.Append("\\f"); break;
                case '\n': sb.Append("\\n"); break;
                case '\r': sb.Append("\\r"); break;
                case '\t': sb.Append("\\t"); break;
                default:
                    if (char.IsControl(ch))
                    {
                        sb.Append("\\u");
                        sb.Append(((int)ch).ToString("x4"));
                    }
                    else
                    {
                        sb.Append(ch);
                    }
                    break;
            }
        }
        sb.Append('"');
    }
}
```

**Usage in your code (e.g., Stella Ops):**

```csharp
var payload = new {
    graphId = "core-vuln-edges",
    version = 3,
    edges = new[]{ new { from = "pkg:nuget/Newtonsoft.Json@13.0.3", to = "pkg:nuget/System.Text.Json@8.0.4" } },
    meta = new { generatedAt = DateTime.UtcNow.ToString("yyyy-MM-ddTHH:mm:ssZ") }
};

// Canonical bytes (UTF-8 + LF) for storage/attestation:
var canon = CanonJson.ToCanonicalUtf8(payload);

// Stable revision id (SHA-256 hex):
var graphRevisionId = CanonJson.ComputeGraphRevisionId(payload);
Console.WriteLine(graphRevisionId);
```

---

### Operational tips

* **Freeze locales:** Always run with `CultureInfo.InvariantCulture` when formatting numbers/dates before they hit JSON.
* **Reject non‑finite numbers:** Don’t allow `NaN`/`Infinity`—they’re not valid JSON and will break canonicalization.
* **One writer, everywhere:** Use this same helper in CI, build agents, and runtime so the hash never drifts.
* **Record the scheme:** Store the **canonicalization version** (e.g., `canon_v="JCS‑like v1"`) alongside the hash to allow future upgrades without breaking verification.

If you want, I can adapt this to stream very large JSONs (avoid `JsonNode`) or emit a **DSSE**/in‑toto style envelope with the canonical bytes as the payload for your attestation chain.
Here’s a concrete, step‑by‑step implementation plan you can hand to the devs so they know exactly what to build and how it all fits together.

I’ll break it into phases:

1. **Design & scope**
2. **Canonical JSON library**
3. **Graph canonicalization & `graph_revision_id` calculation**
4. **Tooling, tests & cross‑platform verification**
5. **Integration & rollout**

---

## 1. Design & scope

### 1.1. Goals

* Produce a **stable, cross‑platform hash** (e.g. SHA‑256) from JSON content.
* This hash becomes your **`graph_revision_id`** for supply‑chain graphs.
* Hash **must not change** due to:

  * OS differences (Windows/Linux/macOS)
  * Locale differences
  * Whitespace/property order differences
  * Unicode normalization issues (e.g. accented chars)

### 1.2. Canonicalization strategy (what devs should implement)

You’ll use **two levels of canonicalization**:

1. **Domain-level canonicalization (graph)**
   Make sure semantically equivalent graphs always serialize to the same in‑memory structure:

   * Sort arrays (e.g. nodes, edges) in a deterministic way (ID, then type, etc.).
   * Remove / ignore non-semantic or unstable fields (timestamps, debug info, transient IDs).
2. **Encoding-level canonicalization (JSON)**
   Convert that normalized object into **canonical JSON**:

   * Object keys sorted lexicographically (`StringComparer.Ordinal`).
   * Strings normalized to **Unicode NFC**.
   * Numbers formatted with **InvariantCulture**, no locale effects.
   * No NaN/Infinity (reject or map them before hashing).
   * UTF‑8 output with **LF (`\n`) only**.

You already have a C# canonical JSON helper from me; this plan is about turning it into a production-ready component and wiring it through the system.

---

## 2. Canonical JSON library

**Owner:** backend platform team
**Deliverable:** `StellaOps.CanonicalJson` (or similar) shared library

### 2.1. Project setup

* Create a **.NET class library**:

  * `src/StellaOps.CanonicalJson/StellaOps.CanonicalJson.csproj`
* Target same framework as your services (e.g. `net8.0`).
* Add reference to `System.Text.Json`.

### 2.2. Public API design

In `CanonicalJson.cs` (or `CanonJson.cs`):

```csharp
namespace StellaOps.CanonicalJson;

public static class CanonJson
{
    // Version of your canonicalization algorithm (important for future changes)
    public const string CanonicalizationVersion = "canon-json-v1";

    public static byte[] ToCanonicalUtf8<T>(T value);

    public static string ToCanonicalString<T>(T value);

    public static byte[] ComputeSha256<T>(T value);

    public static string ComputeSha256Hex<T>(T value);
}
```

**Behavioral requirements:**

* `ToCanonicalUtf8`:

  * Serializes input to a `JsonNode`.
  * Applies canonicalization rules (sort keys, normalize strings, normalize numbers).
  * Writes minimal JSON with:

    * No extra spaces.
    * Keys in lexicographic order.
    * UTF‑8 bytes and LF newlines only.
* `ComputeSha256Hex`:

  * Uses `ToCanonicalUtf8` and computes SHA‑256.
  * Returns lower‑case hex string.

### 2.3. Canonicalization rules (dev checklist)

**Objects (`JsonObject`):**

* Sort keys using `StringComparer.Ordinal`.
* Recursively canonicalize child nodes.

**Arrays (`JsonArray`):**

* Preserve order as given by caller.
  *(The “graph canonicalization” step will make sure this order is semantically stable before JSON.)*

**Strings:**

* Normalize to **NFC**:

  ```csharp
  var normalized = original.Normalize(NormalizationForm.FormC);
  ```
* When writing JSON:

  * Escape `"`, `\`, control characters (`< 0x20`) using `\uXXXX` format.
  * Use `\n`, `\r`, `\t`, `\b`, `\f` for standard escapes.

**Numbers:**

* Support at least `long`, `double`, `decimal`.
* Use **InvariantCulture**:

  ```csharp
  someNumber.ToString("G17", CultureInfo.InvariantCulture);
  ```
* Normalize `-0` to `0`.
* No grouping separators, no locale decimals.
* Reject `NaN`, `+Infinity`, `-Infinity` with a clear exception.

**Booleans & null:**

* Emit `true`, `false`, `null` (lowercase).

**Newlines:**

* Ensure final string has only `\n`:

  ```csharp
  json = json.Replace("\r\n", "\n").Replace("\r", "\n");
  ```

### 2.4. Error handling & logging

* Throw a **custom exception** for unsupported content:

  * `CanonicalJsonException : Exception`.
* Example triggers:

  * Non‑finite numbers (NaN/Infinity).
  * Types that can’t be represented in JSON.
* Log the path to the field where canonicalization failed (for debugging).

---

## 3. Graph canonicalization & `graph_revision_id`

This is where the library gets used and where the semantics of the graph are defined.

**Owner:** team that owns your supply‑chain graph model / graph ingestion.
**Deliverables:**

* Domain-specific canonicalization for graphs.
* Stable `graph_revision_id` computation integrated into services.

### 3.1. Define what goes into the hash

Create a short **spec document** (internal) that answers:

1. **What object is being hashed?**

   * For example:

     ```json
     {
       "graphId": "core-vuln-edges",
       "schemaVersion": "3",
       "nodes": [...],
       "edges": [...],
       "metadata": {
         "source": "scanner-x",
         "epoch": 1732730885
       }
     }
     ```

2. **Which fields are included vs excluded?**

   * Include:

     * Graph identity (ID, schema version).
     * Nodes (with stable key set).
     * Edges (with stable key set).
   * Exclude or **normalize**:

     * Raw timestamps of ingestion.
     * Non-deterministic IDs (if they’re not part of graph semantics).
     * Any environment‑specific details.

3. **Versioning:**

   * Add:

     * `canonicalizationVersion` (from `CanonJson.CanonicalizationVersion`).
     * `graphHashSchemaVersion` (separate from graph schema version).

   Example JSON passed into `CanonJson`:

   ```json
   {
     "graphId": "...",
     "graphSchemaVersion": "3",
     "graphHashSchemaVersion": "1",
     "canonicalizationVersion": "canon-json-v1",
     "nodes": [...],
     "edges": [...]
   }
   ```

### 3.2. Domain-level canonicalizer

Create a class like `GraphCanonicalizer` in your graph domain assembly:

```csharp
public interface IGraphCanonicalizer<TGraph>
{
    object ToCanonicalGraphObject(TGraph graph);
}
```

Implementation tasks:

1. **Choose a deterministic ordering for arrays:**

   * Nodes: sort by `(nodeType, nodeId)` or `(packageUrl, version)`.
   * Edges: sort by `(from, to, edgeType)`.

2. **Strip / transform unstable fields:**

   * Example: external IDs that may change but are not semantically relevant.
   * Replace `DateTime` with a normalized string format (if it must be part of the semantics).

3. **Output DTOs with primitive types only:**

   * Create DTOs like:

     ```csharp
     public sealed record CanonicalNode(
         string Id,
         string Type,
         string Name,
         string? Version,
         IReadOnlyDictionary<string, string>? Attributes
     );
     ```

   * Use simple `record` types / POCOs that serialize cleanly with `System.Text.Json`.

4. **Combine into a single canonical graph object:**

   ```csharp
   public sealed record CanonicalGraphDto(
       string GraphId,
       string GraphSchemaVersion,
       string GraphHashSchemaVersion,
       string CanonicalizationVersion,
       IReadOnlyList<CanonicalNode> Nodes,
       IReadOnlyList<CanonicalEdge> Edges
   );
   ```

   `ToCanonicalGraphObject` returns `CanonicalGraphDto`.

### 3.3. `graph_revision_id` calculator

Add a service:

```csharp
public interface IGraphRevisionCalculator<TGraph>
{
    string CalculateRevisionId(TGraph graph);
}

public sealed class GraphRevisionCalculator<TGraph> : IGraphRevisionCalculator<TGraph>
{
    private readonly IGraphCanonicalizer<TGraph> _canonicalizer;

    public GraphRevisionCalculator(IGraphCanonicalizer<TGraph> canonicalizer)
    {
        _canonicalizer = canonicalizer;
    }

    public string CalculateRevisionId(TGraph graph)
    {
        var canonical = _canonicalizer.ToCanonicalGraphObject(graph);
        return CanonJson.ComputeSha256Hex(canonical);
    }
}
```

**Wire this up in DI** for all services that handle graph creation/update.

### 3.4. Persistence & APIs

1. **Database schema:**

   * Add a `graph_revision_id` column (string, length 64) to graph tables/collections.
   * Optionally add `graph_hash_schema_version` and `canonicalization_version` columns for debugging.

2. **Write path:**

   * On graph creation/update:

     * Build the domain model.
     * Use `GraphRevisionCalculator` to get `graph_revision_id`.
     * Store it alongside the graph.

3. **Read path & APIs:**

   * Ensure all relevant APIs return `graph_revision_id` for clients.
   * If you use it in attestation / DSSE payloads, include it there too.

---

## 4. Tooling, tests & cross‑platform verification

This is where you make sure it **actually behaves identically** on all platforms and input variations.

### 4.1. Unit tests for `CanonJson`

Create a dedicated test project: `tests/StellaOps.CanonicalJson.Tests`.

**Test categories & examples:**

1. **Property ordering:**

   * Input 1: `{"b":1,"a":2}`
   * Input 2: `{"a":2,"b":1}`
   * Assert: `ToCanonicalString` is identical + same hash.

2. **Whitespace variations:**

   * Input with lots of spaces/newlines vs compact.
   * Canonical outputs must match.

3. **Unicode normalization:**

   * One string using precomposed characters.
   * Same text using combining characters.
   * Canonical output must match (NFC).

4. **Number formatting:**

   * `1`, `1.0`, `1.0000000000` → must canonicalize to the same representation.
   * `-0.0` → canonicalizes to `0`.

5. **Booleans & null:**

   * Check exact lowercase output: `true`, `false`, `null`.

6. **Error behaviors:**

   * Try serializing `double.NaN` → expect `CanonicalJsonException`.

### 4.2. Integration tests for graph hashing

Create tests in graph service test project:

1. Build two graphs that are **semantically identical** but:

   * Nodes/edges inserted in different order.
   * Fields ordered differently.
   * Different whitespace in strings (if your app might introduce such).

2. Assert:

   * `CalculateRevisionId` yields the same result.
   * Canonical DTOs match expected snapshots (optional snapshot tests).

3. Build graphs that differ in a meaningful way (e.g., extra edge).

   * Assert that `graph_revision_id` is different.

### 4.3. Cross‑platform smoke tests

**Goal:** Prove same hash on Windows, Linux and macOS.

Implementation idea:

1. Add a small console tool: `StellaOps.CanonicalJson.Tool`:

   * Usage:
     `stella-canon hash graph.json`
   * Prints:

     * Canonical JSON (optional flag).
     * SHA‑256 hex.

2. In CI:

   * Run the same test JSON on:

     * Windows runner.
     * Linux runner.
   * Assert hashes are equal (store expected in a test harness or artifact).

---

## 5. Integration into your pipelines & rollout

### 5.1. Where to compute `graph_revision_id`

Decide (and document) **one place** where the ID is authoritative, for example:

* After ingestion + normalization step, **before** persisting to your graph store.
* Or in a dedicated “graph revision service” used by ingestion pipelines.

Implementation:

* Update the ingestion service:

  1. Parse incoming data into internal graph model.
  2. Apply domain canonicalizer → `CanonicalGraphDto`.
  3. Use `GraphRevisionCalculator` → `graph_revision_id`.
  4. Persist graph + revision ID.

### 5.2. Migration / backfill plan

If you already have graphs in production:

1. Add new columns/fields for `graph_revision_id` (nullable).
2. Write a migration job:

   * Fetch existing graph.
   * Canonicalize + hash.
   * Store `graph_revision_id`.
3. For a transition period:

   * Accept both “old” and “new” graphs.
   * Use `graph_revision_id` where available; fall back to legacy IDs when necessary.
4. After backfill is complete:

   * Make `graph_revision_id` mandatory for new graphs.
   * Phase out any legacy revision logic.

### 5.3. Feature flag & safety

* Gate the use of `graph_revision_id` in high‑risk flows (e.g., attestations, policy decisions) behind a **feature flag**:

  * `graphRevisionIdEnabled`.
* Roll out gradually:

  * Start in staging.
  * Then a subset of production tenants.
  * Monitor for:

    * Unexpected changes in revision IDs on unchanged graphs.
    * Errors from `CanonicalJsonException`.

---

## 6. Documentation for developers & operators

Have a short internal doc (or page) with:

1. **Canonical JSON spec summary:**

   * Sorting rules.
   * Unicode NFC requirement.
   * Number format rules.
   * Non‑finite numbers not allowed.

2. **Graph hashing spec:**

   * Fields included in the hash.
   * Fields explicitly ignored.
   * Array ordering rules for nodes/edges.
   * Current:

     * `graphHashSchemaVersion = "1"`
     * `CanonicalizationVersion = "canon-json-v1"`

3. **Examples:**

   * Sample graph JSON input.
   * Canonical JSON output.
   * Expected SHA‑256.

4. **Operational guidance:**

   * How to run the CLI tool to debug:

     * “Why did this graph get a new `graph_revision_id`?”
   * What to do on canonicalization errors (usually indicates bad data).

---

If you’d like, next step I can do is: draft the **actual C# projects and folder structure** (with file names + stub code) so your team can just copy/paste the skeleton into the repo and start filling in the domain-specific bits.